Structure Magazine-September 2015.pdf
Content
A Joint Publication of NCSEA | CASE | SEI
STRUCTURE
®
September 2015 Concrete
Special Section
NCSEA Structual
Engineering Summit
Las Vegas, NV
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SAND-LIGHTWEIGHT CONCRETE
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(MINIMUM 3,000 PSI)
SAND-LIGHTWEIGHT CONCRETE OR NORMAL WEIGHT CONCRETE OVER
STEEL
DECK
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Flute
(Valley)
(MINIMUM 3,000 PSI)
Upper Flute (Valley)
PowerPowerStud+® SD1 Stud+® SD2
Min. 4-1/2"
Min.
4-1/2"
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Min. 4-1/2"
(Typ)
Min. Edge
Min. Edge
Distance
Distance
Min. Edge
Distance
Min. 4-1/2"
Min.
4-1/2"
(Typ.)
(Typ.)
Min. 4-1/2"
" (Typ.)
(Typ.)
Min. 12-1/2
" (Typ.)
Min. 12-1/2
Lower Flute
(Ridge)
Lower
Flute (Ridge)
Min. 12-1/2" (Typ.)
Flute Edge
Flute Edge
Lower Flute (Ridge)
Min. Edge
Min. Edge
Distance
Distance
Min. Edge
Distance
✔
✔
✔
✔
✔
Lower
Flute
✔
✔
✔
✔
✔
✔
2-1/2"
Minimum
Topping
Thickness
Upper Flute (Valley)
Min. 3-7/8"
Min.
3-7/8"
(Typ.)
(Typ.)
Min. 3-7/8"
(Typ.)
✔
Top of
Deck
Flute Edge
SAND-LIGHTWEIGHT CONCRETE OR NORMAL WEIGHT CONCRETE OVER STEEL DECK
SAND-LIGHTWEIGHT CONCRETE
OR NORMAL
WEIGHT
(MINIMUM
3,000
PSI) CONCRETE OVER STEEL DECK
(MINIMUM 3,000 PSI)
SAND-LIGHTWEIGHT CONCRETE OR NORMAL WEIGHT CONCRETE OVER STEEL DECK
Upper Flute (Valley)
(MINIMUM 3,000 PSI)
Upper Flute (Valley)
Max.
Max.
3"
3"
Max.
3"
Upper
Flute
Min. 3-7/8"
Min.
3-7/8"
(Typ.)
(Typ.)
Min. 3-7/8"
(Typ.)
Lower Flute (Ridge)
Lower Flute (Ridge)
Flute Edge
Flute Edge
Lower Flute (Ridge)
Upper
Flute
✔
✔
Lower
Flute
✔
✔
Flute Edge
Top of
Deck
SAND-LIGHTWEIGHT CONCRETE OR NORMAL WEIGHT CONCRETE OVER STEEL DECK
SAND-LIGHTWEIGHT CONCRETE
OR NORMAL
WEIGHT
(MINIMUM
3,000
PSI) CONCRETE OVER STEEL DECK
(MINIMUM 3,000 PSI)
SAND-LIGHTWEIGHT CONCRETE OR NORMAL WEIGHT CONCRETE OVER STEEL DECK
Upper Flute (Valley)
(MINIMUM 3,000 PSI)
Upper Flute (Valley)
B DECK
Upper Flute (Valley)
1-1/2"
1-1/2"
Max.
Max.
1-1/2"
Max.
2-1/2"
2-1/2"
Min.
Min.
2-1/2"
Min.
Min. Edge
Min. Edge
Distance
Distance
Min. Edge
Distance
Max.
Max.
3-1/2"
3-1/2"
(Typ)
Max.
(Typ)
3-1/2"
(Typ)
Lower Flute Edge
Lower Flute Edge
2-1/2"
Minimum
Topping
Thickness
1-3/4"
1-3/4"
Min.
Min.
1-3/4"
Min.
Lower Flute Edge
Upper
Flute
✔
✔
✔
✔
Lower
Flute
✔
✔
✔
✔
Bang-It
PowerStud+ SD1
PowerStud+ SD2
Snake+
Vertigo+
WedgeBolt+
ESR-3657
ESR-2818
ESR-2502
ESR-2272
ESR-2526
ESR-2526
* See individual ICC-ES Reports for details on each condition
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editorial
7 PBd: a Component in
the Future of Structural
engineering
By Stephen S. Szoke, P.E.
iNFoCuS
11 representation and reality
STRUCTURE
gueSt ColuMN
34 BiM-M Symposium:
generation 1
September 2015
By Daniel Zechmeister, P.E.
StruCtural PerForMaNCe
38 the Most Common errors
in Seismic design
By Jon A. Schmidt, P.E., SECB
By Thomas F. Heausler, P.E., S.E.
teChNologY
iNSightS
12 Modern limit analysis tools
for reinforced Concrete Slabs
By Angus Ramsay, M.Eng, Ph.D.,
C.Eng, Edward Maunder, Ph.D.
and Matthew Gilbert, Ph.D., C.Eng
StruCtural deSigN
16 What is a Masonry
“Flush Pilaster”?
By David L. Pierson, S.E.
hiStoriC StruCtureS
18 the Niagara
Cantilever Bridge
By Frank Griggs, Jr., D. Eng., P.E.
BuildiNg BloCkS
23 Proper Procedures and
Protocol for interception
grouting
By Brent Anderson, P.E.
StruCtural rehaBilitatioN
26 divine design: renovating
and Preserving historic
houses of Worship, Part 4
By Nathaniel B. Smith, P.E. and
Milan Vatovec, P.E., Ph.D.
CodeS aNd StaNdardS
30 Changes in adhesive
anchor System approvals
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Feature
58 Creating Clarity and
Scoping Profits in BiM
with lod 350
NCSea 2015 Summit
Special Section
By Will Ikerd, P.E.
eNgiNeer’S NoteBook
60 Moment-Curvature
and Nonlinearity
By Jerod G. Johnson, Ph.D., S.E.
CaSe BuSiNeSS PraCtiCeS
63 Strategic Planning: a
Comprehensive approach
By Dilip Choudhuri, P.E.
The National Council of Structural Engineers Associations
will host its 2015 Structural Engineering Summit at the Red
Rock Resort in Las Vegas, NV, on September 30th through
October 3rd. Read about the Summit, the extensive program
and vendor information in the Special Summit Section… and
plan to attend this exciting event!
46
Feature
606 West 57 th Street,
New York
eduCatioN iSSueS
69 Structural education
deficiencies
By Sunghwa Han, P.E., S.E. The behavior of structurally-linked
multiple tower structures is largely affected by the effectiveness
of the rigid links made between the towers. Depending on
the interactive dynamic behavior of the adjacent building
parts with one another, a separation joint may be considered.
Read how engineers resolved numerous issues associated with
separation gaps.
By Kevin Dong, P.E., S.E.
SPotlight
75 Newport Beach Civic
Center and Park
By Janice Mochizuki, P.E.,
John Worley, S.E. and
51
Joseph Collins, S.E.
Feature
StruCtural ForuM
82 a “Plug” for Power line
Structures
By David C. Gelder, P.E.
By Richard T. Morgan, P.E.
On the cover Las Vegas CityCenter Block A, structural engineering by Thornton
Tomasetti and architectural design by Pelli Clarke Pelli Architects, is the crown jewel
of the 76-acre CityCenter development on the Las Vegas Strip. The development is the
largest, most complex private construction project completed in the United States to
date. Photo courtesy of Thornton Tomasetti. Join NCSEA at the Red Rock Resort in Las
Vegas, September 30th through October 3rd (see page 42).
Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute
endorsement by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and
advertisers retain sole responsibility for the content of their submissions.
STRUCTURE magazine
42
5
a Need for Speed
By Ramon Gilsanz, P.E., S.E., Philip Murray, P.E.,
Gary Steficek, P.E. and Petr Vancura The fundamental principle
that drives the need for speed in construction is economic, a
major factor for owners. How do you approach fast-paced
construction within a dense urban environment? Read how three
projects in New York City illustrate the use of flat plate concrete
systems, instant communication and in-the-field coordination to
speed up the construction process.
iN everY iSSue
8 Advertiser Index
71 Resource Guide (Anchoring)
76 NCSEA News
78 SEI Structural Columns
80 CASE in Point
September 2015
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ACI 318-14: Reorganized for Design
The American Concrete Institute has recently published the newest edition of ACI 318, “Building Code Requirements for Structural Concrete
(ACI 318-14).” This edition represents the first major change in Code organization in over 40 years and has been completely reorganized from
a designer’s perspective. This seminar will help you get acquainted with the new organization and various technical changes to the code as
quickly as possible and demonstrate how you can ensure that your design fully complies with the new code.
To learn more about ACI seminars and to register, visit www.concreteseminars.org
Pittsburgh, PA—September 10, 2015
Raleigh, NC—September 15, 2015
Chicago, IL—September 17, 2015
New Brunswick, NJ—September 22, 2015
Minneapolis, MN—September 24, 2015
Albany, NY—September 29, 2015
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September 30, 2015
Des Moines, IA—October 1, 2015
Portland, OR—October 6, 2015
Baltimore, MD—October 8, 2015
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Fort Lauderdale, FL—December 3, 2015
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Editorial
PBD:
A Component in the Future of
new trends, new techniques and current industry issues
Structural Engineering
By Stephen S. Szoke, P.E., F.SEI, F.ASCE, F.ACI
P
erformance-Based Design (PBD) has been practiced throughout history, dating back to the Code of Hammurabi, circa
1750 BCE. Today, the three most common applications of
performance based design are:
• Use of innovative engineering technologies or products;
• Enhancement of project performance based on specific needs
of the owners, such as design for special risk assessments like
extreme loading conditions; and
• Economy, where more affordable design and construction options
can demonstrate compliance with the intent of the building code.
Although PBD is already permitted in building codes, perhaps it
is too infrequently practiced. Most building codes are based on
the International Code Council International Building Code (IBC)
which includes alternative means and methods to allow the use of
materials, design techniques, or construction methods not specifically
prescribed by the code. Many jurisdictions also adopt the International
Code Council Performance Code (ICCPC) which permits innovation
and deviations from the prescriptive criteria while maintaining the
intent of the building code. The intent of the ICCPC is: “To provide
appropriate health, safety, welfare, and social and economic value, while
promoting innovative, flexible and responsive solutions that optimize the
expenditure and consumption of resources.”
Today, the trend in structural engineering, often driven by the
potential for litigation, is to exclusively follow the prescriptive design
criteria for loads based on Minimum Design Loads for Buildings and
Other Structures (ASCE/SEI 7) combined with prescriptive load resistance criteria as provided in documents like the American Concrete
Institute’s Building Code Requirements for Structural Concrete; American
Institute of Steel Construction’s Steel Design Manual; and American
Wood Council’s ASD/LRFD Manual for Engineered Wood Construction.
However, an unintended consequence of these prescriptive criteria is
the ability to generate designs compliant with both load and resistance
criteria via computer models. This method of structural design, while
it may still require a stamp by an engineer, limits the freedoms related
to innovation and creativity in structural design. The development of
strategies and mechanisms to expand the acceptance of PBD tend to
better reflect the interests of clients and jurisdictions while elevating
structural engineers as design professionals. A new opportunity to
increase use of PBD may be to encourage acceptance of emerging
philosophies related to design and construction solutions that are
associated with “enhanced resilience” or “community resilience.”
The National Institute for Standards and Technology is in the final
development stages of the Community Resilience Planning Guide which
proposes new concepts for codes and standards related to the design
of building and other infrastructure components. Another strategy
could be related to transparency of consequences to owners and
communities should a disaster occur. This might be in the form of
multiple performance levels within each risk category to better allow
owners and communities to select the appropriate performance levels.
The National Institute of Building Sciences Building Seismic Safety
Council is considering a menu of performance levels in lieu of single
performance levels for respective risk classifications. This would differ
from the current approach, where the standards development process
dictates the acceptable performance level, such as 10% failure for the
STRUCTURE magazine
seismic design of most buildings, those classified in risk category II.
This new approach may extend the role of the structural engineer in
planning to help improve community resilience, the ability to rebound
after disasters, seismic or otherwise.
To address historical and current applications of PBD and the role of
PBD in future, the SEI Board of Governors has established a committee, not to develop criteria for PBD, but to investigate the role of PBD
in the future of structural engineering. Their charge is to champion
the trend toward performance-based design. This aligns with several
aspects of SEI’s A Vision for the Future of Structural Engineering and
Structural Engineers: A case for change:
“…The drive to develop codes and specifications has led to the
outcome that many of the tasks previously done by structural engineers could be and have been automated… …we must curb our
tendency to codify our design decisions and leave those decisions in
the province of qualified structural engineers. If we mandate how
a structure must perform, but leave freedom to how the engineer
provides that performance, we open the possibilities for amazing
solutions to presently unsolvable problems.”
“One avenue for change that has emerged in recent years is the
notion of performance-based design… … performance-based design
would increase the importance of sound engineering judgment in
the design process, rely on better technical knowledge, require the
use of more sophisticated technology in problem solving, result in
more efficient structures, and place the structural engineer in a
better position to drive technological change.”
The new PBD committee met during the 2015 Structures Congress.
Many aspects and implications of PBD will be visited during the process
of developing recommendations, including: development of a series of
enabling documents to compliment current design criteria, possibly
similar to Seismic Rehabilitation of Existing Buildings (ASCE/SEI
41); use PBD to serve as the documents in the public domain moving
prescriptive compliance criteria to other documents maintained by
standards developers; defining professional liability as a standard of
care; and use of shelter-in-place performance levels for
significant natural disasters. This effort, while invaluable,
is a complex, multi-faceted and long-term project for the
advancement of structural engineering as a profession.▪
Stephen S. Szoke, P.E., F.SEI, F.ASCE, F.ACI, is the Senior
Director of Codes and Standards for the Portland Cement
Association. He serves on SEI’s Codes and Standards Division
Executive Committee and represents the division on the SEI Board
of Governors. He serves as the board liaison for the newly formed
board level committee on performance based design. He may be
contacted at [email protected].
The National Institute for Standards and Technology
Community Resilience Planning Guide can be found at
www.nist.gov/el/building_materials/resilience/guide.cfm,
last visited July 2015.
7
September 2015
Advertiser index
PlEaSE SUPPoRT ThESE advERTiSERS
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California Polytechnic State University .... 8
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CTP, Inc................................................ 29
CTS Cement Manufacturing Corp........ 25
Decon USA, Inc. ................................... 64
Ecospan Composite Floor System ......... 61
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ICC – Evaluation Service ...................... 74
Integrated Engineering Software, Inc..... 67
Integrity Software, Inc. .......................... 49
ITT Enidine, Inc. .................................. 57
JVA Inc. ................................................ 32
KPFF Consulting Engineers .................... 8
Legacy Building Solutions ..................... 37
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MAPEI Corp......................................... 62
Powers Fasteners, Inc. .............................. 2
QuakeWrap ........................................... 39
RISA Technologies ................................ 84
S-Frame Software, Inc. ............................ 4
Simpson Strong-Tie........................... 9, 33
SEA of Illinois ....................................... 68
Structural Engineers, Inc. ...................... 20
StructurePoint ....................................... 22
Struware, Inc. ........................................ 36
Tekla ..................................................... 72
USG Corporation ................................. 41
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STRUCTURE
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editoriAL stAFF
Executive Editor Jeanne vogelzang, JD, cae
[email protected]
Editor christine M. Sloat, P.e.
[email protected]
Associate Editor nikki alger
[email protected]
Graphic Designer rob Fullmer
[email protected]
Web Developer William radig
[email protected]
editoriAL BoArd
Chair Jon a. Schmidt, P.e., SecB
Burns & McDonnell, Kansas city, Mo
[email protected]
ARCHITECTURAL ENGINEERING
The Department of Architectural Engineering at Cal Poly, San Luis Obispo, California is
seeking applications for a full-time, academic year tenure track position for the teaching of
structural analysis, design, and construction of buildings. Starting date is September 15, 2016.
For details, qualifications, and to complete a required online faculty application, please visit
WWW.CALPOLYJOBS.ORG and search for Requisition #103762. Review of application will
begin October 15, 2015. Applications received after this date may be considered. EEO.
craig e. Barnes, P.e., SecB
cBI consulting, Inc., Boston, Ma
John a. Dal Pino, S.e.
Degenkolb engineers, San Francisco, ca
Mark W. Holmberg, P.e.
Heath & lineback engineers, Inc., Marietta, Ga
Dilip Khatri, Ph.D., S.e.
Khatri International Inc., Pasadena, ca
roger a. laBoube, Ph.D., P.e.
ccFSS, rolla, Mo
Brian J. leshko, P.e.
HDr engineering, Inc., Pittsburgh, Pa
Brian W. Miller
Davis, ca
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Mike Mota, Ph.D., P.e.
crSI, Williamstown, nJ
evans Mountzouris, P.e.
the DiSalvo engineering Group, ridgefield, ct
Greg Schindler, P.e., S.e.
KPFF consulting engineers, Seattle, Wa
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american Wood council, leesburg, va
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STRUCTURE magazine
8
September 2015
September 2015, Volume 22, Number 9
ISSn 1536-4283. Publications agreement no. 40675118.
owned by the national council of Structural engineers
associations and published in cooperation with caSe and SeI
monthly by c3 Ink. the publication is distributed free of charge to
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inFocus
Representation
new trends, new techniques and
and
current
Reality
industry issues
By Jon A. Schmidt, P.E., SECB
R
epresentation is intrinsic to human life and engineering
practice. We communicate with other people throughout
the design and construction process by means of words,
diagrams, and sketches. We create mental and computational models of materials, loads, and the arrangement of members.
We develop building information models (BIM), drawings, and
specifications to indicate how the various pieces and parts are to be
assembled into the finished structure.
The intent of these representations is to capture the relevant characteristics of reality, which may overlap but are not identical in each
case. The engineer has to ascertain what those are, and then incorporate appropriate assumptions and simplifications accordingly. Two
common strategies are abstraction, which involves neglecting certain
aspects of reality in order to gain a better understanding of the remaining aspects; and idealization, which involves replacing a complicated
and/or complex aspect of reality with a simplified version.
This entails that representations are always less than 100% accurate,
raising the question of how they relate to reality – the domain of semiotics, the study of signs and signification (or semiosis). Conventional
theories are dyadic, emphasizing two components: the signifier and the
signified; the relationship between them is essentially arbitrary. The
limitations of this conceptualization have become evident with the
emergence of deconstruction and other aspects of postmodernism,
in that it effectively precludes objective meaning.
An alternative was developed by American scientist and philosopher
Charles Sanders Peirce (pronounced “purse”) in the late 19th and
early 20th centuries. He founded what eventually came to be known
as pragmatism, but was unhappy with the direction that it ultimately
took in the more popular work of others – most notably William
James and John Dewey – so he coined the name pragmaticism for his
own approach, saying that this term was “ugly enough to be safe from
kidnappers.” Peirce’s theory – which he preferred to call semeiotic – is
triadic, emphasizing three relations: among the sign itself (or representamen), that which it signifies (object), and the effect that is produced
(interpretant), which comes about by a habit of interpretation.
Peirce aligned these elements with the three fundamental categories
that he identified in both our encounter with the world (phenomenology or phaneroscopy) and the underlying nature of reality (metaphysics);
he simply called them Firstness, Secondness, and Thirdness. Firstness
is quality, feeling, possibility, spontaneity, vagueness; Secondness is
difference, reaction, actuality, persistence, particularity; Thirdness is
mediation, purpose, regularity, order, generality. For example, an icon
relates to its object through some kind of resemblance (Firstness), an
index due to a physical or other direct connection (Secondness), and
a symbol by means of a convention or rule (Thirdness). A painting is
an icon, a fingerprint is an index, and a word is a symbol.
For Peirce, then, representation is reality: “…all this universe is
perfused with signs, if it is not composed exclusively of signs.”
Furthermore, all thought consists of signs, and inquiry is the deliberate and collaborative endeavor to process them in a way that results
in genuine knowledge via three basic modes of inference: abduction
(or retroduction), the formulation of a hypothesis or “guess,” often
in response to a surprising event; deduction, the explication of what
STRUCTURE magazine
else would be the case if that explanation is correct; and induction
(or adduction), the examination of whether those consequences ever
fail to materialize.
This “logic of inquiry” applies most directly to science, but it also
serves as a “logic of ingenuity” in engineering practice. Abduction
constitutes the creative process that leads to the selection of one preliminary solution out of multiple potential options (“Engineering as
Willing,” March 2010). Deduction corresponds to the deterministic
analyses that indicate the expected behavior of that design, given
certain presuppositions. Induction operates over time as an engineer
learns from experience – i.e., gets better at abduction – developing
competence, proficiency, and eventually expertise (“The Nature of
Competence,” March 2012).
Both inquiry and ingenuity thus employ signs to make that
which is indeterminate more determinate, although never fully
determinate. The only complete sign is the entirety of reality itself,
which consists of continuous systems of relations, rather than
discrete substances; hence its persistent complexity (“Complicated
+ Complex = Wicked,” July 2015). Truth is the final interpretant
– the opinion on which an infinite community would converge
after an indefinite investigation. In the meantime, we must always
acknowledge the fallibility of our current understanding (“The
Virtues of Ignorance,” May 2015). Uncertainty in representation is
constrained by reality, but not eliminated entirely.
Note that determination occurs primarily as discovery in science
(conforming representation to reality) vs. decision in engineering
(conforming reality to representation). This distinction was important
to Peirce, because while he was a persistent advocate of grounding
science firmly in reason, he was equally adamant that practical matters should be governed primarily by instinct and sentiment. When
it comes to “topics of vital importance,” judgment must rely on one’s
existing beliefs, which are nothing more or less than established
habits of thought and action – much like virtues in Aristotelian ethics
(“Virtuous Engineering,” September 2013).
This column barely scratches the surface of Peirce’s wide-ranging and
often idiosyncratic ideas. He never managed to write a single book –
something that (so far) I have in common with him – but produced
many thousands of pages of articles and manuscripts, leaving the bulk
of them in draft or otherwise unfinished form. The Peirce Edition
Project (www.iupui.edu/~peirce/) has compiled and published key
selections from his philosophical writings in The Essential Peirce (two
volumes, 1992 and 1998). Helpful introductory and summary material is available in The Fate of Meaning (1989) and Charles
Peirce’s Guess at the Riddle (1994) by John K. Sheriff, The
Continuity of Peirce’s Thought (1998) by Kelly A. Parker,
and Peirce’s Theory of Signs (2007) by T. L. Short.▪
11
Jon A. Schmidt, P.E., SECB ([email protected]), is
an associate structural engineer at Burns & McDonnell in Kansas
City, Missouri. He chairs the STRUCTURE magazine Editorial
Board and the SEI Engineering Philosophy Committee, and shares
occasional thoughts at twitter.com/JonAlanSchmidt.
September 2015
Technology
information and updates on
the impact of technology on
structural engineering
A
t a recent workshop, organized by the
University of Sheffield in association
with LimitState and held at the IStructE
Headquarters in London, the authors
of this article presented new computational tools
for the limit analysis of reinforced concrete (RC)
slabs. The workshop was attended by practising
engineers from different fields, including those
involved with the design of RC slabs and those
with an interest in the assessment of existing RC
slabs for changing service loads.
The computational tools presented align closely
with the traditional methods of designing and
assessing RC slabs. The traditional method for
assessing slabs has been Johansen’s yield line
technique which, as an upper-bound method,
relies for its accuracy on the ability of the engineer to postulate a realistic collapse mechanism.
LimitState:SLAB uses the discontinuity layout
optimisation (DLO) method, robustly and efficiently computerising the yield line technique,
automatically identifying collapse mechanisms
that have corresponding
collapse loads very close
to theoretical solutions
(typically within 1%). In
contrast, the traditional
method for designing slabs
has been Hillerborg’s strip
method, which, as a lower-bound method,
provides a set of equilibrium moment fields
that may be used to size and position the
reinforcement. Ramsay Maunder Associate’s
(RMA) equilibrium finite element software,
RMA:EFE, robustly and efficiently automates
this approach to provide a complete equilibrium moment field (which includes torsional
moments) with a corresponding collapse load
very close to the theoretical solution. When
used together, LimitState:SLAB and RMA:EFE
lead to accurate plasticity solutions (typically
within 1 or 2% of each other) that completely
define the limit solution in terms of collapse
mechanism (LimitState:SLAB) and moment
fields (RMA:EFE). The efficiency of these solutions can be measured in the time taken to solve,
typically no more than a few seconds.
Modern Limit Analysis
Tools for Reinforced
Concrete Slabs
By Angus Ramsay, M.Eng, Ph.D.,
C.Eng, FIMechE,
Edward Maunder, MA, DIC,
Ph.D., FIStructE and
Matthew Gilbert, B.Eng, Ph.D.,
C.Eng, MICE, M.ASCE,
The online version of this
article contains detailed
references. Please visit
www.STRUCTUREmag.org.
Modern limit analysis tools such as RMA:EFE
and LimitState:SLAB, when used in combination,
provide the practicing engineer with a way of verifying the solutions (and of ensuring simulation
governance), i.e. the engineer can sleep soundly
at night knowing that the collapse load has been
predicted with good accuracy (since when lower
and upper bound solutions agree, the true solution has been found).
In the absence of a verified solution, the engineer
using the yield line method needs to rely on his
or her good judgment to determine a realistic
collapse mechanism. The engineer might also be
tempted to rely on anecdotal evidence that inherent membrane action within the slab will increase
capacity beyond that derived by consideration of
flexural strength alone, and/or advice offered by
professional bodies that, for example, yield line
solutions are generally no more than 10% above
the true value [1]. Neither of these, of course,
would stand up to a great deal of scrutiny without
further verification or validation work.
In a recent article [2], a solution to a problem published by the first author in 1997, [3], was presented
and used to demonstrate how yield line computations have developed over the last 20 years. Although
the original published result was not intended as
an exact solution, it now turns out, using modern
limit analysis tools, that the collapse load was 40%
above the theoretical value! While it is clear that
experienced engineers might not have accepted the
solution provided in the original publication, it is
considered to be useful to less experienced engineers
working in this field to document an example where
the yield line method has produced an extremely
unsafe result. The problem is defined as the Landing
Slab Problem and automated methods using meshes
of triangular elements together with geometric optimisation are used to demonstrate the state-of-art
from the 1990s.
The Landing Slab Problem
This problem involves a reinforced concrete landing slab typical of the type found in the stairways of
modern buildings. It is a two-way slab in that significant moments are developed in both directions.
The slab is simply supported on three adjacent
Figure 1. Landing slab problem.
12 September 2015
sides, and the reinforcement at the top and
bottom of the slab provides equal isotropic
moment capacity (m). The slab is loaded with
a uniform distributed load (q) (the loading
arrows are placed at the centre of the corresponding slab portion) as shown in Figure 1,
and has a unit load to strength ratio (q/m).
The Automated
Yield Line Technique
(a)
(b)
Figure 2. Results from the 1997 Research ( λ = 5.86). a) Mesh; b) Yield line pattern.
In the 1997 work, the mesh shown in Figure 2
was used. This led to the collapse mechanism
shown with blue lines, representing element
edges where the moment has reached the sagging capacity of the slab and with the symbol
λ representing the load factor.
An analysis of a more refined mesh in 2011
produced the following results shown in
Figure 3.
This result indicates that the 1997 solution
was not correct – the yield lines, while emanating from the corners of the slab, do not
terminate at slab corners. This sort of yield
line pattern, which now involves red lines
where the hogging capacity of the slab has
been reached, appears to provide a qualitatively reasonable representation of the way in
which the slab might crack.
continued on next page
(a)
(b)
Figure 3. Results from the 2011 Research ( λ = 5.47). a) Mesh; b) Yield line pattern.
(a)
(b)
Figure 4. Results for a coarse unstructured mesh from EFE ( λ = 4.38). a) Mesh; b) Yield line pattern.
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Figure 6. RMA:EFE Solution of 2014 using 2484 elements ( λ=4.20).
Figure 5. DLO Solution of 2014 using 4000 nodes ( λ = 4.21).
Geometric optimization of the mechanism
indicated by the 2011 research is shown in
Figure 4 (page 13).
Modern Limit Analysis Tools –
LimitState:SLAB
The results produced by the DLO-based
software LimitState:SLAB [4] are in the
form of yield line patterns with the same
convention as already described for color
and thickness of the yield lines (Figure
5). Note however that whereas the yield
lines in Figures 2, 3 and 4 were based on
moments, those in Figure 5 are based on
rotation (hence the red lines on the supported boundary in Figure 5). This yield
line pattern is similar to the geometrically
optimized pattern of Figure 4 in terms of
the dominant yield lines. However it shows
additional yield lines that point to a more
complicated collapse mechanism for the
slab, with more distributed yielding than
suggested in Figure 4. The load factor from
the DLO method is 4% lower than that
of the geometrically optimized solution
already presented.
Modern Limit Analysis Tools –
RMA:EFE
RMA’s software tool (RMA:EFE) [5] provides a solution to this problem in terms of
equilibrium moment fields. A method of
demonstrating that these fields do not violate
the yield criteria is to consider the utilization
ratio. The utilization ratio, which compares
the moment field with the moment capacity
or yield moment, can be calculated at points
in the model as the degree to which the local
moment field can be scaled up before it causes
yielding. Such a plot is shown for the landing
slab in Figure 6, where the contour colors
range from zero (blue–unutilized) to unity
(red – fully utilized). The regions where the
material is fully utilized correspond well with
the yield line pattern of Figure 5.
With upper-bound (LimitState:SLAB) and
lower-bound (RMA:EFE) solutions to this
problem available, the theoretically exact
collapse load can be predicted within very
tight bounds:
4.20 ≤ λ ≤ 4.21
The load factors are within 1% of each
other and thus give an extremely accurate
prediction of the theoretically exact value.
Erring on the side of safety and using the
lower-bound load factor in the calculation
shows that the published result of 1997 was
40% too high!
Practical Conclusions
This brief article has shown how limit analysis, particularly the yield line technique, has
developed over the last 20 years, and has led
to modern computational tools for the practicing engineer that are able to bound the
theoretical solution to very close tolerances
thereby providing strong simulation governance in the design/assessment of reinforced
concrete slabs.
There is now no need to rely on rules of
thumb, such as the ‘10% rule’, or arguments
that any over-estimate of capacity through
a coarse yield line analysis will implicitly be
accounted for by membrane action (which
for a given slab may in reality not be present). Also noted in the recent workshop,
elastic techniques are increasingly being
used in the design of new RC slabs but,
as a result, reinforcement over columns
becomes significantly greater than indicated
to be required when using a limit analysis
based approach.
The availability of efficient and robust
software for predicting the collapse load
of reinforced concrete flat slabs now means
that one of the original outcomes of the
European Concrete Building Project, to
encourage engineers to design slabs based
on limit analysis techniques [6], can
now safely be realized and applied with
STRUCTURE magazine
14
September 2015
confidence to both conventional and more
complicated and novel slab configurations.
RMA and LimitState encourage engineers
practicing in this field to get involved by
using and driving the future development
of these software tools for their own commercial advantage.▪
Angus Ramsay, M.Eng, Ph.D., C.Eng,
FIMechE, is the owner of Ramsay Maunder
Associates, an engineering consultancy
based in the UK. He is a member of the
NAFEMS Education & Training Working
Group and acts as an Independent Technical
Editor to the NAFEMS Benchmark
Challenge. He can be contacted at
[email protected].
Edward Maunder, MA, DIC, Ph.D.,
FIStructE, is a consultant to Ramsay
Maunder Associates and an honorary
Fellow of the University of Exeter in the
UK. He is a member of the Academic
Qualifications Panel of the Institution of
Structural Engineers. He acts a reviewer
for several international journals, such as
the International Journal for Numerical
Methods in Engineering, Computers
and Structures, and Engineering
Structures. He can be contacted at
[email protected].
Matthew Gilbert, BEng, Ph.D., C.Eng,
MICE, M.ASCE, is Professor and Director
of Research in the Department of Civil and
Structural Engineering at the University
of Sheffield, UK. He is also the Managing
Director of LimitState Ltd, a software
company set up to make numerical methods
developed in the University available to
a wide audience. He can be contacted at
[email protected].
A similar article was published in Concrete
Magazine (July 2015). Content is
reprinted with permission.
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Structural
DeSign
design issues for
structural engineers
S
tructural engineers have a peculiar vocabulary, when you think about it. What
we call “stress” is not much like what
psychologists call “stress”. What we call
“strain” is not what the spectators think about
when watching a weight lifting match. And when
we ask what the moment is, a confused general
public thinks that in our own strange way we are
asking what time it is.
What we call something must be understood
within the context of what we are talking about;
it must be clearly defined. This is particularly
important when we get into the writing of a
legally binding document. If we mean to mandate
something, we need to be clear on what it is that
we are mandating.
Masonry Pilaster Definition
In the latest version of The Masonry Society’s
2013 MSJC Provisions, or the Masonry Building
Code (TMS 402/602), there
are certain provisions that
apply specifically to the
design of masonry pilasters.
However, the writers of the
code have not yet included
a definition for pilaster. So,
should we be allowed to impose our own (or
Webster’s) definition onto the code? It seems
that would be wrong, since the writers of the
code obviously had in mind structural members
with certain characteristics that were intended to
be governed by the specific pilaster provisions.
Although the original authors of the pilaster provisions did not include a definition, they did give
us clues as to what characteristics they envisioned
for pilasters. First we can look at the illustrations
in the commentary. Note that in figure CC-5.4-1,
titled “Typical pilasters”, all of the illustrations
show projections from either one or both faces
of the wall. We can also look at the provisions
to see what they require. The table of contents
for Chapter 5 refers us to Section 5.4 for pilaster provisions. Section 5.4 points us to sections
5.1.1.2.1 through 5.1.1.2.5. Interestingly, section
5.1.1.2 is called “Design of wall intersections”. So,
we can assume that they intended that a pilaster
would look something like that shown in the
figures, and it would have similarities with the
characteristics of intersecting walls. Reading the
provisions of 5.1.1.2, we find references to a flange
that is different than the web of the section. That
is the similarity between intersecting walls and
pilasters, and is shown by the projections in the
illustrations. A pilaster has a web that projects
from the flange(s).
Engineers on the west coast (the author
included, although few would define Utah as
“the west coast”) often forget that the provisions
of TMS 402/602 apply to both reinforced and
What is a Masonry
“Flush Pilaster”?
By David L. Pierson, S.E.
David L. Pierson, S.E., is a
principal at ARW Engineers
in Ogden, Utah. He teaches
Masonry Design at Utah State
University and is also the current
vice-chairman of the TMS
402/602 committee.
unreinforced masonry. Section 5.4 is written to be
generally applicable to both reinforced and unreinforced masonry. This clarifies the geometry even
further. In unreinforced masonry, any geometry
of a pilaster that did not have projections from
the wall would be completely impossible to differentiate from a partially grouted wall.
Flush Pilasters
When confronted with this, many engineers
may ask “But wait – what about those ‘Flush
Pilasters’ I’ve been designing for years?” In
fact, in the 2008 edition of TMS 402/602, the
figure that illustrates pilasters actually included
a sketch showing a “hidden” (or “flush”) pilaster.
Dr. Richard Bennett, current Chairman of the
TMS 402/602 Committee and a member of the
Committee when this was changed, shared some
of the history as to why the figure was changed.
The illustration for the “Hidden Pilaster” was
removed from TMS 402/602 in the 2011 edition.
This was done in response to a public comment
that correctly noted that a hidden pilaster and
a partially grouted wall are essentially indistinguishable. Yet the code allowed for a different
compression width to be utilized for a pilaster
(even a hidden pilaster) than it allowed for bars
in grouted cells of walls. This was obviously not
appropriate. It was wrong for the code to provide
different requirements applicable to the same
element. Dr. Bennett shared the exact language
from the rationale of the ballot item that deleted
that illustration:
“In response to public comment 51a, the commentary is changed to remove references to
hidden pilasters. Note that this does not
preclude the construction shown in Figure
2.1-5(c). Rather it just removes the problem
with the conflict pointed out in the public
comment relative to the compression width
of the bar. This ballot item does not address
adding a definition of pilasters to Section 1.6
(public comments 51a and 69). This non-life
safety issue will be taken up as new business
in the 2013 cycle.”
So, the response to those engineers who still want
to design “Flush Pilasters” would be …
You may call the strengthened portions of
walls whatever you’d like; however, since
the Pilaster provisions in the code are
applicable to a member that doesn’t have
a Flush geometric profile, those members
are not Pilasters within the language of
TMS 402/602.
But, as was noted in the rationale of the ballot
item quoted above, just because they are not
technically “Pilasters” within the definition of
TMS 402/602 does not, in any way, mean that
16 September 2015
they cannot be designed and constructed in
accordance with this code. It must be clearly
understood that those elements always could
be and still can be designed and constructed
in accordance with the code provisions.
The next question is this – What should be
used for “b”, the width of the compression
flange? There are a few options. For illustration we will check it three different ways:
First, assume b = 16 inches, the width of
the element. This is the minimum value that
could be used. With b = 16 inches, 2/kj = 6.16
Design Example
and npj = 0.0726. The masonry stress controls
Take, for instance, the common occurrence the design, with a corresponding np = 0.109.
of what might be termed “Flush Pilasters” So, p = A s /bd = 0.0067, and the required A s
in sound wall systems that are built along = 0.97 square inches of steel.
many roadways. To be technically accurate,
Now, check it with b = 72 inches, the maxicall these Strengthened Sections. Typical mum value allowed in section 5.1.2. For this
construction might be a 12-inch thick condition, 2/kj = 27.7 and npj = 0.016. Now
CMU, with Strengthened Sections occur- steel stress controls the design, with np =
ring between 12 feet and 24 feet apart. The 0.017. Thus, p = 0.00106, and A s = 0.68
Strengthened Section is likely16 inches wide, square inches of steel.
with reinforcing on each face (to get a maxiSo, if we were very conservative we could use
mum “d”) and cantilevers from a concrete pier b = 16 inches. Masonry stress would control
or grade beam. The portion of wall between the design, and we would use (1) #9 or (2)
these Strengthened Sections is supported ver- #7 bars, each face. By not utilizing a larger
tically continuously, but spans horizontally b, I am not being as efficient with the steel.
between the Strengthened Sections to resist
If we use b = 72 inches, we are using the
out-of-plane loads.
maximum b allowed in section 5.1.2. Steel
Below is one possible way to design these stress governs the design, so the steel is being
elements using the Allowable Stress Design used to full efficiency. We would use (1) #8
Provisions. This solution utilizes a method or (2) #6 bars, each face.
found in the Reinforced Masonry Engineering
Finally, if we use b = 20 inches, which is just
Handbook published by MIA (The Masonry 2 inches each side of the section, then np =
Institute of America). It is called the Universal 0.064, and A s = 0.72 square inches. This is
Elastic Flexural Design Technique.
essentially the same answer as using b = 72
Given:
inches. The reason for this is that at b = 20
• Wind Pressure per ASCE 7-10 = 30
inches, steel stress now governs the design.
psf, Load Combination is 0.6W + D
Once this happens, using a larger value for
• Construction: 12-inch CMU, 12 feet
“b” makes very little difference in the answer.
high, with 16-inch wide Strengthened
Some engineers might argue that if we use
Sections spaced every 12 feet.
(2) bars in this “Strengthened Section”, then
• f´m = 2000 psi, Medium Weight
section 5.1.2 would technically limit b to
Block, and Grade 60 reinforcing, so
16 inches (8 inches per bar), based on the
Fs = 32000 psi
“center-to-center bar spacing” requirement.
• Use bars each face, so “d” = 9 inches
The author would argue that, since we could
• The modular ratio n = 29,000,000 /
have used just one bar and only used two
Em = 16.1.
bars because it makes construction simpler,
The Design Loads on the Strengthened we should be allowed to assume that, for this
Section for this load combination are:
situation, the “center-to-center bar spacing”
• Dead Load (self weight of element only) should be considered as the spacing of the
= 165 plf x 12 feet = 2000 pounds
Strengthened Sections. This is a case where
• Wind Load = 18 psf x 12-foot spacing
engineering judgment must be allowed to
= 216 plf
be exercised.
The design moment on the section is 216
In either case, the wall would then be
x 122 / 2, or 15,550 lb-ft (187,000 lb-in). designed to span horizontally between these
(Note: some engineers may wish to reduce this elements, probably with (2) horizontal bars
moment by the resisting moment provided by in bond beams at 48 inches on-center.
the dead load of the element. By choosing not
Whatever you want to call these, this conto, the author is perhaps a bit conservative) struction always has been and continues to
The allowable Fb in the masonry due to be allowed. These elements could also be
flexure is 0.45* f´m, or 900 psi. This must be designed using other design methodologies,
reduced by the axial compression stress due based either on Allowable Stress Design or on
to the weight of the element, which is 11 psi. Strength Design. Results would be similar, if
So, use Fb = 900 – 11 = 889 psi for flexural not identical.
design (see code section 8.3.4.2.2).
STRUCTURE magazine
17
September 2015
Prescriptive Provisions
Beyond section 5.4, the only other significant provisions related to pilaster design
are found in 7.4.3.2.5., where additional
requirements are imposed if the pilaster is
supporting a discontinuous stiff element.
Note that ties are required in pilasters only if:
1) the pilaster is supporting a discontinuous
element as noted in 7.4.3.2.5, or if 2) the
designer is relying on the steel to support
compression loads (in which case the element
essentially becomes a column), or if 3) the
shear stress is so high that ties are needed to
resist shear (which is theoretically possible
but nearly impossible in practice).
There is a caveat to this entire discussion.
It applies to pilasters and strengthened sections of walls in reinforced masonry walls
that are laterally supported at floors and/or
a roof. Regardless of whether or not such
“pilasters” are projecting or are flush, the
design engineer should recognize that the
provisions of ASCE 7 section 12.11.2.2.7
must apply. In other words, although ASCE
7 does not include a definition for pilaster,
common sense indicates that for reinforced
masonry, whether or not the strengthened
section is projecting from the face of the
wall, it is, for the purposes of this section
of ASCE 7, a pilaster.
It is possible that in the next edition
of TMS 402/602, (anticipated to be the
2016 edition), additional definition will
be given to clarify what a pilaster is and
what it is not. If so, this will be simply a
clarification, so that engineers do not have
to wade through the provisions in order to
determine if what they are designing is a
“Pilaster”. It will not change the fact that
strengthened sections of reinforced walls
can still be designed and constructed, no
matter what they are called.
Finally, the next time you are trying to
determine the limit on how much reinforcing you can put into that masonry wall you
are designing, remember that ρmax has a very
different meaning to you than it does to a
spectator at the Harvard-Yale Regatta.▪
Although Mr. Pierson is affiliated with
TMS because of his position on the
TMS 402/602 committee, this article
represents only his opinions. This should
not be construed as an official position
statement from TMS.
Historic
structures
significant structures of the past
Schneider’s Plan for Niagara Bridge.
T
he Niagara River gorge had long separated the United States from Canada.
It varied in depth up to 239 feet and in
width generally between 800 and 1,000
feet between the Falls and Lewiston. Around 1836,
suspension bridges were proposed by Francis Hall
at Lewiston-Queenston and just above the falls.
Charles B. Stuart, in 1845, then working on the
location of the Great Western Railway in Canada,
was looking for
a way to connect
his line with the
Rochester and
Niagara Falls
branch of the
New York Central. He proposed to span the
gorge with a suspension bridge just above the
Whirlpool. Many thought his idea foolhardy, as
the only suspension bridges in the United States,
other than some Finley bridges left over from
the early part of the century, were Charles Ellet’s
Fairmount Bridge over the Schuylkill River built
in 1842 and John A. Roebling’s suspension aqueduct built across the Allegheny River in 1845.
Stuart sent a circular letter to “a number of the
leading Engineers of America and Europe, asking
their opinion of the undertaking.” Of those who
responded, only four thought the project feasible.
Stuart wrote, “Charles Ellet, Jr., John A. Roebling,
Samuel Keefer and Edward Serrell, alone favored
the project...”
Ellet’s proposal was accepted, with modifications, for the sum of $190,000. The span would
be 800 feet with a deck width of 28 feet. The
deck would have two carriage ways, two footways
and one railway track in the center of the floor.
Ellet started by building a 9-foot wide temporary
bridge but, after charging tolls for people to cross,
he had a falling out with the Company in 1849.
John A. Roebling took over the project in 1850,
offering to build the bridge for $180,000 and to
subscribe to $20,000 in stock in the bridge company. He changed his original design from a single
deck structure to a double deck structure, with the
railway on the top level and carriage and footways
on the lower deck. Work would not commence
on the Niagara project until 1852, with Roebling
providing all engineering services including design
as well as construction supervision. His company
The Niagara Cantilever Bridge
By Frank Griggs, Jr., Dist.
M. ASCE, D. Eng., P.E., P.L.S.
Dr. Griggs specializes in the
restoration of historic bridges,
having restored many 19th Century
cast and wrought iron bridges. He
was formerly Director of Historic
Bridge Programs for Clough,
Harbour & Associates LLP in
Albany, NY, and is now an
independent Consulting Engineer.
Dr. Griggs can be reached at
[email protected].
also supplied a significant amount of wire to be
used in the bridge. He completed his 822-foot
span double deck bridge in 1855. A one-track
railroad ran on the upper deck (22 feet wide),
and pedestrians and carriages passed on the lower
deck (15 feet wide).
In 1874, T. C. Clarke, of Clark & Reeves
Company and later Phoenix Bridge and Union
Bridge Companies, was asked by the manager
of the Western Railway of Canada to “report on
the best mode of construction, necessary time
required, and cost of a double track iron bridge.”
He recommended, “a braced arch, hinged in the
center and at the springing. The clear span was
430 feet, and the height or versed sine 175 feet.
The arches were to have been erected by corbelling out as was done at St. Louis.” In 1882, the
Michigan Central Railroad was ready to build its
own bridge at a site near the suspension bridge.
On October 13 they requested Charles Conrad
(C. C.) Schneider to submit a proposal. They
wanted “an estimate for a double-track railroad
bridge of 900 feet clear span, for the purpose
of ascertaining the probable cost of bridging
the Niagara below the Falls, near the Railroad
Suspension Bridge, intimating that a braced arch
reaching from cliff to cliff might be the proper
design for the proposed structure.”
Schneider had also been given the design for an
iron bridge over the Fraser River, which flowed
southerly into Puget Sound just north of the
United States border. The Fraser River was a fast
flowing stream which precluded the placement
of falseworks in the river bed. Schneider, based
upon his previous exposure to the Blackwell’s
Island Bridge competition and Smith’s success
at High Bridge, decided to build a bridge using
a cantilever technique.
He completed the design of the 525-foot span,
located 125 feet above the river, in the spring of
1882. The directors of the line decided to have
the iron rolled and fabricated in England, a result
of Prime Minister MacDonald’s tariff program
that made United States iron and steel excessively priced. Canada had not as yet developed
its own iron and steel industry to any significant
degree. Due to the slowness of the delivery of
the Fraser River Bridge iron (it reportedly took
almost six months for the ship carrying the iron
18 September 2015
Layout of span and reactions, showing suspended span.
ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org
to Canada to make it across the Atlantic),
it would not be completed until 1887
or four years after the Niagara Bridge. It
lasted until 1910 when it was taken down
and re-erected, one of the beauties of a
pin-connected structure, across a chasm,
appropriately called the Niagara Ravine,
on a branch of the Canadian Pacific near
Victoria, B. C.
Upon receiving more exact topographic
information at Niagara, Schneider
“decided that the cantilever plan would
be most feasible and economical for this
location...” He submitted his completed
design to the Central Bridge Works of
Buffalo, New York. They in turn submitted a tender to the Niagara Bridge
Company that was accepted by the Board
of Directors on April 11, 1883. Based
upon better survey and boring information, he modified his pier locations which
changed the span lengths of the cantilever. He also decided to use wrought iron
primarily, with some steel.
He chose to use Squire Whipple’s double
intersection pattern (STRUCTURE
magazine, May 2015), for his anchor and
cantilever spans that George Morison,
his mentor, used on his Missouri River
Bridges and C. S. Smith used on his earlier cantilevers. On the short suspended
span he, used a single intersection truss.
He wanted to have his piers of iron just
as Smith had done at the High Bridge,
but he decided to bring his iron work up
parallel, in a direction perpendicular to
the axis of the bridge. In order to make
the structure determinant, he omitted
the diagonals in panel BC; it is evident
that no other strains can be transmitted between B and C than moments,
the points of support being practically
reduced to 2, and the shearing strain in
panel BC becoming 0.
Schneider took great care in insuring
that all the iron and steel, particularly
the steel, met the specifications. In
accordance with his experience “with
steel for structural purposes which had
STRUCTURE magazine
19
September 2015
Niagara Cantilever.
ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org
to be made according to a specification, there
have always been considerable delays, and
this case was no exception to the rule. The
records of the tests will show that the steel
which has been accepted was of a good uniform quality.” With his design complete and
quality of material acceptable, the fabrication
of the structure took place in the yards of
the Central Bridge Company.
The erection technique worked out by
Central Bridge Company and Schneider
became the pattern that would be followed
on many cantilevers in the future. They
began by building the anchor spans from
falsework resting on the rock banks and
the towers by travelers off of the anchor
span. The travelers worked outward on each
cantilever arm until they reached the end
of the cantilever span.
The suspended span was 120 feet long, and
the maximum reach of each traveler was 40
feet. Schneider did not want the traveler to
go beyond the end of the cantilever span, as
he did not want to overload the span or the
anchorage. This left 40 feet of suspended
span which could not be erected by the travelers. He handled this by placing wooden
beams across the 40-foot gap and erecting
the rest of the truss by hand methods.
The speed at which the bridge was erected
was as impressive. Schneider wrote:
The first metal of the cantilever shore
arm on the American side was placed
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Traveler and erection sequence, showing falsework and traveler.
on the falseworks on September 25 th,
and erection completed on October
15 th. The erection of the cantilever shore
arm on the Canadian side was commenced on October 8 th, and finished
on October 22 nd. The traveler on the
American side was completed on October
25 th, and erection of the river arm commenced on October 28 th. The traveler
on the Canadian side was completed on
October 31 st, and erection of the river
arm commenced on November 4 th. The
last connection was made on November
22 nd, at 11:55 A. M.
The travelers and falsework were removed
and the first track laid on December 6. The
formal opening and testing took place on
December 20, 1883. The bridge contained
almost 4.5 million pounds of iron and steel,
with about 70 percent of it being wrought
iron. What Schneider and Central Bridge
had done was to erect a new style bridge using
new techniques, over 900 feet long and 230
feet over the Niagara River, in less than two
months. The entire Niagara project, which
started with foundation work on April 15,
took only slightly more than eight months to
complete. The bid price for the entire project
was $680,000.
In 1900, or seventeen years after construction, the bridge was reinforced without
material interruption of traffic by the addition of a new center truss midway between
the original trusses and supported on a new
tower trestle and anchorage pier on each
bank. “The new superstructure has the same
STRUCTURE magazine
20
September 2015
general outline and dimensions as the old
one, and the details correspond so far as
possible to those of the old members...It
was decided to strengthen the bridge, not
so much because it is unsafe under present
loads but because the near future will evidently see trains and engines much heavier
than are now being run across the bridge
and heavier than was thought entirely safe
for the original structure. The new truss is
intended to be 50 percent stronger than
either of the old trusses...In order to insure
perfect safety against any uplifting of the
anchorages, anchorage pits are being sunk
about 25 feet under the end piers and the
anchorage made there for the new truss in
addition to the weight of the old pier...The
material for the work is being furnished by
the Detroit Bridge & Iron Works for plans
made under my supervision [Benjamin
Douglas, bridge engineer for the Michigan
Central)...and the erecting is being done by
the regular erecting gang. “
C. C. Schneider’s brainchild was reinforced without any apparent involvement
by its creator. Schneider was still active
in 1900 as Vice President in charge of
Engineering for the newly formed American
Bridge Company, located in New York City.
The bridge was taken out of service and
demolished in 1925 after having a useful life
of over forty years. It was replaced by a steel
arch bridge located between Schneider’s
Bridge and Roebling’s Suspension Bridge
(which was replaced with an arch by Leffert
L. Buck in 1897).▪
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The ACI 562 code provides standard requirements for evaluating existing concrete buildings and the subsequent structural
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Building
Blocks
Fundamentals of
Hardened Concrete
Monolithic concrete with a compressive strength
in excess of 3500 pounds per square inch (psi)
is watertight, except at any irregularities in the
structural element. Typical locations where irregularities occur include overhead decks, floors,
and walls that have cracks, honeycombs, joints,
mechanical/electrical penetrations, and form-tie
supports. Hairline cracks in excess of 1/1000 of
an inch (i.e. 1 mil) commonly leak water if subject
to hydrostatic pressure. Water leakage rate and
volume, or quantity, is related to pressure and
crack width.
updates and information
on structural materials
Concrete Cracking
When concrete is freshly cast, its temperature
is often between 60º and 90º F. Depending on
the in-situ form, materials, temperature, environmental conditions, and composition of the
mix design, concrete hydration may generate
significant additional heat. Thermal expansion
of the semi-plastic structural element will occur
and, depending upon local restraint, may cause
micro-cracking.
Depending on local restraints, minute small
cracks (defects within the cement/aggregate
matrix typically so small they can’t be seen by
the naked eye) develop externally and internally. After the forms are removed, the concrete
continues to shrink from both cooling and loss
of water. This process varies with environmental
conditions and may create cracks capable of
water leakage within hours of form removal,
and within days after wet curing. For most
structural elements less than 14 inches thick,
it takes about 5 years for shrinkage to subside.
In this time, the cracks initiated by thermal
contraction become much larger. These cracks,
depending on reinforcing, sectional dimensions, mix design, and restraint conditions,
can be as large as 5 to 50 mils. If subjected
to water under hydrostatic pressure, serious
leakage will occur.
Ingredients for Corrosion
Corrosion in reinforced concrete requires three
basic ingredients; oxygen, water, and an electrolyte medium. Fundamental to corrosion
mitigation is minimizing at least one of these
three basic ingredients.
Issues from Leakage
One of the biggest concerns with water leakage in
heavily reinforced concrete is that the time for the
onset of corrosion is shortened. It is well understood that if you eliminate oxygen and water from
the immediate environment around reinforcing
steel, corrosion is generally minimal and essentially mitigated. When through-element cracks
Monolithic concrete with a compressive strength in excess
of 3500 PSI is watertight, except at any irregularities.
occur from outside to inside
face, allowing air or dissolved
oxygen in the water to interact
with the steel, all three of the
critical items are now available
for corrosion to occur.
In addition to corrosion, water
leakage can bring salt and various stray minerals that can exacerbate other issues
within the concrete, e.g., sulfate attacks. External
issues with water leakage are many – ice buildup,
slip problems, treatment of contaminated water,
and potential mold issues.
Proper Procedures and
Protocol for Interception
Grouting
By Brent Anderson, P.E.
Fundamentals of
Interception Grouting
Directional Drilling
The objective of interception grouting is to
make the concrete element monolithic. This
can be achieved by pressure injecting a resinous material through one or both concrete
element faces (surface mounted ports), or by
drilling at a 45-degree offset to the defect and
injecting into the defect in the center third
of the concrete element section (interception
grouting). The importance of drilling into the
center of the concrete element is that, during
grouting, the resinous material should flow
equally to the inside and outside face of the
concrete section in a uniform manner. If drilling into the interior third of the section, grout
flow will not extend to the exterior. Drilling
into the outer third of the section will unlikely
allow grout migration to the interior. By proper
placement of drill holes, grout flow will intersect from bottom-to-top or side-to-side with a
relatively high degree of reliability. Long-term
STRUCTURE magazine
23
Brent Anderson, P.E., is the
Moisture Control Solutions Team
Leader at Structural Technologies.
He serves on ACI 332 Residential
Concrete and previously served on
ACI 515 Protective Coatings for
Concrete. Brent can be reached at
[email protected].
Typical water leakage paths.
grouting solutions intercept the defect in
the center; short-term solutions allow shallow drill depth holes. In addition to crack
interception at the concrete element’s center
third, most quality contractors alternate
directional drilling on each side.
Drill Hole Spacing
Generally, the rule of thumb is that drill hole
spacing should be one half to two-thirds the
concrete element thickness. This allows an
overlap of about 20 to 30 percent between
drill holes. Drill hole spacing up to the width
of wall element can be done if cracks are relatively large – i.e. 50 to 100 mils wide.
Interior and/or exterior steel can influence
the drilling angle based on its density and
location. Angles of 30º to 60º are not uncommon provided that interception drilling is
done in the wall center. Because cracks vary
in direction, drilling should be 20 to 25 percent deeper for interception grouting than
what the typical calculations dictate. Drill
hole diameter is not critical and can be left
to contractor preference.
Cleaning
Just as important as intercepting the crack
at the element midsection is cleaning the
drill hole of debris prior to setting any ports.
Injection drill holes should be blown out with
high pressure air and then flushed thoroughly
with a water jet. Some contractors even push
and flush a wire bristle brush down the drill
hole and scrub the area of intersection to
remove surface debris.
Crack Flushing
The next important aspect is to put a port on
the surface and flush the crack. Flushing the
crack is important for two reasons:
1) To push out any mineral deposits
(clay, silt) that may have accumulated
in the crack, and
2) If water is pumped and does not make
it to the surface of the concrete, grout
will not make it through either.
These are often questions as to whether or not
some kind of acidic material (e.g., phosphoric
or muriatic) should be used. Generally, it is
an acceptable approach, but it should come
with some safety precautions and the use of
proper personal protective equipment to keep
acid away from the face.
Acid washing the drill hole and the crack
improves the bond ability of any type of resin
that is injected into the crack later. If the crack
has debris and mineral deposits, the effectiveness of the grout will not be as monolithic
as needed, and secondary or minor leakage
could still occur.
Pressure
Interception grouting should be done in a way
that the internal hydraulic pressures of the grout
never exceed the tensile strength of the concrete.
The tensile strength of concrete is 10% of the
compressive strength. Most concrete that interception grouting will be performed on will have
a tensile strength of 300 to 500 psi. It is recommended not to use pumping grout pressures
in excess of 500 psi. In so doing, the concrete
surface may spall where the drill holes exist and/
or the pressure may hydraulically fracture the
concrete and create additional cracks.
A word of caution, use of high viscosity
resins may lead to internal damage of the
concrete. High viscosity resinous materials
are not as user friendly as low viscosity injection materials. For comparison, water has a
viscosity of one centipoise – so grouts that
have values of 50 to 300 centipoises means
that they are 50 to 300 times more viscous
than water.
It is not uncommon for contractors who do
not have a good understanding of viscosity
and crack width to use resinous grouts with
300 upwards to 500 centipoises and pressures
up to 3000 psi to accomplish placing resinous
material within the crack.
Grout Delivery
There are three types of delivery systems generally utilized: small hand operated pumps,
STRUCTURE magazine
24
September 2015
It is important to intercept the crack at the center
third so that the resinous material flows equally to
the inside and outside face of the concrete section.
small electric operated pumps, and high
volume air driven or piston driven pumps.
Most hand and small electric driven pumps are
for single component resins. The larger piston
pumps can be used for 1-3 components.
Small electric pumps require minimal
maintenance. However, after several uses the
pumps are discarded and new ones are purchased. Others prefer to buy the large piston
drive, both single and multi-ratio. What’s
important is that these pumps have a capacity of ¼ gallon per minute and have pressure
capabilities up to 750 psi.
Injection Packers
There are basically three types of injection
packers – button head, grease zerk, and ball
valve quick connect. The advantage of the
grease zerk packers is that they are inexpensive and can be discarded after one use.
Button head packers are similar and usually
discarded after one use. The ball valve quick
connect packers are more expensive, but can
be reused multiple times. Another advantage
of the ball valve is that you can open and
close the valve to monitor water or grout flow.
Button head and ball valve quick connect
packers generally do not restrict grout flow
and increase pump gauge pressure during
application. Disadvantages of zerk packers
are that they cannot be opened and closed to
monitor grout movement and they are very
restrictive to grout flow, requiring about 100
to 200 psi gauge pressure just to move most
grouts through them.
Causes of Premature
Grout Failure
There are 4 basic causes of premature grout
failure:
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STRONGER
MORE DURABLE
To achieve the right mixing ratio of water to grout,
a multi-ratio pump should be used.
Most quality contractors alternate directional
drilling on each side.
Conclusion
It is important for engineers and contractors
alike to remember that the grout viscosity
needs to match up with the crack width, and
the grout chemical resistance needs to match
the exposure. The most successful grouting
contractors have a good knowledge of chemical resistance and have good field experience
in developing techniques that allow them to
get low viscosity grouts to migrate deeply
within finely cracked concrete.▪
STRUCTURE magazine
25
September 2015
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1) Improper drilling and delivery
It is not uncommon for contractors to
drill directly into the crack or too close to
the surface. By doing this, a seal is created
that is 1/3 to ½ of the crack depth and
water under hydrostatic pressure is still
within the concrete element. Very little
flexural movement causes leakage to recur.
2) Inadequate mixing ratio of water to
grout during application
Most contractors are taught by manufacturers that pre-wetting the crack
prior to urethane grout injection is all
that is needed to activate the material.
This would likely be the case of the wall
4 to 6-inches or less in thickness. Wall
and floor sections greater than 12 inches
would not fit the criteria however, and
a multi-ratio pump for injecting water
reactive urethane grouts should be used.
Some contractors prefer to use two small
electric pumps – one to inject urethane,
one to inject water – and then rotate a
few strokes of water to several strokes
of grout thinking they are getting good
cross-polymerization of water to urethane.
While this may seem a viable solution
because the first grout that comes to
the surface appears to be fully reacted,
it is very common to have areas of water
deprived urethane grout within cracks
and other defects. When these conditions
are subjected to high temperatures in the
environment (in excess of 100 to140º
Fahrenheit), it is common to see a brown,
unreacted urethane resin extrude from the
cracks anywhere from 2 months to 2 years
after the initial grouting. This urethane
resinous material has now contaminated
the crack for future injection. Many
contractors have found that the only
viable way to seal cracks with unreactive
grouts is the backside grouting method.
3) Excessive wall movement
Excessive movement is most prevalent
when the concrete is subject to outdoor temperatures – i.e. exterior tanks,
retaining walls, exposed foundations,
etc. Most resins have some degree of
flexibility. It is not uncommon that
during warm to cold cycles, a 5 mil
crack will open to a 10 mil crack. Most
resinous grouts, even though they are
called flexible, cannot sustain repeated
opening and closing of the crack and
will fail. Grout adhesion to the substrate
may fail during expansion and contraction of the crack if surface contaminants
on the grout sidewall are prevalent.
4) Chemical attack
Chemical attack is very common in the
industrial environment, and this type
of issue usually takes several years to
work its way through the grout matrix.
Residue hydrocarbons within water will
commonly attack many of the grout formulations. This is exacerbated if chemical
attack and thermal expansion/contraction are occurring simultaneously.
3000 PSI IN 1 HOUR
Structural
rehabilitation
renovation and restoration of
existing structures
T
his series of articles discusses a number
of commonly encountered structural
issues on renovation and restoration
projects that focus on historic houses
of worship, and provides guidance on ways to
address them. Parts one, two, and three of this
series dealt with foundations, wall systems, and
roof framing in historic houses of worship. This
article addresses interior architectural components
and finishes.
Architectural components and finishes are often
the most visible and identifiable elements inside
historic houses of worship. They define the ambiance and “feel” of the space, reflect the cultural
and religious sense, and are often a testament
to history and development of communities in
which these structures were built. Given their
effect and significance, a lot of thought should
be placed on their appearance, performance, and
serviceability. However, if designed or installed
improperly, if exposed to severe or unplanned conditions, or if not regularly
maintained and repaired,
they may undergo accelerated deterioration and
decay, or can be subject
to distress that can cut
their expected service life
short. Therefore, when
planning repair, renovation, or rehabilitation projects, understanding the
basic material properties of common architectural
components and finishes, addressing their potential vulnerabilities and exposure limitations, and
considering structural support, compatibility, and
constraint issues, is paramount.
Divine Design: Renovating
and Preserving Historic
Houses of Worship
Part 4: Architectural
Components and Finishes
By Nathaniel B. Smith, P.E. and
Milan Vatovec, P.E., Ph.D.
Wood Components and Finishes
Nathaniel B. Smith, P.E., is a
Senior Project Manager at Simpson
Gumpertz & Heger’s office in New
York City. He can be reached at
[email protected].
Dr. Milan Vatovec is a Senior
Principal at Simpson Gumpertz &
Heger Inc. He can be reached at
[email protected].
Wood is a natural building material known for
its workability, high strength-to-weight ratio, and
durability. Wood’s natural beauty is unequaled.
Wood is also the only truly organic building product that is renewable and sustainable. As such,
wood has successfully been used for centuries in
a structural role and, perhaps more prominently,
as a go-to material for architectural components
and decorative finishes in houses of worship. Its
ability to be milled and carved, and its ability
to receive stains and paints, has made it a great
option for finish work and flooring, and exposed
structural and architectural members.
Wood, however, can also be challenging to work
with. It comes in many varieties (species), with
each variety having its own unique characteristics.
Sawn lumber can have natural-growth defects
(e.g. knots, splits, excessive slope of grain). Wood
properties can vary significantly even between
pieces of lumber taken from the same tree. The
makeup of the cell structure of the tree trunk
causes sawn wood to be orthotropic; it behaves
differently in three principal orientations (directions), defined basically with respect to the
configuration of a tree trunk. The orthotropic
behavior comes into play in terms of strength
and stiffness differences, resulting in a number of
design and detailing consequences (e.g. never load
wood in tension perpendicular to grain). It is also
a large factor when it comes to physical properties,
most notably orientation-dependent differences
in shrinkage and swelling (dimensional-change
reaction to moisture intake and release in response
to environmental changes), durability, and, last
but not least, appearance. Finally, wood is susceptible to attack by microorganisms, which requires
special care and consideration both in design
and in-service. Because of all this, optimal use of
wood often depends on special knowledge that
requires integration of material science, engineering, and familiarity with construction practices
and detailing.
When it comes to structural design, engineers
tend to place high importance on the mechanical
properties of wood components, which typically
includes variability in properties, natural-growth
characteristics, and orthotropic-behavior considerations. By and large, this is accounted
for through established design processes (e.g.
stress grades and associated design values, etc.).
Vulnerability to biological attack and propensity
to dimensional change in service are generally
addressed through standard detailing. Often,
however, issues that affect non-structural wood
components in service, and particularly in historic
structures, involve non-standard use or detailing, or are not within the domain of a structural
engineer. In these situations, architects, builders,
and other practitioners that design, fabricate, and
install wood components and finishes are required
to pay special attention to a number of additional
parameters, often related to all phases in the “life”
of the wood component: harvesting, milling,
drying, conditioning, installation, environmental
exposure, geometric and boundary constraints,
type and duration of loads, etc.
The most common problems with wood in
service are related to deterioration from unanticipated exposure or to distress resulting from
dimensional changes. Both of these problems are
driven predominantly by exposure to and effects
of moisture (either as humidity in air or as liquid
water). In general, moisture is considered to be
the number one contributor to problems with
wood and its performance in service. While wood
deterioration due to decay (a.k.a. rot) from moisture exposure is likely the greatest contributor
to loss of wood material in service in the world,
the implications of water exposure, the resulting
change in properties, and ultimately the damage
caused by fungal action will not be discussed in
detail here; the focus of this article will be placed
on dimensional stability and associated issues.
26 September 2015
Wood elements and components meant for
interior use will typically be in what is considered
a “dry” condition immediately before, during,
and after installation; they would have undergone either an air or kiln-drying process before
delivery. However, the actual moisture content
of interior wood, while in general considered
dry, will fluctuate, sometimes significantly, in
wood’s attempt to be in equilibrium with its
environment. As the temperature and relative
humidity (RH) of air surrounding wood components fluctuate (seasonally or otherwise), the
wood’s moisture content (MC) will fluctuate as
well, albeit with some inherent lag. As the MC
goes up or down, wood elements will swell or
shrink, respectively. Even for interior use, the
expected yearly MC swing of wood components could be on the order of 5% (especially
in spaces where RH is not controlled), which,
depending on wood species, can translate into
approximately 1 to 2% of cross-grain shrinkage
or swelling (Wood Handboook, Forest Product
Laboratory, 2010, Tables 4-2 and 4-3). To further complicate things, cross grain movement
is not uniform; expected movement in the tangential direction is approximately two times
larger than in the radial direction (relative to
orientation of tree rings). Therefore, the extent
and uniformity of movement will depend on
the orientation of the wood grain within the
piece, which is dictated by where the piece was
milled from the tree.
Given all of the above, it is not surprising
that dimensional compatibility and restraint
problems are often encountered with wood in
service. If not designed or installed properly,
shrinkage will cause joints between adjacent
pieces of wood to open, whereas expansion
will make the joints tight, and, in extreme
situations, buckling or other distress will
ensue. The buckling problem is often most
pronounced in wood floors that are exposed
to high levels of moisture (e.g. leakage), floors
that were installed too wet (or on the high end
of the expected equilibrium spectrum), or are
not detailed to allow for sufficient expansion
without causing distress.
Other types of architectural components or
finishes may also be subject to restraint-related
distress, if not detailed to allow movement. It
is not uncommon to see infill boards or trim
panels crack or otherwise become distressed
because they were too “tightly” connected to
their frames. Veneers and other thin elements
may crack or be subject to localized buckling
(waviness) when “married” to a substrate that
does not undergo similar moisture-driven
dimensional changes.
Depending on the orientation of the grain,
individual members not restrained against
movement can also be subjected to distress.
Buckled wood flooring.
Cupping and twisting may occur even when
wood undergoes small MC changes in service because of the difference in cumulative
dimensional movement between the tangential and radial directions.
Simply put, wood will move with moisture fluctuations, and it does not like to be
constrained against that movement. If it is,
problems that may be difficult or very expensive to address will likely occur. Ironically,
engineers, who are typically not involved
with design, detailing, or specifying nonstructural components and finishes, are often
best equipped to deal with existing issues, or
to predict (and therefore avoid) problems
in-service related to wood material behavior.
Tools and knowledge exist.
Having foresight, and respecting wood
behavior and its response to the design
environment, is key. Similarly, proper detailing, especially if developing new, non-vetted
systems, is paramount. Finally, acclimatization, selection, treatment (if any), and proper
installation of wood components should all
be carefully considered and incorporated
into the specifications for renovation and
remedial projects.
Plaster Finishes
Plaster is one of the most common interior
finishes found in historic houses of worship,
with typical applications for wall and ceiling
surfaces. Ornate, molded plaster finishes (trim,
finials, florets, etc.) are often incorporated into
the overall finish work. While plaster is a tried
and true finish that has been used for centuries,
Splitting of infill panel in wood bench.
STRUCTURE magazine
27
September 2015
it is not without its limitations. Plaster in its
simplest form is a combination of hydraulic
lime, sand, and water. Water reacts with the
hydraulic lime, causing it to chemically bond
to the sand particles creating a solid substance.
The plaster stays in a “fluid” state for a limited
time, allowing it to be applied by trowel to
walls and ceilings, or it can be placed into
molds to take specific shapes prior to solidifying. Plaster for walls and ceilings is typically
applied in two layers. The base layer, often
called a “brown coat,” contains relatively coarse
sand particles and helps give the plaster its
strength. The top coat, or “finish coat,” typically contains fine sands, which gives the top
coat its smooth finish.
Plaster can be applied directly to masonry or
terra cotta, as the hydrated lime will bond with
stone and clay particles within these materials.
However, plaster for walls and ceilings is often
supported by lathe, which is typically wood
or metal mesh. Older construction typically
features a wood-lathe substrate, which is a
series of parallel wood strips about ¼ inch
thick, 1 inch wide, spaced about ¼ inch to
½ inch apart. When the plaster is applied
to the lathe, it is pushed through the spaces
between the wood strips and tends to ooze
over the backside, creating a plaster “key”.
This “key” helps hold the plaster in place. A
similar process occurs with metal lathe as the
plaster oozes through the wire mesh.
Plaster keys are a critical component of overhead plaster applications. Sufficient keying
needs to be created to hold the ceiling in place.
Lack of adequate keys can cause portions of
the ceiling to become loose, to debond, and
potentially fall. Plaster keys in ceilings can also
break over the life of a building through the
course of regular maintenance and alterations.
Installation of new lighting or mechanical
equipment from within attic spaces can often
break keys, resulting in the potential for ceiling failures. Detecting failures or distress in
plaster keys is often difficult and may require
specialized access and equipment (e.g. minimally-destructive testing instruments such
as boroscopes).
continued on next page
Typical wood lathe plaster ceiling with broken keys
and lathe from light fixture installation.
There are numerous available options to
address broken keys. Several of the more
common options include:
• Remove and Replace: One option to
address broken keys is to remove the
affected portion of the plaster and
replace it. This will certainly address
the issue but can be cost prohibitive
due to access and coordination
constraints (scaffolding likely required).
It can also be a time consuming process
as the plaster needs to be removed, new
plaster installed and allowed to dry,
then sanded and painted to match the
surrounding areas. Special blending
of paint is needed to match the
surrounding areas as well. Also, plaster
on metal lathe will likely require new
lathe to be installed, as salvaging the
existing lathe may be difficult.
• Additional Mechanical Support: The
affected portions of the plaster can
be reattached to wood lathe through
mechanical means, such as screws.
Screws with large plastic washers are
typically installed through the plaster
into the lathe or ceiling framing. This
option also requires access from the
underside of the ceiling to allow for
placement of a skim coat of plaster over
the fasteners to conceal them, followed
by a fresh coat of paint.
• Cover-board: In some circumstances,
placing a new ceiling below the original
and fastening it through the existing
ceiling is a preferred option. Gypsum
drywall, often used in this application,
is placed on the underside of the
existing plaster. With this option, care
should be taken to ensure that the
new drywall sheets are supported by
the ceiling framing and not the wood
lathe. Wood lathe in historic structures
is often fastened to the ceiling framing
with cut nails (tapered nails cut from
flat stock), which may withdraw under
the additional load of the drywall.
• Consolidation: Another option that
seems to be gaining popularity, due
to its minimally invasive nature, is a
consolidation process. The process
includes applying an acrylic resin to the
backside of the plaster, typically from
within attic spaces or through small holes
drilled in the plaster. The resin permeates
into the plaster and then cures to create
a solid mass that is stronger than plain
plaster. This process can reestablish keys,
fill in small cracks, and strengthen the
plaster. This process also has the benefit
of having a minimal impact on the
finished face of the plaster.
Choosing the correct plaster remediation
option depends on numerous factors, including the condition of the existing ceiling,
ceiling framing, and architectural features of
the ceiling. If the ceiling is of architectural
significance, options that leave the existing
ceiling in place should be explored first. While
leaving a ceiling in place may be the ultimate
goal, understanding the limitations of the
plaster and support system is a critical step in
order to make an informed decision.
Structural engineers are often called upon to
evaluate the plaster-ceiling support system to
determine if it has adequate capacity to support
additional ceiling loads (cover-board) or other
Plaster ceiling framing can be quite complex.
STRUCTURE magazine
28
September 2015
architectural features (lighting, insulation, etc.),
or in some cases partial removal to accommodate access. In other cases, these framing
systems require evaluation to determine if their
condition renders them inadequate to continue carrying the ceiling loads. Understanding
the ceiling-framing layout is a key step in this
process. The support framing for flat-ceiling
systems is typically straightforward, with a
series of parallel joists supporting the lathe
and plaster; these systems are easy to assess and
analyze for additional loads. However, many
houses of worship are not flat and feature very
intricate ceiling geometries, often with gothic
arches. Despite the large level of redundancy,
the framing for such ceilings is often independent from the main roof structure and can be
much more difficult to analyze due to complex
geometry, a multitude of components (with
various stages of effectiveness or deterioration
that may be difficult to quantify), unclear load
paths, and lack of accessibility.
Non-Standard Components
and Furnishings
Many renovation projects in historic houses of
worship call for installation of new furnishings,
or components that need to be incorporated
with and supported by the existing structure.
These new components may be related to
accessibility (new ADA ramps or elevators),
improvement of mechanical systems (e.g. new
chiller units), or could simply be related to
aesthetic or other improvements (new organs,
chandeliers, heavy furniture, statues, etc.).
While structural engineers will often consider
the load associated with furnishings as part of
the uniform live load, some of the proposed
components can be quite heavy and may
require special attention. For example, many
religious furnishings and statues are made of
solid stone, are quite heavy, and require proper
support analysis and design.
Often, the hardest part of determining how to
support the new loads is actually determining
what the load is. Some of the furnishings are old
and do not come with established weights, so
an estimate needs to be made. Sometimes, fairly
detailed historical or material research is needed
to gain a comfortable level of understanding of
the component materials and geometry, and to
be able to develop reasonable loads for use in
design of the support components.
Similar to other situations where structural
modifications to the original structure are proposed, addition of heavy loads requires that
the load path and all elements that may be
affected along it be well understood. Given the
likely absence of any structural drawings, this
frequently requires a probing program where
finishes are removed to expose the underlying
structure. This process is not always straightforward and may require several iterations before
full or sufficient understanding of the load
path and the involved structural components is
gained. In addition, material characteristics of
or alternate load paths that can be evaluated,
including sistering, shortening the span,
adding supplemental supports or cross section to the existing members, etc. If the loads
are excessive, it may be easier to provide an
alternate load path through installation of
new members or systems, in lieu of reinforcing. The best option will depend on the
specifics of the furnishings, the existing framing, and the ultimate needs of the owner.
Economics and ease of installation, along
with the needs of the surrounding programming space all need to be considered when
making recommendations.
Non-standard furnishings require proper support.
all the involved structural components need to
be understood. Historic buildings often feature
a variety of structural framing materials including wood, timber, cast iron, and steel, and it is
not unusual to see any combination of these
within the load path. The material properties
for each can be difficult to ascertain, and, if
conservative estimates cannot yield effective
design, sampling and subsequent laboratory
testing may be required.
If a deficiency in the load path is found,
there are numerous options for strengthening
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STRUCTURE magazine
29
September 2015
Conclusion
While not always considered to be in the
wheelhouse (or even within the scope of services) of structural engineers, consideration
of mechanical and other material properties
of non-structural components in the design
phases of historic renovation projects is critical. Regardless of whether the project revolves
around design and installation of new systems or evaluation and retrofit of existing
systems, special care aimed at understanding and anticipating the in-service behavior
of architectural components and finishes is
required of everyone involved.▪
Codes and
standards
updates and discussions
related to codes and standards
P
rovisions for the design of cast-in-place
and post-installed anchors were introduced into the American Concrete
Institute (ACI) publication Building
Code Requirements for Structural Concrete (ACI
318) in 2002 (ACI 318-02) via Appendix D –
Anchoring to Concrete. Since ACI 318 is referenced
in the International Building Code (IBC), these
provisions are thereby incorporated into IBC
Chapter 19 – CONCRETE.
Cast-in-place headed bolts and headed studs are
generic products that can be used directly with
Appendix D provisions. However, post-installed
anchors must be qualified for use with the provisions of Appendix D due to the inherent diversity
of adhesive and mechanical anchor products. For
example, hybrid adhesives have different performance and behavioral characteristics versus epoxy
adhesives. Likewise, epoxy adhesives can vary widely
in performance due to differences in their chemical
makeup, and in their installation requirements.
Given the wide array of
post-installed anchor types
and performance characteristics, ACI developed two standards to qualify these
anchors for use with the Anchoring to Concrete provisions in the ACI 318 code. ACI 355.2 Qualification
of Post-Installed Mechanical Anchors in Concrete
was first printed in 2002. ACI 355.4 Qualification
of Post-Installed Adhesive Anchors in Concrete was
first printed in 2011. These standards serve as
baseline provisions for two International Code
Council Evaluation Service (ICC-ES) Acceptance
Criteria: AC193 Acceptance Criteria for Mechanical
Anchors in Concrete Elements (first printed 2002)
and AC308 Acceptance Criteria for Post-Installed
Adhesive Anchors in Concrete Elements (first printed
in 2006). AC193 and AC308 contain programs to
evaluate an anchor system for recognition under
an IBC version adopted by a local jurisdiction.
Design parameters and data from this evaluation
are given in an ICC-ES Evaluation Service Report
(ESR). Therefore, a post-installed anchor system
evaluated per AC193 or AC308, having an ESR
noting recognition under an IBC, can be designed
using the Anchoring to Concrete provisions of the
ACI 318 code.
In January 2015, ESRs for adhesive anchor systems began to list compliance with the 2012 IBC.
There are changes with respect to the information
contained in these reports compared to reports
having recognition under previous versions of the
IBC. This article explains what changes have been
implemented into 2012 IBC-compliant adhesive
anchor ESRs, and how these changes affect adhesive anchor design.
Changes in Adhesive
Anchor System Approvals
By Richard T. Morgan, P.E.
Richard T. Morgan, P.E., is
the Manager for Software and
Literature in the Technical
Marketing Department of Hilti
North America. He is responsible
for PROFIS Anchor and PROFIS
Rebar software. He can be reached
at [email protected].
Review of the ICC-ES
Acceptance Criteria AC308
The primary test programs for evaluating adhesive
anchor systems in cracked and uncracked concrete
are given in its Tables 3.1, 3.2 and 3.3 in AC308.
AC308 evaluation of adhesive anchor systems for
design using threaded rods, internally threaded
inserts and torque-controlled elements include
various types of tests:
• reference tests establish the baseline bond
strength of the adhesive
• reliability tests determine sensitivity to
installation and load conditions
• service condition tests evaluate concrete
conditions during the service life of the
anchor, establish minimum spacing and
edge distance requirements, and
evaluate performance in simulated
seismic conditions.
Adhesive anchor ESRs based on evaluation per
AC308 were first issued in November 2007,
for recognition under the 2006 IBC. As such,
an adhesive anchor system could be evaluated
per AC308 and designed with the Anchoring to
Concrete provisions of ACI 318-05 Appendix
D. However, since ACI 318-05 Appendix D
did not include provisions for adhesive anchor
systems, AC308 was a stand-alone document
that included a section titled 3.3 Strength design
– amendments to ACI 318, which also contained equations and parameters for calculating
bond strength in tension and concrete pryout
strength in shear. The 2006 IBC-compliant
adhesive anchor ESRs likewise began including these AC308 equations and parameters via
Section 4.0 DESIGN AND INSTALLATION.
Therefore, even though the scope of ACI
318-05 Appendix D did not include adhesive
anchor systems, adhesive anchor design using
Appendix D provisions could be performed via
an ESR having 2006 IBC recognition. Adhesive
anchor ESRs having 2009 IBC recognition also
included the AC308 bond strength equations
and parameters via Section 4.0, thereby permitting design per ACI 318-08 Appendix D.
The ACI 318-11 code now includes adhesive
anchor systems in Appendix D as referenced in
Part D.2.2 – Scope, and ACI 355.4 is referenced
in Part D.2.3 (d) as the standard to qualify
adhesive anchor systems for use with Appendix
D provisions. Part D.5.5 – Bond strength of
adhesive anchor in tension contains provisions
for calculating nominal bond strength in tension. Part D.6.3 – Concrete pryout strength of
anchor in shear contains provisions for calculating nominal pryout strength in shear.
30 September 2015
AC308 (original) projected distance parameter Scr,Na
ACI 318-11 Appendix D projected distance parameter CNa
τk,uncr
√ 1450
Scr,Na
2
τk,uncr = 1670 psi
CNa
Scr,Na = 20da
da = 0.75 in
CNa = 10da
τuncr
√ 1100
τuncr = 1670 psi
da = 0.75 in
CNa
Scr,Na
2
2
Scr,Na = (20)(0.75 in)(1670 psi/1450 psi)0.5
CNa = (10)(0.75 in)(1670 psi/1100 psi)0.5
Scr,Na
2
Scr,Na
2
Scr,Na = one half the ciritical spacing
2
between two anchors
= 16 in
CNa
Scr,Na
2 = (16 in)/2 = 8 in
Figure 1. AC308 (original projected distance parameter).
Harmonization Between
AC308 and ACI 355.4
With the development of ACI 355.4 in 2011
to qualify adhesive anchor systems, ACI 355.4
and AC308 needed to be harmonized because
ACI 355.4 will now serve as the baseline for
AC308. Recall that AC308 was developed as
a stand-alone document prior to the existence
of ACI 355.4. Since adhesive anchor systems
receive IBC recognition in an ESR via testing
per AC308, the original AC308 provisions
needed to be modified to coincide with the
new baseline provisions of ACI 355.4. The
significance of this is that the inclusion of
adhesive anchor qualification and design provisions into the ACI 318 code has resulted
in bond strength equations no longer being
necessary in either AC308, or in adhesive
anchor ESRs.
Beginning with 2012 IBC-compliant adhesive anchor ESRs (issued January 2015),
bond strength equations are no longer
included in the report because they are
now given in ACI 318-11 Appendix D Part
D.5.5. This means that adhesive anchor
design under the 2009 IBC/ACI 318-08 or
under the 2006 IBC/ACI 318-05 should also
be performed using the equations of ACI
318-11 Appendix D Part D.5.5, because
the original AC308 bond strength equations
given in previous ESR versions are no longer
presumed to be “code compliant”.
Comparisons between Previous
Bond Strength Calculations
ACI 355.4 “prescribes testing and evaluation
requirements for post-installed adhesive anchor
systems intended for use in concrete under the
provisions of ACI 318.” It includes test programs for evaluating adhesive anchor systems
in cracked and uncracked concrete. Similar
to AC308, the test programs in ACI 355.4
cover various conditions:
CNa
Figure 2. ACI 318-11 Appendix D projected distance parameter.
• reference tests to establish the bond
strength of the adhesive
• reliability tests to determine sensitivity
to installation and load conditions
• service condition tests to evaluate possible
concrete conditions during the service
life of the anchor, establish minimum
spacing and edge distance requirements,
and evaluate performance in simulated
seismic conditions.
Although the ACI 355.4 test program is similar to the AC308 test program, it is important
to note that ACI 318-11 Appendix D bond
strength calculations, per the provisions given
in Part D.5.5 Bond strength of adhesive
anchor in tension, are based on parameters
established in ACI 355.4. The D.5.5 calculation results will differ from bond strength
calculations based on parameters previously
established in AC308. The calculations for
nominal bond strength per the original version
of AC308, i.e. pre-ACI 355.4, used a parameter corresponding to the spacing between two
adhesive anchors, scr,Na, and the equations for
calculating nominal bond strength utilized
either scr,Na or scr,Na /2. Nominal bond strength
calculations in ACI 318-11 Appendix D are
now based on a parameter corresponding to
the projected distance from the center of an
adhesive anchor to one side of the anchor,
cNa, which does not equal the original AC308
value scr,Na /2. The value calculated for cNa is
greater than that calculated for scr,Na /2. Figure 1
and Figure 2 illustrate why the original AC308
parameter scr,Na /2 differs from the new ACI
318-11 Appendix D parameter cNa.
Looking at Figure 1, assume the characteristic bond stress (τk,uncr) equals 1670 pounds
per square inch, and the anchor element consists of a ¾-inch diameter (da) threaded rod.
The value for scr,Na calculated per the original
AC308 Equation (D-16d) would equal 16
inches and the value calculated for scr,Na /2
would equal 8 inches. Looking at Figure 2,
using the same values for τuncr and da, the value
STRUCTURE magazine
= 9.24 in
CNa = projected distance from
the center of one anchor
to one side of the anchor
31
September 2015
for cNa calculated per ACI 318-11 Equation
(D-21) would equal 9.24 inches. Therefore,
cNa is greater than scr,Na /2, which means ACI
318-11 Appendix D bond strength calculation
results using cNa will differ from the original
AC308 calculation results using scr,Na or scr,Na /2.
Adhesive Anchor Design Per
ACI 318-11 Part D.5.5
Bond strength data published in 2012
IBC-compliant ESR tables titled BOND
STRENGTH DESIGN INFORMATION
is derived from adhesive anchor qualification testing per ACI 355.4/AC308, and is
product-specific. This data is used to design
the adhesive anchor system per the provisions
of ACI 318-11 Part D.5.5. The parameter corresponding to the characteristic bond stress (τ)
of an adhesive is a key parameter used in ACI
318-11 bond strength calculations. Values
for τ given in the ESR bond strength tables
are designated τk,cr for the characteristic bond
stress of the adhesive in cracked concrete,
and τk,uncr for the characteristic bond stress in
uncracked concrete.
Characteristic bond stress (τ) is used either
directly or indirectly in the ACI 318-11 equations (D-21), (D-22) and (D-27) to calculate
cNa, the basic bond strength Nba, and the critical edge distance cac, respectively.
Another parameter relevant to the characteristic bond stress (τ) is the concrete temperature
range. The ESR bond strength tables include
a footnote that defines the concrete temperature ranges for which the adhesive has been
tested. Temperatures corresponding to the
“maximum short term” and “maximum long
term” concrete temperatures for a given range
are defined, and the characteristic bond stress
(τ) values corresponding to these temperature
ranges are given in the ESR bond strength
tables. The concrete temperatures are defined
in terms of “short term” and “long term”.
Short term concrete temperatures are defined
3.2 Bond Strength
Nag =
( AA ) Ψ
Na
Na0
ec1,Na
Ψec2,Na Ψed,Na Ψcp,Na Nba
ACI 318-11 Eq. (D-19)
ɸNag ≥ Nua
ANa = see ACI 318-11, Part D.5.5.1, Fig. RD.5.5.1(b)
ANa0 = (2 cNa)2
τuncr
cNa = 10 da 1100
1
e
≤ 1.0
Ψec,Na =
1+ N
cNa
ca,min
≤ 1.0
Ψed,Na = 0.7 + 0.3
cNa
ca,min , cNa
Ψcp,Na = MAX
≤ 1.0
cac cac
Nba = λa – τk,c – αNsels – κbond – � – da – hef
√
(
(
Variables
τk,c,uncr [psi]
1670
ec1,N [in.]
ACI 318-11 Table D.4.1.1
ACI 318-11 Eq. (D-20)
ACI 318-11 Eq. (D-21)
)
(
ACI 318-11 Eq. (D-23)
)
)
ACI 318-11 Eq. (D-25)
ACI 318-11 Eq. (D-27)
ACI 318-11 Eq. (D-22)
da [in.]
hef [in.]
ca,min [in.]
τk,c [psi]
1.000
ec2,N [in.]
15.000
cac [in.]
6.000
κbond
805
λa
αN,sels
1.00
1.000
1.000
0.000
Calculations
cNa [in.]
0.000
23.146
ANa [in.2]
ANa0 [in.2]
Ψed,Na
12.266
Ψec1,Na
1032.60
Ψec2,Na
601.80
Ψcp,Na
0.847
Nba [lb]
1.000
Results
Nag [lb]
1.000
1.000
37935
ɸbond
ɸseismic
ɸnonductile
ɸNag [lb]
Nua [lb]
55115
0.650
0.750
0.400
10747
7450
Figure 3. PROFIS anchor bond strength calculations.
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as “temperatures that occur over brief intervals,
e.g., as a result of diurnal cycling,” and long
term concrete temperatures are defined as
temperatures that are “roughly constant over
significant periods of time.”
The harmonization of AC308 with ACI
355.4 has resulted in some of the maximum
short term temperature/maximum long
term temperature values being increased.
Characteristic bond stress (τ) values are correspondingly reduced as a result of these
changes. ESRs that are 2012-compliant
are the first ESRs to include these changes.
Reference each ESR for changes specific to a
particular adhesive anchor system.
Adhesive anchor ESRs having 2012IBC compliance are used with the bond
strength provisions of ACI 318-11 to design
an anchorage in jurisdictions recognizing
IBC 2012/ACI 318-11. Adhesive anchor
design in jurisdictions recognizing previous
IBC/ACI 318 versions should also utilize
the ACI 318-11 provisions in order to be
presumed “code compliant” because (a) the
original AC308 bond strength equations
have been removed from the ESRs, and
(b) bond strength equations for adhesive
anchor design are now given in ACI 318-11
Appendix D. There has understandably
been some confusion regarding the requirement, and feasibility, of using ACI 318-11
bond strength provisions to design adhesive anchors in jurisdictions that have not
yet adopted IBC 2012/ACI 318-11. Since
AC308 (compliance January 15, 2015) no
longer contains equations for calculating
bond strength, use of the original AC308
equations given in pre-2012 IBC compliant
ESRs needs to be justified by the Engineer
of Record (EOR). When an ESR is updated,
the previous version is no longer used unless
justified by the EOR. Therefore, in order
to be presumed code compliant, adhesive
anchor design in jurisdictions still recognizing IBC 2009/ACI 318-08, for example,
should be performed using the most current (2012 IBC-compliant) ESR and the
ACI 318-11 equations unless justified by
the EOR. Pre-2012 IBC ESR bond strength
equations conflict with ACI 318-11 bond
strength equations. Therefore, use of the
pre-2012 IBC ESR bond strength equations
must be justified for use in lieu of the equations now given in ACI 318-11.
STRUCTURE magazine
32
September 2015
Other anchor calculations, such as seismic
calculations, will be based on the IBC/ACI
318 code version currently adopted by the
jurisdiction because there is nothing in the
2012 IBC-compliant ESRs that conflicts with
these code versions.
Figure 3 shows calculations performed with
Hilti PROFIS Anchor software using the data
given in ESR-3187 (revised January 2015)
for the HIT-HY 200 adhesive anchor system.
Design using the seismic provisions of ACI
318-08 Part D.3.3.6 was selected. Besides the
0.75 seismic factor defined in ACI 318-08
Part D.3.3.3, Part D.3.3.6 requires an additional factor to be applied to non-ductile design
strengths. The 0.75 seismic factor is shown
below as φseismic, and the D.3.3.6 non-ductile
factor is shown as φnonductile. Note that the calculations for nominal bond strength (Nag) are
based on ACI 318-11 Part D.5.5, but the seismic calculations are based on ACI 318-08 Part
D.3.3.3 and Part D.3.3.6. Therefore, the design
strength calculations (φNag) performed per ACI
318-08 Appendix D seismic provisions, and
the nominal bond strength calculations (Nag)
performed per ACI 318-11 Part D.5.5 are
presumed to be “code compliant”.
Summary
ACI 318-11 Appendix D now includes provisions for calculating the nominal bond
strength of adhesive anchor systems in
Part D.5.5. Prior to ACI 318-11, adhesive
anchor systems were not within the scope of
Appendix D; however, ICC-ES developed the
acceptance criteria AC308 to qualify adhesive anchor systems for recognition under the
IBC, and to design adhesive anchor systems
with the provisions of Appendix D. The original AC308 included provisions for calculating
nominal bond strength since no provisions
were available in Appendix D.
With the development of ACI 318-11 Part
D.5.5, ACI developed a test standard, ACI
355.4, to qualify adhesive anchor systems for
use with Appendix D provisions. AC308 has
been harmonized with ACI 355.4, resulting
in the only provisions recognized under the
IBC for calculating bond strength being given
in ACI 318-11 Appendix D. Revised bond
strength calculations are now based on the
projected distance from an anchor instead of
the spacing between anchors. Characteristic
bond strength values have also been revised
per the changes in maximum short term/
maximum long term temperature ranges.
Adhesive anchor design for pre-2012 IBC jurisdictions should use the provisions of ACI 318-11
Appendix D to be presumed “code compliant”
unless justified by the Engineer of Record.▪
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© 2015 Simpson
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Guest
Column
dedicated to the dissemination
of information from other
organizations
O
n April 9-10, 2015 the Building
Information for Modeling Masonry
(BIM-M) Initiative held their first
Symposium in St. Louis, MO at the
St. Louis Masonry Center. Since the beginning, the
initiative has been following its mission statement:
To unify the masonry industry and all supporting industries through the development
and implementation of BIM for masonry
software to facilitate smoother workflows
and collaboration across all disciplines from
owner, architect, engineer, manufacturer,
mason, contractor, construction manager,
and maintenance professionals.
While the BIM-M Initiative has been progressing
for over two years, many structural engineers may
not have been aware of this major effort. This
article provides some of the highlights of BIM-M
and the symposium, and their relevance to structural engineers. It is important to remember that
the term BIM represents both an object (a model),
and a process (modeling).
Why BIM-Masonry? To
give masonry an opportunity to compete with other
building materials while
simultaneously improving
the industry. The BIM-M
Initiative began in 2012 and represents the
masonry industry in the United States and parts
of Canada.
The Symposium opened by welcoming the many
architects, structural engineers, manufacturers,
contractors, suppliers, supporters, and guests. The
audience learned that Phase II (Development)
based on the original roadmap has been completed. Phase II contained four projects; 1)
Masonry Unit Model (MUD) Definition, 2)
Masonry BIM Benchmark, 3) Masonry Wall
Model Definition, and 4) BIM-M Contractor
BIM-M Symposium:
Generation 1
By Daniel Zechmeister, P.E.
Daniel Zechmeister, P.E., is
the Executive Director of the
Masonry Institute of Michigan
and a member of the Executive
Committee of BIM-M representing
The Masonry Society. He is active
in ASTM and the Masonry
Standards Joint Committee,
which is responsible for the TMS
402 code and the TMS 602
specification. He can be reached at
[email protected].
Input. BIM-M also announced that an updated
Roadmap, a report for developing and deploying BIM for masonry, has now been posted on
the website (www.bimformasonry.org). The
proposed timeline for Phases III and IV begins
now and will run until the end of 2017 with the
completion of Generation 1.
What is Generation 1 BIM-M? Generation 1
is defined as the conceptual termination of the
BIM-M Initiative’s initial efforts to make masonry
more accessible to architects, structural engineers,
masons, contractors, manufacturers, and owners
using BIM. Some aspirations for what Generation
1 will include are:
• Masonry unit database accessible to all
BIM users.
• Masonry wall definitions for Level of
Development (LOD) with standard details.
• BIM software upgrades that achieve LOD
350 or greater for design (Figure1).
• BIM software that allows contractors
to achieve LOD 400 or greater for
construction purposes, and can detect
clashes with specific masonry features (bond
beams, grouted cells, shelf angles, etc.)
• BIM software upgrades that will operate
with other masonry specific software.
• New and/or improved design tools
(software upgrades, add-ins, plugs-ins)
that provide for modularity, early project
pricing, and masonry detailing.
Masonry Unit Model Definition
Over the course of the last two years, the BIM-M
Masonry Unit Working Group, led by Jeff Elder,
SE, Interstate Brick, HC Muddox and Western
States Clay Products developed a spreadsheet to
represent the majority of data parameters and
specification information to be used by BIM
Figure 1. LOD 350 for design.
34 September 2015
software developers for the design, purchasing,
shop drawing and sustainability of clay, CMU
and cast stone. This data set was based upon
geometric and material attributes provided
by numerous manufacturers. The physical
properties entity includes attributes for both
mechanical properties and thermal properties
of masonry units, including; weight, density,
compressive strength, modulus of elasticity,
modulus of rigidity, shrinkage coefficient,
coefficient of thermal expansion, and creep
coefficient.
For structural engineers, this means there
will be on-line access to geometrical and material properties for modeling masonry in BIM
software as well as for analytical programs that
interact with BIM.
BIM-M Benchmark
The original intent of the BIM Benchmark
project was to focus on software capabilities
and to understand the role of software in the
masonry industry at all project phases. The
Phase II project, led by Russell Gentry, PE,
Project Manager, Digital Building Laboratory,
Georgia Institute of Technology, extended
this scope to focus not only on software but
also on BIM processes, that is, how masonry
stakeholders use BIM or other tools. The primary goal was to develop a vision for “future
state” processes that can take advantage of the
Generation 1 BIM-M software. The original
proposal called for the analysis of three project
types: brick/CMU, structural masonry, and
complex masonry. Georgia Tech, along with
the University of Pennsylvania, completed
nine building case studies of various building types. The Benchmark Project focused
on three areas:
Task 1 – Framework Development
Task 2 – Process Documentation
Task 3 – Process Model Evaluation
For structural engineers, this will lead to better
interaction between analytical programs and
BIM modeling during design and construction.
Masonry Wall
Model Definition
Figure 2. Cover of 2014 LOD Specification.
to track individual masonry units in an entire
building. Therefore, the masonry BIM data
structure must include the definition of wall
types, and must provide the means to map
these wall types onto regular and irregular
regions on wall surfaces. The working group
discussed and suggested a level of development (LOD) of 350 for architects and
structural engineers.
Also, one of the four new tasks for Phase III
is to develop and publish a Best Practices Guide
for Modeling of Masonry using Autodesk Revit
in cooperation with The Masonry Society
(TMS). The Guide has a three-fold purpose,
including: 1) informing users on how current
BIM tools may be used to model masonry,
2) to define what collaboration and modeling
tools are lacking, and 3) to create a wish-list
of modeling tools that would be helpful to
the industry.
Structural engineers will have more efficient
modeling tools that will carry over into the
analytic programs.
BIM-M Contractor Input
This project is at the core of masonry BIM
and is managed by Jamie Davis, PE of Ryan
Biggs/Clark Davis through the TMS BIM
Committee. Because masonry BIM is a computational model of masonry construction,
and masonry walls are the fundamental assembly in masonry construction, it is critical that
the data representation of the masonry wall
support all of the functionality that is envisioned for BIM-M. Currently, it is simply not
computationally practical for BIM software
It has been clearly determined that mason
contractors and masons will benefit from
BIM-M. In this project, BIM-M proposes
that mason contractors explore in greater
detail the potential benefits of BIM, and document their current work processes and their
use of software in current practice. Input from
general contractors will be solicited as well,
to identify areas where general contractors
desire interaction with masonry construction in their BIM models – for example, in
coordination of masonry with structural,
STRUCTURE magazine
35
September 2015
mechanical and other building systems for
clash detection.
The keynote speaker was Will Ikerd II, PE,
from Ikerd Associates, Dallas, TX. He also
represents the BIM Forum and chairs the SEI
BIM Committee. He began his presentation
by stating BIM is about giving a “common
vocabulary”. Will discussed the various levels
of development (LODs). He pointed out that,
in 2008, an AIA document for the first time
defined LODs. In giving his opinion, he
described the LODs simplistically as:
• LOD 100 – symbolic
• LOD 200 – approximate
• LOD 300 – specific
• LOD 350 – detailed (interfaces with
other building systems)
• LOD 400 – detailing and fabrication
Will announced to the audience that the
Level of Development (LOD) Specification is
a reference that enables practitioners in the
AEC Industry to specify and articulate with a
high level of clarity the content and reliability
of Building Information Models (BIMs) at
various stages in the design and construction process. Shown on the cover of the 2014
LOD Specification are the various LODs for
masonry (Figure 2). The specification is a free
download from store.bimforum.org.
Two specific presentations came from BIM-M
consultants who are providing modeling tips
and tricks for masonry, which will be released
later this year as Best Practices Guide. BIM-M
has tasked them with demonstrating the modeling of masonry using current software and
recommending future improvements.
Best Practices #1
Presenters from the architecture and engineering firm Integrus Architecture from Seattle,
WA included Mike Adams, BIM Manager;
Morgan Weise, EIT; and Clint Bailey, AIA
showed some features of what they will be
contributing to the Best Practices Guide.
The most common masonry elements in
BIM are walls which are always modeled in
three-dimensions. However, many masonry
details are presently handled in two-dimensions. The current strategy for creating
drawings is to take the three-dimensional
model and slice it to reveal the information
that is desired.
Integrus demonstrated the three-dimensional detailing function. Because these views
are live or three-dimensional, any changes that
are made in them affect the rest of the model.
For example, BIM software typically includes
a number of pre-made families including
openings with arched tops. In the BIM-M
project, Integrus used three-dimensional
Figure 3. Three-dimensionally reinforced wall.
Figure 4. CMU wall in structural model and remaining wall layers
in architectural model.
sweeps (model elements) to represent stone
sills, lintels, and quoining.
Another example dealt with representing
reinforcement in models. The current advantages of two-dimensional reinforcement are
detail line, components or groups; fast to make
changes; and easy to export details from project
to project. The current disadvantages are an
absence of embedded information (no clash,
no scheduling and no tagging), everything
fits and no warnings as things move. Integrus
noted that the current advantages of modeling reinforcement in three-dimensions are
improved coordination, accurate schedules,
tagging, and correct warnings when things are
moved. The current disadvantages are longer
modeling time, all walls are treated equal and
an enlarged model file size (Figure 3).
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Concrete beams with/without torsion ($45.00).
Demos at: www.struware.com
Best Practices #2
The second BIM-M consultant was Shawn
Zirbes, Cad Technology Center (CTC) from
Minneapolis, MN. Shawn used the BIM
Forum LOD 2014 Level of Development
Specification and displayed the BIM-M for
Masonry LOD examples for levels 300, 350
and 400. Shawn showed a structural model
of the Brick Office Building with brick on
CMU backup on a portion, and brick with
metal stud backup on the remaining portion.
The model was then split into an exterior shell
model and an interior model. For both the
brick with block backup wall and brick with
metal stud backup wall, Shawn presented
the LOD 300 with a plan and section view,
respectively. He then displayed LOD 350
for the block (CMU) backup showing the
grouted cells where the CMU wall is placed
in a structural model and the remaining wall
layers (brick veneer, wall ties and drainage
panel, rigid insulation, and air barrier) are
modeled as individual wall types in an architectural model (Figure 4). With respect to
the LOD 350 for metal stud backup, all wall
layers (brick veneer, wall ties, rigid insulation, air barrier, sheathing, metal studs and
gypsum board) are modeled as individual
wall types in an architectural model. Anchor
type placement was shown for both systems
in plan and sectional view. Brick patterns were
developed as model hatch patterns showing
running bond (primary), stacked bond and
STRUCTURE magazine
36
September 2015
Flemish bond. This allows for architects and
structural engineers to check modularity in
their designs.
Contractor Software for
Use by Engineers
Bill Pacetti and Bill Pacetti, Jr., from
Tradesmen’s Software, Inc., Morris, IL,
presented their software. This software was
developed for mason contractors but has
features that could be valuable to architects
and structural engineers including cost
estimating, evaluating aesthetics by varying
units, checking dimensions for modularity
of units, and more.
BIM-M and
Structural Software
In Phase III, BIM-M will start a new project
associated with structural engineering. In an
attempt to improve modeling techniques and
interoperability of analytical software with
BIM authoring tools, consultants will be
selected to examine various software packages
and their use with BIM packages. Structural
engineers interested in being considered for
this work should contact BIM-M through
its website.
While this article has provided an overview,
free downloads of videos, presentations and
reports for BIM-M are available from the
website also.▪
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performance issues relative
to extreme events
T
his article identifies common errors
that structural engineers make when
performing seismic design and calculations. The intent is to help engineers
avoid those errors and misapplications. This
article is written in checklist format such that
an engineer can verify adequate self-knowledge,
as well as review the work of others on a project. It is based upon the 2012 International
Building Code (IBC), the American Society of
Civil Engineers’ ASCE/SEI 7-10, the American
Concrete Institute’s ACI 318-11, the American
Institute of Steel Construction’s AISC 360-10,
AISC 341-10, and other current standards. For
ease of identification, referenced sections are
noted in brackets and refer to ASCE/SEI 7-10
section numbers, unless otherwise noted.
diaphragms, walls, etc. However, in addition to
those specifics, the engineer is required to provide a continuous load path for all inertial forces
from their origin to the foundation. Such load
paths must conform to the relative stiffness and
strength of the elements that exist in the structure.
See [12.1.3].
1) Seismic Design Category A
4) R Factor
When in seismic design category (SDC) A, it
is not necessary to use any of the provisions of
Chapter 12. Instead, the
general structural integrity provisions of Section
1.4 apply. Note that these
provisions include some
loads that may often be
erroneously neglected.
The required lateral forces include 1% of dead
load, 5% of dead plus live load for beam (axial
load) connections, and 20% of wall weight for
wall connections. Non-structural components in
SDC A are exempt from seismic design requirements. See [1.4], [11.4.1], and [11.7].
The response modification coefficient, R, is
part of a concept where an elastic design may
be performed, but with due consideration of
the overstrength and ductility inherent in the
lateral force resisting system. In order to ensure
reliability, many requirements are triggered with
each R factor. The “R” Tables, [Table 12.2-1] and
[Table 15.4-1, 2], list the corresponding detailing requirements. The “strings attached” can
be extremely significant, especially for concrete
structures that fall under ACI 318-11 Chapter 21
and steel structures with R greater than 3 (AISC
341 Seismic).
The Most Common Errors
in Seismic Design
… & How to Avoid Them
By Thomas F. Heausler, P.E., S.E.
2) Importance Factor
Thomas F. Heausler, P.E., S.E.
([email protected]), has 33
years of experience in structural
and seismic engineering and
has been a voting member of
ASCE/SEI 7 Seismic Provisions
since 2006. He provides seismic
expertise and senior review to
engineering firms for building
and industrial projects.
The importance factor is based upon the risk
category and the associated life safety, hazard
or essential nature of the structure. Both [Table
1.5-1] and [IBC Table 1604.5] should be reviewed.
A typical building can sometimes evolve into
an Ie equal to 1.25 or 1.5 when occupancy or
use expands. Examples include relatively small
churches (expanding to an occupancy greater than
300) or a building where hazardous materials are
stored. It should be noted that for building design,
Ie = 1.0, 1.25, or 1.5; but for non-structural components, Ip = 1.0 or 1.5 only [13.1.3], such that
Ip may not equal Ie, and in some instances Ip may
be less than Ie. See [11.5.1] and [Table 1.5-2].
3) Continuous Load Path
ASCE/SEI 7-10 has very specific provisions for
many elements such as collectors, connections,
… a checklist to verify
self-knowledge as well as
check the work of others
on a project.
5) Irregularity Triggers
[Table 12.3-1] and [Table 12.3-2] describe various
horizontal and vertical irregularities, respectively,
which trigger specific provisions. Each referenced
section must be reviewed. Triggered provisions
include modal analysis, three-dimensional analysis, redundancy factor, force amplification, torsion
amplification, and collector force increases. See
[12.3.2.1] and [12.3.2.2].
6) Overstrength – Ωo
The variable Ωo is an amplification factor
applied to the forces in certain elements in
the seismic load path. It is required so as to
prevent a weak link from occurring prior to the
full energy dissipation and ductility potential of
the primary lateral-force-resisting system. For
example, in a steel braced frame, in order for
the diagonal brace to yield and dissipate energy
in a controlled and reliable manner, all other
portions of the load path (e.g., connections,
When you select an R factor from the Table, you are
obliged to implement the associated “strings attached.”
38 September 2015
bolts, welds, gusset plates, anchor bolts,
columns and collectors) need to be stronger
than the maximum anticipated strength or
force in the brace. Therefore, Ωo amplification and load combinations are specifically
triggered for those elements, in the sections
mentioned below and in Material Standards
such as AISC 341-10 and ACI 318-11. For
example, AISC 341-10 states that anchor
bolt forces must be amplified by Ω o, which
is typically 2.0 or greater. This applies to
all steel buildings where R is greater than
3, unless you can prove otherwise via
an advanced and rigorous analysis. See
[12.4], [12.2.5.2], [12.10.2.1], [12.3.3.3],
[12.13.6.5], and [AISC 341 when R>3, ACI
Chapter 21, Appendix D, etc.].
7) Redundancy – Rho
Rho is a factor that penalizes structures that
do not have redundancy. Rho is equal to either
1.0 or 1.3. Rho is equal to 1.0 for SDC B
and C, for drift calculations, non-structural
component forces, collectors, Ωo load combinations, and diaphragms. See [12.3.4].
8) Vertical Seismic Load Effect – Ev
[12.4.2.2] requires that a vertical load effect
equal to 0.2 SDs be applied to dead load. It is
applied as a dead load factor adjustment and
…anchor bolt forces shall be multiplied by
Ωo, which is typically 2.0 or greater.
may act downward or upward. It is at the
strength design level, so it may be multiplied
by 0.7 for allowable stress design (ASD). The
values of Ie, Ip, Rho and R are not applied
to Ev.
SDC D, E, and F be considered with 100% of
forces in one direction plus 30% in the other.
It should be noted that IEEE 693 (Electrical
Equipment) applies orthogonal effects to all
elements, including corner anchor bolts.
9) Load Combinations and Allowable
Stress Design – 0.7 E
11) Effective Seismic Weight
For ASD load combinations [12.4.2.3],
[12.4.2] shall be used in lieu of [2.3.2] and
[2.4.1]. Earthquake forces are at strength
level, so for the ASD combinations, use 0.7
E. The 0.7 E applies to non-structural component forces (Fp). See [13.3.1].
10) Orthogonal Effects
Earthquake forces must be calculated for each
of the two primary orthogonal directions. In
order to consider the effects of earthquake
forces at some angle other than those two
directions, “orthogonal effects” must be
considered. [12.5] requires that irregular
buildings in SDC C and corner columns in
[12.7.2] defines the effective seismic weight,
W. Except for as mentioned below, live load is
not included in the inertial force; however, the
seismic force is later combined with dead and
live loads in the load combinations. [12.7.2]
stipulates that W must include the following
masses: 25% of storage live load, partition load
of 10 psf [4.3.2], industrial operating weight
and unbalanced conditions, 20% of snow if
greater than 30 psf, and weight of roof gardens.
12) Distribute Base Shear over Height
Once the base shear, V, is calculated, it must
be distributed over the height of the structure.
For a one-story building, all of the base shear
would be applied at the roof. For multi-story
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September 2015
6/10/2015 6:37:49 PM
structures, the base shear must be distributed
to each floor, not only in proportion to each
floor’s mass, but also in proportion to the
distance of the floor from the base. A triangular distribution of force results for regular
multi-story buildings. For distributed-mass
structures like stacks and masonry fences, the
centroid of the load should result at 2/3 of the
height above the base, not at ½ the height or
at the center of gravity. See [12.8.3].
13) Modal Response Spectrum Analysis
When a structure has significant vertical or
horizontal irregularities, the equation [12.812] (triangular force distribution) becomes
inaccurate, and therefore a modal response
spectrum analysis is required. See [12.6],
[Table 12.6-1] and [12.9]. The purpose is
not to refine the magnitude of the base shear,
but to perform the following more accurately:
1) Distribute base shear over height.
2) Quantify horizontal torsional effects.
3) Account for higher mode effects.
Note that the “NP” entry in [Table 12.6-1]
includes many common irregularities, including horizontal type 1a, 1b and vertical type
1a, 1b, 2 and 3, and thus a modal analysis is
triggered for those structures.
14) Accidental Torsion
In addition to inherent torsion, accidental
torsion must be applied. This is to prevent
weak torsional resisting arrangements, as well
as account for unexpected distribution of live
load and unexpected stiffness of structural
and non-structural elements. This provision
applies to non-building structures, as well as
buildings. For torsionally irregular buildings,
amplification of the accidental torsion may
be required as per [12.8.4.3]. See [12.8.4.2].
15) Drift Check
Results from the elastic analysis must be
amplified by Cd to render expected deflections. Note that Cd is a very large value,
typically a factor of about 4 or 5. The drift
is then divided by Ie, because the allowable
drifts are organized into a table that considers
risk category. One should be careful when
using ASD load combinations not to apply
the 0.7E to drift calculations. See [12.8.6],
[12.12], and [Table 12.12-1].
16) Diaphragm Forces
Forces at lower floor diaphragms may be
higher than those used for the lateral force
resisting system [Equation 12.8-12]. This
is due to higher mode effects (i.e., modes
higher than the first mode) where the lower
floors may be accelerating higher than calculated. Note that Fpx minimums of [Equation
12.10-2] often govern for the lower floors.
See [12.10.1.1].
17) Non-structural Components
Non-structural components may also experience higher local accelerations due to higher
mode effects, as well as amplification of the
force within the non-structural element itself.
See [Equation 13.3.1]. Industrial structures
often feature very large forces. It is unlikely
that the forces on two different floors would
occur at the same point in time. Therefore,
one method of accounting for the forces in a
computer model is to evaluate two conditions.
1) Run a load case with the weight
of the equipment included in the
seismic weight of the floor and the
base shear, V, distributed over the
height as per [Equation 12.8-12].
2) Run a load case with only the nonstructural component force for one
piece of equipment, so as to verify
an adequate load path to the vertical
system and/or foundation.
Note that it is necessary to apply Ev
to load combinations with nonstructural component forces. The
factor Ωo does not apply to such load
combinations, except in some ACI
318-11 Appendix D calculations.
Note also that when non-structural
components get very large – i.e.,
25% or more of total structure mass
– then [15.3] provisions apply. For
these heavy components, the stiffness
and design coefficients of both the
component and the primary structure
must be considered together in a
computer model.
18) Wall Design
Connections to wall panels made of concrete
and concrete masonry units (CMU) have
performed poorly in past earthquakes. The
equations of [12.11.1] and [12.11.2.1] should
be implemented, as well as ACI 318-11
Appendix D for anchorage.
19) Foundation Ties
Foundation ties are required as per [12.13.6.2]
in order to ensure that the foundation system
acts as an integral unit, not permitting one
column or wall to move appreciably relative
to another. This applies to pile caps in SDC
C, D,E and F, and spread footings for SDC
E and F.
20) Reduction of Foundation
Overturning
[12.13.4] allows for a reduction of the bearing pressures at the soil-foundation interface.
STRUCTURE magazine
40
September 2015
Forces may be reduced by 25% in recognition
that the first mode triangular force distribution will likely not occur without higher mode
effects occurring and negating the direction of
the first mode, resulting in reduced maximum
overturning moments.
21) Errata
The ASCE/SEI 7-10 and IBC 2012 websites
have the latest errata for those documents.
Significant entries due to typographical mistakes or unintended consequences of revisions
are corrected in the errata.
22) IBC Overrides
IBC 2012 contains amendments to ASCE/
SEI 7-10. See [IBC 1613], [IBC 1613.5],
and [IBC Chapters 18 through 23]. ASCE/
SEI 7 is on a six-year update cycle, and IBC
is on a three-year cycle. Technical changes
to IBC often have to be approved well
before the issue date. Inevitably, coordination between ASCE 7, IBC and referenced
material standards (e.g. ACI, AISC, etc.)
often occur through errata, supplements
or IBC-published amendments. It is essential to check for these changes periodically.
Individual state and local governments may
also adopt amendments that affect projects
located within their jurisdiction.
23) ASCE/SEI 7-10 Third Printing
It is recommended that the user make use
of the ASCE/SEI 7-10 Expanded Seismic
Commentary, which provides 135 pages
of valuable background information. It is
incorporated in the third printing of ASCE/
SEI 7-10 only. For those who own a first or
second printing, you may download a PDF
file of the commentary for free from the
ASCE website. This Commentary was developed by the National Earthquake Hazard
Reduction Program/Building Seismic Safety
Council/Provisions Update Committee
(NEHRP/BSSC/PUC) and describes the
reasons for the individual provisions of
ASCE/SEI 7-10.
Conclusion
A concerted effort to avoid errors is essential. Errors can be minimized by applying
knowledge and experience. This article is
intended to assist in that effort. The above
listing of common errors was developed
by the author during frequent reviews of
other engineers’ work. It is based upon the
author’s experience and should not be construed as a consensus document prepared or
endorsed by the ASCE/SEI 7-10 or NCSEA
Seismic Committees.▪
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Take Your Practice to New Heights at the
2015 Structural Engineering Summit
National Council of Structural Engineers Associations
September 30 – October 3rd
Red Rock Resort Las Vegas, NV
th
STAY CONNECTED BY USING THE HASHTAG #NCSEASummit
Wednesday, September 30
8:00 – 5:00
8:00 – 12:00
5:30 – 6:30
6:30 – 8:30
evacuation refuge structures, based on the new ASCE 7-6 chapter Tsunami
Loads & Effects.
Gary Chock is Chair of the ASCE 7 Tsunami Loads and Effects Subcommittee that in
2015 completed the first national standard for tsunami-resistant design for the upcoming
2016 edition of the ASCE 7 Standard.
Committee Meetings
NCSEA Board of Directors Meeting
Young Engineer Reception
SECB Reception
B.) Effective Communication: Tips for
Improving Your Skills
Thursday, October 1
7:00
8:00
Delegate Interaction Meeting
Welcome & Introduction
Kirsten Zeydel, S.E., President, ZO Consulting and
Annie Kao, P.E., Field Engineer, Simpson Strong-Tie
8:15 – 9:30
Keynote
STRUCTURAL ENGINEERING:
The Profession, The Grandeur, and The Glory
Ashraf Habibullah, S.E., President & CEO,
Computers & Structures, Inc.
Ashraf brings into focus the invaluable socio-economic contributions of
structural engineering by recognizing its unmatched impact on humanity.
He will highlight the ways in which the intellect and talent of structural
engineers have literally saved hundreds of millions of lives, spared us from
death and destruction, and preserved and protected progress and property.
Ashraf Habibullah is a registered Civil and Structural Engineer who founded CSI in 1975
and has led the development of CSI’s products, including SAP2000 and ETABS, for the last
four decades. CSI’s software is used by thousands of engineering firms in over 160 countries.
9:45 – 11:00
Basis for ASCE 7 Seismic Design Maps
ASCE 7-10 and IC-2012 introduced the concept of risk-adjusted Maximum
Considered Earthquake (MCE-R) shaking derived to produce a 1% chance
in 50 years that buildings will experience earthquake-induced collapse. As
compared with older MCE definitions, this resulted in reduction of design
ground motions in much of the U.S. while assuring design risk comparable
to that already accepted in the Western U.S. The basis for this change and
its significance are presented.
NCSEA Past President and Past Code Advisory Committee chair, Ron Hamburger,
is Senior Principal with Simpson Gumpertz and Heger in San Francisco and the current chair of the ASCE-7 Committee. He is presently chairing a joint USGS-BSSC
planning committee, formalizing plans to develop a new generation of seismic risk maps
for the building codes.
11:00 – 12:00
Building Rating, Retrofit Ordinances, and
Community Resilience
A.) Wood & Cold-Formed Light Steel
Frame Construction – Deficiency in
IBC Special Inspections
The session will compare light frame construction inspection
requirements to other structural systems, identify the areas of deficiency in
the Code, and present strategies to address these deficiencies.
Kirk Harman is President and Managing Principal of The Harman Group, headquartered in Philadelphia, PA. He served for 10 years as Chairman of the NCSEA
Code Advisory Committee’s sub-committee on Special Inspections.
B.) Find the Lost Dollars:
6 Steps to Improve Profits
June Jewell, CPA, AEC Business Solutions
Learn to get the most from people, processes and technology
to gain a competitive edge. June Jewell will show you how to
improve your firm’s performance and prepare the firm’s future leaders to
successfully take the reins.
June Jewell is a speaker and business management consultant to the A&E industry, and
author of Find The Lost Dollars: 6 Steps to Increase Profits in Architecture, Engineering,
and Environmental Firms.
Concurrent Sessions 4:00 – 5:00
Panel from Structural Engineers Association of California
Moderator: Ryan A. Kersting, S.E., Associate Principal
Buehler & Buehler Structural Engineers, Inc.
A.) Changes to Wind Loading in ASCE 7-16
Don Scott, S.E., PCS Structural Solutions
The panel will discuss building rating systems, performance based design,
renewed efforts for retrofit ordinances, and emerging concepts of community resilience that have launched a wave of discussions, innovations,
and political involvement by California’s structural engineering community.
Concurrent Sessions 1:00 – 2:15
A.) The ASCE 7-16 Tsunami Loads Design Standard
The session will provide an overview of the technical basis
and methodology for tsunami-resilient design of critical
and essential facilities, taller building structures and tsunami
STRUCTURE magazine
Concurrent Sessions 2:45 – 3:45
Kirk Harman, P.E., S.E., SECB, President, The Harman Group
Ron Hamburger, P.E., S.E., SECB, Senior Principal,
Simpson Gumpertz & Heger
Gary Chock, S.E., President, Martin & Chock
Instant communication – email, Facebook, LinkedIn, Twitter,
Snapchat, and more – doesn’t mean that we are communicating effectively.
You will hear concrete tips to improve your written, verbal, and non-verbal
communication skills.
Kirsten Zeydel has over 15 years of experience leading over 200 projects and is the
President of ZO Consulting, Inc. located in Orange, CA. ZO Consulting specializes in
cold-formed steel and evaluating/coordinating exterior facades .
Annie Kao is a field engineer for Simpson Strong-Tie, where she connects with and educates
engineers, architects, building officials, and contractors on design and product solutions
for wood, concrete, steel, and masonry construction in the Southwest region of the U.S.
This session will identify significant changes to the wind load
provisions of ASCE 7-16 and the rationale for these changes.
These include new wind speed maps, changes to component
and cladding pressure coefficients, expanded commentary on tornado design,
and more.
Don Scott has been a member of the ASCE 7 Wind Load Committee since 1996 and currently serves as chair, shaping future IBC provisions for wind design. He is also a member of
the ASCE 7 General Provisions committee and the ASCE 7 Steering Committee, Chairman
of the NCSEA Wind Committee and Past-Chair of the SEAW Wind Load Committee.
42
Register today at www.ncsea.com!
September 2015
B.) BIM and Structural Engineering
Desiree Mackey, P.E., S.E., BIM Manager, Martin/Martin
What is the future of Building Information Modeling (BIM) in
structural engineering? This session will cover the processes,
collaboration, and coordination with clients and other project
participants, with an open forum for questions.
Desirée (Dezi) Mackey is the BIM Manager at Martin/Martin, Inc., in Denver. Dezi
has been using Revit for most of her career, and she is extremely active in the BIM community as a regular speaker at conferences, co-founder of the Rocky Mountain Building
Information Society, and Chair of SEAC’s BIM Committee.
Welcome Reception on Trade Show Floor
(Red) Rock ‘n’ Bowl with NCSEA
6:30 – 8:30
8:30 – 11:30
Friday, October 2
8:00 – 10:00
8:00 – 10:00
Member Organization Reports
Vendor Product Presentations
Cliff Schwinger is a Vice President and Quality Assurance Manager at The Harman
Group. He serves on the AISC Manuals Committee and has over 30 years of experience
designing building structures.
Concurrent Sessions 2:45 – 3:45
A.) Concrete & CMU Elements in
Bending + Compression
John Tawresey, S.E, retired, KPFF Consulting Engineers
John Tawresey will present the applied mechanics equations
for cracked elements subject to bending plus compression in
a form more understandable for the practicing engineer and will then relate
these to the latest masonry and concrete code requirements.
JohnTawresey is a past president of The Masonry Society, past president of the Structural
Engineers Risk Management Council (SERMC), past chair of the SERMC Claims
Committee, past president of SEI and current member of the ASCE 7 Main Committee
and TMS 402/602 Main Committee.
B.) The Decline of Engineering Judgment
Jon Schmidt, P.E., SECB, Associate Structural Engineer,
Burns & McDonnell
Concurrent Sessions 10:15 – 11:30
A.) Lateral Design of Buildings with
Sloped Diaphragms
Steven Call, P.E., S.E., Call Engineering
Buildings constructed with slope roof diaphragms are often
designed as if they had a flat roof diaphragm. The significant
differences between the lateral designs of sloped vs. flat diaphragms will be
presented, including the proper diaphragm depth, the effect on the wall-todiaphragm connection, and the effect on the design of shear walls with a
sloped connection to the diaphragm.
Steven Call has over 25 years of experience in structural design of buildings, including
17 years as the president of Call Engineering, and is an instructor on design and analysis
of diaphragms for Boise State University.
Modern society increasingly embraces theoretical knowledge
and technical rationality – i.e., science and technology – while
downplaying practical judgment. For structural engineers, this is especially
evident in the constantly growing size and complexity of the codes and standards. Jon Schmidt will discuss the implications, unintended consequences,
and potential alternatives.
Jon Schmidt is an associate structural engineer at Burns & McDonnell. He chairs the
editorial board for STRUCTURE magazine and authors a bimonthly “InFocus” column
in which he often explores the relationship between philosophy and engineering.
Concurrent Sessions 4:00 – 5:00
A.) Creative Problem Solving for Repairing
Wood Structures
B.) Working with Multiple Generations
Panel Discussion with the NCSEA Young Member Group
Support Committee
Moderator: Emily Guglielmo, S.E., Associate,
Martin/Martin Inc.
Structural engineering firms find themselves managing four generations of
employees, while working to attract, train and retain staff. This session will
explore differences and similarities between generations, ways to leverage
their uniqueness, and suggestions for successful integration of a multigenerational workplace.
Kimberlee McKitish, P.E., Nutec Group
Kimberlee McKitish will showcase four mini-case studies with creative solutions to wood repair issues. The
case studies will look at the problems encountered, alternative repair
options, and the thought process that led to the chosen solutions.
Kim McKitish is a structural engineer with NuTec Design Associates, Inc. A licensed
professional engineer, her area of expertise is in the design, repair, and reuse of manufacturing and industrial buildings.
B.) Business Ownership Transfer
Craig Barnes, P.E., SECB, Founding Principal, CBI Consulting
Concurrent Sessions 1:00 – 2:30
A.) Lateral Analysis: Right Way/Wrong Way
with Software
Sam Rubenzer, P.E., S.E., Structural Engineer, FORSE Consulting
Lateral load requirements and corresponding analysis methods
continue to increase. Sam Rubenzer will discuss the key points
in lateral analysis when using different software, and will guide engineers
regarding what is right and what is wrong in modeling loads.
Sam Rubenzer founded FORSE Consulting in 2010 and has been assisting other
structural engineers with, and comparing the attributes of, an assortment of structural
engineering design software.
B.) Quality Assurance for Structural
Engineering Firms
Craig Barnes and a likeminded structural engineer started CBI
Consulting Inc. in 1984. In 2002 he designed and implemented
a detailed buyout transition program with two of his long-term
employees, to enable them to continue operations of what is now a multidiscipline engineering consulting firm. This presentation will be of benefit
to attendees looking toward, or involved in, ownership transfer.
Craig Barnes worked for a structural engineering firm, an architectural firm, and a national
multi-disciplined consulting firm before joining with a fellow engineer to start and grow a
new firm to an engineering architectural company with 35 employees.
6:00 – 7:00
7:00 – 10:00
Cliff Schwinger, P.E., SECB, Vice President & Quality
Assurance Manager, The Harman Group
BIM modeling, sophisticated analysis and design software,
increasingly complex building codes and young engineers taking on more
responsibility earlier in their careers, all emphasize the need for a formal inhouse Quality Assurance program. This seminar reviews the components
of a model Quality Assurance program, as well as the methodologies for
performing in-house Quality Assurance reviews.
STRUCTURE magazine
Awards Reception
(formal attire encouraged, but not required)
NCSEA Banquet & Awards Presentation,
featuring the NCSEA Excellence in Structural
Engineering Awards and the NCSEA Special
Awards (see pages 76 – 77 for honorees)
Saturday, October 3
8:00 – 12:00
12:30 – 2:00
43
NCSEA Annual Business Meeting
NCSEA Board of Directors Meeting
September 2015
Take Your Practice to New Heights at the
2015 Structural Engineering Summit
Trade Show Hours: Thursday, October 1st – 10 a.m. to 3:30 p.m. & 6:30 to 8:30 p.m.
Friday, October 2nd – 7 a.m. to 12 p.m.
(###) Booth number
Denotes NCSEA membership
(138) AISC
(114) Simpson Strong Tie
(135) Alpine ITW
(106) Star Seismic
www.aisc.org
www.strongtie.com
www.trussteel.com
www.starseismic.net
www.concrete.org/
www.sdi.org/
www.armadillonvinc.com
www.steeljoist.org
www.atlastube.com
www.steeltubeinstitue.org
www.azzgalv.com
www.strand7.com
www.bekaert.com/building
www.cscworld.com
www.herculesbolt.com
www.usg.com
www.castconnex.com
www.valmonttubing.com
www.corebrace.com
www.vector-corrosion.com
www.dlubal.com
www.nucor.com/products/products/matrix/
www.euclidchemical.com
www.vulcraft.com
www.fabreeka.com
www.vulcanmaterials.com
(120) Steel Deck Institue
(143) American Concrete Institute
(119) Steel Joist Institute
(134) Armatherm (armadillo)
(140) Steel Tube Institute
(126) Atlas Tube
(144) Strand7 PTY LTD
(125) AZZ Galvanizing
(149) TEKLA/CSC Inc
(108) Bekaert
(141) USG
(146) Blind Bolt
(131) Valmont Tubing
(129) Cast Connex Corporation
(130) Vector Corrosion Technologies
(137) CoreBrace Buckling Restrained Braces
(136a) Verco Decking, A Nucor Co.
(117) Dlubal Software, Inc
(136b) Vulcraft-Nucor
(128) Euclid Chemical
(139) Vulcan Materials Company
(127) Fabreeka International INC
(123) Fyfe Co./Fibrwrap Construction
Please visit www.ncsea.com for the most current list of exhibitors.
www.fyfeco.com
(115) Geopier Foundation Company/TENSAR
www.geopier.com
Reserved
(122) Hilti
www.us.hilti.com/engineering
100
101
102
Available
103
104
105
106
107
(133) Holcim Inc
www.holcim.us
113
112
111
110
109
108
114
115
116
117
118
119
(121) Lindapter
125
124
123
122
121
120
(118)Meadow Burke LLC
126
127
128
129
130
131
(116) Independence Tube Corporation
www.independencetube.com
(124) ITW Red Head, Ramset and Buildex
www.itwredhead.com
www.lindapterusa.com
133
Entrance
www.meadowburke.com
132
(107) MiTek, USP Connectors, Hardy Frame
www.mitekbuilderproducts.com
141
(132) Nemetschek Scia
140
134
www.nemetschek-scia.com
149
(147) New Millennium Building Systems
148
147
146
142
139
www.NEWMILL.com
135
(142) Powers Fasteners
www.powers.com
(148) RISA
www.risa.com
143
138
144
137
136a
(145) Side Plate Systems
www.sideplate.com
145
STRUCTURE magazine
44
September 2015
136b
BAR
National Council of Structural Engineers Associations
September 30th to October 3rd
Red Rock Resort Las Vegas, NV
Sponsors
NCSEA extends its appreciation to the sponsors
of the NCSEA Annual Conference.
Platinum
Gold
Copper
Registration
Contributing
Full conference registration includes:
AZZ Galvanizing Services
• 17 educational sessions & resources on 2 tracks, geared
toward the practicing structural engineer
• Wednesday evening receptions
• Thursday’s Gala Opening Reception
• All breakfasts, lunches & refreshment breaks
• Access to the NCSEA Trade Show
• The NCSEA Awards Banquet, featuring the
Excellence in Structural Engineering Awards and
NCSEA Special Awards
Conference Hotel
The Red Rock Resort is located just 10 miles from the
Las Vegas strip. Enjoy 4-diamond accommodations,
the unmatched combination of comfort, extravagance
and value for just $180/night + the discounted resort fee
of $15. Reserve your room online at www.ncsea.com
to take advantage of the group rate. Please contact
NCSEA if you have trouble securing a room.
Transportation to Hotel
There will be plenty of opportunities to network with
structural engineers from across the country at the
sessions and these special events:
The hotel is accessible by shuttle from the McCarran
Airport. The complimentary shuttle is included in
your $15 resort fee.
• Young Engineer Reception
• SECB Reception
• NCSEA Red Rock ‘n Bowl Event on Thursday
More than just a conference hotel!
Whether you like gambling, entertainment, shopping
or outdoor activities, the Red Rock area of Las Vegas
has you covered!
The host hotel, Red Rock Resort & Casino, features
restaurants, lounges, a movie theatre and bowling alley,
and a walkway to Downtown Summerlin, with shops,
dining and entertainment options. If you want to check
out The Strip, the hotel has a shuttle to take you there.
If you prefer outdoor options, a high desert wonderland
is located just minutes from the hotel.
Special Offers!
Engineers 35 years of age or younger pay only $250 for complete
registration, which also includes special Young Engineer activities.
First-Time Attendees to the NCSEA Annual Conference pay only $600.
STRUCTURE magazine
REGISTER TODAY!
Reservation information is available at www.ncsea.com.
45
September 2015
606
West 57th street,
New York
Design of Structurally-linked
Multiple Tower Structures
By Sunghwa Han, P.E., S.E., LEED AP
T
he behavior of structurally-linked multiple tower structures is largely affected by the effectiveness of the rigid
links made between towers at the bases or at the tops.
These links have a strong influence on the distribution of
wind and earthquake loads. Depending on the interactive dynamic
behavior of the adjacent building parts with one another, a separation may or may not be needed. If the links are rigid enough, then
two linked towers can be considered to be one integral structure.
But if the links cannot be made strong enough, one might consider
placing a separation joint.
Project Description
The project consists of a shared base with two levels below grade and
two residential towers (1.2 million square feet of gross building area
holding 1,028 apartments): a 42-story tall tower on the east and a
17-story tall tower on the west side of the site. The two towers are
connected by a shared podium below the 7th floor, and the podium
footprint is enlarged below the 2nd floor. These two towers are structurally separate above the 7th floor. However, the occupants of the two
towers require access between the two at every floor. Therefore, there
is a separate, 10-story tall, 7-foot wide and 30-foot long cast-in-place
concrete “bridge” structure (the west bridge) between two towers.
This bridge structure will provide a continuous means of egress for
each floor of the 17-story west tower.
STRUCTURE magazine
Figure 1. Building perspective (south elevation).
The 42-story east tower is comprised of three sections (Figure 1).
Two towers emanate from the 2nd floor, and each rises up to the 28th
floor on the east side of the site. On top of these two towers, there
is an additional 13-story tall building section rigidly connecting
the two towers above the 28th floor. The two eastern towers are 30
feet apart below the 28th floor and have another seven-foot wide
46
September 2015
Figure 2. Site plan.
and 14-inch thick concrete slab pedestrian corridor-bridge (the
east bridge) connecting them at every floor from the 3rd floor to
the 28th floor. The corridor bridges are fixed to one tower but rest
on sliding bearing pads on the other tower. This allows the two
eastern towers to sway independently of one another from the 3rd
floor to the 28th floor.
The ground level gently slopes down to the west in the site. Thus, a
portion of the ground floor is exposed above grade at the southwest
corner of the site. Top of rock elevation gradually slopes to the west,
but drops drastically at the northwest corner of the site. Spread footings
or excavated piers resting on an allowable bearing capacity of 40 tons
per square foot (tsf ) bedrock was recommended in the eastern portion
of the site. The site is surrounded by the existing low-rise buildings
ranging in height from three to seven stories tall. Most of the existing
buildings are planned to be underpinned except the relatively newer
buildings at the west end of the site. These buildings were found to
be supported by caissons. The structure will also have caissons in this
western portion of the site, where the top of rock elevation is low.
Structural System of Towers
A combination of cast-in-place concrete (CIP) shear walls and 10-inch
thick flat plates supported by CIP columns and shear walls is utilized
to resist gravity loads, wind loads and earthquake loads. Some of the
tower columns need to be transferred to accommodate a variation in
the architectural layouts.
The main elevator core located in the middle of the site (one of two
eastern towers – Figure 2) provides vertical transportation for occupants
of other towers. This main core is constructed with concrete shear walls.
It is the primary source of the overall building stiffness, resisting the
lateral loads and reducing the calculated displacements of the east tower.
The seismic load resisting system of the buildings is defined to be a
“Shear wall-Frame Interactive System with Ordinary Moment Frames
and Ordinary Reinforced Concrete Shear walls” per the New York City
Building Code (NYCBC) 2008. This system allows utilizing frame
elements as a part of the seismic load resisting system for a building
with a seismic design category B rating. It was beneficial to consider
contribution of frames in the seismic load resisting system to reduce
the calculated building displacements.
STRUCTURE magazine
Structural System of Two Bridges
and Separation Joints
Originally, both bridges (west and east) were designed as a concrete
slab pedestrian corridor-bridge fixed to one tower and supported on a
sliding connection resting on the other tower at every floor. The lateral
displacements of each tower were calculated, and the largest relative
displacement was used to determine the distance of the separation
joint for these elements shared by the adjacent towers.
The displacements due to wind loads were calculated using the results
from the wind tunnel test performed by Rowan Williams Davies &
Irwin Inc. (RWDI). The elastic displacements due to the seismic loads
were also calculated based on the elastic dynamic analysis (response
spectrum analysis). These calculated displacements were magnified
using the deflection amplification factor of Cd = 5 for Shear Wall-Frame
Interactive System to compute the inelastic maximum displacements
as per ASCE 7. These calculated inelastic maximum displacements
were significantly larger than the displacements due to the wind loads.
The required distance of separation joints was calculated to be 2
inches at the sliding connection of the east bridge and approximately
9 inches at the sliding connection of the west bridge, assuming
two towers can be moving in opposite directions at the same time.
The 2 inches of movement can be easily accommodated, but the
9 inches seismic separation requirement became a critical issue to
the cladding design.
Code Requirements for Building Separation
The building code allows the use of alternate methods to compute
the distance of separation gaps which generally produce preferable
results. When considering a seismic separation at the lot line, it is
acceptable to set back structure from the property line by 1 inch for
every 50 feet in height according to the NYCBC 2008 for structures
assigned to seismic design category A, B or C (the project building
is assigned to Seismic Design Category B). This section of the code
may be applied to separate structures, assuming that the provided
separation is sufficient enough to avoid significant damage to the
adjoining structures.
47
continued on next page
September 2015
The design team has adopted a more advanced analysis method
(Nonlinear Response History Analysis – NLRHA) to ensure the
sufficient separation gap between adjacent structures. The structural system of the west bridge was modified to become a separate
ten story tall structure consisting of a 14-inch thick flat plate and
four corner columns supported by the transfer beams at the 7th
floor. This independently supported west bridge structure, with
separation gaps at both ends, would be able to accommodate
larger differential movements of two adjacent towers than the
previously considered system (a flat plate supported on a sliding
connection at one end).
A 6-inch seismic gap (magnified by less than Cd) is tentatively
provided at both ends of the west bridge. This will allow 3½ inches
of movement of the buildings, after the compressible material in the
gap joints is fully compressed. This net 3½ inches of separation has
been verified through the recent NLRHA.
1
Period Range
of Interest
(0.72 sec – 5.4 sec)
Spectral Acceleration (g)
0.1
0.01
Development of
Ground Motion Time Histories
Initially, the site-specific seismic design spectra were developed for
design of the structures. For NLRHA, three sets of ground motion
time histories consisting of two horizontal components were provided by Amec Foster Wheeler, Environment & Infrastructure,
Inc. Three sets of seed time history (1999 Chi-Chi Earthquake)
were selected. Then, these time histories were scaled to match
their response spectra with the site-specific design response spectrum as per Section 16.1.3.2 of ASCE 7-10 Chapter 16. This
design spectrum (Figure 3) represents the Maximum Considered
Earthquake (MCE) with a mean recurrence interval of 2475 years
(2% probability of exceedance in 50 years).
606 West 57th Street
Target
Average of SRSS
GRN180
GRN270
KAU078N
KAU078W
TAP078N
TAP078W
0.001
0.01
0.1
Period (Sec)
1
Figure 3. Comparison of response spectra and 3 sets of scaled time histories
prepared by Amec.
Estimating Required Seismic Separation
The Nonlinear Time History Analyses were performed using Perform
3D, a commercial analysis software which considers material nonlinearity. The analysis model on Perform 3D includes the cellar floor
excluding foundation walls. The flat plates were modelled as slab-beam
elements with an effective width reduced from a full panel width as
recommended in ASCE 41. Stiffness of slab-beam elements and columns was further reduced in consideration of nonlinear behavior of
structural members. Shear walls were modelled using fiber sections,
and link beams are modelled using beam elements with an inelastic
hinge at both ends of the link beams.
Figure 4. Wind load cases maximizing differential loading between towers.
Wind Loads on Structurally Linked Structures
SUBSTRUCTURE 1
In general, for a typical single tower, the wind tunnel testing results
are combined with the local climate data and the dynamic properties
of the structure to generate the design wind loads. Wind loads are
provided in the form of static point loads applied at each floor, along
with the multiple load cases representing loading that imposes the
maximum effect on the structural members. Each set of wind loads is
represented by the corresponding load combination factors for each
component (X, Y and Torsion) which are applied simultaneously to
the tower to determine the internal forces acting in each member of
the lateral load resisting system.
For buildings with rigid links or shared components, additional
loading scenarios must be considered. Load cases maximizing their
effects on each tower will be separately generated first. When the
foundation, podium or the linked portions such as a bridge between
STRUCTURE magazine
SUBSTRUCTURE 3
SUBSTRUCTURE 4
SUBSTRUCTURE 2
Figure 5. Multi-blocks (substructures) approach used in wind tunnel study.
48
September 2015
10
Figure 6. Sample displacement time history (at top of the west tower in E-W direction).
towers are involved, additional simultaneous loading conditions maximizing differential loading between linked towers can be generated.
These load cases (Figure 4) were used to design the two bridges and
the 29th floor slab, which is the lowest rigid link of the top 13-story
tall section spanning the two towers rising up to the 28th floor in the
east tower. The differential movements of the adjacent towers were
calculated using these load cases, and compared with the maximum
calculated displacements for the seismic loads to finalize the distance
of separation gaps.
For an appropriate analysis of the wind tunnel data and accurate
assessment of wind-induced responses, the entire building was
“divided” into five blocks or “sub-structures” as shown in Figure
5 and presented in the RWDI’s wind study report. Diaphragms
assigned in the analysis model, using ETABS®, are matched with this
substructure configuration.
Currently, the foundation is under construction and the
super-structure is scheduled to be completed by 2017. Danny
Jadeja, P.E., Senior Associate, was the project manager and
Ben Pimentel, P.E., President, was the engineer of record.▪
Sunghwa Han, P.E., S.E., LEED AP, is a senior associate at
Rosenwasser/Grossman Consulting Engineers, P.C. and in
charge of conceptual structural design and analyses, including a
nonlinear response history analysis. She can be reached by email
at [email protected].
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Owner: TF Cornerstone Inc.
Structural Engineer: Rosenwasser/Grossman Consulting
Engineers, P.C.
Design Architect: Arquitectonica
Architect of Record: SLCE Architects, LLP
Geo-technical Engineering Consultant: RA Consultants LLC
Geo-seismic Engineering Consultant: Amec Foster Wheeler,
Environment & Infrastructures, Inc.
Wind Engineering Consultant: Rowan Williams Davies &
Irwin Inc. (RWDI)
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STRUCTURE magazine
49
September 2015
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The site is approximately 550 feet in the east-west direction by 200
feet in the north-south direction. The base of the towers is designed
as one single structure without any expansion joint. In order to
minimize shrinkage cracks, one 4-foot wide control strip is placed
between the west tower and the east tower in the podium floors. It
is located at approximately 2/3 of the building length in east-west
direction (Figure 2).
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A Need for Speed
Coordinating
Fast PaCed
Urban
ConstrUCtion
By Ramon Gilsanz, P.E., S.E., F.SEI,
Phil Murray, P.E.,
Gary Steficek, P.E.
and Petr Vancura
F
Figure 1. Avalon West Chelsea. View from High Line Park.
ast-paced construction within a dense urban environment like
New York City has several distinctive rationales, approaches,
constraints, and requirements that necessitate careful coordination. The fundamental principle that drives the need
for speed in construction is economic. The sooner a new building is
completed and put into operation, the lower are the carried financing costs and the sooner the project can recapture generated revenue
streams. There are numerous approaches and structural systems that
can speed up the construction process. This article focuses on characteristics of flat plate concrete systems which, when floor plates are
repetitious and identical, can achieve fast superstructure builds by
using a 2-day concrete placement cycle. However, in tight urban
locations, spatial constraints for staging, installation, material, and
labor, as well as complexity of architectural/design coordination, can
potentially interrupt the cycle and cause delays. Instant communication and in-the-field coordination are keys to maintaining the fast
paced schedule and to minimizing mistakes. The structural engineer
needs to be fully immersed in the day-to-day construction process to
ensure successful and timely completion of the project.
Three projects in New York City are presented to illustrate coordination issues that are particular to this type of construction: Avalon
West Chelsea, 41-42 24th Street (aka “QLIC”), and 150 Charles
Street. These developments are primarily multi-family residential,
but also feature street-level retail, at- and below-grade parking, and
amenity features at upper levels including planted green roofs and
terraces. Both Avalon West Chelsea and QLIC are rental buildings
that required high-speed construction. In contrast, 150 Charles
Street is a luxury condominium development.
Avalon West Chelsea
Avalon West Chelsea is a recently completed 588,000 square-foot
“L-shaped” building located in the prime Chelsea Arts District of
STRUCTURE magazine
Manhattan (Figure 1). Programmatically, this building consists of
two distinct components: a 31-story tower featuring 309 luxury
apartments, and a 14-story mid-rise that extends from the tower
at the west to the elevated rail structure, now known as High
Line Park, at the east, housing 405 units geared toward a younger
demographic. The LEED Silver certified property also includes 142
affordable housing units, roof-top terraces, green roofs, rear yards,
a fitness center, lounge areas, a 140-car parking garage, and retail
space at street level.
QLIC
QLIC, a 400,000 square-foot development at Queens Plaza North in
Long Island City, is nearly complete (Figure 2). The 21-story tower
holds 421 rental units, double-height retail at grade and parking for
120 cars below grade. The building’s 28,000 square feet of amenity
space includes a rooftop pool, cabanas, a roof deck with an open-air
theater and barbecue, a landscaped courtyard with a fire pit, media
lounge, game room, fitness center, and other amenities on an accessible terrace.
150 Charles Street
This 300,000 square-foot, 16-story luxury residential development in
Manhattan’s West Village consists of 98 condominium units (Figure
3). The project incorporates the façade structure of an existing 4-story
warehouse for the lower podium floors. Above, two corner towers flank
a mid-block volume and each floor steps back, forming a cascade of
terraces toward the Hudson River. The superstructure accommodates
high gravity loads due to precast façade assemblies as well as 40,000
square feet of landscaped courtyards, green-roofs and planted terraces
with up to five feet of soil cover. The building’s total landscaped area
is equivalent to the combined areas of four small neighboring parks.
continued on next page
51
September 2015
Figure 2. QLIC – architect’s rendering.
Structural Systems
The structural systems of the three buildings consist of reinforced
cast-in-place concrete flat plates, which is the most common slab
structural system for high-rise residential construction in New York
City (Figure 4). Compared to other structural systems, flat-plate
construction maximizes usable floor-to-ceiling space (no beams or
suspended ceilings) and also provides flexibility in the architectural
layout of interiors since columns are not constrained to gridlines. This
type of construction affords both lower costs and, depending on the
uniformity of design, faster erection. Concrete construction is also
inherently fireproof and, with sufficient slab thickness, is minimally
susceptible to vibration and noise transmission between floors.
At Avalon West Chelsea, floor slabs are supported by almost
200 columns that range from one story to thirty-one stories, and
seven shear wall configurations around two vertical cores. QLIC
employs 120 columns and four cores. Despite its smaller size,
150 Charles Street has over 300 columns, though few of these
extend the full height of the building. Columns are transferred
from level to level, because each floor has a distinct architectural
layout (Figure 5, page 54). For contrast: 1) QLIC included 10
column sizes and 4 transfers, 2) Avalon West Chelsea had 14
column sizes and approximately 20 transfers, primarily at the
13th floor connection between the tower and the mid-rise, and 3)
150 Charles included 41 various column sizes and 250 transfers,
whereby columns substantially changed location, size/shape, or
orientation between floors. Shear walls are located around building cores that house elevator shafts and egress stairs to provide a
structural and fireproof enclosure of these spaces and to minimize
the architectural impact of the walls. The 8-inch slabs used at each
of these buildings accommodate multiple in-slab mechanical and
plumbing services, as well as electrical conduits.
The smaller-footprint repetitious upper floors of Avalon West Chelsea
and QLIC were erected using one concrete pour on a two-day cycle (see
below for explanation), whereas the larger lower levels required several
pours. At 150 Charles, due to the irregular and constantly changing
floor layouts, slab elevation steps, and the larger quantity of column
sizes (requiring differently sized formwork), concrete placement took
16 days on average per floor. At QLIC, the locations of construction
Figure 3. 150 Charles Street – architect’s rendering.
STRUCTURE magazine
52
September 2015
joints between the two or three pours at the 27,000 square-foot
horseshoe-shaped lower eight floors were assessed and determined
in the field by the inspector-engineer. In-house Special Inspections
therefore served to expedite this coordination in the field. At Avalon
West Chelsea, however, the 575-foot-long floor slabs of the lower
14 floors demanded an advanced construction sequence analysis to
understand changes in temperature and shrinkage of concrete. The
structural design thus enabled a four-part pour sequence without
the need for any expansion joints. All three projects incorporated
crack-control reinforcing at column exteriors, shear wall corners,
and re-entrant corners.
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Coordination
During superstructure erection of highrise buildings, materials and equipment
must be lifted to the top level using a
tower crane, which all trades share. If a
delay in delivery or staging prevents a
component’s lift, placement crews must
improvise using materials that are available
©2015 MiTek, All Rights Reserved
STRUCTURE magazine
53
September 2015
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The tower portions of Avalon West
Chelsea (above the 14th floor) and QLIC
(above the 16th floor) were built using a
2-day cycle whereby an entire floor slab
is poured every two days (Figure 6 ). The
maximum feasible floor size that can
achieve a 2-day cycle is around 20,000
square feet, with floor plates around 65
feet wide. This dimension is typical of
multifamily rental buildings organized
around double-loaded corridors, and
was the case for both buildings. Only
a skilled labor force, experienced with
this method of construction, can execute
the cycle because it requires a specific
sequence of tasks before crews can proceed to subsequent floors. These tasks
include installation of: deck slab formwork, bottom mats, MEP duct/conduit/
pipe & blockouts, top mats, concrete for
deck slab, column/shear wall formwork,
reinforcing steel, and concrete for columns/shear walls. Therefore, a setback of
any single step of the process can potentially “domino” into a delay of an entire
work day.
With the advent of computer aided
analysis and design, buildings are more
complex, less repetitive, and less conservative than they were in the 1950s, when
this technique was developed. Highperformance buildings today also hold
many more systems and services, so there
are more trades and more congestion on
the construction site. As a result, buildings
with a 2-day cycle today are more challenging than they were half a century ago.
on the deck, rather than wait for subsequent lifts. The engineer must
be available to assess if each ad hoc substitution is structurally acceptable. Moreover, at dense urban construction sites that have limited
space for staging and storage, contractors may request temporary
slab openings in order to reposition materials and equipment, or
achieve clearance for installation. These logistics are not included
on construction documents and are typically decided in the field.
In the event that the designed slab reinforcement gets displaced as a
result, the structural engineer is on-hand to coordinate its relocation.
Coordination of mechanical, electrical and plumbing (MEP)
trades typically occurs during shop drawing review, and layouts of
these systems remain schematic until finalization of construction
documents. MEP subcontractors often respond to field conditions
Figure 4. Flat plate concrete construction at QLIC.
by proposing amendments to sizes or locations of slab penetrations,
which may impact the structural design. Such substitutions require
the structural engineer’s review to confirm that the integrity of
the slab is not compromised.
Foundations
The foundation of QLIC is a combination of spread footings and a
3-foot mat foundation over rocky geology. The columns and shear
walls at Avalon West Chelsea are supported by more than 1,000 piles
within a 67,000 square-foot site containing varying rock and soil
conditions. Here, the underlying rock stratum was found to be so
shallow in about one-third of the site that the piles were too short to
achieve substantial lateral resistance capacity. However, the remaining
piles were able to provide sufficient lateral resistance to eliminate the
need for footings or additional foundation elements. A foundation
slab ties all the piles together. As the floor slabs are designed without
an expansion joint, the structure engages all the piles jointly. The
stiffness of the slab without expansion joints enables the 14-story
mid-rise structure to laterally support the tower.
Envelope
Avalon West Chelsea employs a standard masonry/curtain wall façade.
The building envelope system of QLIC, however, is comprised of
STRUCTURE magazine
Figure 5. Column transfer at 150 Charles. This transfer occurs at the slab edge
and uses a concrete beam segment. Transfers at slab interior employ beams or
thicker slab sections.
54
September 2015
prefabricated metal-stud-reinforced panels
with thin brick veneer. These components were
assembled on Long Island along with windows
fabricated in Buffalo, and then shipped to the
construction site in Queens. These panels with
pre-installed windows were lifted and attached
to the building using a crane. While the price
of this system is comparable to traditional
masonry façade systems, utilizing prefabricated
panels saved roughly 20% of the time required
to enclose the building.
The combination of using the pre-assembled
façade panels and just-in-time shipping (a
delivery method whereby material arrives
to the site at the time it is to be installed)
resulted in multiple benefits for the design
and construction team. By assembling the
panels in the shop, the working conditions
and consistent temperatures allowed for higher Figure 6. Avalon West Chelsea. Tower (at right) is on a 2-day cycle, with staging on mid-rise roof deck.
quality water- and air-tightness, improving
the energy efficiency of the building. Just-in-time delivery allowed
Having both structural and building envelope teams in-house
the Contractor to minimize staging and storage space while efficiently allowed communication of structural requirements internally, withenclosing the building.
out the need for time-consuming Request For Information (RFI)
While 150 Charles also used pre-fabricated panel components (in processes through the architect, thus enabling speedy communication
this case pre-cast concrete with brick exterior), the entire building and coordination of interacting structural and envelope systems.
featured additional façade systems including masonry cavity walls, Another aspect that facilitated coordination at QLIC was the use of
curtain walls, window walls, stone cladding & storefront assemblies. Building Information Modeling (BIM), whereby all trades (strucIn most locations, the 13-inch precast panels are at least as thick as tural, mechanical, electrical, etc.) could be coordinated within a single
the building frame to which they are attached (Figure 7, page 56).
Uniformity
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Uniformity of design and repetition of structural elements enables
efficiency of construction, which in turn results in economies of
scale. This approach allows installation crews to maintain consistent
work processes and reuse formwork, rather than needing to adjust
for each individual location. This speeds-up erection. At Avalon
West Chelsea and QLIC, approximately 80% of the columns have
the same cross section and reinforcing. At Avalon West Chelsea,
80% of pile caps are also typical.
The varying areas of the floor plates and architectural amenity features
at 150 Charles required a different interior layout for every floor, as
well as numerous slab elevation changes at each level. This provided
opportunities for innovative solutions to structural challenges associated with shifting and rotating columns between the floors through
slab transfers. While the structural design responds to the architectural
requirements to achieve real estate marketing objectives, such a design is
not conducive to sustaining a 2-day cycle. The complexity and variety
of floor layouts result in lathers relocating their staging at each level.
The work space is further congested by MEP trades that also deal with
offsetting mechanical shafts and plumbing risers at each floor.
Team Interconnectedness
The structural engineer’s continuous presence in the field allows for
quick responses to coordination issues. Since Gilsanz Murray Steficek
(GMS), the project’s Structural Engineer, also served as special inspector
of concrete and steel at each project, the engineer-inspector was often
on-site. A direct line of communication between the construction team
and the design team allowed challenges to be immediately resolved
with the contractor, trades and other design team members, as needed.
STRUCTURE magazine
55
September 2015
digital 3D model during design development and pre-construction.
Few unanticipated conditions remained in the design by the time
the first shovel hit the ground.
Economics
The speed of construction translates directly to cost of the project. New
York City construction projects with the scale and complexity of Avalon
West Chelsea typically employ approximately 150 union workers on
a given day of superstructure erection. According to local prevailing
wages, this project would incur a cost of over $100,000 for a delay of
a single day for labor alone. This does not include other costs associated with remobilization or equipment rentals. At the same time, the
owner continues to maintain high-interest construction loans and his
receipt of operating revenues is also delayed. As a result, field changes
after concrete placement, such as demolition/removal/re-placement
of concrete, or fiber-reinforced polymer applications for topical reinforcement or modification/repairs, while expensive, tend to be more
economical to both contractor and developer as opposed to stalling the
construction cycle for design coordination.
The impact of construction speed upon a project’s overall economics,
however, depends largely on the type of asset that is being developed.
Avalon West Chelsea and QLIC are both rental apartment buildings.
Other types of buildings, such as residential condominiums, follow
a different economic formula focused on the apartment buyer. The
target market with high sales prices demands diversity of unique units
and amenity-rich architecture which cannot be easily systematized into
repetitive workflows. Unlike rental buildings, where tenants constantly
change, condominium building design is driven by the ability to sell
the apartments. 150 Charles sold out with asking prices ranging from
$3-$35 million (or approximately $3,200 per square foot). In comparison,
Avalon West Chelsea currently rents at around $78 per square foot per
year. This translates to a property value of approximately $312 per gross
square foot, as assessed by the New York City Department of Finance.
(Note that this incorporates the building’s operating expenses).
Despite the structural design challenges at 150 Charles, the added
costs of longer construction duration are absorbed by the condominium project since returns on investment are realized immediately
upon completion and sale of the units, whereas rental revenue streams
are distributed over the course of a building’s operation.
Summary
Not all projects rely on speed to maintain profitability. Those that
do, achieve efficiencies through uniformity of design, systematized
construction methods, and the engineer’s engagement during
construction. Moreover, when members of the design and construction teams have direct mutual access to information
through all phases of project design, preconstruction
and construction, coordination conflicts during erection can be immediately resolved.▪
Team: Avalon West Chelsea
Owner/Developer: AvalonBay Communities
Structural Engineer: Gilsanz Murray Steficek
Architect: SLCE Architects
Geotechnical Engineer: Mueser Rutledge
MEP Engineer: MG Engineering
Construction: AvalonBay Communities
Concrete: SBF Construction
Team: QLIC
Owner/Developer: World Wide Group
Structural Engineer: Gilsanz Murray Steficek
Architect: Perkins Eastman
Geotechnical Engineer: Langan Engineering
MEP Engineer: MG Engineering
Construction: Lettire Construction Corp.
Concrete: RNC Construction
Team: 150 Charles Street
Owner/Developer: Witkoff Group
Structural Engineer: Gilsanz Murray Steficek
Architect: Cook + Fox Architects
Geotechnical Engineer: RA Consultants
MEP Engineer: Flack+Kurtz
Construction: Plaza Construction
Concrete: Navillus
Ramon Gilsanz, P.E., S.E., F.SEI, is founding partner of Gilsanz
Murray Steficek and project manager for Avalon West Chelsea.
He currently serves as Chair of the New York City Department
of Buildings’ Structural Technical Committee and Chair of
the American Council of Engineering Companies of New York
Metropolitan Section Structural Code Committee. Ramon can be
reached at [email protected].
Phil Murray, P.E., is founding partner of Gilsanz Murray
Steficek and project manager for QLIC. Phil can be reached
at [email protected].
Gary Steficek, P.E., is founding partner of Gilsanz Murray Steficek
and project manager for 150 Charles Street. Gary can be reached at
[email protected].
Petr Vancura is Director of Communications at Gilsanz Murray
Steficek and has experience in construction management, real
estate development and urban planning. Petr can be reached at
[email protected].
Figure 7. 13-inch precast façade panel at 150 Charles Street.
STRUCTURE magazine
56
September 2015
InSIghtS
new trends, new techniques and current industry issues
Creating Clarity and Scoping Profits in BIM with LOD 350
By Will Ikerd, P.E., CM-BIM, LEED AP
C
learly defined structural engineering contract scopes save engineers
time, profit, and – most importantly – the personal satisfaction
of their profession. Building Information
Modeling (BIM) can improve this scope clarity if addressed proactively, or compound the
difficulties in achieving clarity if ignored. The
construction industry has reached a point
where the use of BIM is not self-explanatory:
it could be used to create 2D shop drawings,
coordinate trades, or estimate cost. Since
BIM came into existence, the industry has
lacked a vocabulary for communicating the
Level of Development (LOD) between parties. The BIM Forum™ Level of Development
(LOD) Specification 2015 (BIMforum.org/
LOD) is an industry-changing reference that
enables structural engineers to clarify their
scope with BIM, providing the solution to
this paramount problem of vague BIM scope
definition.
Previous to this development, many model
element authors were unaware of expectations upon entering a project. The LOD
Specification now provides a way to define
the scope of detail and input minimums for
each particular component of the design. It
is simply a collection of definitions describing input and information requirements and
graphic/model examples of the different levels
of development for building elements. The
document does not outline the necessary
levels of development for different steps in
the construction process, leaving these determinations for each project team. Instead, it
gives a common vocabulary for use between
parties on a project team. It is important
to note that the document is now in its 3rd
edition, with the 2015 version released for
public comment. Key aspects of the document
are its support and input from the national
BIM Masonry (BIMforMasonry.org), Steel
Joist Institute (SteelJoist.org), Steel Deck
Institute (SDI.org), ACI (Concrete.org),
and the National Institute of Steel Detailers
(NISD.org).
LOD definitions in terms of model elements* (emphasis added):
• LOD 100 The Model Element may
be graphically represented in the
Model with a symbol or other generic
representation, but does not satisfy
A masonry wall element progression shown from LOD 200 through 400. Copyright, BIM Forum
(BIMforum.org/LOD) & IKERD Consulting (IKERD.com) 2015.
the requirements for LOD 200.
Information related to the Model
Element (i.e. cost per square foot,
tonnage of HVAC, etc.) can be derived
from other Model Elements.
• LOD 200 The Model Element is
graphically represented within the
Model as a generic system, object, or
assembly with approximate quantities,
size, shape, location, and orientation.
Non-graphic information may also be
attached to the Model Element.
• LOD 300 The Model Element is
graphically represented within the
Model as a specific system, object or
assembly in terms of quantity, size,
shape, location, and orientation.
Non-graphic information may also be
attached to the Model Element.
• LOD 350 The Model Element is
graphically represented within the
Model as a specific system, object, or
assembly in terms of quantity, size,
shape, orientation, and interfaces with
other building systems. Non-graphic
information may also be attached to
the Model Element.
• LOD 400 The Model Element is
graphically represented within the
Model as a specific system, object
or assembly in terms of size, shape,
location, quantity, and orientation
with detailing, fabrication, assembly,
and installation information. Nongraphic information may also be
attached to the Model Element.
STRUCTURE magazine
58
September 2015
It is important to note that there is no LOD
of an entire model; the model is a mixture
of different elements within different LODs.
For permit drawings, which will be
required for the foreseeable future on building projects, elements are typically only
modeled to LOD 300. However, for full
trade coordination, higher LOD is required,
short of fabrication LOD. For this reason,
the author proposed LOD 350 for bridging the gap between element development
at permit drawings and fabrication level.
LOD 300 does not include the information
necessary for full cross trade coordination,
while LOD 400 requires information that
may not yet be available.
LOD 300 represents model elements traditionally shown in the plan view of a set
of construction documents. This would
include main structural members with information such as specific location and type.
Construction Documents made from the
LOD 300 model are accompanied by 2D
information: general notes, typical details,
specific details and specifications to define
higher level information not typically shown
in 1/8-inch scale plans or modeled for permit
drawings. For coordination, model elements
with an LOD of 350 represent information generally shown with typical details
in construction drawings. This information requires trade-knowledgeable input
to model accurately. Most main structural
member elements are at LOD 300. However,
structural engineers must be mindful that
LOD 300 requires elements to be in the
correct location. For example, although the
2D plans may appear to be correct, sloping
roof members that are modeled flat are not
at LOD 300. Also, design-level open web
bar joists at LOD 300 are not acceptable
for trade coordination with MEP, as they
do not have the specific manufacturer’s web
profiles to detect conflicts. Other areas of
misunderstanding are structural elements
shared with architecture, such as tilt walls,
slabs and load bearing masonry walls.
A masonry wall element, for example, is
shown in the progression from LOD 200
through 400 (see the accompanying graphic).
Note that most structural design models would
only take the wall elements to LOD 300 to
create sealed 2D construction permit drawings. The wall at LOD 300 would specifically
identify the masonry system, and would reference typical details and project specifications
for higher levels of development details. This
higher LOD information, such as but not limited to jam conditions, bond beams, grouted
cells, dowel locations, and joints, would not
appear until LOD 350 and higher. These
higher LOD aspects would typically be modeled as part of the construction side submittal
process. LOD 400 masonry modeling is currently found on more progressive BIM projects
in limited areas of building as part of virtual
mockups for water proofing review at key
building transition areas. Situations such as this
make a compelling case for using LOD 350 as
an important step between specific assemblies
and detailed assemblies for coordination with
manufacturer’s specific content. The structural engineer’s scope should address who is
responsible for modeling such information
at higher LOD, as owner and lead designers
begin requesting higher LOD model elements.
As more projects require detailed 3D coordination, the need for accurate MEP models
will become even clearer to lower the risk
of the entire design team (A & E). There
is little value in above ceiling coordination
in taking the architectural and structural
model elements to LOD 300 (specific in the
actual orientation) if MEP model elements
are only at LOD 200 (generic in approximate
location). Structural engineers should consider
adding additional services in their contracts
for manual MEP coordination review if the
MEP model elements are not to LOD 300.
This represents the added time the structural
engineer will have to invest in the project
during construction administration to deal
with changes in the MEP due to lack of
model definition (and MEP design). For
instance, all gravity plumbing lines must
slope for these elements to be at LOD 300,
whereas many MEP design models do not
slope these lines. This creates the risk of failing to discover that the line will not fit below
the structure and above the ceiling if the lines
are not modeled at LOD 300 (with slopes).
The structural engineer may then be forced
to consider adding web openings in their
beams or redesigning shallower beams, losing
time and profit.
Profit is vital in the business of any profession; structural engineering with BIM is no
different. Clearly defined scopes in BIM and
LOD 350 is a key to creating clarity in the
design-to-construction process and aiding
structural engineers in the opportunity to find
profits in clearly defined project BIM scopes.▪
Will Ikerd, P.E., CM-BIM, LEED AP, is a
principal at IKERD. He currently co-chairs
both the Designers Forum of the AGC’s
national BIM Forum and the Structural
Engineering Institute’s national BIM
Committee. Additionally, he co-chairs the
AGC BIM Forum – AIA workgroup on
Structural LOD. He may be contacted at
[email protected].
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STRUCTURE magazine
59
September 2015
EnginEEr’s notEbook
aids for the structural engineer’s toolbox
Moment-Curvature and Nonlinearity
A Fundamental Discussion
By Jerod G. Johnson, Ph.D., S.E.
N
early every day in our careers as
structural engineers, we consider
the following equations:
Mn = As fy(d-a/2), Mn = Fy Z x
Readers will no doubt recognize these as the
nominal flexural strengths utilized in beam
designs for reinforced concrete and steel, also
known as (among other things) the flexural
limit state. While there are variations reflecting
unbraced lengths, the presence of compression
reinforcement, axial loads and other considerations, these are the fundamental relationships.
What exactly does this mean?
Structural engineers understand that the
capacities represented by these equations do
not correspond to the loads that we actually
expect the members to see during a typical service condition. Rather, these are the approximate
magnitudes of loads that the members would
experience in the unlikely event that they are
pressed toward ultimate failure. This will hopefully never occur for members that are part of
the ‘gravity’ system. Likewise, this will hopefully not occur for a large but rare transient
event in members that are part of the ‘lateral’
system. Either way, the fundamental objective
is to ensure that designs have φMn greater than
Mu, the maximum flexural factored load effect.
Now consider the ‘middle ground’ in this
scenario – the flexural behavior that occurs
between zero load and a condition where Mu
equals Mn. Doing so offers a glimpse of basic
nonlinear behavior and the formation of flexural mechanisms that hopefully reflect stable
and ductile performance.
For the concrete beam scenario, at a load
equal to Mn it is assumed that the reinforcement has yielded in tension following
the idealized elastic-to-plastic relationship,
with a constant stress equal to yield stress
(fy) with a strain somewhere beyond the
yield strain of approximately 0.00207 (for
Grade 60 bars). It is also assumed that the
concrete acting in compression has reached
a strain of 0.003 and that at this point, it
is theoretically being crushed at its extreme
compressive surface. To understand what
has happened in the beam while reaching this point requires developing a series
of calculations reflecting various levels of
reinforcement strain, from zero all the way
Moment vs. curvature relationship for reinforced concrete beam.
up to the net tensile strain (εt) which occurs
at a theoretical load of Mn.
For each one of these calculations, it is possible to develop resultant forces based on
relative strains in the tension steel and the
concrete compression zone, and a momentcouple relationship based on the distance
between the resultant forces. This relationship
is relatively simple, since we know from statics
that the resultants of tension and compression
must always be equal in magnitude and opposite in direction. While many theories have led
to the development of models reflecting the
distribution of stress in the concrete compression zone, assuming a uniform compression
zone as prescribed by ACI 318 is valid and
greatly simplifies the calculation, enabling the
a/2 portion of the equation previously shown.
For each series of calculations, the curvature
value is simply taken as the strain in flexural
reinforcement divided by its distance from the
theoretical neutral axis. Plotting the values of
Mn and curvature yields a load-deformation
(curvature) relationship, an example of which
is shown in the Figure.
Among the interesting things observable in
this figure is that nominal moment capacity
is nearly reached at the point where the tensile reinforcement first yields – long before the
member reaches is ultimate capable curvature
at Mn. What does this mean in a practical sense?
Observe that the nominal flexural strength is
approximately 240 kip-ft and that this particular
member reached this capacity at a curvature just
beyond 0.0002/in. However, the member was
able to sustain this load to a curvature nearly five
times this value, thereby demonstrating the ductile behavior toward which the codes are geared.
This exercise demonstrates that failure of this
member would be preceded by deformations
STRUCTURE magazine
60
September 2015
likely to present a serviceability issue, thus giving
occupants warning of trouble.
As an interesting exercise, consider increasing the area of reinforcement to the balanced
or over-reinforced condition. The results will
demonstrate a smaller ratio of maximum capable curvature vs. yield curvature, which grows
ever smaller as the amount of reinforcement
increases. This demonstrates the pitfall of simply
adding reinforcement to improve strength.
It is also worthwhile to consider seismic
response. The Figure demonstrates the potential for favorable hysteretic behavior as the area
under the curve is proportional to the energy
release occurring through each cycle of flexural
load and rotation. If the reinforced concrete
is detailed correctly, this is a favorable, stable
and controlled method for dissipating energy
during an earthquake, thereby preventing it
from becoming manifest elsewhere. The same
holds true for steel beams, provided that they
are appropriately sized and detailed to promote
fundamental material nonlinearity, as opposed
to other forms of ‘macro’ nonlinearity such as
global or local buckling.
Observations of the projected theoretical
behavior of mechanisms such as this are worthwhile. They offer a glimpse into the basis for
code provisions that we often take for granted.▪
Jerod G. Johnson, Ph.D., S.E.
([email protected]), is a principal
with Reaveley Engineers + Associates in
Salt Lake City, Utah.
A similar article was published in the
Structural Engineers Association-Utah
(SEAU) Monthly Newsletter (September
2011). Content is reprinted with permission.
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CASE BuSinESS PrACtiCES
Strategic Planning: A Comprehensive Approach
By Dilip Choudhuri, P.E.
M
ost high-performing firms that
are successful over the long
term are those which truly
embrace strategic planning.
If you have been part of a strategic planning
process in your firm and are still skeptical
about the importance of such a process, you
should revisit the goals of your firm’s last two
strategic planning sessions and assess how
your firm has changed as a result. You will
likely be amazed!
Walter P Moore has been in business for 84
years; its latest comprehensive strategic plan
was developed in 2012 and is currently being
implemented. The firm has the benefit of the
historical perspective of the last five strategic
plans that outlined its trajectory and validated
the importance of building upon previous
strategies. Walter P Moore’s successful strategic planning under the author’s leadership
is the basis for this article.
people “outside the room” should be engaged
for various efforts, increasing engagement
and buy-in.
Deciding on an Approach
There are many approaches that can be
used for comprehensive strategic planning.
For example, you could chose to conduct
a vision-based, goal-based, issue-based, or
scenario-based planning session. Some of the
most widely used books which should be
read prior to deciding on a strategic planning
approach include The Balanced Scorecard by
Kaplan and Norton, Blue Ocean Strategy by
Kim and Mauborgne, and Good to Great by
Collins. Each approach has its special nuance
and benefit. However, whichever approach is
ultimately chosen, the successful implementation of the resulting initiatives requires a
strong commitment from the core strategic
planning team.
Hiring a Facilitator
Planning Framework
Getting Started
Ideally you want to start the process by having
the firm’s senior leadership team agree on the
need for a new strategic plan. This should be
followed by hiring the strategic planning consultant, providing the selected consultant with
necessary firm background and deciding on
two important facets of the proposed strategic
planning work – (i) the ideal number of core
team members and (ii) the methodology for
the strategic planning session. You want to
have the largest number of people in the room
that the facilitator is comfortable including,
without any adverse effects on sessions for
the chosen strategic planning approach. This
will afford you greater flexibility on the issue
of being inclusive with team members from
across the firm who are at different stages of
their professional career.
Selection of the core group should be well
thought out and incorporate new leaders
within the firm as well as senior leadership
for a balanced perspective. Preferably, these
core strategic planning team members are
either principals or senior project managers. Consistent communication firm-wide
about the ongoing process can build excitement, especially among those not actively
involved in the planning sessions. These
Working with an expert facilitator knowledgeable about your selected approach, and one
who is intimately familiar with firms in the
A/E/C space, is critical. Indeed, most successful
strategic planning efforts require firms to hire
an outside specialty consultant to facilitate the
process. The external facilitator, by virtue of
being an outsider, has tremendous freedom
of expression and inquiry, and can maintain
objectivity, which is understandably difficult
to do from an insider perspective.
At Walter P Moore, the external facilitator
who was selected used The Balanced Scorecard
approach to guide five strategic planning sessions that spanned a 12-month period for the
2012 strategic planning. The session was a
goal-based strategic planning session which
was tested for alignment with the firm’s overall vision. The core strategic planning group
of twenty-two leaders met for two days for
each of the five sessions. These meetings were
held within Walter P Moore’s facilities, which
made it efficient from a logistics point of view
and also signaled to others in the office that
the firm’s leaders were planning the future
of the firm in plain view. When working in
your own facilities, it is even more important
to stay focused and observe the ground rules.
There were always assignments between the
sessions for the entire group of twenty-two.
The facilitator was very successful in making
STRUCTURE magazine
63
September 2015
Culture and strategy are intertwined.
sure that the conversations at these sessions
were not dominated by a few of the most
outspoken in the room.
Assessing Firm Culture
For strategic initiatives to be successful, a
supportive cultural environment is a must.
It is critically important to seek the answer
to “How are things done within the firm?”
Personal mastery guru David Aitken of the
Aitken Leadership Group says, “Any good
strategy is going to depend on culture to
support it. So culture and strategy become
synergistic, part of a system diagram.” Hence,
knowing the cultural predisposition of your
firm is an important first step in a successful
strategic planning process.
Conducting a cultural scan at the early
stages of the strategic planning process is also
a great way to engage all members of your
firm. Typically, your strategic planning consultant will need to depend on a specialized
personal mastery expert to develop the parameters of a cultural scan and then interpret the
findings. There are well-established ways in
which organizational behavior experts collect
valuable qualitative data through employee
surveys with respect to the cultural aspects
of a given firm.
At Walter P Moore, all employees responded
to a confidential survey that helped develop
the cultural scan for the firm. From the data,
the firm recognized the collective wisdom of
how employees viewed what made Walter P
Moore successful in the past, how things get
done, and how they envisioned the firm’s future
– very valuable insight for all involved. It was
also recognized that, as a firm, organic growth
continued on page 65
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was preferred over growth through mergers and
acquisitions because it allows maintenance and
reinforcement of its culture across the firm.
Walter P Moore has made just four acquisitions
in its history, so an acquisition is rare. Culture
is important; hence, the firm is much more
deliberate about determining the cultural fit in
the due diligence process as it approaches any
acquisition opportunities for growth.
Four Basic Steps
to Strategic Planning
Steps for strategic planning.
Expecting linearity in the strategic planning
process is unrealistic. The overall process is
highly non-linear; hence, having a high level
of comfort and trust in the selected facilitator is of utmost importance. The facilitator
must guide the sessions while retaining the
flexibility to modify the direction of the
sessions to elicit open dialogue concerning
the four basic steps to strategic planning –
Current State Analysis, Desired Future State,
Understanding of Barriers, and Development
of a Strategic Plan. These steps do not necessarily occur in sequence.
Rod Hoffman, CEO of S&H Consulting,
a strategic planning firm, likes to use The
Balanced Scorecard as a framework for strategic
planning sessions. Hoffman says, “Strategic
planning is about connecting the dots so
that everyone can see the picture.” A comprehensive strategic planning exercise typically
requires multiple sessions over multiple days.
The benefit of having the core team attend all
of these sessions is the continuity component,
and the team building that happens through
group exercises during the sessions and informal conversations outside of the sessions.
1.0 Current State Analysis
Context for the current state analysis is
established by restating the vision, mission, and core values, and by sharing the
updated firm-wide cultural scan with the
core strategic planning group. It is critical
for any strategic planning exercise to do a
deep dive into the current state of the firm,
and the current internal environment as
perceived by the internal core team, members of the firm, and clients of the firm. To
understand the current state of the firm, a
basic Strengths, Weaknesses, Opportunities,
Threats (SWOT) analysis should be conducted by the core team. In addition, key
production leaders who may not be part of
the core strategic planning group can be
surveyed for additional SWOT data points.
A select group of the firm’s clients can be
surveyed, via a series of prepared questions,
on their thoughts on Social, Technological,
Environmental, Economic, and Political
trends affecting their industry (STEEP
analysis) in the next five years. These client
response data sets can then be aggregated to
enhance the current state analysis. This is
yet another example of where others can be
engaged who may not be part of the core strategic planning group to improve the overall
process. The core strategic team can then be
engaged to see what trends are working in
the firm’s advantage (also known as tailwinds)
and those that are working against the firm
(headwinds). During the strategic planning
process at Walter P Moore, the firm confidentially turned to about 40 trusted clients
across market sectors to provide answers for
the STEEP analysis. These were very useful
client touches in that they educated the firm
about their client’s business realities in their
specific sector while showing Walter P Moore’s
interest in them. The data collected was sorted
by the various categories to understand the
impact of these client-specific realities. Some
created opportunities and some required the
strategic direction as a firm to be altered.
2.0 Desired Future State
This desired future state analysis should not
be limited to business growth opportunities,
but should also examine internal and cultural
aspects of the firm’s future. This goes back to
the central idea that business strategic growth
is very much intertwined with culture. The
growth opportunities can be categorized as
those that can be achieved through an increase
in market share, change of portfolio, and
through acquisition of new lines or divesting from a current line of business. There are
many exercises that can be developed by the
facilitator to have a dialogue within the core
group about these topics, and also engage the
group members in smaller working groups
with a report out process.
In Walter P Moore’s 2012 strategic planning process, the core team of twenty-two
leaders each had five votes to endorse various growth and cultural strategies that were
the result of the planning work. In addition,
the full corporate Board of Directors had an
STRUCTURE magazine
65
September 2015
opportunity to vote on each of the stated
growth and internal/cultural initiatives. This
was another way to formally get the board
as a group to review selected initiatives and
provide their wisdom with respect to prioritization of the strategic initiatives. The votes
from the Board of Directors were weighted
and then tabulated in addition to those of
the core strategic planning group. Corporate
boards tend to like to weigh in on strategic
initiatives because they, as a group, do have
strategic thinkers who have taken on the
responsibility. It is also much easier for the
board to support the CEO when they are
implementing the strategy, because they are
familiar with it and have provided a voice to
the plan. Walter P Moore’s core team settled
on thirteen initiatives – seven growth initiatives and six internal/cultural initiatives.
3.0 Understanding of Barriers
This phase of strategic planning builds on the
current state analysis described in Step 1 and
the desired future state analysis described in
Step 2. There is clearly a need to have an open
and robust discussion about the culture of the
firm and the current state of the external barriers that impact the attainment of the desired
future state. If you have a large core strategic
planning team (20-24 people), you can use
group work and a voting process to continue
engagement and maintain focus. This phase of
planning provides insight into potential cultural initiatives needed for success, and can test
the durability of your core practice areas. Such
informative insights into the firm likely would
not have been discovered without having gone
through this comprehensive process.
4.0 Development of a Strategic Plan
Potential growth and cultural strategies should
be voted on by the core group and the Board
of Directors of the organization. Each strategy
should be associated with a weighting system
to allow ranking by levels of importance. The
development of the final strategic plan requires
the core team to consider three horizons or
time-frames of growth. Horizon 1 includes
strategies that affect the core business and are
things that need to be addressed immediately.
Horizon 2 contains those strategies that need to
be addressed in three to five years and are about
building emerging practice areas. Horizon 3
strategies are those that are very ‘blue-sky’
growth opportunities achievable further out
– five years plus into the future. In general,
there should be more initiatives in Horizons
1 and 2 than in Horizon 3.
Stair-step to growth – starting a new practice while limiting risk.
Strategic Implementation
Once a strategic direction is identified, the
final step and bigger task is to develop a
preliminary schedule of implementation for
each strategic initiative adopted. Once implementation plans are developed, they should
be reviewed by the Board or a subset of the
Board for acceptance and authorization. The
strategies for Horizon 2 or 3 require better
risk management since they are considered
relatively uncharted territory compared to
the core business strategies. The CEO should
create a detailed communication plan to share
the strategic direction with firm members
who were external to the process. He or she
should regularly communicate updates of the
strategic plan’s implementation as items are
completed or revised. This keeps the strategic
plan front and center for the entire firm.
One can consider a stair-step implementation
process for those initiatives in Horizon 2 and 3.
The first step is to conduct small-scale experiments of a service or practice area, followed by
a validation of the service or practice area – is it
profitable? Is it something that fits our firm well?
Once the service or practice area is validated,
one can replicate and then scale the practice
area within the firm. Think carefully about key
performance indicators for each of the strategies
being implemented. As it is said, “what cannot
be measured cannot be improved.”
Once a firm-wide implementation plan is
developed, individual business units or groups
within a firm need to develop complementary
implementation plans that are shorter-term
and co-exist with firm-wide strategic direction.
Walter P Moore’s 2012 plan outlined several
strategic growth initiatives that were specific to
select individual business units (business unit =
a group of complementary practice areas with
service offerings). It was then the responsibility
of each business unit to develop the strategic
implementation plans for the growth initiative.
The implementation plan was then reviewed
by a review committee consisting of members
from across the firm. Seventy-five percent of
the review committee membership consisted
of people within the business unit for the specific growth initiative and the remainder from
outside the business unit. In 2014, a Strategy
Council was created as part of the organizational structure which is chaired by the CEO
and has the business unit leaders from each
operating group and two additional members
that are appointed by the CEO. The Strategy
Council meets on a quarterly basis to focus on
the strategic agenda of the firm. The implementation plans are subsequently submitted to the
Strategy Council and the Board of Directors
for formal authorization and approval.
Achieving Results
Team members within high-performing firms
will want to see results of the strategic planning process. Results primarily depend on
solid execution of the strategic plan. The old
project management adage that you have to
“plan the work and then work the plan” is
true for strategic initiatives, too.
In a multi-discipline firm, the number of concurrent strategic initiatives can be numerous and
overwhelming. It may be acceptable to have
multiple growth and internal/cultural strategic
initiatives, as long as the implementation team
5 Key Takeaways
1) Use an external facilitator familiar
with the A/E/C industry for your
strategic planning.
2) Conduct a cultural scan of your entire
firm and try to communicate the
importance of the survey for a high
response rate.
3) A long-range view of the strategic
planning process is important. This
allows you to make sure that you focus
on the progress and not worry about
small delays that are bound to occur.
4) Communicate the final strategic plan
widely with your entire team. Strategic
implementation happens both from
the top down and the bottom up.
5) Devote ample time to developing
actionable implementation plans. The
goals of the implementation plans
should be revisited at least quarterly to
ensure their achievement.
STRUCTURE magazine
66
September 2015
members are selected from across the organization and also across various practice areas of the
firm. There are many reasons for this: implementers bring passion to their initiative of choice
(ask for volunteers for some initiatives), they
bring subject matter expertise, their service to
the firm should be linked to their personal action
plans and annual performance goals. When
leaders stop going to the same ‘four’ people for
all strategic implementation needs, you have the
unintended and beneficial consequence of getting broad based buy-in for the implementation
of the strategic plan. For a multidiscipline firm
or firms in multiple geographies, it becomes
vital to energize some of the non-core practice
areas or emerging offices that have the potential
to blossom in the near future.
Conclusion
A comprehensive strategic planning process
requires a huge commitment of resources
for any professional services firm, but yields
incredible benefits. Having the entire senior
leadership team support the effort, without any
questions, is critical since the strategic planning
process will intrude on your firm’s immediate needs and other tasks that are critically
important today. A comprehensive strategic
planning and implementation process is akin to
a marathon rather than a sprint. To succeed, we
must maintain collective focus on the critically
important initiatives for the three horizons –
short, medium and long-term.
Walter P Moore implemented a new organizational structure as a direct result of one
of the strategic planning initiatives from the
firm’s 2012 Strategic Plan. Operating under
a new organizational paradigm for the firm
for just over a year now, Walter P Moore has
successfully deployed a flat, responsive organizational structure to address the challenges
of a changing marketplace and client needs.▪
Dilip Choudhuri, P.E., is President and CEO
of Walter P Moore. Dilip can be reached
at [email protected] and
followed on Twitter @dilipC66.
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checks, bearing pressure, punching
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IES, Inc.
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core requirements and lifelong learning for structural engineers
Education issuEs
Structural Education Deficiencies
Timber and Masonry
By Kevin Dong, P.E., S.E. on behalf of the Basic Education Committee
O
ne of the concerns of professionals in the structural engineering
community is the limited exposure to timber and masonry
design for graduating civil/structural engineering majors. A majority of smaller scale
structures are constructed using timber/
masonry separately or a combination of these
materials; yet most civil/structural engineering
curriculums emphasize steel and concrete as
building materials and provide less of a focus
on timber and masonry design. Additionally,
the timber industry has evolved beyond the
typical traditional stick-framed construction
Suggested Timber/Masonry
Module One
1) Wood Buildings and Design Criteria
using allowable stress design (ASD)
2) Properties of Wood & Lumber Grades
3) Beam & Joist Design – Sawn
Lumber, Glued Laminated Timber,
Manufactured Lumber
4) Stud & Column Design – Axial
members (buckling versus crushing)
and combined axial and bending
5) Shear Wall Design – Segmented and
perforated wall concepts. Calculations
for segmented wall method only
6) Diaphragm Design – Sheathing,
chords and collectors for flexible
diaphragms
7) Connector capacity – Behavior and
capacity of nails and bolts
8) Masonry Buildings and the history
of masonry as a building material,
ASD versus LRFD
9) Construct-ability, sequencing, and
terminology for masonry construction,
material strengths and lab testing
10) Beam Design (LRFD) – flexural
model, failure modes, shear
requirements, deflections using
cracked section properties
11) Column/Pilaster Design – role of
longitudinal and transverse, pure axial
and combined axial and bending
12) Shear Wall design – in-plane design
for shear, flexure, and introduction
of the axial-moment relationship
13) Wall Design – out of plane design,
including second order effects
to a more advanced and innovative building
material, and many students will be unprepared to design buildings without this as
part of their curriculum. As noted in prior
STRUCTURE® articles, the National Council
of Structural Engineers Associations (NCSEA)
promotes a varied curriculum that includes a
balance of analysis, design, and other technical skills. Timber and masonry design are an
integral part of the recommended curriculum.
And although NCSEA believes timber and
masonry should each be provided as its own
course, a timber/masonry material design curriculum can be organized into two modules:
element design and building systems design.
In the first module, the basics are introduced,
such as: the properties of a given material,
advantages and limitations of a given building
material, design of beams (flexural), columns
(axial and combined axial and bending), shear
walls or structural panels, and diaphragms
Suggested Timber/Masonry
Module Two
1) Building configuration
2) IBC load requirements (gravity
and lateral)
3) Selection of roof and floor systems
4) Preliminary design process
5) Structural design computations using
allowable stress design (ASD) for
timber and LRFD for masonry, then
develop working drawings (notes,
plans, elevations, details) for structural
systems including:
a. floor framing – sawn lumber,
I joists, manufactured lumber,
glulams, etc.
b. roof framing – sheathing, stick
framing, prefab trusses, tiebacks/
anchorage etc.
c. wall framing – sheathing, studs,
posts, headers, masonry, trim
requirements at openings etc.
d. shear walls – sheathing/block
selection, chords, connections,
segmented, perforated (optional) for
plywood and masonry, etc.
e. diaphragms – sheathing, chords,
collectors, sub-diaphragms, cross-ties,
flexible vs. rigid, cantilever, etc.
6) Configuration & design of connections
STRUCTURE magazine
69
September 2015
(where applicable). The second module links
the use of building codes and standards,
such as the International Building Code,
American Concrete Institute’s Building Code
Requirements for Structural Concrete, American
Institute of Steel Construction’s Specification
for Structural Steel Buildings, American Wood
Council’s National Design Specification for
Wood Construction, and Masonry Standards
Joint Committee’s Building Code Requirements
for Masonry Structures, with structural analysis
to design small scale (and regular) buildings.
The curriculum includes developing a framing
system for both lateral and vertical loading
to emphasize the concept of load path and
to gain exposure to building irregularities in
structural systems. Then there is determining the gravity and lateral loads to establish
loading and design criteria, followed with
designing beams, columns, structural panels,
diaphragms, collectors, and connectors to
resist gravity and lateral load requirements.
Finally, there is the development of structural drawings (plans and connection details)
to connect analytical work to the communication tool used for construction. The
last step exposes students to a critical part
of design, but also to constructability and
building sequencing. Together, Module One
and Module Two encompass the NCSEA
Core Curriculum suggestions for Timber and
Masonry. It’s envisioned that the first module
is either a combined timber/masonry course, as
currently offered at some institutions, or as two
separate timber and masonry courses. Schools
limited by a variety of constraints can implement Module One to expose students to both
materials. Module One is sufficiently intense to
provide a student with a basic understanding
of both materials so that self-teaching can raise
the student to a higher level of understanding. In either scenario, 60 (semester) lecture
hours are proposed to introduce the basics of
material design for wood and masonry. The
second module would include the design of a
regular building with the two materials, and
a comparative study of using either masonry
or wood as the lateral load resisting elements,
such as shear walls. Although this module may
be more demanding, 60 lecture or contact
hours are foreseen as a minimum to cover the
recommended material.▪
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ANCHORING GUIDE
American Wood Council
Phone: 202-463-2766
Email: [email protected]
Web: www.awc.org
Product: Special Design Provisions for Wind and
Seismic standard
Description: Provides criteria for proportioning,
designing, and detailing engineered wood systems,
members, and connections in lateral force resisting
systems. Allowable stress design (ASD) or load and
resistance factor design (LRFD). Nominal shear
capacities of diaphragms and shear walls are provided
for reference assemblies.
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Phone: 800-236-8539
Email: [email protected]
Web: www.bentley.com/
Product: RAM Connection
Description: Perform analysis and design of virtually
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Construction Tie Products
Phone: 219-878-1427
Email: [email protected]
Web: www.ctpanchors.com
Product: Stitch-Tie
Description: Stainless steel helical anchors for
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(8mm & 10mm) for re-attaching existing brick
veneers to masonry, wood, concrete, tile and steel stud.
Replicates missing wall ties, but stronger and stiffer.
Installs easily and is concealed when completed.
Decon® USA Inc.
Phone: 866-332-6687
Email: [email protected]
Web: www.deconusa.com
Product: Anchor Channels
Description: Exclusive representative of Jordahl in
North America. Hot rolled Anchor Channels are
embedded in concrete and used to securely transfer
high loads. Their main application is for flexible
connections of glazing panels to high-rise buildings.
Anchor Channels with welded-on rebar or corner
pieces are available.
Product: Studrails®
Description: The North American standard for
punching shear enhancement at slab-column
connections. Studrails are produced to the
specifications of ASTM A1044, ACI 318-08, AND
ICC ES 2494. Decon Studrails are increasingly used
to reinforce against bursting stresses in banded posttension anchor zones.
All Resource Guide forms for the 2015 & 2016
Editorial Calendar are now available on the
website, www.STRUCTUREmag.org.
Anchor Bolts, Concrete, Façade, Geotechnical, Masonry, Post-Tensioning,
Reinforcing and Utility Anchors, and General Hardware & Ties
Gripple Inc.
Powers Fasteners
Halfen USA, Inc.
Product: Powers Submittal Generator (PSG)
Description: PSG is a submittal and substitution
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users can include all applicable code reports and
technical details. Contact us for a free demonstration.
Phone: 630-952-2113
Email: [email protected]
Web: www.gripple.com
Product: Anchor Hanger Kits for Suspended Services
Description: Cable hanger kits suspend
mechanical & electrical services like HVAC,
lighting, conduit racks, and cable basket. Spider
Kit is a cast-in-place concrete insert hanger kit
that’s ready-to-use, has a safe working load of up to
200 lbs, and includes a Spider insert, cable hanger,
and a Gripple fastener.
Phone: 800-423-9140
Email: [email protected]
Web: www.halfenusa.com
Product: HALFEN HCW Curtain Wall System
Description: Designed to anchor curtain wall façade
elements quickly, securely, and economically to the
main structure. Offers various configurations for ‘top
of slab’ and ‘edge of slab’ applications. Utilized to
ensure quick, efficient, and adjustable connections
to account for on-site conditions and engineered to
resist any load combination (horizontal, vertical, and
longitudinal) as required by the project.
Product: HALFEN HSD-LD Lockable Dowel System
Description: For temporary movement joints,
commonly found in post-tensioned concrete slabs.
Dowels allow initial shrinkage of the concrete to
take place and are then locked in position with a
mechanical plate and a controlled amount of epoxy
resin. The locked dowels continue to transfer shear,
but pervert further movement.
Product: HALFEN HGB Handrail Anchor Channels
Description: HALFEN HGB Anchor Channels for
handrail connections enable safe anchoring of railing
posts to the edge of thin concrete slabs. These Anchor
Channels allow strong connections to the edge of
concrete slabs as thin as 4 inches (100mm).
Hardy Frame
Phone: 800-754-3030
Email: [email protected]
Web: www.hardyframe.com
Product: Hardy Frame Shear Walls
Description: Hardy Frame now offers pre-engineered
anchorage solutions that drastically reduce large pad
footings that can be associated with pre-fabricated
Shear Wall Panels; standard details are available for
inclusion with plan submittals.
IES, Inc.
Phone: 800-707-0816
Email: [email protected]
Web: www.iesweb.com
Product: IES VisualAnalysis
Description: VisualAnalysis offers ACI Anchor
Design checks with the base plate design feature
included in VAConnect. Use VisualAnalysis for a wide
variety of analysis and design projects. It is simple,
productive and versatile.
STRUCTURE magazine
71
September 2015
Phone: 845-230-7533
Email: [email protected]
Web: www.powers.com
Product: Powers Design Assist (PDA)
Description: Anchor design software provides
calculations in accordance with ACI 318-11 and CSA
A23.3 for mechanical, adhesive and cast-in place
anchors. Includes seismic provisions and concrete-filled
metal deck profiles. Download or update to version
2.3 for free today to take advantage of the most current
code standards.
RISA Technologies
Phone: 949-951-5815
Email: [email protected]
Web: www.risa.com
Product: RISABase
Description: Uses an automated finite element
solution to provide exact bearing pressures, plate
stresses, and anchor bolt pull out capacities,
eliminating the guess work of hand methods. Define
bi-axial loads and eccentric column locations.
Choose from several connection types and specify
custom bolt locations.
S-FRAME Software Inc.
Phone: 203-421-4800
Email: [email protected]
Web: www.s-frame.com
Product: S-FOUNDATION
Description: Quickly design, analyze and detail your
structure’s foundations with a complete foundation
management solution. Run as a stand-alone application,
or utilize S-FRAME Analysis’ powerful 2-way integration
links for a detailed soil-structure interaction study.
Automatically manages the meshed foundation model
and includes powerful Revit and Tekla BIM links.
continued on next page
CADRE Pro 6 for Windows
Solves virtually any type of structure for
internal loads, stresses, displacements,
and natural modes. Easy to use modeling
tools including import from CAD. Much
more than just FEA. Provides complete
structural validation with advanced
features for stability, buckling, vibration,
shock and seismic analyses.
CADRE Analytic
Tel: 425-392-4309
www.cadreanalytic.com
Modeling Software for
Structural Engineering
Achieve the highest quality of
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Tekla provides a BIM (Building Information Modeling) software that enables engineers to coordinate and deliver the structural
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engineers can:
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- Model steel and connections plus concrete and rebar
- Create high quality engineering drawings
- Integrate with analysis software
- Collaborate more closely with contractors / fabricators to speed up construction
a http://tek.la/ch
ANCHORING GUIDE
Product: S-CONCRETE
Description: Easily view instantaneous results
as you optimize and design reinforced concrete
walls, beams and columns. Automate workflow
by checking thousands of concrete section designs
in one run. With comprehensive ACI 31811 code support plus additional design codes,
S-CONCRETE produces detailed reports that
include clause references, intermediate results
and diagrams.
Simpson Strong-Tie
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Anchor Bolts, Concrete, Façade, Geotechnical, Masonry, Post-Tensioning,
Reinforcing and Utility Anchors, and General Hardware & Ties
Standards Design Group
Phone: 806-792-5086
Email: [email protected]
Web: www.standardsdesign.com
Product: Wind Loads on Structures 4
Description: Performs computations in ASCE 7-98,
02 or 05, Section 6 and ASCE 7-10, Chapters 26-31
computes wind loads by analytical method rather than
the simplified method, provides basic wind speeds from
a built-in version of the wind speed, allows the user to
enter wind speed. Has numerous specialty calculators.
Phone: 800-999-5099
Email: [email protected]
Web: www.strongtie.com
Product: Adhesive Piston Plug Delivery System
Description: Offers an easy-to-use means to
dispense adhesive into drilled holes for threaded rod
and rebar dowel installations at overhead, upwardly
inclined and horizontal orientations. The matched
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hole virtually eliminates the formation of voids and
air pockets during adhesive dispensing.
Strand7 Pty Ltd
Product: Titen HD® Screw Anchor
Description: The patented, high-strength Titen
HD screw anchor for concrete and masonry offers
optimum performance in both cracked and uncracked
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Tekla, Inc.
Phone: 252-504-2282
Email: [email protected]
Web: www.strand7.com
Product: Strand7
Description: An advanced FEA system used worldwide
by engineers for a wide range of structural analysis
applications. It comprises preprocessing, a complete
set of solvers and post processing. It includes a range of
material models suitable for the analysis of soil allowing
for simulations of the complete soil/structure system.
Phone: 770-426-5101
Email: [email protected]
Web: www.tekla.com
Product: Tedds
Description: Automating your everyday structural
designs, Tedds’ broad library includes anchor bolt
design per ACI 318 Appendix D. The calculation
includes comprehensive checks for tensile and shear
failure of anchors and is available as part of a free
trial of the website.
Product: Tekla Structural Designer
Description: Revolutionary software that provides
the power to analyze and design steel and concrete
buildings efficiently and profitably. Physical,
information-rich models contain all the intelligence
needed to fully automate the design and document
your project, including all end force reactions
communicated with two-way BIM integration,
comprehensive reports and drawings.
Product: Tekla Structures
Description: An Open BIM modeling software that
can model all types of anchors required to create a
100% constructible 3D model. Anchors can either be
created inside the software or imported directly from
vendors that have 3D CAD files of their products.
Williams Form Engineering Corp.
Phone: 616-866-0815
Email: [email protected]
Web: www.williamsform.com
Product: Anchor Systems
Description: Providing threaded steel bars and
accessories for rock anchors, soil anchors, high
capacity concrete anchors, micro piles, tie rods, tie
backs, strand anchors, hollow bar anchors, post
tensioning systems, and concrete forming hardware
systems in the construction industry for over 90 years.
All Resource Guide forms for the 2015 & 2016
Editorial Calendar are now available on the
website, www.STRUCTUREmag.org. Listings
are provided as a courtesy. STRUCTURE®
magazine is not responsible for errors.
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STRUCTURE magazine
73
September 2015
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14-10497
award winners and outstanding projects
Spotlight
Newport Beach Civic Center and Park
Inspiring Community through Holistic Design
By Janice Mochizuki, P.E., LEEP AP, John Worley, S.E., LEED AP and Joseph Collins, S.E.
Arup was an Outstanding Award Winner for the Newport Beach Civic
Center and Park project in the 2014 NCSEA Annual Excellence in Structural
Engineering awards program (Category – New Buildings over $100M).
A
spiring to create a civic center that
would bring the community together,
the coastal city of Newport Beach,
California chose to position the
new development in the geographic and
cultural center of the expanded population.
Newport Beach’s old city hall, built in 1948,
was no longer positioned to serve the needs
of the community. The team of architects
from Bohlin Cywinski Jackson (BCJ) aimed
to provide a civic center that would be an
inspiring place for the community to converge
and to provide a transparent civic institution.
Contributing and collaborating on this design
vision was PWP Landscape Architecture and
the Arup multidisciplinary team from the
San Francisco office consisting of structural,
mechanical, electrical, plumbing, and civil
engineering, as well as lighting, sustainability,
and telecommunications consulting services.
C.W. Driver was the general contractor.
The Newport Beach Civic Center and Park
is positioned on a narrow, 20 acre plot of land
partially inhabited by protected wetlands and
flanked by three major roads. The project
consists of a new city hall, community room,
council chambers, parking garage, parkland,
4 pedestrian bridges, and an addition to an
existing library.
Straddling the wetlands are three modest
pedestrian bridges amongst the 14 acres of
park land and picnic areas. The two separate
parcels of the site are connected with a sightline compatible, low-profile pedestrian bridge
spanning 150 feet over a main thoroughfare,
San Miguel Drive. The San Miguel Bridge has
a 52-foot observation platform that provides
views of the Santa Catalina Islands. It was
created by cantilevering steel supports off of
the concrete shear wall elevator tower and
perching the main bridge girders on those
supports to allow for longitudinal movement.
The 17,000 square-foot addition to the
existing Central Library, which was located
adjacent to the site, was built to serve the
high demand for reading room space and
the need for a children’s area and high-tech
media center. Over the new grand library
entrance, a dramatic
50-foot cantilever
faces the civic center
and provides covered
exterior spaces that
can be used as an
Courtesy of David Wakely.
entertainment stage.
A pair of built-up king post roof trusses with lighting) were carefully routed through web
tension cables provides a column free space openings in the wave roof beams to achieve
in the 150 seat council chambers. The special a clean look while exposing the structural
concentric brace frame building has a curved steel. The shape and directional placement of
and canted wall that provides support for the the roofs allows for ideal placement of future
iconic Polytetrafluoroethylene (PTFE) backlit solar panels.
exterior “sail”.
The building is stabilized against wind and
Located between the council chambers and seismic loads by buckling restrained braced
the city hall is a double-height, 4,500 square- frames (BRB). Due to the discontinuity of the
foot community. It is a continuation of the city roof diaphragm resulting from the repeating
hall’s architectural expression with large sliding- wave roof layout, each 20-foot wave roof bay
door facades that allow for the room to open functions as its own local diaphragm. Two
up to the park and sheltered outdoor spaces. horizontal lines of pinned-ended, round HSS
The 89,000 square-foot city hall building collectors pick up the lateral force from the
is a two-story architecturally exposed struc- wave roofs to deliver it to the BRBs located
tural steel (AESS) building clad with a glass in the cores and the ends of the building.
curtain wall, envisioned by BCJ as an expresThe aesthetic of the pinned-ended, round
sion to the public of a transparent structure HSS members is carried throughout the
and civic institution. Wave roofs, one of project. Double-height exterior axial-only colthe most multi-functional design elements umns that support the overhanging wave roofs
of the project, top the second floor of the are round HSS members with a pinned base
city hall and pay homage to the marine sur- connection. The exposed BRBs, provided by
roundings. North facing operable clerestory CoreBrace, have meticulously crafted pinnedwindows that are equipped with automated ends and a round HSS casing with a custom
motorized dampers provide natural ventila- made collar to conceal the cruciform core.
tion and lighting. Wide flange beams were
Through holistic decisions and collaboration
sculpted into their double radiused form by of the entire project team from design through
SME Steel. The higher elevation side of the construction, the Civic Center earned a
wave sits on top of a vierendeel truss created LEED Gold Certification while creating a
from commonly available wide flange chords place for the community to enjoy.▪
and vertical members. By using the vierendeel truss layout, the window elements and
Janice Mochizuki, P.E., LEEP AP
lighting fixtures are nicely nestled within the
([email protected]), is a
structure. The wave roofs extend beyond the
Senior Engineer in Arup’s structural buildings
curtain wall facades to create sunshade for the
group. John Worley, S.E., LEED AP
building and exterior spaces surrounding the
([email protected]), is a Principal
structure. A result of implementing a raised
in the structural buildings group. Joseph
floor system, and early design coordination
Collins, S.E. ([email protected]),
between Arup and BCJ, was concealing many
is an Associate in the structural buildings
of the distribution services. The few required
group. All three are located in Arup’s San
overhead services (fire sprinklers and overhead
Francisco office.
STRUCTURE magazine
75
September 2015
GINEERS
ASS
O NS
STRUCTU
OCIATI
RAL
EN
COUNCI L
NCSEA News
News form the National Council of Structural Engineers Associations
NATIONAL
The 2015 NCSEA Special Awards Honorees
The following awards will be presented at the Awards Banquet on October 2 nd during the 2015 NCSEA Structural Engineering
Summit in Las Vegas. For more information on the Annual Conference, see pages 42 – 45.
The James M. Delahay Award
The James M. Delahay Award is presented at the recommendation of the NCSEA Code Advisory Committee to recognize outstanding
individual contributions towards the development of building codes and standards. It is given in the spirit of its namesake, a person
who made a long and lasting contribution to the code development process.
Donald R. Scott, S.E., F.SEI, F.ASCE
Donald R. Scott is the Vice President and Director of Engineering at PCS Structural Solutions, a 50-person
firm with offices in both Tacoma and Seattle, Washington. He has been a Principal of the firm since 1986 and
has led many of the firm’s educational, commercial, institutional and private projects for new and renovated
construction. Don is a civil and structural engineering graduate of the University of Idaho with civil and
structural engineering licenses in Washington and seven other states.
Don has authored many technical publications and has presented numerous seminars and NCSEA webinars
on wind design throughout the country. He has been a member of the ASCE 7 Wind Load Committee since
1996, shaping future IBC provisions for wind design, and currently serves as Chairman. He is also a member of the ASCE 7
General Provisions committee, a member of the ASCE 7 Steering Committee, Chairman of the NCSEA Wind Committee,
and a former Chair of the SEAW Wind Load Committee.
The NCSEA Service Award
The NCSEA Service Award is presented to an individual or individuals who have worked for the betterment of NCSEA to a degree
that is beyond the norm of volunteerism. It is given to someone who has made a clear and indisputable contribution to the organization
and therefore to the profession.
Craig Barnes, P.E., SECB
Craig Barnes founded CBI Consulting Inc. in 1984 and is licensed in 20 states. Craig helped establish the
National Council of Structural Engineers Associations (NCSEA) in 1993, was President of NCSEA from
1995-1996, and received the NCSEA Robert Cornforth Award in 2005. He is a member of STRUCTURE
Magazine’s Editorial Board, as well as a continuing contributor to the publication. Craig is a Past President of
the Boston Association of Structural Engineers, as well as the Structural Engineers Association of Massachusetts.
He chaired NCSEA’s Basic Education Committee for several years, where he was instrumental in creating a
highly-recognized list of Basic Education requirements for students in the structural engineering field. Craig
has provided consulting services for exhibits at Boston’s Museum of Fine Arts and their affiliates abroad, and he spent two weeks
in Port-au-Prince following the catastrophic earthquake in 2010, reviewing and commenting on reports prepared by Haitian
consultants to determine if buildings were safe for occupancy.
The Robert Cornforth Award
This award is presented to an individual for exceptional dedication and exemplary service to a Member Organization and to the
profession. Nominees are submitted to the NCSEA Board by the Member Organizations.
Carl Josephson, S.E., SECB
Carl Josephson is a Principal Structural Engineer with Josephson-Werdowatz & Associates, a structural
engineering firm located in San Diego, California with additional offices in Sacramento, Las Vegas, and
Scottsdale. Carl is a licensed Professional or Structural Engineer in twelve states.
He has served as Convention Chair, Director, and President of SEAOC. He is currently Chair of SEAOC’s
Professional Licensing & Certification Committee and SEAOC’s recently reestablished Legislative Committee.
He was elected to the SEAOC College of Fellows in 2007. He is a member of NCSEA’s Professional Licensing
Committee and is a member of SEI’s Professional Activities Committee. In 2010, Carl was appointed by
former Gov. Schwarzenegger as the SE member of the California Board for Professional Engineers, Land Surveyors and Geologists,
(BPELSG), and he now serves as an Emeritus member of, and consultant to, BPELSG. He is active in the National Council
of Examiners for Engineers and Surveyors (NCEES) and has served on their SE Exam Committee and Mobility Task Force.
STRUCTURE magazine
76
September 2015
The Susan M. Frey NCSEA Educator Award is presented to an individual who has a genuine interest in, and extraordinary talent for,
effective instruction for practicing structural engineers. The award was established to honor the memory of Sue Frey, one of NCSEA’s
finest instructors. Nominees are submitted to the NCSEA Board.
Emily Guglielmo, S.E.
Emily Guglielmo is an Associate with Martin/Martin, Inc. and also serves as manager of the Northern
California office. Emily is deeply committed to assisting structural engineers in solving real world engineering
problems with simple, reasonable solutions. Toward that goal, she has served as a frequent lecturer for several
Structural Engineering Associations on topics ranging from wind and seismic loads to serviceability design.
Emily is a member of the ASCE 7 Seismic Committee and the NCSEA Publications Committee, and is a
founding member and current Chair of the NCSEA Young Member Group Support Committee. Outside of
the profession, Emily enjoys hiking and traveling with her husband and three children. Deeply honored by her
receipt of the prestigious Sue Frey Educator Award, Emily’s goal is to contribute to Sue’s legacy through her educational efforts.
NCSEA News
The Susan M. Frey NCSEA Educator Award
More information on the NCSEA Structural Engineering Summit can be found on pages 42 – 45.
NCSEA Awards Six Young Member Scholarships to Annual Conference
Thomas Mendez, S.E.
A Structural Engineer with Halvorson and
Partners, Chicago, Illinois, Thomas is a member
of the Structural Engineers Association of Illinois.
Matthew McCarty, S.E., P.E.
A Project Structural Engineer with Whitman,
Requardt & Associates, Monrovia, Maryland,
Matthew is a member of the Virginia Structural
Engineers Council.
Matthew Ernst, E.I.
A Structural Staff Engineer with Engineering
Ventures, PC, Burlington, Vermont, Matthew is
a member of the Structural Engineers Association
of Vermont.
Greg McCool, P.E.
A Structural Engineer with Ericksen Roed &
Associates, St. Paul, Minnesota, Greg is a member
of the Minnesota Structural Engineers Association.
Yasmin Chaudhry
A graduate student at Montana State University
and an intern at Morrison-Maierle, Inc., Bozeman,
Montana, Yasmin is a member of the Structural
Engineers Association of Montana.
NCSEA Webinars
News from the National Council of Structural Engineers Associations
For the third year, NCSEA awarded Young Member
Scholarships for the NCSEA Structural Engineering Summit.
The scholarship competition was open to any current member of
an NCSEA Member Organization who was under 36 years old.
Applicants were asked to compose an essay or video answering
one of three questions, as well as write a brief essay upon attending the Summit. Scholarships included Summit registration
and a travel stipend. The winners of this year’s scholarships are:
Michelle Quinn, P.E.
A Design Engineer with Ensign Engineering,
Sandy, Utah, Michelle is a member of the
Structural Engineers Association of Utah.
October 27, 2015
GINEERS
RAL
UC
AT
IO
ED
IN
NT
CO
EN
STRUCTURE magazine
77
September 2015
O NS
NATIONAL
OCIATI
Diamond
Reviewed
Non-CalOES courses award 1.5 hours of continuing
education. Approved for CE credit in all 50 States
through the NCSEA Diamond Review Program.
ASS
UIN
N
NCSEA
STRUCTU
RS
EE
GIN
UR
AL
More detailed information on the webinars and a registration
link can be found at www.ncsea.com. Subscriptions are available!
EN
Observations & Reflections on the 2014 South
Napa Earthquake
Five speakers from Degenkolb Engineers: David Bonneville, S.E.;
John Dal Pino, S.E.; Mahmoud Hachem, S.E.;
Kirk Johnston, S.E., LEED AP; Roger Parra, S.E.
Calculating & Applying Design Wind Loads on Buildings
Using the Envelope Procedure in ASCE 7
T. Eric Stafford, P.E., President, T. Eric Stafford & Associates
RU
CT
October 22, 2015
November 3, 2015
ST
What You Need to Know About the Seismic Peer
Review Process
Farzad Naeim, Ph.D., S.E., Esq., President, Farzad Naeim, Inc.
G
October 6, 2015
Significant Changes to the Wind Provisions
of ASCE 7-10
T. Eric Stafford, P.E., President, T. Eric Stafford & Associates
COUNCI L
Second ATC-SEI Conference on Improving the Seismic
Performance of Existing Buildings and Other Structures
Structural Columns
The Newsletter of the Structural Engineering Institute of ASCE
December 10 – 12, 2015, San Francisco, California
REGISTRATION NOW OPEN
The ATC-SEI Conference on Improving the Seismic Performance
of Existing Buildings and Other Structures is an opportunity
for structural engineers, business owners, and users of ASCE
seismic standards to learn the latest in seismic evaluation and
rehabilitation.
Earn up to 14 Professional Development Hours (PDHs)
The conference technical program offers a wide variety of
valuable sessions, including:
• Seismic Resilience–Lessons from the Field
• Performance-Based Seismic Evaluation of Reinforced
Concrete Structures, in Conjunction with ASCE/SEI 41
• Innovative Approaches and Codes for Historic Structures
• Performance Assessment of Tall Buildings
• Recent Legal Developments Affecting Owners and
Designers: Using Performance Targets to Manage Seismic
Risk in the Legal Arena
• Multiple case studies on Evaluation and Retrofit of
Existing Buildings
Each day will begin with two compelling Keynote Speakers
and will include multiple opportunities for networking with
colleagues and leaders in the field. Don’t miss the Champions
of Earthquake Resilience Awards Dinner benefiting the ATC
Endowment Fund and the SEI Futures Fund.
Visit the conference website at www.atc-sei.org for complete
information and to register.
Young Professional Scholarship Forensic Engineering
th
Congress
Apply for the SEI Young Professional (age 35 and younger) 7
Scholarship to the Geotechnical & Structural Engineering
Congress, February 14 – 17, 2016, in Phoenix, Arizona. SEI
is committed to the future of structural engineering and offers
a scholarship for Young Professionals to participate and get
involved at the annual Congress. Many find this event to be a
career-changing and energizing experience, opening up networking opportunities and expanding horizons to new and emerging
trends. Applications are on the SEI website at www.asce.org/
structural-engineering/sei-young-professionals-scholarshipapplication/ and are due November 2.
Registration Now Open
Advance to SEI Fellow
ASCE’S “Game Changers”
Highlights Innovative Infrastructure
The SEI Fellow grade of membership recognizes accomplished SEI members as leaders
and mentors in the structural engineering
profession. The benefits of becoming an SEI
Fellow include recognition via SEI communications and at the annual Structures Congress
along with a distinctive SEI Fellow wall plaque
and pin, and use of the F.SEI designation. SEI members
who meet the SEI Fellow criteria are encouraged to submit
application packages online by November 1 to advance to
the SEI Fellow grade of membership and be recognized at the
Geotechnical & Structural Engineering Congress, February
14–17, 2016 in Phoenix, Arizona. Visit the Fellows webpage
at www.asce.org/structural-engineering/sei-fellows/ to
learn more.
STRUCTURE magazine
78
Registration is now open for the ASCE Forensic Engineering 7th
Congress, November 15 – 18, 2015, in Miami, Florida. Learn
alongside professionals who share the same challenges in their
work to identify and address the root causes and consequences
of design errors and construction defects. Register today at
www.forensiccongress.org/.
Americans are all too
aware of infrastructure challenges, yet
many states and communities are finding and implementing
innovative solutions that deserve wider recognition. ASCE
recently released Infrastructure #GameChangers, a report and
associated website identifying top trends in energy, freight,
transportation, and water, and the ways they are transforming
how infrastructure is designed, planned, and built. Explore more
than 30 examples at http://ascegamechangers.org/.
September 2015
February 14 – 17, 2016, Phoenix, Arizona
• Structural Wall Research: Recent Research &
International Collaboration
In addition several sessions explore topics that include both
structural and geotechnical engineering. Joint sessions include:
The Geo-Institute (G-I) and Structural Engineering Institute
• Bridge Scour & Erosion: Th
e Way Forward
(SEI) of the American Society of Civil Engineers (ASCE) are
• Novel Methods of Educating Geotechnical & Structural
coming together to create this fi rst-of-its-kind event. By comEngineers
bining the best of both Institutes’ annual conferences into one
• Managing Risk in Geotechnical & Structural Analysis &
unique conference, you will profit from unmatched networking
Design
opportunities with colleagues within and across disciplines.
• Foundations for Specialized Structures
With a large and varied technical program, the joint congress
• Structural Design of Deep Foundations
will offer structural engineers ample educational opportunities.
These structural sessions include:
Join the conversation: #GeoSEI2016
• Experimental & Analytical Investigation of Robustness
Visit the Joint Congress website at www.Geo-Structures.org
of Structures
for complete information and to register.
• Seismic Performance of Tall Buildings
• Lifecycle Analysis & Carbon Calculation: Parts 1 & 2
• Alternative Approaches to Multi-Hazard Analysis &
Design of Structures
WITH SEI SUSTAINING ORGANIZATION MEMBERSHIP
• Bridge Analysis
• Analysis of Nonbuilding Structures
REGISTRATION NOW OPEN
Connect | Collaborate | Build
REACH SEI MEMBERS
Errata
SEI posts up-to-date errata information for our publications at
www.asce.org/SEI. Click on “Publications” on our menu, and
select “Errata.” If you have any errata that you would like to
submit, please email it to Jon Esslinger at [email protected].
www.asce.org/SEI-Sustaining-Org-Membership
Electrical Transmission & Substation Structures Conference
September 27 – October 1, 2015, Branson, Missouri
REGISTRATION NOW OPEN
Can you afford to wait until 2018? This is your last chance
to register for the premier conference on transmission line
and substation structures, and foundation construction issues.
Don’t miss out on an excellent opportunity to network with
professionals in your industry.
Grid Modernization – Technical Challenges
& Innovative Solutions
The conference will feature three days of technical sessions, four
days of exhibits, a pre-conference workshop, and an exciting
construction-oriented demonstration day that will offer many
opportunities to share international knowledge on grid modernization from a structural and construction standpoint. Attendees
will experience a unique setting in which to learn and network
with peers, industry leaders, and knowledgeable suppliers.
The conference features a compelling, single track program
of sessions chaired by moderators that are leaders in the field:
• Structural Analysis 1 – Mike Miller, P.E., M.ASCE
• Special Design Considerations – Marlon Vogt, P.E., M.ASCE
STRUCTURE magazine
• Managing Aging Infrastructure – Gary Bowles, P.E., F.SEI,
M.ASCE
• Structural Analysis 2 – Robert Nickerson, P.E., F.SEI,
M.ASCE
• Case Studies – Frank Agnew, P.E., M.ASCE
• Foundations – David Todd, P.E., M.ASCE
• Substation Design Issues – Jerry Wong, P.E., F.SEI, M.ASCE
• Construction Challenges – Dana Crissey, P.E., M.ASCE
• Line Design – Wesley Oliphant, P.E., F.SEI, M.ASCE
• Rerating and Upgrading – Tim Cashman, P.E., M.ASCE
• Codes and Standards – Otto Lynch, P.E., F.SEI, M.ASCE
• Conference Wrap up – Otto Lynch, P.E., F.SEI, M.ASCE
The pre-conference workshop, Panel Discussion of Storm
Hardening, Resiliency and Security Issues, gives attendees an
additional educational opportunity. All the major companies
in the industry will display their latest products and services
in the exhibit hall, one of the highlights of the conference. The
conference will close with a demonstration day offering participants unique opportunities to witness several overhead power
line construction and supplier demonstrations in a single day.
Earn up to 19 PDHs.
Visit the conference website at www.etsconference.org for
complete information and to register.
79
September 2015
The Newsletter of the Structural Engineering Institute of ASCE
Increase your exposure to more
than 25,000 SEI members through
www.asce.org/SEI, SEI Update
e-newsletter, STRUCTURE magazine,
and at SEI conferences year round.
Structural Columns
Geotechnical & Structural Engineering Congress 2016
CASE in Point
The Newsletter of the Council of American Structural Engineers
CASE Risk Management Contracts Available
CASE #1 An Agreement for the Provision of Limited
Professional Services
This is a sample agreement for small projects, or investigations
of limited scope and time duration. It contains the essentials of
a good agreement including scope of services, fee arrangement
and terms and conditions.
CASE #2 An Agreement between Client and Structural
Engineer of Record for Professional Services
This agreement form may be used when the client, e.g. owner,
contractor developer, etc., wishes to retain the Structural Engineer
of Record directly. The contract contains an easy to understand
matrix of services that will simplify the “what’s included and
what’s not” questions in negotiations with a prospective client.
This agreement may also be used with a client who is an architect
when the architect-owner agreement is not an AIA agreement.
CASE #3 An Agreement between Structural Engineer of
Record and Consulting Design Professional for Services
The Structural Engineer of Record, when serving in the role
of Prime Design Professional or as a Consultant, may find it
necessary to retain the services of a sub-consultant or architect. This agreement provides a form that outlines the services
and requirements, in a matrix so that the services of the subconsultant may be readily defined and understood.
CASE #4 An Agreement between Owner and
Structural Engineer for Special Inspection Services
Special Inspection services provided by a Structural Engineer
are normally contracted directly by the Owner of a project
during the construction phase. This agreement has a Scope of
Service that directly relates to the applicable code or industry
standard requirements. The Structural Engineer of Record or
another structural engineer providing these services may use this
agreement. The language for coordinating laboratory testing
work is also included within this agreement.
CASE #5 An Agreement for Structural Peer
Review Services
A request to perform a peer review of another structural engineer’s design brings with it a different responsibility than that
of the Structural Engineer of Record. The CASE #5 document
addresses the responsibilities and the limitations of performing
a peer review. This service is typically performed for an Owner,
but may be altered to provide peer review services to others.
CASE #6 Commentary on AIA Document C141
Standard Form of Agreement between Architect and
Consultant, 1997 Edition and AIA Document C142
Abbreviated Standard Form of Agreement between
Architect and Consultant, 2009 Edition
This document provides a form letter of agreement to be used with
adoption by reference to AIA Document C401. This Agreement
is intended for use when owner-architect agreement is an AIA
B-series. A scope of services is included. The purpose of the commentary is to point out provisions that merit special attention.
CASE #6A Commentary on AIA Document B-141
Standard Form of Agreement between Owner and
Architect with Standard Form of Architect’s Services,
1997 Edition
The purpose of this Commentary is to point out provisions
which merit special attention, or which some have found to
contain “pitfalls”.
CASE #8 An Agreement between Client and Specialty
Structural Engineer for Professional Services
When structural engineering services are provided to a contractor or a sub-contractor for work to be included in a project where
you are not the Structural Engineer of Record, but you are a
specialty structural engineer. Your contractual relationship differs
from the norm, and the typical contract forms will not suffice.
The CASE #8 document is tailored to this particular situation.
CASE #9 An Agreement between Structural Engineer
of Record and Testing Laboratory
The Structural Engineer of Record may be required to include testing services as a part of its agreement. If a testing laboratory must
be subcontracted for this service, CASE # 9 may be used. It can
also be altered for use between an Owner and a testing laboratory.
You can purchase these and the
other Risk Management Tools at
www.acec.org/coalitions/coalition-publications/.
WANTED Engineers to Lead, Direct, and Get Involved with
CASE Committees!
If you’re looking for ways to expand and strengthen your business skillset, look no further than serving on one (or more!)
CASE Committees. Join us to sharpen your leadership skills
– promote your talent and expertise – to help guide CASE
programs, services, and publications.
We have a committee ready for your service:
• Risk Management Toolkit Committee: Develops and
maintains documents such as business practices manuals
and policies for engineers under CASE’s Ten Foundations
for Risk Management.
Please submit the following information to [email protected]:
• Letter of interest
• Brief bio (no more than 2 paragraphs)
STRUCTURE magazine
80
Expectations and Requirements
To apply, you should
• be a current member of the Council of American
Structural Engineers (CASE)
• be able to attend the groups’ two face-to-face meetings
per year: August, February (hotel, travel partially
reimbursed)
• be available to engage with the working group via email
and conference call
• have some specific experience and/or expertise to
contribute to the group
Thank you for your interest in contributing to your professional association!
September 2015
III. Membership Committee – Stacy Bartoletti
([email protected])
• Preparing for membership recruitment campaign with
CASE staff members, target date September 2015
• Working on educating CASE Members about new
Community sites and how to use while updating new
benefits of membership
IV. Programs and Communications Committee –
Nils Ericson ([email protected])
• Confirmed/finalized sessions for 2016 ASCE/SEI
Structures Congress
• Working on sessions for 2016 AISC Conference and the
ACEC Annual Convention
• Putting together the 2015/2016 editorial calendar for
articles to Structure Magazine from CASE
V. Toolkit Committee – Brent White
([email protected])
• Finished updates on the following tools:
• Tool 4-3: Sample Correspondence Letters
• Tool 10-1: Site Visit Cards
• Working on the following new tools:
• Tool 1-3: Sample Office Policies
• Tool 8-3: Contract Clause Commentary
• Tool 10-3: Deferred Submittals
• Committee will be surveying CASE membership on
ideas for future tools and what would be helpful for their
business and/or risk management plan
The 2016 CASE Winter Planning Meeting is scheduled for
February 11-12 in Phoenix, AZ. If you are interested in attending the meeting or have any suggested topics/ideas from a firm
perspective for the committees to pursue, please contact Heather
Talbert at [email protected].
ACEC Fall Conference Features CASE Risk Management
Convocation and More!
October 13 – 17 ACEC is holding its Fall Conference at the You will not want to miss these additional important risk manWestin Copley Place, Boston, MA. CASE will be holding a agement sessions:
convocation on Thursday, October 15. Sessions include:
Managing Uncertainty and Expectations in Building
Design and Construction
10:45am How to Reduce Your Risk on Alternative
Clark Davis, Cameron MacAllister Group; Stephen Jones,
Delivery Projects
Dodge Data & Analytics
Moderator: Beth Larkin: HNTB
Building Resilient Infrastructure for Future Cities
Speakers: Mary Conway, HNTB; George Wolf, Shook
Terry Bennet, Autodesk Inc.; Donna Huey, Atkins Global;
Hardy & Bacon; David Hatem, Donovan Hatem
Marty Janowitz, Stantec
1:45pm Dead in the Water: A Case Study of Claims
Missouri’s Peer Review Law–Should Your State Have One?
Facing Civil Engineers
Karen Erger, Lockton Companies
Dan Buelow & Bob Stanton, Willis A/E
How to Reduce Your Professional Liability Costs
3:30pm Non-Negotiable Contracts: What’s Plan B?
Tim Corbett, SmartRisk
Karen Erger & Bob Fogle, Lockton Co.; Eric Miller,
The Conference also features:
Ice Miller; Jennie Muscarella, Kenny, Shelton, Liptak,
• General Session addresses by Pulitzer Prize-winning author
Nowak LLP
Doris Kearns-Goodwin; 2015 ACEC Distinguished
5:15pm ACEC/Coalition Meet and Greet
Award of Merit Honoree Dr. Robert Ballard
• CEO roundtables;
For more information and to register go to www.acec.org/
• Exclusive CFO, CIO, Architect tracks;
• Numerous ACEC coalition, council, and forum events; and
conferences/fall-conference-2015/registration.
• Earn up to 21PDHs
STRUCTURE magazine
81
September 2015
CASE is a part of the American Council of Engineering Companies
On August 6-7, the CASE Winter Planning Meeting took place
in Chicago, IL with over 30 CASE committee members and
guests in attendance, making this a well-attended and productive
meeting. Included in the planning meeting was a roundtable
discussion lead by Stacy Bartoletti, Degenkolb Engineers and
Brent White, ARW Engineers on Real Life Lessons Learned:
Project Claims Impacting Structural Engineers.
During the meeting, break-out sessions were held by the CASE
Contracts, Guidelines, Membership, Toolkit, and Programs &
Communications Committees. Listed below are the current
CASE initiatives being developed by the committees:
I. Contracts Committee – Ed Schweiter
([email protected])
• Finished working on revisions to the entire CASE
Contract Document library; release of updated Contract
Library prior to ACEC Fall Conference
• Will be creating a “How to” sheet educating people on
using the CASE Contract Documents
II. Guidelines Committee – John Dal Pino
([email protected])
• Finishing current revisions to the following Practice
Guideline Documents:
• CASE 962B – National Practice Guidelines for Specialty
Structural Engineers
• CASE 962-E – Self-Study Guide for the Performance of
Site Visits During Construction
• CASE 962-F – A Guideline Addressing the Bidding
and Construction Administration Phases for the
Structural Engineer
• Guide to Special Inspections and Quality Assurance
• Working on the following new documents:
• Commentary on ASCE-7 Wind Design Provisions
• Commentary on ASCE-7 Seismic Design Provisions
CASE in Point
CASE Summer Planning Meeting Update
Structural Forum
opinions on topics of current importance to structural engineers
A “Plug” for Power Line Structures
By David C. Gelder, P.E.
W
ithin the structural community, there seems to be
a lack of awareness, as well
as a growing opportunity,
regarding overhead electrical transmission and
distribution structures. In the United States
alone there are millions of miles of corridor
consisting of aging single- and double-pole
structures and lattice towers. These structures
form an impressive network, supporting high
and extra-high voltage wires (12 kV to 765
kV) and delivering power from generation
facilities to customers located hundreds of
miles away. This enormous infrastructure,
known as the electric grid, is a critical system
to society and constitutes a specialty market
for structural engineers. I wish to “put in a
plug” for power line structures to increase
awareness and interest among fellow structural engineers.
In 2011, when I graduated, it was still difficult to get an interview – let alone a job – with
a structural firm. Given the slow job market, I
pursued a master’s degree. The following year,
I graduated and found employment, though
not designing buildings as I had supposed,
but rather designing transmission structures.
Interestingly, five fellow graduate students
found similar entry-level positions designing either transmission structures or wind
turbines – all structures within energy sector
markets. In retrospect, this hiring trend may
not have been coincidence, but rather a lesson
in diversification: the energy market showed
signs of growth during the recession, while the
commercial building market all but collapsed.
I was both excited and curious about my
first engineering job in this non-traditional
field. After all, power lines are electrical systems, right? While they are indeed electrical
systems, there is also a huge civil engineering component – as well as environmental,
archeology, survey, construction, permitting,
and other disciplines. It seems obvious now,
but many fellow civil and structural engineers
have yet to realize that we are more academically prepared than any other discipline to
design transmission structures, including the
poles, towers, wires, and foundations.
While considered an eyesore by many, these
structures are undoubtedly critical to society.
When properly designed, power lines provide
an invaluable service to consumers; however,
when defective or deteriorated, power lines
may yield devastating consequences to the
public – particularly during extreme weather
and loading conditions. Transmission lines
have failed in a variety of ways. In extreme
cases, power lines have been blamed for igniting wildfires leading to loss of life, extensive
loss of property, and environmental damage.
Failure has also triggered power outages such
as the infamous Northeast Blackout of 2003,
which led to loss of life, water supply contamination, transportation system closures,
and billions of dollars in negative economic
impact. Not all failures pose equal risk, but
clearly proper design of poles and towers of all
voltages is critical to safeguard public health
and safety.
Transmission structures are typically
designed to withstand ice accumulation,
as well as extreme wind and temperature
loading using at least 50-year recurrence
intervals. Originally most wire systems were
copper; now most modern wires are aluminum, including aluminum conductor
steel-reinforced (ACSR) pulled to thousands
of pounds of tension. They are designed
to meet ground and wire-to-wire clearance
requirements at all times in accordance with
the Institute of Electrical and Electronics
Engineers (IEEE) National Electrical Safety
Code (NESC) and other codes. Loading
is of course unique from buildings. For
example, loads on a single-pole foundation
may consist of relatively light axial load
(10-30 kips) combined with heavy shear
(50-100 kips) and heavy bending moment
(1,000-3,000 kip-ft). Poles and towers
have a relatively low seismic base shear;
therefore, earthquake loads rarely govern
the design. Some additional tools used by
today’s practicing transmission engineers
include modern nonlinear finite element
software and Light Detection And Ranging
(LiDAR) data, which are widely used in all
aspects of design and analysis. ASCE/SEI
issues Standards 10 and 48 – for designing
steel towers and poles, respectively – and
hosts the triennial Electrical Transmission
& Substation Conference (this year it will
be held September 27 – October 1, 2015 in
Branson, MO).
On the business side, historically power lines
were designed, built, and maintained for the
most part in-house by electric utilities. Now,
much of the design knowledge base and workforce has transferred to consulting firms, so
many utilities rely on them to help complete
projects. Large projects are often offered as
engineer-procure-construct (EPC) contracts –
similar to design-build contracts – while many
smaller projects are simply awarded as part of
a master service agreement (MSA). Due to the
increasing demand for power, the aging infrastructure, and a retiring workforce, there is a
growing need for transmission engineers. This
poses an opportunity for structural engineers
either individually or as a firm. For example,
some structural engineers have chosen to
pursue transmission engineering as a means
of specialization. Additionally, some large civil
engineering firms have chosen to offer power
delivery services in order to diversify, though
newcomers have found the market extremely
difficult to penetrate.
In summary, power line design can be an
enjoyable and rewarding career path for
structural engineers, and the power delivery market can be a means of diversification
for their firms. The greater civil and structural engineering communities will benefit
by recognizing and promoting these poles
and towers as civil structures. Lastly, power
line structures may be viewed by some as
an eyesore, but for others, they represent
an opportunity.▪
David C. Gelder, P.E.
([email protected]), is
licensed as a professional engineer in
the State of California and works as a
Transmission Engineer for TRC
in Salt Lake City, UT.
Structural Forum is intended to stimulate thoughtful dialogue and debate among structural engineers and other participants in the design and
construction process. Any opinions expressed in Structural Forum are those of the author(s) and do not necessarily reflect the views of NCSEA,
CASE, SEI, C 3 Ink, or the STRUCTURE® magazine Editorial Board.
STRUCTURE magazine
82
September 2015
STRUCTURE
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(Typ)
Min. Edge
Min. Edge
Distance
Distance
Min. Edge
Distance
Min. 4-1/2"
Min.
4-1/2"
(Typ.)
(Typ.)
Min. 4-1/2"
" (Typ.)
(Typ.)
Min. 12-1/2
" (Typ.)
Min. 12-1/2
Lower Flute
(Ridge)
Lower
Flute (Ridge)
Min. 12-1/2" (Typ.)
Flute Edge
Flute Edge
Lower Flute (Ridge)
Min. Edge
Min. Edge
Distance
Distance
Min. Edge
Distance
✔
✔
✔
✔
✔
Lower
Flute
✔
✔
✔
✔
✔
✔
2-1/2"
Minimum
Topping
Thickness
Upper Flute (Valley)
Min. 3-7/8"
Min.
3-7/8"
(Typ.)
(Typ.)
Min. 3-7/8"
(Typ.)
✔
Top of
Deck
Flute Edge
SAND-LIGHTWEIGHT CONCRETE OR NORMAL WEIGHT CONCRETE OVER STEEL DECK
SAND-LIGHTWEIGHT CONCRETE
OR NORMAL
WEIGHT
(MINIMUM
3,000
PSI) CONCRETE OVER STEEL DECK
(MINIMUM 3,000 PSI)
SAND-LIGHTWEIGHT CONCRETE OR NORMAL WEIGHT CONCRETE OVER STEEL DECK
Upper Flute (Valley)
(MINIMUM 3,000 PSI)
Upper Flute (Valley)
Max.
Max.
3"
3"
Max.
3"
Upper
Flute
Min. 3-7/8"
Min.
3-7/8"
(Typ.)
(Typ.)
Min. 3-7/8"
(Typ.)
Lower Flute (Ridge)
Lower Flute (Ridge)
Flute Edge
Flute Edge
Lower Flute (Ridge)
Upper
Flute
✔
✔
Lower
Flute
✔
✔
Flute Edge
Top of
Deck
SAND-LIGHTWEIGHT CONCRETE OR NORMAL WEIGHT CONCRETE OVER STEEL DECK
SAND-LIGHTWEIGHT CONCRETE
OR NORMAL
WEIGHT
(MINIMUM
3,000
PSI) CONCRETE OVER STEEL DECK
(MINIMUM 3,000 PSI)
SAND-LIGHTWEIGHT CONCRETE OR NORMAL WEIGHT CONCRETE OVER STEEL DECK
Upper Flute (Valley)
(MINIMUM 3,000 PSI)
Upper Flute (Valley)
B DECK
Upper Flute (Valley)
1-1/2"
1-1/2"
Max.
Max.
1-1/2"
Max.
2-1/2"
2-1/2"
Min.
Min.
2-1/2"
Min.
Min. Edge
Min. Edge
Distance
Distance
Min. Edge
Distance
Max.
Max.
3-1/2"
3-1/2"
(Typ)
Max.
(Typ)
3-1/2"
(Typ)
Lower Flute Edge
Lower Flute Edge
2-1/2"
Minimum
Topping
Thickness
1-3/4"
1-3/4"
Min.
Min.
1-3/4"
Min.
Lower Flute Edge
Upper
Flute
✔
✔
✔
✔
Lower
Flute
✔
✔
✔
✔
Bang-It
PowerStud+ SD1
PowerStud+ SD2
Snake+
Vertigo+
WedgeBolt+
ESR-3657
ESR-2818
ESR-2502
ESR-2272
ESR-2526
ESR-2526
* See individual ICC-ES Reports for details on each condition
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editorial
7 PBd: a Component in
the Future of Structural
engineering
By Stephen S. Szoke, P.E.
iNFoCuS
11 representation and reality
STRUCTURE
gueSt ColuMN
34 BiM-M Symposium:
generation 1
September 2015
By Daniel Zechmeister, P.E.
StruCtural PerForMaNCe
38 the Most Common errors
in Seismic design
By Jon A. Schmidt, P.E., SECB
By Thomas F. Heausler, P.E., S.E.
teChNologY
iNSightS
12 Modern limit analysis tools
for reinforced Concrete Slabs
By Angus Ramsay, M.Eng, Ph.D.,
C.Eng, Edward Maunder, Ph.D.
and Matthew Gilbert, Ph.D., C.Eng
StruCtural deSigN
16 What is a Masonry
“Flush Pilaster”?
By David L. Pierson, S.E.
hiStoriC StruCtureS
18 the Niagara
Cantilever Bridge
By Frank Griggs, Jr., D. Eng., P.E.
BuildiNg BloCkS
23 Proper Procedures and
Protocol for interception
grouting
By Brent Anderson, P.E.
StruCtural rehaBilitatioN
26 divine design: renovating
and Preserving historic
houses of Worship, Part 4
By Nathaniel B. Smith, P.E. and
Milan Vatovec, P.E., Ph.D.
CodeS aNd StaNdardS
30 Changes in adhesive
anchor System approvals
®
Feature
58 Creating Clarity and
Scoping Profits in BiM
with lod 350
NCSea 2015 Summit
Special Section
By Will Ikerd, P.E.
eNgiNeer’S NoteBook
60 Moment-Curvature
and Nonlinearity
By Jerod G. Johnson, Ph.D., S.E.
CaSe BuSiNeSS PraCtiCeS
63 Strategic Planning: a
Comprehensive approach
By Dilip Choudhuri, P.E.
The National Council of Structural Engineers Associations
will host its 2015 Structural Engineering Summit at the Red
Rock Resort in Las Vegas, NV, on September 30th through
October 3rd. Read about the Summit, the extensive program
and vendor information in the Special Summit Section… and
plan to attend this exciting event!
46
Feature
606 West 57 th Street,
New York
eduCatioN iSSueS
69 Structural education
deficiencies
By Sunghwa Han, P.E., S.E. The behavior of structurally-linked
multiple tower structures is largely affected by the effectiveness
of the rigid links made between the towers. Depending on
the interactive dynamic behavior of the adjacent building
parts with one another, a separation joint may be considered.
Read how engineers resolved numerous issues associated with
separation gaps.
By Kevin Dong, P.E., S.E.
SPotlight
75 Newport Beach Civic
Center and Park
By Janice Mochizuki, P.E.,
John Worley, S.E. and
51
Joseph Collins, S.E.
Feature
StruCtural ForuM
82 a “Plug” for Power line
Structures
By David C. Gelder, P.E.
By Richard T. Morgan, P.E.
On the cover Las Vegas CityCenter Block A, structural engineering by Thornton
Tomasetti and architectural design by Pelli Clarke Pelli Architects, is the crown jewel
of the 76-acre CityCenter development on the Las Vegas Strip. The development is the
largest, most complex private construction project completed in the United States to
date. Photo courtesy of Thornton Tomasetti. Join NCSEA at the Red Rock Resort in Las
Vegas, September 30th through October 3rd (see page 42).
Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute
endorsement by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and
advertisers retain sole responsibility for the content of their submissions.
STRUCTURE magazine
42
5
a Need for Speed
By Ramon Gilsanz, P.E., S.E., Philip Murray, P.E.,
Gary Steficek, P.E. and Petr Vancura The fundamental principle
that drives the need for speed in construction is economic, a
major factor for owners. How do you approach fast-paced
construction within a dense urban environment? Read how three
projects in New York City illustrate the use of flat plate concrete
systems, instant communication and in-the-field coordination to
speed up the construction process.
iN everY iSSue
8 Advertiser Index
71 Resource Guide (Anchoring)
76 NCSEA News
78 SEI Structural Columns
80 CASE in Point
September 2015
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The American Concrete Institute has recently published the newest edition of ACI 318, “Building Code Requirements for Structural Concrete
(ACI 318-14).” This edition represents the first major change in Code organization in over 40 years and has been completely reorganized from
a designer’s perspective. This seminar will help you get acquainted with the new organization and various technical changes to the code as
quickly as possible and demonstrate how you can ensure that your design fully complies with the new code.
To learn more about ACI seminars and to register, visit www.concreteseminars.org
Pittsburgh, PA—September 10, 2015
Raleigh, NC—September 15, 2015
Chicago, IL—September 17, 2015
New Brunswick, NJ—September 22, 2015
Minneapolis, MN—September 24, 2015
Albany, NY—September 29, 2015
ACI Headquarters—Farmington Hills, MI—
September 30, 2015
Des Moines, IA—October 1, 2015
Portland, OR—October 6, 2015
Baltimore, MD—October 8, 2015
Little Rock, AR—October 9, 2015
Houston, TX—October 13, 2015
Tampa, FL—October 15, 2015
St. Louis, MO—October 20, 2015
Cincinnatti, OH—October 22, 2015
Indianapolis, IN—October 27, 2015
Savannah, GA—October 29, 2015
Nashville, TN—November 3, 2015
Denver, CO—November 12, 2015
Emeryville, CA—November 17, 2015
Richmond, VA—November 19, 2015
New Orleans, LA—December 1, 2015
Fort Lauderdale, FL—December 3, 2015
Dallas, TX—December 10, 2015
San Diego, CA—December 15, 2015
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Editorial
PBD:
A Component in the Future of
new trends, new techniques and current industry issues
Structural Engineering
By Stephen S. Szoke, P.E., F.SEI, F.ASCE, F.ACI
P
erformance-Based Design (PBD) has been practiced throughout history, dating back to the Code of Hammurabi, circa
1750 BCE. Today, the three most common applications of
performance based design are:
• Use of innovative engineering technologies or products;
• Enhancement of project performance based on specific needs
of the owners, such as design for special risk assessments like
extreme loading conditions; and
• Economy, where more affordable design and construction options
can demonstrate compliance with the intent of the building code.
Although PBD is already permitted in building codes, perhaps it
is too infrequently practiced. Most building codes are based on
the International Code Council International Building Code (IBC)
which includes alternative means and methods to allow the use of
materials, design techniques, or construction methods not specifically
prescribed by the code. Many jurisdictions also adopt the International
Code Council Performance Code (ICCPC) which permits innovation
and deviations from the prescriptive criteria while maintaining the
intent of the building code. The intent of the ICCPC is: “To provide
appropriate health, safety, welfare, and social and economic value, while
promoting innovative, flexible and responsive solutions that optimize the
expenditure and consumption of resources.”
Today, the trend in structural engineering, often driven by the
potential for litigation, is to exclusively follow the prescriptive design
criteria for loads based on Minimum Design Loads for Buildings and
Other Structures (ASCE/SEI 7) combined with prescriptive load resistance criteria as provided in documents like the American Concrete
Institute’s Building Code Requirements for Structural Concrete; American
Institute of Steel Construction’s Steel Design Manual; and American
Wood Council’s ASD/LRFD Manual for Engineered Wood Construction.
However, an unintended consequence of these prescriptive criteria is
the ability to generate designs compliant with both load and resistance
criteria via computer models. This method of structural design, while
it may still require a stamp by an engineer, limits the freedoms related
to innovation and creativity in structural design. The development of
strategies and mechanisms to expand the acceptance of PBD tend to
better reflect the interests of clients and jurisdictions while elevating
structural engineers as design professionals. A new opportunity to
increase use of PBD may be to encourage acceptance of emerging
philosophies related to design and construction solutions that are
associated with “enhanced resilience” or “community resilience.”
The National Institute for Standards and Technology is in the final
development stages of the Community Resilience Planning Guide which
proposes new concepts for codes and standards related to the design
of building and other infrastructure components. Another strategy
could be related to transparency of consequences to owners and
communities should a disaster occur. This might be in the form of
multiple performance levels within each risk category to better allow
owners and communities to select the appropriate performance levels.
The National Institute of Building Sciences Building Seismic Safety
Council is considering a menu of performance levels in lieu of single
performance levels for respective risk classifications. This would differ
from the current approach, where the standards development process
dictates the acceptable performance level, such as 10% failure for the
STRUCTURE magazine
seismic design of most buildings, those classified in risk category II.
This new approach may extend the role of the structural engineer in
planning to help improve community resilience, the ability to rebound
after disasters, seismic or otherwise.
To address historical and current applications of PBD and the role of
PBD in future, the SEI Board of Governors has established a committee, not to develop criteria for PBD, but to investigate the role of PBD
in the future of structural engineering. Their charge is to champion
the trend toward performance-based design. This aligns with several
aspects of SEI’s A Vision for the Future of Structural Engineering and
Structural Engineers: A case for change:
“…The drive to develop codes and specifications has led to the
outcome that many of the tasks previously done by structural engineers could be and have been automated… …we must curb our
tendency to codify our design decisions and leave those decisions in
the province of qualified structural engineers. If we mandate how
a structure must perform, but leave freedom to how the engineer
provides that performance, we open the possibilities for amazing
solutions to presently unsolvable problems.”
“One avenue for change that has emerged in recent years is the
notion of performance-based design… … performance-based design
would increase the importance of sound engineering judgment in
the design process, rely on better technical knowledge, require the
use of more sophisticated technology in problem solving, result in
more efficient structures, and place the structural engineer in a
better position to drive technological change.”
The new PBD committee met during the 2015 Structures Congress.
Many aspects and implications of PBD will be visited during the process
of developing recommendations, including: development of a series of
enabling documents to compliment current design criteria, possibly
similar to Seismic Rehabilitation of Existing Buildings (ASCE/SEI
41); use PBD to serve as the documents in the public domain moving
prescriptive compliance criteria to other documents maintained by
standards developers; defining professional liability as a standard of
care; and use of shelter-in-place performance levels for
significant natural disasters. This effort, while invaluable,
is a complex, multi-faceted and long-term project for the
advancement of structural engineering as a profession.▪
Stephen S. Szoke, P.E., F.SEI, F.ASCE, F.ACI, is the Senior
Director of Codes and Standards for the Portland Cement
Association. He serves on SEI’s Codes and Standards Division
Executive Committee and represents the division on the SEI Board
of Governors. He serves as the board liaison for the newly formed
board level committee on performance based design. He may be
contacted at [email protected].
The National Institute for Standards and Technology
Community Resilience Planning Guide can be found at
www.nist.gov/el/building_materials/resilience/guide.cfm,
last visited July 2015.
7
September 2015
Advertiser index
PlEaSE SUPPoRT ThESE advERTiSERS
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California Polytechnic State University .... 8
Construction Specialties ........................ 15
CTP, Inc................................................ 29
CTS Cement Manufacturing Corp........ 25
Decon USA, Inc. ................................... 64
Ecospan Composite Floor System ......... 61
Enercalc, Inc. .......................................... 3
Fyfe ....................................................... 19
Geopier Foundation Company.............. 50
Halfen USA, Inc. .................................. 70
Hardy Frame ......................................... 53
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ICC – Evaluation Service ...................... 74
Integrated Engineering Software, Inc..... 67
Integrity Software, Inc. .......................... 49
ITT Enidine, Inc. .................................. 57
JVA Inc. ................................................ 32
KPFF Consulting Engineers .................... 8
Legacy Building Solutions ..................... 37
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MAPEI Corp......................................... 62
Powers Fasteners, Inc. .............................. 2
QuakeWrap ........................................... 39
RISA Technologies ................................ 84
S-Frame Software, Inc. ............................ 4
Simpson Strong-Tie........................... 9, 33
SEA of Illinois ....................................... 68
Structural Engineers, Inc. ...................... 20
StructurePoint ....................................... 22
Struware, Inc. ........................................ 36
Tekla ..................................................... 72
USG Corporation ................................. 41
V2 Composites, Inc............................... 55
STRUCTURE
®
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Executive Editor Jeanne vogelzang, JD, cae
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Associate Editor nikki alger
[email protected]
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editoriAL BoArd
Chair Jon a. Schmidt, P.e., SecB
Burns & McDonnell, Kansas city, Mo
[email protected]
ARCHITECTURAL ENGINEERING
The Department of Architectural Engineering at Cal Poly, San Luis Obispo, California is
seeking applications for a full-time, academic year tenure track position for the teaching of
structural analysis, design, and construction of buildings. Starting date is September 15, 2016.
For details, qualifications, and to complete a required online faculty application, please visit
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begin October 15, 2015. Applications received after this date may be considered. EEO.
craig e. Barnes, P.e., SecB
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John a. Dal Pino, S.e.
Degenkolb engineers, San Francisco, ca
Mark W. Holmberg, P.e.
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Dilip Khatri, Ph.D., S.e.
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roger a. laBoube, Ph.D., P.e.
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Mike Mota, Ph.D., P.e.
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STRUCTURE magazine
8
September 2015
September 2015, Volume 22, Number 9
ISSn 1536-4283. Publications agreement no. 40675118.
owned by the national council of Structural engineers
associations and published in cooperation with caSe and SeI
monthly by c3 Ink. the publication is distributed free of charge to
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For change of address or duplicate copies, contact your member
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or the Structure editorial Board.
Structure® is a registered trademark of national council of
Structural engineers associations (ncSea). articles may not be
reproduced in whole or in part without the written permission of
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inFocus
Representation
new trends, new techniques and
and
current
Reality
industry issues
By Jon A. Schmidt, P.E., SECB
R
epresentation is intrinsic to human life and engineering
practice. We communicate with other people throughout
the design and construction process by means of words,
diagrams, and sketches. We create mental and computational models of materials, loads, and the arrangement of members.
We develop building information models (BIM), drawings, and
specifications to indicate how the various pieces and parts are to be
assembled into the finished structure.
The intent of these representations is to capture the relevant characteristics of reality, which may overlap but are not identical in each
case. The engineer has to ascertain what those are, and then incorporate appropriate assumptions and simplifications accordingly. Two
common strategies are abstraction, which involves neglecting certain
aspects of reality in order to gain a better understanding of the remaining aspects; and idealization, which involves replacing a complicated
and/or complex aspect of reality with a simplified version.
This entails that representations are always less than 100% accurate,
raising the question of how they relate to reality – the domain of semiotics, the study of signs and signification (or semiosis). Conventional
theories are dyadic, emphasizing two components: the signifier and the
signified; the relationship between them is essentially arbitrary. The
limitations of this conceptualization have become evident with the
emergence of deconstruction and other aspects of postmodernism,
in that it effectively precludes objective meaning.
An alternative was developed by American scientist and philosopher
Charles Sanders Peirce (pronounced “purse”) in the late 19th and
early 20th centuries. He founded what eventually came to be known
as pragmatism, but was unhappy with the direction that it ultimately
took in the more popular work of others – most notably William
James and John Dewey – so he coined the name pragmaticism for his
own approach, saying that this term was “ugly enough to be safe from
kidnappers.” Peirce’s theory – which he preferred to call semeiotic – is
triadic, emphasizing three relations: among the sign itself (or representamen), that which it signifies (object), and the effect that is produced
(interpretant), which comes about by a habit of interpretation.
Peirce aligned these elements with the three fundamental categories
that he identified in both our encounter with the world (phenomenology or phaneroscopy) and the underlying nature of reality (metaphysics);
he simply called them Firstness, Secondness, and Thirdness. Firstness
is quality, feeling, possibility, spontaneity, vagueness; Secondness is
difference, reaction, actuality, persistence, particularity; Thirdness is
mediation, purpose, regularity, order, generality. For example, an icon
relates to its object through some kind of resemblance (Firstness), an
index due to a physical or other direct connection (Secondness), and
a symbol by means of a convention or rule (Thirdness). A painting is
an icon, a fingerprint is an index, and a word is a symbol.
For Peirce, then, representation is reality: “…all this universe is
perfused with signs, if it is not composed exclusively of signs.”
Furthermore, all thought consists of signs, and inquiry is the deliberate and collaborative endeavor to process them in a way that results
in genuine knowledge via three basic modes of inference: abduction
(or retroduction), the formulation of a hypothesis or “guess,” often
in response to a surprising event; deduction, the explication of what
STRUCTURE magazine
else would be the case if that explanation is correct; and induction
(or adduction), the examination of whether those consequences ever
fail to materialize.
This “logic of inquiry” applies most directly to science, but it also
serves as a “logic of ingenuity” in engineering practice. Abduction
constitutes the creative process that leads to the selection of one preliminary solution out of multiple potential options (“Engineering as
Willing,” March 2010). Deduction corresponds to the deterministic
analyses that indicate the expected behavior of that design, given
certain presuppositions. Induction operates over time as an engineer
learns from experience – i.e., gets better at abduction – developing
competence, proficiency, and eventually expertise (“The Nature of
Competence,” March 2012).
Both inquiry and ingenuity thus employ signs to make that
which is indeterminate more determinate, although never fully
determinate. The only complete sign is the entirety of reality itself,
which consists of continuous systems of relations, rather than
discrete substances; hence its persistent complexity (“Complicated
+ Complex = Wicked,” July 2015). Truth is the final interpretant
– the opinion on which an infinite community would converge
after an indefinite investigation. In the meantime, we must always
acknowledge the fallibility of our current understanding (“The
Virtues of Ignorance,” May 2015). Uncertainty in representation is
constrained by reality, but not eliminated entirely.
Note that determination occurs primarily as discovery in science
(conforming representation to reality) vs. decision in engineering
(conforming reality to representation). This distinction was important
to Peirce, because while he was a persistent advocate of grounding
science firmly in reason, he was equally adamant that practical matters should be governed primarily by instinct and sentiment. When
it comes to “topics of vital importance,” judgment must rely on one’s
existing beliefs, which are nothing more or less than established
habits of thought and action – much like virtues in Aristotelian ethics
(“Virtuous Engineering,” September 2013).
This column barely scratches the surface of Peirce’s wide-ranging and
often idiosyncratic ideas. He never managed to write a single book –
something that (so far) I have in common with him – but produced
many thousands of pages of articles and manuscripts, leaving the bulk
of them in draft or otherwise unfinished form. The Peirce Edition
Project (www.iupui.edu/~peirce/) has compiled and published key
selections from his philosophical writings in The Essential Peirce (two
volumes, 1992 and 1998). Helpful introductory and summary material is available in The Fate of Meaning (1989) and Charles
Peirce’s Guess at the Riddle (1994) by John K. Sheriff, The
Continuity of Peirce’s Thought (1998) by Kelly A. Parker,
and Peirce’s Theory of Signs (2007) by T. L. Short.▪
11
Jon A. Schmidt, P.E., SECB ([email protected]), is
an associate structural engineer at Burns & McDonnell in Kansas
City, Missouri. He chairs the STRUCTURE magazine Editorial
Board and the SEI Engineering Philosophy Committee, and shares
occasional thoughts at twitter.com/JonAlanSchmidt.
September 2015
Technology
information and updates on
the impact of technology on
structural engineering
A
t a recent workshop, organized by the
University of Sheffield in association
with LimitState and held at the IStructE
Headquarters in London, the authors
of this article presented new computational tools
for the limit analysis of reinforced concrete (RC)
slabs. The workshop was attended by practising
engineers from different fields, including those
involved with the design of RC slabs and those
with an interest in the assessment of existing RC
slabs for changing service loads.
The computational tools presented align closely
with the traditional methods of designing and
assessing RC slabs. The traditional method for
assessing slabs has been Johansen’s yield line
technique which, as an upper-bound method,
relies for its accuracy on the ability of the engineer to postulate a realistic collapse mechanism.
LimitState:SLAB uses the discontinuity layout
optimisation (DLO) method, robustly and efficiently computerising the yield line technique,
automatically identifying collapse mechanisms
that have corresponding
collapse loads very close
to theoretical solutions
(typically within 1%). In
contrast, the traditional
method for designing slabs
has been Hillerborg’s strip
method, which, as a lower-bound method,
provides a set of equilibrium moment fields
that may be used to size and position the
reinforcement. Ramsay Maunder Associate’s
(RMA) equilibrium finite element software,
RMA:EFE, robustly and efficiently automates
this approach to provide a complete equilibrium moment field (which includes torsional
moments) with a corresponding collapse load
very close to the theoretical solution. When
used together, LimitState:SLAB and RMA:EFE
lead to accurate plasticity solutions (typically
within 1 or 2% of each other) that completely
define the limit solution in terms of collapse
mechanism (LimitState:SLAB) and moment
fields (RMA:EFE). The efficiency of these solutions can be measured in the time taken to solve,
typically no more than a few seconds.
Modern Limit Analysis
Tools for Reinforced
Concrete Slabs
By Angus Ramsay, M.Eng, Ph.D.,
C.Eng, FIMechE,
Edward Maunder, MA, DIC,
Ph.D., FIStructE and
Matthew Gilbert, B.Eng, Ph.D.,
C.Eng, MICE, M.ASCE,
The online version of this
article contains detailed
references. Please visit
www.STRUCTUREmag.org.
Modern limit analysis tools such as RMA:EFE
and LimitState:SLAB, when used in combination,
provide the practicing engineer with a way of verifying the solutions (and of ensuring simulation
governance), i.e. the engineer can sleep soundly
at night knowing that the collapse load has been
predicted with good accuracy (since when lower
and upper bound solutions agree, the true solution has been found).
In the absence of a verified solution, the engineer
using the yield line method needs to rely on his
or her good judgment to determine a realistic
collapse mechanism. The engineer might also be
tempted to rely on anecdotal evidence that inherent membrane action within the slab will increase
capacity beyond that derived by consideration of
flexural strength alone, and/or advice offered by
professional bodies that, for example, yield line
solutions are generally no more than 10% above
the true value [1]. Neither of these, of course,
would stand up to a great deal of scrutiny without
further verification or validation work.
In a recent article [2], a solution to a problem published by the first author in 1997, [3], was presented
and used to demonstrate how yield line computations have developed over the last 20 years. Although
the original published result was not intended as
an exact solution, it now turns out, using modern
limit analysis tools, that the collapse load was 40%
above the theoretical value! While it is clear that
experienced engineers might not have accepted the
solution provided in the original publication, it is
considered to be useful to less experienced engineers
working in this field to document an example where
the yield line method has produced an extremely
unsafe result. The problem is defined as the Landing
Slab Problem and automated methods using meshes
of triangular elements together with geometric optimisation are used to demonstrate the state-of-art
from the 1990s.
The Landing Slab Problem
This problem involves a reinforced concrete landing slab typical of the type found in the stairways of
modern buildings. It is a two-way slab in that significant moments are developed in both directions.
The slab is simply supported on three adjacent
Figure 1. Landing slab problem.
12 September 2015
sides, and the reinforcement at the top and
bottom of the slab provides equal isotropic
moment capacity (m). The slab is loaded with
a uniform distributed load (q) (the loading
arrows are placed at the centre of the corresponding slab portion) as shown in Figure 1,
and has a unit load to strength ratio (q/m).
The Automated
Yield Line Technique
(a)
(b)
Figure 2. Results from the 1997 Research ( λ = 5.86). a) Mesh; b) Yield line pattern.
In the 1997 work, the mesh shown in Figure 2
was used. This led to the collapse mechanism
shown with blue lines, representing element
edges where the moment has reached the sagging capacity of the slab and with the symbol
λ representing the load factor.
An analysis of a more refined mesh in 2011
produced the following results shown in
Figure 3.
This result indicates that the 1997 solution
was not correct – the yield lines, while emanating from the corners of the slab, do not
terminate at slab corners. This sort of yield
line pattern, which now involves red lines
where the hogging capacity of the slab has
been reached, appears to provide a qualitatively reasonable representation of the way in
which the slab might crack.
continued on next page
(a)
(b)
Figure 3. Results from the 2011 Research ( λ = 5.47). a) Mesh; b) Yield line pattern.
(a)
(b)
Figure 4. Results for a coarse unstructured mesh from EFE ( λ = 4.38). a) Mesh; b) Yield line pattern.
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Figure 6. RMA:EFE Solution of 2014 using 2484 elements ( λ=4.20).
Figure 5. DLO Solution of 2014 using 4000 nodes ( λ = 4.21).
Geometric optimization of the mechanism
indicated by the 2011 research is shown in
Figure 4 (page 13).
Modern Limit Analysis Tools –
LimitState:SLAB
The results produced by the DLO-based
software LimitState:SLAB [4] are in the
form of yield line patterns with the same
convention as already described for color
and thickness of the yield lines (Figure
5). Note however that whereas the yield
lines in Figures 2, 3 and 4 were based on
moments, those in Figure 5 are based on
rotation (hence the red lines on the supported boundary in Figure 5). This yield
line pattern is similar to the geometrically
optimized pattern of Figure 4 in terms of
the dominant yield lines. However it shows
additional yield lines that point to a more
complicated collapse mechanism for the
slab, with more distributed yielding than
suggested in Figure 4. The load factor from
the DLO method is 4% lower than that
of the geometrically optimized solution
already presented.
Modern Limit Analysis Tools –
RMA:EFE
RMA’s software tool (RMA:EFE) [5] provides a solution to this problem in terms of
equilibrium moment fields. A method of
demonstrating that these fields do not violate
the yield criteria is to consider the utilization
ratio. The utilization ratio, which compares
the moment field with the moment capacity
or yield moment, can be calculated at points
in the model as the degree to which the local
moment field can be scaled up before it causes
yielding. Such a plot is shown for the landing
slab in Figure 6, where the contour colors
range from zero (blue–unutilized) to unity
(red – fully utilized). The regions where the
material is fully utilized correspond well with
the yield line pattern of Figure 5.
With upper-bound (LimitState:SLAB) and
lower-bound (RMA:EFE) solutions to this
problem available, the theoretically exact
collapse load can be predicted within very
tight bounds:
4.20 ≤ λ ≤ 4.21
The load factors are within 1% of each
other and thus give an extremely accurate
prediction of the theoretically exact value.
Erring on the side of safety and using the
lower-bound load factor in the calculation
shows that the published result of 1997 was
40% too high!
Practical Conclusions
This brief article has shown how limit analysis, particularly the yield line technique, has
developed over the last 20 years, and has led
to modern computational tools for the practicing engineer that are able to bound the
theoretical solution to very close tolerances
thereby providing strong simulation governance in the design/assessment of reinforced
concrete slabs.
There is now no need to rely on rules of
thumb, such as the ‘10% rule’, or arguments
that any over-estimate of capacity through
a coarse yield line analysis will implicitly be
accounted for by membrane action (which
for a given slab may in reality not be present). Also noted in the recent workshop,
elastic techniques are increasingly being
used in the design of new RC slabs but,
as a result, reinforcement over columns
becomes significantly greater than indicated
to be required when using a limit analysis
based approach.
The availability of efficient and robust
software for predicting the collapse load
of reinforced concrete flat slabs now means
that one of the original outcomes of the
European Concrete Building Project, to
encourage engineers to design slabs based
on limit analysis techniques [6], can
now safely be realized and applied with
STRUCTURE magazine
14
September 2015
confidence to both conventional and more
complicated and novel slab configurations.
RMA and LimitState encourage engineers
practicing in this field to get involved by
using and driving the future development
of these software tools for their own commercial advantage.▪
Angus Ramsay, M.Eng, Ph.D., C.Eng,
FIMechE, is the owner of Ramsay Maunder
Associates, an engineering consultancy
based in the UK. He is a member of the
NAFEMS Education & Training Working
Group and acts as an Independent Technical
Editor to the NAFEMS Benchmark
Challenge. He can be contacted at
[email protected].
Edward Maunder, MA, DIC, Ph.D.,
FIStructE, is a consultant to Ramsay
Maunder Associates and an honorary
Fellow of the University of Exeter in the
UK. He is a member of the Academic
Qualifications Panel of the Institution of
Structural Engineers. He acts a reviewer
for several international journals, such as
the International Journal for Numerical
Methods in Engineering, Computers
and Structures, and Engineering
Structures. He can be contacted at
[email protected].
Matthew Gilbert, BEng, Ph.D., C.Eng,
MICE, M.ASCE, is Professor and Director
of Research in the Department of Civil and
Structural Engineering at the University
of Sheffield, UK. He is also the Managing
Director of LimitState Ltd, a software
company set up to make numerical methods
developed in the University available to
a wide audience. He can be contacted at
[email protected].
A similar article was published in Concrete
Magazine (July 2015). Content is
reprinted with permission.
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Structural
DeSign
design issues for
structural engineers
S
tructural engineers have a peculiar vocabulary, when you think about it. What
we call “stress” is not much like what
psychologists call “stress”. What we call
“strain” is not what the spectators think about
when watching a weight lifting match. And when
we ask what the moment is, a confused general
public thinks that in our own strange way we are
asking what time it is.
What we call something must be understood
within the context of what we are talking about;
it must be clearly defined. This is particularly
important when we get into the writing of a
legally binding document. If we mean to mandate
something, we need to be clear on what it is that
we are mandating.
Masonry Pilaster Definition
In the latest version of The Masonry Society’s
2013 MSJC Provisions, or the Masonry Building
Code (TMS 402/602), there
are certain provisions that
apply specifically to the
design of masonry pilasters.
However, the writers of the
code have not yet included
a definition for pilaster. So,
should we be allowed to impose our own (or
Webster’s) definition onto the code? It seems
that would be wrong, since the writers of the
code obviously had in mind structural members
with certain characteristics that were intended to
be governed by the specific pilaster provisions.
Although the original authors of the pilaster provisions did not include a definition, they did give
us clues as to what characteristics they envisioned
for pilasters. First we can look at the illustrations
in the commentary. Note that in figure CC-5.4-1,
titled “Typical pilasters”, all of the illustrations
show projections from either one or both faces
of the wall. We can also look at the provisions
to see what they require. The table of contents
for Chapter 5 refers us to Section 5.4 for pilaster provisions. Section 5.4 points us to sections
5.1.1.2.1 through 5.1.1.2.5. Interestingly, section
5.1.1.2 is called “Design of wall intersections”. So,
we can assume that they intended that a pilaster
would look something like that shown in the
figures, and it would have similarities with the
characteristics of intersecting walls. Reading the
provisions of 5.1.1.2, we find references to a flange
that is different than the web of the section. That
is the similarity between intersecting walls and
pilasters, and is shown by the projections in the
illustrations. A pilaster has a web that projects
from the flange(s).
Engineers on the west coast (the author
included, although few would define Utah as
“the west coast”) often forget that the provisions
of TMS 402/602 apply to both reinforced and
What is a Masonry
“Flush Pilaster”?
By David L. Pierson, S.E.
David L. Pierson, S.E., is a
principal at ARW Engineers
in Ogden, Utah. He teaches
Masonry Design at Utah State
University and is also the current
vice-chairman of the TMS
402/602 committee.
unreinforced masonry. Section 5.4 is written to be
generally applicable to both reinforced and unreinforced masonry. This clarifies the geometry even
further. In unreinforced masonry, any geometry
of a pilaster that did not have projections from
the wall would be completely impossible to differentiate from a partially grouted wall.
Flush Pilasters
When confronted with this, many engineers
may ask “But wait – what about those ‘Flush
Pilasters’ I’ve been designing for years?” In
fact, in the 2008 edition of TMS 402/602, the
figure that illustrates pilasters actually included
a sketch showing a “hidden” (or “flush”) pilaster.
Dr. Richard Bennett, current Chairman of the
TMS 402/602 Committee and a member of the
Committee when this was changed, shared some
of the history as to why the figure was changed.
The illustration for the “Hidden Pilaster” was
removed from TMS 402/602 in the 2011 edition.
This was done in response to a public comment
that correctly noted that a hidden pilaster and
a partially grouted wall are essentially indistinguishable. Yet the code allowed for a different
compression width to be utilized for a pilaster
(even a hidden pilaster) than it allowed for bars
in grouted cells of walls. This was obviously not
appropriate. It was wrong for the code to provide
different requirements applicable to the same
element. Dr. Bennett shared the exact language
from the rationale of the ballot item that deleted
that illustration:
“In response to public comment 51a, the commentary is changed to remove references to
hidden pilasters. Note that this does not
preclude the construction shown in Figure
2.1-5(c). Rather it just removes the problem
with the conflict pointed out in the public
comment relative to the compression width
of the bar. This ballot item does not address
adding a definition of pilasters to Section 1.6
(public comments 51a and 69). This non-life
safety issue will be taken up as new business
in the 2013 cycle.”
So, the response to those engineers who still want
to design “Flush Pilasters” would be …
You may call the strengthened portions of
walls whatever you’d like; however, since
the Pilaster provisions in the code are
applicable to a member that doesn’t have
a Flush geometric profile, those members
are not Pilasters within the language of
TMS 402/602.
But, as was noted in the rationale of the ballot
item quoted above, just because they are not
technically “Pilasters” within the definition of
TMS 402/602 does not, in any way, mean that
16 September 2015
they cannot be designed and constructed in
accordance with this code. It must be clearly
understood that those elements always could
be and still can be designed and constructed
in accordance with the code provisions.
The next question is this – What should be
used for “b”, the width of the compression
flange? There are a few options. For illustration we will check it three different ways:
First, assume b = 16 inches, the width of
the element. This is the minimum value that
could be used. With b = 16 inches, 2/kj = 6.16
Design Example
and npj = 0.0726. The masonry stress controls
Take, for instance, the common occurrence the design, with a corresponding np = 0.109.
of what might be termed “Flush Pilasters” So, p = A s /bd = 0.0067, and the required A s
in sound wall systems that are built along = 0.97 square inches of steel.
many roadways. To be technically accurate,
Now, check it with b = 72 inches, the maxicall these Strengthened Sections. Typical mum value allowed in section 5.1.2. For this
construction might be a 12-inch thick condition, 2/kj = 27.7 and npj = 0.016. Now
CMU, with Strengthened Sections occur- steel stress controls the design, with np =
ring between 12 feet and 24 feet apart. The 0.017. Thus, p = 0.00106, and A s = 0.68
Strengthened Section is likely16 inches wide, square inches of steel.
with reinforcing on each face (to get a maxiSo, if we were very conservative we could use
mum “d”) and cantilevers from a concrete pier b = 16 inches. Masonry stress would control
or grade beam. The portion of wall between the design, and we would use (1) #9 or (2)
these Strengthened Sections is supported ver- #7 bars, each face. By not utilizing a larger
tically continuously, but spans horizontally b, I am not being as efficient with the steel.
between the Strengthened Sections to resist
If we use b = 72 inches, we are using the
out-of-plane loads.
maximum b allowed in section 5.1.2. Steel
Below is one possible way to design these stress governs the design, so the steel is being
elements using the Allowable Stress Design used to full efficiency. We would use (1) #8
Provisions. This solution utilizes a method or (2) #6 bars, each face.
found in the Reinforced Masonry Engineering
Finally, if we use b = 20 inches, which is just
Handbook published by MIA (The Masonry 2 inches each side of the section, then np =
Institute of America). It is called the Universal 0.064, and A s = 0.72 square inches. This is
Elastic Flexural Design Technique.
essentially the same answer as using b = 72
Given:
inches. The reason for this is that at b = 20
• Wind Pressure per ASCE 7-10 = 30
inches, steel stress now governs the design.
psf, Load Combination is 0.6W + D
Once this happens, using a larger value for
• Construction: 12-inch CMU, 12 feet
“b” makes very little difference in the answer.
high, with 16-inch wide Strengthened
Some engineers might argue that if we use
Sections spaced every 12 feet.
(2) bars in this “Strengthened Section”, then
• f´m = 2000 psi, Medium Weight
section 5.1.2 would technically limit b to
Block, and Grade 60 reinforcing, so
16 inches (8 inches per bar), based on the
Fs = 32000 psi
“center-to-center bar spacing” requirement.
• Use bars each face, so “d” = 9 inches
The author would argue that, since we could
• The modular ratio n = 29,000,000 /
have used just one bar and only used two
Em = 16.1.
bars because it makes construction simpler,
The Design Loads on the Strengthened we should be allowed to assume that, for this
Section for this load combination are:
situation, the “center-to-center bar spacing”
• Dead Load (self weight of element only) should be considered as the spacing of the
= 165 plf x 12 feet = 2000 pounds
Strengthened Sections. This is a case where
• Wind Load = 18 psf x 12-foot spacing
engineering judgment must be allowed to
= 216 plf
be exercised.
The design moment on the section is 216
In either case, the wall would then be
x 122 / 2, or 15,550 lb-ft (187,000 lb-in). designed to span horizontally between these
(Note: some engineers may wish to reduce this elements, probably with (2) horizontal bars
moment by the resisting moment provided by in bond beams at 48 inches on-center.
the dead load of the element. By choosing not
Whatever you want to call these, this conto, the author is perhaps a bit conservative) struction always has been and continues to
The allowable Fb in the masonry due to be allowed. These elements could also be
flexure is 0.45* f´m, or 900 psi. This must be designed using other design methodologies,
reduced by the axial compression stress due based either on Allowable Stress Design or on
to the weight of the element, which is 11 psi. Strength Design. Results would be similar, if
So, use Fb = 900 – 11 = 889 psi for flexural not identical.
design (see code section 8.3.4.2.2).
STRUCTURE magazine
17
September 2015
Prescriptive Provisions
Beyond section 5.4, the only other significant provisions related to pilaster design
are found in 7.4.3.2.5., where additional
requirements are imposed if the pilaster is
supporting a discontinuous stiff element.
Note that ties are required in pilasters only if:
1) the pilaster is supporting a discontinuous
element as noted in 7.4.3.2.5, or if 2) the
designer is relying on the steel to support
compression loads (in which case the element
essentially becomes a column), or if 3) the
shear stress is so high that ties are needed to
resist shear (which is theoretically possible
but nearly impossible in practice).
There is a caveat to this entire discussion.
It applies to pilasters and strengthened sections of walls in reinforced masonry walls
that are laterally supported at floors and/or
a roof. Regardless of whether or not such
“pilasters” are projecting or are flush, the
design engineer should recognize that the
provisions of ASCE 7 section 12.11.2.2.7
must apply. In other words, although ASCE
7 does not include a definition for pilaster,
common sense indicates that for reinforced
masonry, whether or not the strengthened
section is projecting from the face of the
wall, it is, for the purposes of this section
of ASCE 7, a pilaster.
It is possible that in the next edition
of TMS 402/602, (anticipated to be the
2016 edition), additional definition will
be given to clarify what a pilaster is and
what it is not. If so, this will be simply a
clarification, so that engineers do not have
to wade through the provisions in order to
determine if what they are designing is a
“Pilaster”. It will not change the fact that
strengthened sections of reinforced walls
can still be designed and constructed, no
matter what they are called.
Finally, the next time you are trying to
determine the limit on how much reinforcing you can put into that masonry wall you
are designing, remember that ρmax has a very
different meaning to you than it does to a
spectator at the Harvard-Yale Regatta.▪
Although Mr. Pierson is affiliated with
TMS because of his position on the
TMS 402/602 committee, this article
represents only his opinions. This should
not be construed as an official position
statement from TMS.
Historic
structures
significant structures of the past
Schneider’s Plan for Niagara Bridge.
T
he Niagara River gorge had long separated the United States from Canada.
It varied in depth up to 239 feet and in
width generally between 800 and 1,000
feet between the Falls and Lewiston. Around 1836,
suspension bridges were proposed by Francis Hall
at Lewiston-Queenston and just above the falls.
Charles B. Stuart, in 1845, then working on the
location of the Great Western Railway in Canada,
was looking for
a way to connect
his line with the
Rochester and
Niagara Falls
branch of the
New York Central. He proposed to span the
gorge with a suspension bridge just above the
Whirlpool. Many thought his idea foolhardy, as
the only suspension bridges in the United States,
other than some Finley bridges left over from
the early part of the century, were Charles Ellet’s
Fairmount Bridge over the Schuylkill River built
in 1842 and John A. Roebling’s suspension aqueduct built across the Allegheny River in 1845.
Stuart sent a circular letter to “a number of the
leading Engineers of America and Europe, asking
their opinion of the undertaking.” Of those who
responded, only four thought the project feasible.
Stuart wrote, “Charles Ellet, Jr., John A. Roebling,
Samuel Keefer and Edward Serrell, alone favored
the project...”
Ellet’s proposal was accepted, with modifications, for the sum of $190,000. The span would
be 800 feet with a deck width of 28 feet. The
deck would have two carriage ways, two footways
and one railway track in the center of the floor.
Ellet started by building a 9-foot wide temporary
bridge but, after charging tolls for people to cross,
he had a falling out with the Company in 1849.
John A. Roebling took over the project in 1850,
offering to build the bridge for $180,000 and to
subscribe to $20,000 in stock in the bridge company. He changed his original design from a single
deck structure to a double deck structure, with the
railway on the top level and carriage and footways
on the lower deck. Work would not commence
on the Niagara project until 1852, with Roebling
providing all engineering services including design
as well as construction supervision. His company
The Niagara Cantilever Bridge
By Frank Griggs, Jr., Dist.
M. ASCE, D. Eng., P.E., P.L.S.
Dr. Griggs specializes in the
restoration of historic bridges,
having restored many 19th Century
cast and wrought iron bridges. He
was formerly Director of Historic
Bridge Programs for Clough,
Harbour & Associates LLP in
Albany, NY, and is now an
independent Consulting Engineer.
Dr. Griggs can be reached at
[email protected].
also supplied a significant amount of wire to be
used in the bridge. He completed his 822-foot
span double deck bridge in 1855. A one-track
railroad ran on the upper deck (22 feet wide),
and pedestrians and carriages passed on the lower
deck (15 feet wide).
In 1874, T. C. Clarke, of Clark & Reeves
Company and later Phoenix Bridge and Union
Bridge Companies, was asked by the manager
of the Western Railway of Canada to “report on
the best mode of construction, necessary time
required, and cost of a double track iron bridge.”
He recommended, “a braced arch, hinged in the
center and at the springing. The clear span was
430 feet, and the height or versed sine 175 feet.
The arches were to have been erected by corbelling out as was done at St. Louis.” In 1882, the
Michigan Central Railroad was ready to build its
own bridge at a site near the suspension bridge.
On October 13 they requested Charles Conrad
(C. C.) Schneider to submit a proposal. They
wanted “an estimate for a double-track railroad
bridge of 900 feet clear span, for the purpose
of ascertaining the probable cost of bridging
the Niagara below the Falls, near the Railroad
Suspension Bridge, intimating that a braced arch
reaching from cliff to cliff might be the proper
design for the proposed structure.”
Schneider had also been given the design for an
iron bridge over the Fraser River, which flowed
southerly into Puget Sound just north of the
United States border. The Fraser River was a fast
flowing stream which precluded the placement
of falseworks in the river bed. Schneider, based
upon his previous exposure to the Blackwell’s
Island Bridge competition and Smith’s success
at High Bridge, decided to build a bridge using
a cantilever technique.
He completed the design of the 525-foot span,
located 125 feet above the river, in the spring of
1882. The directors of the line decided to have
the iron rolled and fabricated in England, a result
of Prime Minister MacDonald’s tariff program
that made United States iron and steel excessively priced. Canada had not as yet developed
its own iron and steel industry to any significant
degree. Due to the slowness of the delivery of
the Fraser River Bridge iron (it reportedly took
almost six months for the ship carrying the iron
18 September 2015
Layout of span and reactions, showing suspended span.
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to Canada to make it across the Atlantic),
it would not be completed until 1887
or four years after the Niagara Bridge. It
lasted until 1910 when it was taken down
and re-erected, one of the beauties of a
pin-connected structure, across a chasm,
appropriately called the Niagara Ravine,
on a branch of the Canadian Pacific near
Victoria, B. C.
Upon receiving more exact topographic
information at Niagara, Schneider
“decided that the cantilever plan would
be most feasible and economical for this
location...” He submitted his completed
design to the Central Bridge Works of
Buffalo, New York. They in turn submitted a tender to the Niagara Bridge
Company that was accepted by the Board
of Directors on April 11, 1883. Based
upon better survey and boring information, he modified his pier locations which
changed the span lengths of the cantilever. He also decided to use wrought iron
primarily, with some steel.
He chose to use Squire Whipple’s double
intersection pattern (STRUCTURE
magazine, May 2015), for his anchor and
cantilever spans that George Morison,
his mentor, used on his Missouri River
Bridges and C. S. Smith used on his earlier cantilevers. On the short suspended
span he, used a single intersection truss.
He wanted to have his piers of iron just
as Smith had done at the High Bridge,
but he decided to bring his iron work up
parallel, in a direction perpendicular to
the axis of the bridge. In order to make
the structure determinant, he omitted
the diagonals in panel BC; it is evident
that no other strains can be transmitted between B and C than moments,
the points of support being practically
reduced to 2, and the shearing strain in
panel BC becoming 0.
Schneider took great care in insuring
that all the iron and steel, particularly
the steel, met the specifications. In
accordance with his experience “with
steel for structural purposes which had
STRUCTURE magazine
19
September 2015
Niagara Cantilever.
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to be made according to a specification, there
have always been considerable delays, and
this case was no exception to the rule. The
records of the tests will show that the steel
which has been accepted was of a good uniform quality.” With his design complete and
quality of material acceptable, the fabrication
of the structure took place in the yards of
the Central Bridge Company.
The erection technique worked out by
Central Bridge Company and Schneider
became the pattern that would be followed
on many cantilevers in the future. They
began by building the anchor spans from
falsework resting on the rock banks and
the towers by travelers off of the anchor
span. The travelers worked outward on each
cantilever arm until they reached the end
of the cantilever span.
The suspended span was 120 feet long, and
the maximum reach of each traveler was 40
feet. Schneider did not want the traveler to
go beyond the end of the cantilever span, as
he did not want to overload the span or the
anchorage. This left 40 feet of suspended
span which could not be erected by the travelers. He handled this by placing wooden
beams across the 40-foot gap and erecting
the rest of the truss by hand methods.
The speed at which the bridge was erected
was as impressive. Schneider wrote:
The first metal of the cantilever shore
arm on the American side was placed
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Traveler and erection sequence, showing falsework and traveler.
on the falseworks on September 25 th,
and erection completed on October
15 th. The erection of the cantilever shore
arm on the Canadian side was commenced on October 8 th, and finished
on October 22 nd. The traveler on the
American side was completed on October
25 th, and erection of the river arm commenced on October 28 th. The traveler
on the Canadian side was completed on
October 31 st, and erection of the river
arm commenced on November 4 th. The
last connection was made on November
22 nd, at 11:55 A. M.
The travelers and falsework were removed
and the first track laid on December 6. The
formal opening and testing took place on
December 20, 1883. The bridge contained
almost 4.5 million pounds of iron and steel,
with about 70 percent of it being wrought
iron. What Schneider and Central Bridge
had done was to erect a new style bridge using
new techniques, over 900 feet long and 230
feet over the Niagara River, in less than two
months. The entire Niagara project, which
started with foundation work on April 15,
took only slightly more than eight months to
complete. The bid price for the entire project
was $680,000.
In 1900, or seventeen years after construction, the bridge was reinforced without
material interruption of traffic by the addition of a new center truss midway between
the original trusses and supported on a new
tower trestle and anchorage pier on each
bank. “The new superstructure has the same
STRUCTURE magazine
20
September 2015
general outline and dimensions as the old
one, and the details correspond so far as
possible to those of the old members...It
was decided to strengthen the bridge, not
so much because it is unsafe under present
loads but because the near future will evidently see trains and engines much heavier
than are now being run across the bridge
and heavier than was thought entirely safe
for the original structure. The new truss is
intended to be 50 percent stronger than
either of the old trusses...In order to insure
perfect safety against any uplifting of the
anchorages, anchorage pits are being sunk
about 25 feet under the end piers and the
anchorage made there for the new truss in
addition to the weight of the old pier...The
material for the work is being furnished by
the Detroit Bridge & Iron Works for plans
made under my supervision [Benjamin
Douglas, bridge engineer for the Michigan
Central)...and the erecting is being done by
the regular erecting gang. “
C. C. Schneider’s brainchild was reinforced without any apparent involvement
by its creator. Schneider was still active
in 1900 as Vice President in charge of
Engineering for the newly formed American
Bridge Company, located in New York City.
The bridge was taken out of service and
demolished in 1925 after having a useful life
of over forty years. It was replaced by a steel
arch bridge located between Schneider’s
Bridge and Roebling’s Suspension Bridge
(which was replaced with an arch by Leffert
L. Buck in 1897).▪
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The ACI 562 code provides standard requirements for evaluating existing concrete buildings and the subsequent structural
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requirements for stability and shoring of construction, and inspection and testing of repairs. Commentary provides application guidance as well as references for additional information.
The new guide is separated into two main components: chapter
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Building
Blocks
Fundamentals of
Hardened Concrete
Monolithic concrete with a compressive strength
in excess of 3500 pounds per square inch (psi)
is watertight, except at any irregularities in the
structural element. Typical locations where irregularities occur include overhead decks, floors,
and walls that have cracks, honeycombs, joints,
mechanical/electrical penetrations, and form-tie
supports. Hairline cracks in excess of 1/1000 of
an inch (i.e. 1 mil) commonly leak water if subject
to hydrostatic pressure. Water leakage rate and
volume, or quantity, is related to pressure and
crack width.
updates and information
on structural materials
Concrete Cracking
When concrete is freshly cast, its temperature
is often between 60º and 90º F. Depending on
the in-situ form, materials, temperature, environmental conditions, and composition of the
mix design, concrete hydration may generate
significant additional heat. Thermal expansion
of the semi-plastic structural element will occur
and, depending upon local restraint, may cause
micro-cracking.
Depending on local restraints, minute small
cracks (defects within the cement/aggregate
matrix typically so small they can’t be seen by
the naked eye) develop externally and internally. After the forms are removed, the concrete
continues to shrink from both cooling and loss
of water. This process varies with environmental
conditions and may create cracks capable of
water leakage within hours of form removal,
and within days after wet curing. For most
structural elements less than 14 inches thick,
it takes about 5 years for shrinkage to subside.
In this time, the cracks initiated by thermal
contraction become much larger. These cracks,
depending on reinforcing, sectional dimensions, mix design, and restraint conditions,
can be as large as 5 to 50 mils. If subjected
to water under hydrostatic pressure, serious
leakage will occur.
Ingredients for Corrosion
Corrosion in reinforced concrete requires three
basic ingredients; oxygen, water, and an electrolyte medium. Fundamental to corrosion
mitigation is minimizing at least one of these
three basic ingredients.
Issues from Leakage
One of the biggest concerns with water leakage in
heavily reinforced concrete is that the time for the
onset of corrosion is shortened. It is well understood that if you eliminate oxygen and water from
the immediate environment around reinforcing
steel, corrosion is generally minimal and essentially mitigated. When through-element cracks
Monolithic concrete with a compressive strength in excess
of 3500 PSI is watertight, except at any irregularities.
occur from outside to inside
face, allowing air or dissolved
oxygen in the water to interact
with the steel, all three of the
critical items are now available
for corrosion to occur.
In addition to corrosion, water
leakage can bring salt and various stray minerals that can exacerbate other issues
within the concrete, e.g., sulfate attacks. External
issues with water leakage are many – ice buildup,
slip problems, treatment of contaminated water,
and potential mold issues.
Proper Procedures and
Protocol for Interception
Grouting
By Brent Anderson, P.E.
Fundamentals of
Interception Grouting
Directional Drilling
The objective of interception grouting is to
make the concrete element monolithic. This
can be achieved by pressure injecting a resinous material through one or both concrete
element faces (surface mounted ports), or by
drilling at a 45-degree offset to the defect and
injecting into the defect in the center third
of the concrete element section (interception
grouting). The importance of drilling into the
center of the concrete element is that, during
grouting, the resinous material should flow
equally to the inside and outside face of the
concrete section in a uniform manner. If drilling into the interior third of the section, grout
flow will not extend to the exterior. Drilling
into the outer third of the section will unlikely
allow grout migration to the interior. By proper
placement of drill holes, grout flow will intersect from bottom-to-top or side-to-side with a
relatively high degree of reliability. Long-term
STRUCTURE magazine
23
Brent Anderson, P.E., is the
Moisture Control Solutions Team
Leader at Structural Technologies.
He serves on ACI 332 Residential
Concrete and previously served on
ACI 515 Protective Coatings for
Concrete. Brent can be reached at
[email protected].
Typical water leakage paths.
grouting solutions intercept the defect in
the center; short-term solutions allow shallow drill depth holes. In addition to crack
interception at the concrete element’s center
third, most quality contractors alternate
directional drilling on each side.
Drill Hole Spacing
Generally, the rule of thumb is that drill hole
spacing should be one half to two-thirds the
concrete element thickness. This allows an
overlap of about 20 to 30 percent between
drill holes. Drill hole spacing up to the width
of wall element can be done if cracks are relatively large – i.e. 50 to 100 mils wide.
Interior and/or exterior steel can influence
the drilling angle based on its density and
location. Angles of 30º to 60º are not uncommon provided that interception drilling is
done in the wall center. Because cracks vary
in direction, drilling should be 20 to 25 percent deeper for interception grouting than
what the typical calculations dictate. Drill
hole diameter is not critical and can be left
to contractor preference.
Cleaning
Just as important as intercepting the crack
at the element midsection is cleaning the
drill hole of debris prior to setting any ports.
Injection drill holes should be blown out with
high pressure air and then flushed thoroughly
with a water jet. Some contractors even push
and flush a wire bristle brush down the drill
hole and scrub the area of intersection to
remove surface debris.
Crack Flushing
The next important aspect is to put a port on
the surface and flush the crack. Flushing the
crack is important for two reasons:
1) To push out any mineral deposits
(clay, silt) that may have accumulated
in the crack, and
2) If water is pumped and does not make
it to the surface of the concrete, grout
will not make it through either.
These are often questions as to whether or not
some kind of acidic material (e.g., phosphoric
or muriatic) should be used. Generally, it is
an acceptable approach, but it should come
with some safety precautions and the use of
proper personal protective equipment to keep
acid away from the face.
Acid washing the drill hole and the crack
improves the bond ability of any type of resin
that is injected into the crack later. If the crack
has debris and mineral deposits, the effectiveness of the grout will not be as monolithic
as needed, and secondary or minor leakage
could still occur.
Pressure
Interception grouting should be done in a way
that the internal hydraulic pressures of the grout
never exceed the tensile strength of the concrete.
The tensile strength of concrete is 10% of the
compressive strength. Most concrete that interception grouting will be performed on will have
a tensile strength of 300 to 500 psi. It is recommended not to use pumping grout pressures
in excess of 500 psi. In so doing, the concrete
surface may spall where the drill holes exist and/
or the pressure may hydraulically fracture the
concrete and create additional cracks.
A word of caution, use of high viscosity
resins may lead to internal damage of the
concrete. High viscosity resinous materials
are not as user friendly as low viscosity injection materials. For comparison, water has a
viscosity of one centipoise – so grouts that
have values of 50 to 300 centipoises means
that they are 50 to 300 times more viscous
than water.
It is not uncommon for contractors who do
not have a good understanding of viscosity
and crack width to use resinous grouts with
300 upwards to 500 centipoises and pressures
up to 3000 psi to accomplish placing resinous
material within the crack.
Grout Delivery
There are three types of delivery systems generally utilized: small hand operated pumps,
STRUCTURE magazine
24
September 2015
It is important to intercept the crack at the center
third so that the resinous material flows equally to
the inside and outside face of the concrete section.
small electric operated pumps, and high
volume air driven or piston driven pumps.
Most hand and small electric driven pumps are
for single component resins. The larger piston
pumps can be used for 1-3 components.
Small electric pumps require minimal
maintenance. However, after several uses the
pumps are discarded and new ones are purchased. Others prefer to buy the large piston
drive, both single and multi-ratio. What’s
important is that these pumps have a capacity of ¼ gallon per minute and have pressure
capabilities up to 750 psi.
Injection Packers
There are basically three types of injection
packers – button head, grease zerk, and ball
valve quick connect. The advantage of the
grease zerk packers is that they are inexpensive and can be discarded after one use.
Button head packers are similar and usually
discarded after one use. The ball valve quick
connect packers are more expensive, but can
be reused multiple times. Another advantage
of the ball valve is that you can open and
close the valve to monitor water or grout flow.
Button head and ball valve quick connect
packers generally do not restrict grout flow
and increase pump gauge pressure during
application. Disadvantages of zerk packers
are that they cannot be opened and closed to
monitor grout movement and they are very
restrictive to grout flow, requiring about 100
to 200 psi gauge pressure just to move most
grouts through them.
Causes of Premature
Grout Failure
There are 4 basic causes of premature grout
failure:
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To achieve the right mixing ratio of water to grout,
a multi-ratio pump should be used.
Most quality contractors alternate directional
drilling on each side.
Conclusion
It is important for engineers and contractors
alike to remember that the grout viscosity
needs to match up with the crack width, and
the grout chemical resistance needs to match
the exposure. The most successful grouting
contractors have a good knowledge of chemical resistance and have good field experience
in developing techniques that allow them to
get low viscosity grouts to migrate deeply
within finely cracked concrete.▪
STRUCTURE magazine
25
September 2015
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1) Improper drilling and delivery
It is not uncommon for contractors to
drill directly into the crack or too close to
the surface. By doing this, a seal is created
that is 1/3 to ½ of the crack depth and
water under hydrostatic pressure is still
within the concrete element. Very little
flexural movement causes leakage to recur.
2) Inadequate mixing ratio of water to
grout during application
Most contractors are taught by manufacturers that pre-wetting the crack
prior to urethane grout injection is all
that is needed to activate the material.
This would likely be the case of the wall
4 to 6-inches or less in thickness. Wall
and floor sections greater than 12 inches
would not fit the criteria however, and
a multi-ratio pump for injecting water
reactive urethane grouts should be used.
Some contractors prefer to use two small
electric pumps – one to inject urethane,
one to inject water – and then rotate a
few strokes of water to several strokes
of grout thinking they are getting good
cross-polymerization of water to urethane.
While this may seem a viable solution
because the first grout that comes to
the surface appears to be fully reacted,
it is very common to have areas of water
deprived urethane grout within cracks
and other defects. When these conditions
are subjected to high temperatures in the
environment (in excess of 100 to140º
Fahrenheit), it is common to see a brown,
unreacted urethane resin extrude from the
cracks anywhere from 2 months to 2 years
after the initial grouting. This urethane
resinous material has now contaminated
the crack for future injection. Many
contractors have found that the only
viable way to seal cracks with unreactive
grouts is the backside grouting method.
3) Excessive wall movement
Excessive movement is most prevalent
when the concrete is subject to outdoor temperatures – i.e. exterior tanks,
retaining walls, exposed foundations,
etc. Most resins have some degree of
flexibility. It is not uncommon that
during warm to cold cycles, a 5 mil
crack will open to a 10 mil crack. Most
resinous grouts, even though they are
called flexible, cannot sustain repeated
opening and closing of the crack and
will fail. Grout adhesion to the substrate
may fail during expansion and contraction of the crack if surface contaminants
on the grout sidewall are prevalent.
4) Chemical attack
Chemical attack is very common in the
industrial environment, and this type
of issue usually takes several years to
work its way through the grout matrix.
Residue hydrocarbons within water will
commonly attack many of the grout formulations. This is exacerbated if chemical
attack and thermal expansion/contraction are occurring simultaneously.
3000 PSI IN 1 HOUR
Structural
rehabilitation
renovation and restoration of
existing structures
T
his series of articles discusses a number
of commonly encountered structural
issues on renovation and restoration
projects that focus on historic houses
of worship, and provides guidance on ways to
address them. Parts one, two, and three of this
series dealt with foundations, wall systems, and
roof framing in historic houses of worship. This
article addresses interior architectural components
and finishes.
Architectural components and finishes are often
the most visible and identifiable elements inside
historic houses of worship. They define the ambiance and “feel” of the space, reflect the cultural
and religious sense, and are often a testament
to history and development of communities in
which these structures were built. Given their
effect and significance, a lot of thought should
be placed on their appearance, performance, and
serviceability. However, if designed or installed
improperly, if exposed to severe or unplanned conditions, or if not regularly
maintained and repaired,
they may undergo accelerated deterioration and
decay, or can be subject
to distress that can cut
their expected service life
short. Therefore, when
planning repair, renovation, or rehabilitation projects, understanding the
basic material properties of common architectural
components and finishes, addressing their potential vulnerabilities and exposure limitations, and
considering structural support, compatibility, and
constraint issues, is paramount.
Divine Design: Renovating
and Preserving Historic
Houses of Worship
Part 4: Architectural
Components and Finishes
By Nathaniel B. Smith, P.E. and
Milan Vatovec, P.E., Ph.D.
Wood Components and Finishes
Nathaniel B. Smith, P.E., is a
Senior Project Manager at Simpson
Gumpertz & Heger’s office in New
York City. He can be reached at
[email protected].
Dr. Milan Vatovec is a Senior
Principal at Simpson Gumpertz &
Heger Inc. He can be reached at
[email protected].
Wood is a natural building material known for
its workability, high strength-to-weight ratio, and
durability. Wood’s natural beauty is unequaled.
Wood is also the only truly organic building product that is renewable and sustainable. As such,
wood has successfully been used for centuries in
a structural role and, perhaps more prominently,
as a go-to material for architectural components
and decorative finishes in houses of worship. Its
ability to be milled and carved, and its ability
to receive stains and paints, has made it a great
option for finish work and flooring, and exposed
structural and architectural members.
Wood, however, can also be challenging to work
with. It comes in many varieties (species), with
each variety having its own unique characteristics.
Sawn lumber can have natural-growth defects
(e.g. knots, splits, excessive slope of grain). Wood
properties can vary significantly even between
pieces of lumber taken from the same tree. The
makeup of the cell structure of the tree trunk
causes sawn wood to be orthotropic; it behaves
differently in three principal orientations (directions), defined basically with respect to the
configuration of a tree trunk. The orthotropic
behavior comes into play in terms of strength
and stiffness differences, resulting in a number of
design and detailing consequences (e.g. never load
wood in tension perpendicular to grain). It is also
a large factor when it comes to physical properties,
most notably orientation-dependent differences
in shrinkage and swelling (dimensional-change
reaction to moisture intake and release in response
to environmental changes), durability, and, last
but not least, appearance. Finally, wood is susceptible to attack by microorganisms, which requires
special care and consideration both in design
and in-service. Because of all this, optimal use of
wood often depends on special knowledge that
requires integration of material science, engineering, and familiarity with construction practices
and detailing.
When it comes to structural design, engineers
tend to place high importance on the mechanical
properties of wood components, which typically
includes variability in properties, natural-growth
characteristics, and orthotropic-behavior considerations. By and large, this is accounted
for through established design processes (e.g.
stress grades and associated design values, etc.).
Vulnerability to biological attack and propensity
to dimensional change in service are generally
addressed through standard detailing. Often,
however, issues that affect non-structural wood
components in service, and particularly in historic
structures, involve non-standard use or detailing, or are not within the domain of a structural
engineer. In these situations, architects, builders,
and other practitioners that design, fabricate, and
install wood components and finishes are required
to pay special attention to a number of additional
parameters, often related to all phases in the “life”
of the wood component: harvesting, milling,
drying, conditioning, installation, environmental
exposure, geometric and boundary constraints,
type and duration of loads, etc.
The most common problems with wood in
service are related to deterioration from unanticipated exposure or to distress resulting from
dimensional changes. Both of these problems are
driven predominantly by exposure to and effects
of moisture (either as humidity in air or as liquid
water). In general, moisture is considered to be
the number one contributor to problems with
wood and its performance in service. While wood
deterioration due to decay (a.k.a. rot) from moisture exposure is likely the greatest contributor
to loss of wood material in service in the world,
the implications of water exposure, the resulting
change in properties, and ultimately the damage
caused by fungal action will not be discussed in
detail here; the focus of this article will be placed
on dimensional stability and associated issues.
26 September 2015
Wood elements and components meant for
interior use will typically be in what is considered
a “dry” condition immediately before, during,
and after installation; they would have undergone either an air or kiln-drying process before
delivery. However, the actual moisture content
of interior wood, while in general considered
dry, will fluctuate, sometimes significantly, in
wood’s attempt to be in equilibrium with its
environment. As the temperature and relative
humidity (RH) of air surrounding wood components fluctuate (seasonally or otherwise), the
wood’s moisture content (MC) will fluctuate as
well, albeit with some inherent lag. As the MC
goes up or down, wood elements will swell or
shrink, respectively. Even for interior use, the
expected yearly MC swing of wood components could be on the order of 5% (especially
in spaces where RH is not controlled), which,
depending on wood species, can translate into
approximately 1 to 2% of cross-grain shrinkage
or swelling (Wood Handboook, Forest Product
Laboratory, 2010, Tables 4-2 and 4-3). To further complicate things, cross grain movement
is not uniform; expected movement in the tangential direction is approximately two times
larger than in the radial direction (relative to
orientation of tree rings). Therefore, the extent
and uniformity of movement will depend on
the orientation of the wood grain within the
piece, which is dictated by where the piece was
milled from the tree.
Given all of the above, it is not surprising
that dimensional compatibility and restraint
problems are often encountered with wood in
service. If not designed or installed properly,
shrinkage will cause joints between adjacent
pieces of wood to open, whereas expansion
will make the joints tight, and, in extreme
situations, buckling or other distress will
ensue. The buckling problem is often most
pronounced in wood floors that are exposed
to high levels of moisture (e.g. leakage), floors
that were installed too wet (or on the high end
of the expected equilibrium spectrum), or are
not detailed to allow for sufficient expansion
without causing distress.
Other types of architectural components or
finishes may also be subject to restraint-related
distress, if not detailed to allow movement. It
is not uncommon to see infill boards or trim
panels crack or otherwise become distressed
because they were too “tightly” connected to
their frames. Veneers and other thin elements
may crack or be subject to localized buckling
(waviness) when “married” to a substrate that
does not undergo similar moisture-driven
dimensional changes.
Depending on the orientation of the grain,
individual members not restrained against
movement can also be subjected to distress.
Buckled wood flooring.
Cupping and twisting may occur even when
wood undergoes small MC changes in service because of the difference in cumulative
dimensional movement between the tangential and radial directions.
Simply put, wood will move with moisture fluctuations, and it does not like to be
constrained against that movement. If it is,
problems that may be difficult or very expensive to address will likely occur. Ironically,
engineers, who are typically not involved
with design, detailing, or specifying nonstructural components and finishes, are often
best equipped to deal with existing issues, or
to predict (and therefore avoid) problems
in-service related to wood material behavior.
Tools and knowledge exist.
Having foresight, and respecting wood
behavior and its response to the design
environment, is key. Similarly, proper detailing, especially if developing new, non-vetted
systems, is paramount. Finally, acclimatization, selection, treatment (if any), and proper
installation of wood components should all
be carefully considered and incorporated
into the specifications for renovation and
remedial projects.
Plaster Finishes
Plaster is one of the most common interior
finishes found in historic houses of worship,
with typical applications for wall and ceiling
surfaces. Ornate, molded plaster finishes (trim,
finials, florets, etc.) are often incorporated into
the overall finish work. While plaster is a tried
and true finish that has been used for centuries,
Splitting of infill panel in wood bench.
STRUCTURE magazine
27
September 2015
it is not without its limitations. Plaster in its
simplest form is a combination of hydraulic
lime, sand, and water. Water reacts with the
hydraulic lime, causing it to chemically bond
to the sand particles creating a solid substance.
The plaster stays in a “fluid” state for a limited
time, allowing it to be applied by trowel to
walls and ceilings, or it can be placed into
molds to take specific shapes prior to solidifying. Plaster for walls and ceilings is typically
applied in two layers. The base layer, often
called a “brown coat,” contains relatively coarse
sand particles and helps give the plaster its
strength. The top coat, or “finish coat,” typically contains fine sands, which gives the top
coat its smooth finish.
Plaster can be applied directly to masonry or
terra cotta, as the hydrated lime will bond with
stone and clay particles within these materials.
However, plaster for walls and ceilings is often
supported by lathe, which is typically wood
or metal mesh. Older construction typically
features a wood-lathe substrate, which is a
series of parallel wood strips about ¼ inch
thick, 1 inch wide, spaced about ¼ inch to
½ inch apart. When the plaster is applied
to the lathe, it is pushed through the spaces
between the wood strips and tends to ooze
over the backside, creating a plaster “key”.
This “key” helps hold the plaster in place. A
similar process occurs with metal lathe as the
plaster oozes through the wire mesh.
Plaster keys are a critical component of overhead plaster applications. Sufficient keying
needs to be created to hold the ceiling in place.
Lack of adequate keys can cause portions of
the ceiling to become loose, to debond, and
potentially fall. Plaster keys in ceilings can also
break over the life of a building through the
course of regular maintenance and alterations.
Installation of new lighting or mechanical
equipment from within attic spaces can often
break keys, resulting in the potential for ceiling failures. Detecting failures or distress in
plaster keys is often difficult and may require
specialized access and equipment (e.g. minimally-destructive testing instruments such
as boroscopes).
continued on next page
Typical wood lathe plaster ceiling with broken keys
and lathe from light fixture installation.
There are numerous available options to
address broken keys. Several of the more
common options include:
• Remove and Replace: One option to
address broken keys is to remove the
affected portion of the plaster and
replace it. This will certainly address
the issue but can be cost prohibitive
due to access and coordination
constraints (scaffolding likely required).
It can also be a time consuming process
as the plaster needs to be removed, new
plaster installed and allowed to dry,
then sanded and painted to match the
surrounding areas. Special blending
of paint is needed to match the
surrounding areas as well. Also, plaster
on metal lathe will likely require new
lathe to be installed, as salvaging the
existing lathe may be difficult.
• Additional Mechanical Support: The
affected portions of the plaster can
be reattached to wood lathe through
mechanical means, such as screws.
Screws with large plastic washers are
typically installed through the plaster
into the lathe or ceiling framing. This
option also requires access from the
underside of the ceiling to allow for
placement of a skim coat of plaster over
the fasteners to conceal them, followed
by a fresh coat of paint.
• Cover-board: In some circumstances,
placing a new ceiling below the original
and fastening it through the existing
ceiling is a preferred option. Gypsum
drywall, often used in this application,
is placed on the underside of the
existing plaster. With this option, care
should be taken to ensure that the
new drywall sheets are supported by
the ceiling framing and not the wood
lathe. Wood lathe in historic structures
is often fastened to the ceiling framing
with cut nails (tapered nails cut from
flat stock), which may withdraw under
the additional load of the drywall.
• Consolidation: Another option that
seems to be gaining popularity, due
to its minimally invasive nature, is a
consolidation process. The process
includes applying an acrylic resin to the
backside of the plaster, typically from
within attic spaces or through small holes
drilled in the plaster. The resin permeates
into the plaster and then cures to create
a solid mass that is stronger than plain
plaster. This process can reestablish keys,
fill in small cracks, and strengthen the
plaster. This process also has the benefit
of having a minimal impact on the
finished face of the plaster.
Choosing the correct plaster remediation
option depends on numerous factors, including the condition of the existing ceiling,
ceiling framing, and architectural features of
the ceiling. If the ceiling is of architectural
significance, options that leave the existing
ceiling in place should be explored first. While
leaving a ceiling in place may be the ultimate
goal, understanding the limitations of the
plaster and support system is a critical step in
order to make an informed decision.
Structural engineers are often called upon to
evaluate the plaster-ceiling support system to
determine if it has adequate capacity to support
additional ceiling loads (cover-board) or other
Plaster ceiling framing can be quite complex.
STRUCTURE magazine
28
September 2015
architectural features (lighting, insulation, etc.),
or in some cases partial removal to accommodate access. In other cases, these framing
systems require evaluation to determine if their
condition renders them inadequate to continue carrying the ceiling loads. Understanding
the ceiling-framing layout is a key step in this
process. The support framing for flat-ceiling
systems is typically straightforward, with a
series of parallel joists supporting the lathe
and plaster; these systems are easy to assess and
analyze for additional loads. However, many
houses of worship are not flat and feature very
intricate ceiling geometries, often with gothic
arches. Despite the large level of redundancy,
the framing for such ceilings is often independent from the main roof structure and can be
much more difficult to analyze due to complex
geometry, a multitude of components (with
various stages of effectiveness or deterioration
that may be difficult to quantify), unclear load
paths, and lack of accessibility.
Non-Standard Components
and Furnishings
Many renovation projects in historic houses of
worship call for installation of new furnishings,
or components that need to be incorporated
with and supported by the existing structure.
These new components may be related to
accessibility (new ADA ramps or elevators),
improvement of mechanical systems (e.g. new
chiller units), or could simply be related to
aesthetic or other improvements (new organs,
chandeliers, heavy furniture, statues, etc.).
While structural engineers will often consider
the load associated with furnishings as part of
the uniform live load, some of the proposed
components can be quite heavy and may
require special attention. For example, many
religious furnishings and statues are made of
solid stone, are quite heavy, and require proper
support analysis and design.
Often, the hardest part of determining how to
support the new loads is actually determining
what the load is. Some of the furnishings are old
and do not come with established weights, so
an estimate needs to be made. Sometimes, fairly
detailed historical or material research is needed
to gain a comfortable level of understanding of
the component materials and geometry, and to
be able to develop reasonable loads for use in
design of the support components.
Similar to other situations where structural
modifications to the original structure are proposed, addition of heavy loads requires that
the load path and all elements that may be
affected along it be well understood. Given the
likely absence of any structural drawings, this
frequently requires a probing program where
finishes are removed to expose the underlying
structure. This process is not always straightforward and may require several iterations before
full or sufficient understanding of the load
path and the involved structural components is
gained. In addition, material characteristics of
or alternate load paths that can be evaluated,
including sistering, shortening the span,
adding supplemental supports or cross section to the existing members, etc. If the loads
are excessive, it may be easier to provide an
alternate load path through installation of
new members or systems, in lieu of reinforcing. The best option will depend on the
specifics of the furnishings, the existing framing, and the ultimate needs of the owner.
Economics and ease of installation, along
with the needs of the surrounding programming space all need to be considered when
making recommendations.
Non-standard furnishings require proper support.
all the involved structural components need to
be understood. Historic buildings often feature
a variety of structural framing materials including wood, timber, cast iron, and steel, and it is
not unusual to see any combination of these
within the load path. The material properties
for each can be difficult to ascertain, and, if
conservative estimates cannot yield effective
design, sampling and subsequent laboratory
testing may be required.
If a deficiency in the load path is found,
there are numerous options for strengthening
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STRUCTURE magazine
29
September 2015
Conclusion
While not always considered to be in the
wheelhouse (or even within the scope of services) of structural engineers, consideration
of mechanical and other material properties
of non-structural components in the design
phases of historic renovation projects is critical. Regardless of whether the project revolves
around design and installation of new systems or evaluation and retrofit of existing
systems, special care aimed at understanding and anticipating the in-service behavior
of architectural components and finishes is
required of everyone involved.▪
Codes and
standards
updates and discussions
related to codes and standards
P
rovisions for the design of cast-in-place
and post-installed anchors were introduced into the American Concrete
Institute (ACI) publication Building
Code Requirements for Structural Concrete (ACI
318) in 2002 (ACI 318-02) via Appendix D –
Anchoring to Concrete. Since ACI 318 is referenced
in the International Building Code (IBC), these
provisions are thereby incorporated into IBC
Chapter 19 – CONCRETE.
Cast-in-place headed bolts and headed studs are
generic products that can be used directly with
Appendix D provisions. However, post-installed
anchors must be qualified for use with the provisions of Appendix D due to the inherent diversity
of adhesive and mechanical anchor products. For
example, hybrid adhesives have different performance and behavioral characteristics versus epoxy
adhesives. Likewise, epoxy adhesives can vary widely
in performance due to differences in their chemical
makeup, and in their installation requirements.
Given the wide array of
post-installed anchor types
and performance characteristics, ACI developed two standards to qualify these
anchors for use with the Anchoring to Concrete provisions in the ACI 318 code. ACI 355.2 Qualification
of Post-Installed Mechanical Anchors in Concrete
was first printed in 2002. ACI 355.4 Qualification
of Post-Installed Adhesive Anchors in Concrete was
first printed in 2011. These standards serve as
baseline provisions for two International Code
Council Evaluation Service (ICC-ES) Acceptance
Criteria: AC193 Acceptance Criteria for Mechanical
Anchors in Concrete Elements (first printed 2002)
and AC308 Acceptance Criteria for Post-Installed
Adhesive Anchors in Concrete Elements (first printed
in 2006). AC193 and AC308 contain programs to
evaluate an anchor system for recognition under
an IBC version adopted by a local jurisdiction.
Design parameters and data from this evaluation
are given in an ICC-ES Evaluation Service Report
(ESR). Therefore, a post-installed anchor system
evaluated per AC193 or AC308, having an ESR
noting recognition under an IBC, can be designed
using the Anchoring to Concrete provisions of the
ACI 318 code.
In January 2015, ESRs for adhesive anchor systems began to list compliance with the 2012 IBC.
There are changes with respect to the information
contained in these reports compared to reports
having recognition under previous versions of the
IBC. This article explains what changes have been
implemented into 2012 IBC-compliant adhesive
anchor ESRs, and how these changes affect adhesive anchor design.
Changes in Adhesive
Anchor System Approvals
By Richard T. Morgan, P.E.
Richard T. Morgan, P.E., is
the Manager for Software and
Literature in the Technical
Marketing Department of Hilti
North America. He is responsible
for PROFIS Anchor and PROFIS
Rebar software. He can be reached
at [email protected].
Review of the ICC-ES
Acceptance Criteria AC308
The primary test programs for evaluating adhesive
anchor systems in cracked and uncracked concrete
are given in its Tables 3.1, 3.2 and 3.3 in AC308.
AC308 evaluation of adhesive anchor systems for
design using threaded rods, internally threaded
inserts and torque-controlled elements include
various types of tests:
• reference tests establish the baseline bond
strength of the adhesive
• reliability tests determine sensitivity to
installation and load conditions
• service condition tests evaluate concrete
conditions during the service life of the
anchor, establish minimum spacing and
edge distance requirements, and
evaluate performance in simulated
seismic conditions.
Adhesive anchor ESRs based on evaluation per
AC308 were first issued in November 2007,
for recognition under the 2006 IBC. As such,
an adhesive anchor system could be evaluated
per AC308 and designed with the Anchoring to
Concrete provisions of ACI 318-05 Appendix
D. However, since ACI 318-05 Appendix D
did not include provisions for adhesive anchor
systems, AC308 was a stand-alone document
that included a section titled 3.3 Strength design
– amendments to ACI 318, which also contained equations and parameters for calculating
bond strength in tension and concrete pryout
strength in shear. The 2006 IBC-compliant
adhesive anchor ESRs likewise began including these AC308 equations and parameters via
Section 4.0 DESIGN AND INSTALLATION.
Therefore, even though the scope of ACI
318-05 Appendix D did not include adhesive
anchor systems, adhesive anchor design using
Appendix D provisions could be performed via
an ESR having 2006 IBC recognition. Adhesive
anchor ESRs having 2009 IBC recognition also
included the AC308 bond strength equations
and parameters via Section 4.0, thereby permitting design per ACI 318-08 Appendix D.
The ACI 318-11 code now includes adhesive
anchor systems in Appendix D as referenced in
Part D.2.2 – Scope, and ACI 355.4 is referenced
in Part D.2.3 (d) as the standard to qualify
adhesive anchor systems for use with Appendix
D provisions. Part D.5.5 – Bond strength of
adhesive anchor in tension contains provisions
for calculating nominal bond strength in tension. Part D.6.3 – Concrete pryout strength of
anchor in shear contains provisions for calculating nominal pryout strength in shear.
30 September 2015
AC308 (original) projected distance parameter Scr,Na
ACI 318-11 Appendix D projected distance parameter CNa
τk,uncr
√ 1450
Scr,Na
2
τk,uncr = 1670 psi
CNa
Scr,Na = 20da
da = 0.75 in
CNa = 10da
τuncr
√ 1100
τuncr = 1670 psi
da = 0.75 in
CNa
Scr,Na
2
2
Scr,Na = (20)(0.75 in)(1670 psi/1450 psi)0.5
CNa = (10)(0.75 in)(1670 psi/1100 psi)0.5
Scr,Na
2
Scr,Na
2
Scr,Na = one half the ciritical spacing
2
between two anchors
= 16 in
CNa
Scr,Na
2 = (16 in)/2 = 8 in
Figure 1. AC308 (original projected distance parameter).
Harmonization Between
AC308 and ACI 355.4
With the development of ACI 355.4 in 2011
to qualify adhesive anchor systems, ACI 355.4
and AC308 needed to be harmonized because
ACI 355.4 will now serve as the baseline for
AC308. Recall that AC308 was developed as
a stand-alone document prior to the existence
of ACI 355.4. Since adhesive anchor systems
receive IBC recognition in an ESR via testing
per AC308, the original AC308 provisions
needed to be modified to coincide with the
new baseline provisions of ACI 355.4. The
significance of this is that the inclusion of
adhesive anchor qualification and design provisions into the ACI 318 code has resulted
in bond strength equations no longer being
necessary in either AC308, or in adhesive
anchor ESRs.
Beginning with 2012 IBC-compliant adhesive anchor ESRs (issued January 2015),
bond strength equations are no longer
included in the report because they are
now given in ACI 318-11 Appendix D Part
D.5.5. This means that adhesive anchor
design under the 2009 IBC/ACI 318-08 or
under the 2006 IBC/ACI 318-05 should also
be performed using the equations of ACI
318-11 Appendix D Part D.5.5, because
the original AC308 bond strength equations
given in previous ESR versions are no longer
presumed to be “code compliant”.
Comparisons between Previous
Bond Strength Calculations
ACI 355.4 “prescribes testing and evaluation
requirements for post-installed adhesive anchor
systems intended for use in concrete under the
provisions of ACI 318.” It includes test programs for evaluating adhesive anchor systems
in cracked and uncracked concrete. Similar
to AC308, the test programs in ACI 355.4
cover various conditions:
CNa
Figure 2. ACI 318-11 Appendix D projected distance parameter.
• reference tests to establish the bond
strength of the adhesive
• reliability tests to determine sensitivity
to installation and load conditions
• service condition tests to evaluate possible
concrete conditions during the service
life of the anchor, establish minimum
spacing and edge distance requirements,
and evaluate performance in simulated
seismic conditions.
Although the ACI 355.4 test program is similar to the AC308 test program, it is important
to note that ACI 318-11 Appendix D bond
strength calculations, per the provisions given
in Part D.5.5 Bond strength of adhesive
anchor in tension, are based on parameters
established in ACI 355.4. The D.5.5 calculation results will differ from bond strength
calculations based on parameters previously
established in AC308. The calculations for
nominal bond strength per the original version
of AC308, i.e. pre-ACI 355.4, used a parameter corresponding to the spacing between two
adhesive anchors, scr,Na, and the equations for
calculating nominal bond strength utilized
either scr,Na or scr,Na /2. Nominal bond strength
calculations in ACI 318-11 Appendix D are
now based on a parameter corresponding to
the projected distance from the center of an
adhesive anchor to one side of the anchor,
cNa, which does not equal the original AC308
value scr,Na /2. The value calculated for cNa is
greater than that calculated for scr,Na /2. Figure 1
and Figure 2 illustrate why the original AC308
parameter scr,Na /2 differs from the new ACI
318-11 Appendix D parameter cNa.
Looking at Figure 1, assume the characteristic bond stress (τk,uncr) equals 1670 pounds
per square inch, and the anchor element consists of a ¾-inch diameter (da) threaded rod.
The value for scr,Na calculated per the original
AC308 Equation (D-16d) would equal 16
inches and the value calculated for scr,Na /2
would equal 8 inches. Looking at Figure 2,
using the same values for τuncr and da, the value
STRUCTURE magazine
= 9.24 in
CNa = projected distance from
the center of one anchor
to one side of the anchor
31
September 2015
for cNa calculated per ACI 318-11 Equation
(D-21) would equal 9.24 inches. Therefore,
cNa is greater than scr,Na /2, which means ACI
318-11 Appendix D bond strength calculation
results using cNa will differ from the original
AC308 calculation results using scr,Na or scr,Na /2.
Adhesive Anchor Design Per
ACI 318-11 Part D.5.5
Bond strength data published in 2012
IBC-compliant ESR tables titled BOND
STRENGTH DESIGN INFORMATION
is derived from adhesive anchor qualification testing per ACI 355.4/AC308, and is
product-specific. This data is used to design
the adhesive anchor system per the provisions
of ACI 318-11 Part D.5.5. The parameter corresponding to the characteristic bond stress (τ)
of an adhesive is a key parameter used in ACI
318-11 bond strength calculations. Values
for τ given in the ESR bond strength tables
are designated τk,cr for the characteristic bond
stress of the adhesive in cracked concrete,
and τk,uncr for the characteristic bond stress in
uncracked concrete.
Characteristic bond stress (τ) is used either
directly or indirectly in the ACI 318-11 equations (D-21), (D-22) and (D-27) to calculate
cNa, the basic bond strength Nba, and the critical edge distance cac, respectively.
Another parameter relevant to the characteristic bond stress (τ) is the concrete temperature
range. The ESR bond strength tables include
a footnote that defines the concrete temperature ranges for which the adhesive has been
tested. Temperatures corresponding to the
“maximum short term” and “maximum long
term” concrete temperatures for a given range
are defined, and the characteristic bond stress
(τ) values corresponding to these temperature
ranges are given in the ESR bond strength
tables. The concrete temperatures are defined
in terms of “short term” and “long term”.
Short term concrete temperatures are defined
3.2 Bond Strength
Nag =
( AA ) Ψ
Na
Na0
ec1,Na
Ψec2,Na Ψed,Na Ψcp,Na Nba
ACI 318-11 Eq. (D-19)
ɸNag ≥ Nua
ANa = see ACI 318-11, Part D.5.5.1, Fig. RD.5.5.1(b)
ANa0 = (2 cNa)2
τuncr
cNa = 10 da 1100
1
e
≤ 1.0
Ψec,Na =
1+ N
cNa
ca,min
≤ 1.0
Ψed,Na = 0.7 + 0.3
cNa
ca,min , cNa
Ψcp,Na = MAX
≤ 1.0
cac cac
Nba = λa – τk,c – αNsels – κbond – � – da – hef
√
(
(
Variables
τk,c,uncr [psi]
1670
ec1,N [in.]
ACI 318-11 Table D.4.1.1
ACI 318-11 Eq. (D-20)
ACI 318-11 Eq. (D-21)
)
(
ACI 318-11 Eq. (D-23)
)
)
ACI 318-11 Eq. (D-25)
ACI 318-11 Eq. (D-27)
ACI 318-11 Eq. (D-22)
da [in.]
hef [in.]
ca,min [in.]
τk,c [psi]
1.000
ec2,N [in.]
15.000
cac [in.]
6.000
κbond
805
λa
αN,sels
1.00
1.000
1.000
0.000
Calculations
cNa [in.]
0.000
23.146
ANa [in.2]
ANa0 [in.2]
Ψed,Na
12.266
Ψec1,Na
1032.60
Ψec2,Na
601.80
Ψcp,Na
0.847
Nba [lb]
1.000
Results
Nag [lb]
1.000
1.000
37935
ɸbond
ɸseismic
ɸnonductile
ɸNag [lb]
Nua [lb]
55115
0.650
0.750
0.400
10747
7450
Figure 3. PROFIS anchor bond strength calculations.
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as “temperatures that occur over brief intervals,
e.g., as a result of diurnal cycling,” and long
term concrete temperatures are defined as
temperatures that are “roughly constant over
significant periods of time.”
The harmonization of AC308 with ACI
355.4 has resulted in some of the maximum
short term temperature/maximum long
term temperature values being increased.
Characteristic bond stress (τ) values are correspondingly reduced as a result of these
changes. ESRs that are 2012-compliant
are the first ESRs to include these changes.
Reference each ESR for changes specific to a
particular adhesive anchor system.
Adhesive anchor ESRs having 2012IBC compliance are used with the bond
strength provisions of ACI 318-11 to design
an anchorage in jurisdictions recognizing
IBC 2012/ACI 318-11. Adhesive anchor
design in jurisdictions recognizing previous
IBC/ACI 318 versions should also utilize
the ACI 318-11 provisions in order to be
presumed “code compliant” because (a) the
original AC308 bond strength equations
have been removed from the ESRs, and
(b) bond strength equations for adhesive
anchor design are now given in ACI 318-11
Appendix D. There has understandably
been some confusion regarding the requirement, and feasibility, of using ACI 318-11
bond strength provisions to design adhesive anchors in jurisdictions that have not
yet adopted IBC 2012/ACI 318-11. Since
AC308 (compliance January 15, 2015) no
longer contains equations for calculating
bond strength, use of the original AC308
equations given in pre-2012 IBC compliant
ESRs needs to be justified by the Engineer
of Record (EOR). When an ESR is updated,
the previous version is no longer used unless
justified by the EOR. Therefore, in order
to be presumed code compliant, adhesive
anchor design in jurisdictions still recognizing IBC 2009/ACI 318-08, for example,
should be performed using the most current (2012 IBC-compliant) ESR and the
ACI 318-11 equations unless justified by
the EOR. Pre-2012 IBC ESR bond strength
equations conflict with ACI 318-11 bond
strength equations. Therefore, use of the
pre-2012 IBC ESR bond strength equations
must be justified for use in lieu of the equations now given in ACI 318-11.
STRUCTURE magazine
32
September 2015
Other anchor calculations, such as seismic
calculations, will be based on the IBC/ACI
318 code version currently adopted by the
jurisdiction because there is nothing in the
2012 IBC-compliant ESRs that conflicts with
these code versions.
Figure 3 shows calculations performed with
Hilti PROFIS Anchor software using the data
given in ESR-3187 (revised January 2015)
for the HIT-HY 200 adhesive anchor system.
Design using the seismic provisions of ACI
318-08 Part D.3.3.6 was selected. Besides the
0.75 seismic factor defined in ACI 318-08
Part D.3.3.3, Part D.3.3.6 requires an additional factor to be applied to non-ductile design
strengths. The 0.75 seismic factor is shown
below as φseismic, and the D.3.3.6 non-ductile
factor is shown as φnonductile. Note that the calculations for nominal bond strength (Nag) are
based on ACI 318-11 Part D.5.5, but the seismic calculations are based on ACI 318-08 Part
D.3.3.3 and Part D.3.3.6. Therefore, the design
strength calculations (φNag) performed per ACI
318-08 Appendix D seismic provisions, and
the nominal bond strength calculations (Nag)
performed per ACI 318-11 Part D.5.5 are
presumed to be “code compliant”.
Summary
ACI 318-11 Appendix D now includes provisions for calculating the nominal bond
strength of adhesive anchor systems in
Part D.5.5. Prior to ACI 318-11, adhesive
anchor systems were not within the scope of
Appendix D; however, ICC-ES developed the
acceptance criteria AC308 to qualify adhesive anchor systems for recognition under the
IBC, and to design adhesive anchor systems
with the provisions of Appendix D. The original AC308 included provisions for calculating
nominal bond strength since no provisions
were available in Appendix D.
With the development of ACI 318-11 Part
D.5.5, ACI developed a test standard, ACI
355.4, to qualify adhesive anchor systems for
use with Appendix D provisions. AC308 has
been harmonized with ACI 355.4, resulting
in the only provisions recognized under the
IBC for calculating bond strength being given
in ACI 318-11 Appendix D. Revised bond
strength calculations are now based on the
projected distance from an anchor instead of
the spacing between anchors. Characteristic
bond strength values have also been revised
per the changes in maximum short term/
maximum long term temperature ranges.
Adhesive anchor design for pre-2012 IBC jurisdictions should use the provisions of ACI 318-11
Appendix D to be presumed “code compliant”
unless justified by the Engineer of Record.▪
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Guest
Column
dedicated to the dissemination
of information from other
organizations
O
n April 9-10, 2015 the Building
Information for Modeling Masonry
(BIM-M) Initiative held their first
Symposium in St. Louis, MO at the
St. Louis Masonry Center. Since the beginning, the
initiative has been following its mission statement:
To unify the masonry industry and all supporting industries through the development
and implementation of BIM for masonry
software to facilitate smoother workflows
and collaboration across all disciplines from
owner, architect, engineer, manufacturer,
mason, contractor, construction manager,
and maintenance professionals.
While the BIM-M Initiative has been progressing
for over two years, many structural engineers may
not have been aware of this major effort. This
article provides some of the highlights of BIM-M
and the symposium, and their relevance to structural engineers. It is important to remember that
the term BIM represents both an object (a model),
and a process (modeling).
Why BIM-Masonry? To
give masonry an opportunity to compete with other
building materials while
simultaneously improving
the industry. The BIM-M
Initiative began in 2012 and represents the
masonry industry in the United States and parts
of Canada.
The Symposium opened by welcoming the many
architects, structural engineers, manufacturers,
contractors, suppliers, supporters, and guests. The
audience learned that Phase II (Development)
based on the original roadmap has been completed. Phase II contained four projects; 1)
Masonry Unit Model (MUD) Definition, 2)
Masonry BIM Benchmark, 3) Masonry Wall
Model Definition, and 4) BIM-M Contractor
BIM-M Symposium:
Generation 1
By Daniel Zechmeister, P.E.
Daniel Zechmeister, P.E., is
the Executive Director of the
Masonry Institute of Michigan
and a member of the Executive
Committee of BIM-M representing
The Masonry Society. He is active
in ASTM and the Masonry
Standards Joint Committee,
which is responsible for the TMS
402 code and the TMS 602
specification. He can be reached at
[email protected].
Input. BIM-M also announced that an updated
Roadmap, a report for developing and deploying BIM for masonry, has now been posted on
the website (www.bimformasonry.org). The
proposed timeline for Phases III and IV begins
now and will run until the end of 2017 with the
completion of Generation 1.
What is Generation 1 BIM-M? Generation 1
is defined as the conceptual termination of the
BIM-M Initiative’s initial efforts to make masonry
more accessible to architects, structural engineers,
masons, contractors, manufacturers, and owners
using BIM. Some aspirations for what Generation
1 will include are:
• Masonry unit database accessible to all
BIM users.
• Masonry wall definitions for Level of
Development (LOD) with standard details.
• BIM software upgrades that achieve LOD
350 or greater for design (Figure1).
• BIM software that allows contractors
to achieve LOD 400 or greater for
construction purposes, and can detect
clashes with specific masonry features (bond
beams, grouted cells, shelf angles, etc.)
• BIM software upgrades that will operate
with other masonry specific software.
• New and/or improved design tools
(software upgrades, add-ins, plugs-ins)
that provide for modularity, early project
pricing, and masonry detailing.
Masonry Unit Model Definition
Over the course of the last two years, the BIM-M
Masonry Unit Working Group, led by Jeff Elder,
SE, Interstate Brick, HC Muddox and Western
States Clay Products developed a spreadsheet to
represent the majority of data parameters and
specification information to be used by BIM
Figure 1. LOD 350 for design.
34 September 2015
software developers for the design, purchasing,
shop drawing and sustainability of clay, CMU
and cast stone. This data set was based upon
geometric and material attributes provided
by numerous manufacturers. The physical
properties entity includes attributes for both
mechanical properties and thermal properties
of masonry units, including; weight, density,
compressive strength, modulus of elasticity,
modulus of rigidity, shrinkage coefficient,
coefficient of thermal expansion, and creep
coefficient.
For structural engineers, this means there
will be on-line access to geometrical and material properties for modeling masonry in BIM
software as well as for analytical programs that
interact with BIM.
BIM-M Benchmark
The original intent of the BIM Benchmark
project was to focus on software capabilities
and to understand the role of software in the
masonry industry at all project phases. The
Phase II project, led by Russell Gentry, PE,
Project Manager, Digital Building Laboratory,
Georgia Institute of Technology, extended
this scope to focus not only on software but
also on BIM processes, that is, how masonry
stakeholders use BIM or other tools. The primary goal was to develop a vision for “future
state” processes that can take advantage of the
Generation 1 BIM-M software. The original
proposal called for the analysis of three project
types: brick/CMU, structural masonry, and
complex masonry. Georgia Tech, along with
the University of Pennsylvania, completed
nine building case studies of various building types. The Benchmark Project focused
on three areas:
Task 1 – Framework Development
Task 2 – Process Documentation
Task 3 – Process Model Evaluation
For structural engineers, this will lead to better
interaction between analytical programs and
BIM modeling during design and construction.
Masonry Wall
Model Definition
Figure 2. Cover of 2014 LOD Specification.
to track individual masonry units in an entire
building. Therefore, the masonry BIM data
structure must include the definition of wall
types, and must provide the means to map
these wall types onto regular and irregular
regions on wall surfaces. The working group
discussed and suggested a level of development (LOD) of 350 for architects and
structural engineers.
Also, one of the four new tasks for Phase III
is to develop and publish a Best Practices Guide
for Modeling of Masonry using Autodesk Revit
in cooperation with The Masonry Society
(TMS). The Guide has a three-fold purpose,
including: 1) informing users on how current
BIM tools may be used to model masonry,
2) to define what collaboration and modeling
tools are lacking, and 3) to create a wish-list
of modeling tools that would be helpful to
the industry.
Structural engineers will have more efficient
modeling tools that will carry over into the
analytic programs.
BIM-M Contractor Input
This project is at the core of masonry BIM
and is managed by Jamie Davis, PE of Ryan
Biggs/Clark Davis through the TMS BIM
Committee. Because masonry BIM is a computational model of masonry construction,
and masonry walls are the fundamental assembly in masonry construction, it is critical that
the data representation of the masonry wall
support all of the functionality that is envisioned for BIM-M. Currently, it is simply not
computationally practical for BIM software
It has been clearly determined that mason
contractors and masons will benefit from
BIM-M. In this project, BIM-M proposes
that mason contractors explore in greater
detail the potential benefits of BIM, and document their current work processes and their
use of software in current practice. Input from
general contractors will be solicited as well,
to identify areas where general contractors
desire interaction with masonry construction in their BIM models – for example, in
coordination of masonry with structural,
STRUCTURE magazine
35
September 2015
mechanical and other building systems for
clash detection.
The keynote speaker was Will Ikerd II, PE,
from Ikerd Associates, Dallas, TX. He also
represents the BIM Forum and chairs the SEI
BIM Committee. He began his presentation
by stating BIM is about giving a “common
vocabulary”. Will discussed the various levels
of development (LODs). He pointed out that,
in 2008, an AIA document for the first time
defined LODs. In giving his opinion, he
described the LODs simplistically as:
• LOD 100 – symbolic
• LOD 200 – approximate
• LOD 300 – specific
• LOD 350 – detailed (interfaces with
other building systems)
• LOD 400 – detailing and fabrication
Will announced to the audience that the
Level of Development (LOD) Specification is
a reference that enables practitioners in the
AEC Industry to specify and articulate with a
high level of clarity the content and reliability
of Building Information Models (BIMs) at
various stages in the design and construction process. Shown on the cover of the 2014
LOD Specification are the various LODs for
masonry (Figure 2). The specification is a free
download from store.bimforum.org.
Two specific presentations came from BIM-M
consultants who are providing modeling tips
and tricks for masonry, which will be released
later this year as Best Practices Guide. BIM-M
has tasked them with demonstrating the modeling of masonry using current software and
recommending future improvements.
Best Practices #1
Presenters from the architecture and engineering firm Integrus Architecture from Seattle,
WA included Mike Adams, BIM Manager;
Morgan Weise, EIT; and Clint Bailey, AIA
showed some features of what they will be
contributing to the Best Practices Guide.
The most common masonry elements in
BIM are walls which are always modeled in
three-dimensions. However, many masonry
details are presently handled in two-dimensions. The current strategy for creating
drawings is to take the three-dimensional
model and slice it to reveal the information
that is desired.
Integrus demonstrated the three-dimensional detailing function. Because these views
are live or three-dimensional, any changes that
are made in them affect the rest of the model.
For example, BIM software typically includes
a number of pre-made families including
openings with arched tops. In the BIM-M
project, Integrus used three-dimensional
Figure 3. Three-dimensionally reinforced wall.
Figure 4. CMU wall in structural model and remaining wall layers
in architectural model.
sweeps (model elements) to represent stone
sills, lintels, and quoining.
Another example dealt with representing
reinforcement in models. The current advantages of two-dimensional reinforcement are
detail line, components or groups; fast to make
changes; and easy to export details from project
to project. The current disadvantages are an
absence of embedded information (no clash,
no scheduling and no tagging), everything
fits and no warnings as things move. Integrus
noted that the current advantages of modeling reinforcement in three-dimensions are
improved coordination, accurate schedules,
tagging, and correct warnings when things are
moved. The current disadvantages are longer
modeling time, all walls are treated equal and
an enlarged model file size (Figure 3).
StruWare, Inc
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Floor Vibration for Steel Bms & Joists ($75.00).
Concrete beams with/without torsion ($45.00).
Demos at: www.struware.com
Best Practices #2
The second BIM-M consultant was Shawn
Zirbes, Cad Technology Center (CTC) from
Minneapolis, MN. Shawn used the BIM
Forum LOD 2014 Level of Development
Specification and displayed the BIM-M for
Masonry LOD examples for levels 300, 350
and 400. Shawn showed a structural model
of the Brick Office Building with brick on
CMU backup on a portion, and brick with
metal stud backup on the remaining portion.
The model was then split into an exterior shell
model and an interior model. For both the
brick with block backup wall and brick with
metal stud backup wall, Shawn presented
the LOD 300 with a plan and section view,
respectively. He then displayed LOD 350
for the block (CMU) backup showing the
grouted cells where the CMU wall is placed
in a structural model and the remaining wall
layers (brick veneer, wall ties and drainage
panel, rigid insulation, and air barrier) are
modeled as individual wall types in an architectural model (Figure 4). With respect to
the LOD 350 for metal stud backup, all wall
layers (brick veneer, wall ties, rigid insulation, air barrier, sheathing, metal studs and
gypsum board) are modeled as individual
wall types in an architectural model. Anchor
type placement was shown for both systems
in plan and sectional view. Brick patterns were
developed as model hatch patterns showing
running bond (primary), stacked bond and
STRUCTURE magazine
36
September 2015
Flemish bond. This allows for architects and
structural engineers to check modularity in
their designs.
Contractor Software for
Use by Engineers
Bill Pacetti and Bill Pacetti, Jr., from
Tradesmen’s Software, Inc., Morris, IL,
presented their software. This software was
developed for mason contractors but has
features that could be valuable to architects
and structural engineers including cost
estimating, evaluating aesthetics by varying
units, checking dimensions for modularity
of units, and more.
BIM-M and
Structural Software
In Phase III, BIM-M will start a new project
associated with structural engineering. In an
attempt to improve modeling techniques and
interoperability of analytical software with
BIM authoring tools, consultants will be
selected to examine various software packages
and their use with BIM packages. Structural
engineers interested in being considered for
this work should contact BIM-M through
its website.
While this article has provided an overview,
free downloads of videos, presentations and
reports for BIM-M are available from the
website also.▪
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Performance
performance issues relative
to extreme events
T
his article identifies common errors
that structural engineers make when
performing seismic design and calculations. The intent is to help engineers
avoid those errors and misapplications. This
article is written in checklist format such that
an engineer can verify adequate self-knowledge,
as well as review the work of others on a project. It is based upon the 2012 International
Building Code (IBC), the American Society of
Civil Engineers’ ASCE/SEI 7-10, the American
Concrete Institute’s ACI 318-11, the American
Institute of Steel Construction’s AISC 360-10,
AISC 341-10, and other current standards. For
ease of identification, referenced sections are
noted in brackets and refer to ASCE/SEI 7-10
section numbers, unless otherwise noted.
diaphragms, walls, etc. However, in addition to
those specifics, the engineer is required to provide a continuous load path for all inertial forces
from their origin to the foundation. Such load
paths must conform to the relative stiffness and
strength of the elements that exist in the structure.
See [12.1.3].
1) Seismic Design Category A
4) R Factor
When in seismic design category (SDC) A, it
is not necessary to use any of the provisions of
Chapter 12. Instead, the
general structural integrity provisions of Section
1.4 apply. Note that these
provisions include some
loads that may often be
erroneously neglected.
The required lateral forces include 1% of dead
load, 5% of dead plus live load for beam (axial
load) connections, and 20% of wall weight for
wall connections. Non-structural components in
SDC A are exempt from seismic design requirements. See [1.4], [11.4.1], and [11.7].
The response modification coefficient, R, is
part of a concept where an elastic design may
be performed, but with due consideration of
the overstrength and ductility inherent in the
lateral force resisting system. In order to ensure
reliability, many requirements are triggered with
each R factor. The “R” Tables, [Table 12.2-1] and
[Table 15.4-1, 2], list the corresponding detailing requirements. The “strings attached” can
be extremely significant, especially for concrete
structures that fall under ACI 318-11 Chapter 21
and steel structures with R greater than 3 (AISC
341 Seismic).
The Most Common Errors
in Seismic Design
… & How to Avoid Them
By Thomas F. Heausler, P.E., S.E.
2) Importance Factor
Thomas F. Heausler, P.E., S.E.
([email protected]), has 33
years of experience in structural
and seismic engineering and
has been a voting member of
ASCE/SEI 7 Seismic Provisions
since 2006. He provides seismic
expertise and senior review to
engineering firms for building
and industrial projects.
The importance factor is based upon the risk
category and the associated life safety, hazard
or essential nature of the structure. Both [Table
1.5-1] and [IBC Table 1604.5] should be reviewed.
A typical building can sometimes evolve into
an Ie equal to 1.25 or 1.5 when occupancy or
use expands. Examples include relatively small
churches (expanding to an occupancy greater than
300) or a building where hazardous materials are
stored. It should be noted that for building design,
Ie = 1.0, 1.25, or 1.5; but for non-structural components, Ip = 1.0 or 1.5 only [13.1.3], such that
Ip may not equal Ie, and in some instances Ip may
be less than Ie. See [11.5.1] and [Table 1.5-2].
3) Continuous Load Path
ASCE/SEI 7-10 has very specific provisions for
many elements such as collectors, connections,
… a checklist to verify
self-knowledge as well as
check the work of others
on a project.
5) Irregularity Triggers
[Table 12.3-1] and [Table 12.3-2] describe various
horizontal and vertical irregularities, respectively,
which trigger specific provisions. Each referenced
section must be reviewed. Triggered provisions
include modal analysis, three-dimensional analysis, redundancy factor, force amplification, torsion
amplification, and collector force increases. See
[12.3.2.1] and [12.3.2.2].
6) Overstrength – Ωo
The variable Ωo is an amplification factor
applied to the forces in certain elements in
the seismic load path. It is required so as to
prevent a weak link from occurring prior to the
full energy dissipation and ductility potential of
the primary lateral-force-resisting system. For
example, in a steel braced frame, in order for
the diagonal brace to yield and dissipate energy
in a controlled and reliable manner, all other
portions of the load path (e.g., connections,
When you select an R factor from the Table, you are
obliged to implement the associated “strings attached.”
38 September 2015
bolts, welds, gusset plates, anchor bolts,
columns and collectors) need to be stronger
than the maximum anticipated strength or
force in the brace. Therefore, Ωo amplification and load combinations are specifically
triggered for those elements, in the sections
mentioned below and in Material Standards
such as AISC 341-10 and ACI 318-11. For
example, AISC 341-10 states that anchor
bolt forces must be amplified by Ω o, which
is typically 2.0 or greater. This applies to
all steel buildings where R is greater than
3, unless you can prove otherwise via
an advanced and rigorous analysis. See
[12.4], [12.2.5.2], [12.10.2.1], [12.3.3.3],
[12.13.6.5], and [AISC 341 when R>3, ACI
Chapter 21, Appendix D, etc.].
7) Redundancy – Rho
Rho is a factor that penalizes structures that
do not have redundancy. Rho is equal to either
1.0 or 1.3. Rho is equal to 1.0 for SDC B
and C, for drift calculations, non-structural
component forces, collectors, Ωo load combinations, and diaphragms. See [12.3.4].
8) Vertical Seismic Load Effect – Ev
[12.4.2.2] requires that a vertical load effect
equal to 0.2 SDs be applied to dead load. It is
applied as a dead load factor adjustment and
…anchor bolt forces shall be multiplied by
Ωo, which is typically 2.0 or greater.
may act downward or upward. It is at the
strength design level, so it may be multiplied
by 0.7 for allowable stress design (ASD). The
values of Ie, Ip, Rho and R are not applied
to Ev.
SDC D, E, and F be considered with 100% of
forces in one direction plus 30% in the other.
It should be noted that IEEE 693 (Electrical
Equipment) applies orthogonal effects to all
elements, including corner anchor bolts.
9) Load Combinations and Allowable
Stress Design – 0.7 E
11) Effective Seismic Weight
For ASD load combinations [12.4.2.3],
[12.4.2] shall be used in lieu of [2.3.2] and
[2.4.1]. Earthquake forces are at strength
level, so for the ASD combinations, use 0.7
E. The 0.7 E applies to non-structural component forces (Fp). See [13.3.1].
10) Orthogonal Effects
Earthquake forces must be calculated for each
of the two primary orthogonal directions. In
order to consider the effects of earthquake
forces at some angle other than those two
directions, “orthogonal effects” must be
considered. [12.5] requires that irregular
buildings in SDC C and corner columns in
[12.7.2] defines the effective seismic weight,
W. Except for as mentioned below, live load is
not included in the inertial force; however, the
seismic force is later combined with dead and
live loads in the load combinations. [12.7.2]
stipulates that W must include the following
masses: 25% of storage live load, partition load
of 10 psf [4.3.2], industrial operating weight
and unbalanced conditions, 20% of snow if
greater than 30 psf, and weight of roof gardens.
12) Distribute Base Shear over Height
Once the base shear, V, is calculated, it must
be distributed over the height of the structure.
For a one-story building, all of the base shear
would be applied at the roof. For multi-story
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September 2015
6/10/2015 6:37:49 PM
structures, the base shear must be distributed
to each floor, not only in proportion to each
floor’s mass, but also in proportion to the
distance of the floor from the base. A triangular distribution of force results for regular
multi-story buildings. For distributed-mass
structures like stacks and masonry fences, the
centroid of the load should result at 2/3 of the
height above the base, not at ½ the height or
at the center of gravity. See [12.8.3].
13) Modal Response Spectrum Analysis
When a structure has significant vertical or
horizontal irregularities, the equation [12.812] (triangular force distribution) becomes
inaccurate, and therefore a modal response
spectrum analysis is required. See [12.6],
[Table 12.6-1] and [12.9]. The purpose is
not to refine the magnitude of the base shear,
but to perform the following more accurately:
1) Distribute base shear over height.
2) Quantify horizontal torsional effects.
3) Account for higher mode effects.
Note that the “NP” entry in [Table 12.6-1]
includes many common irregularities, including horizontal type 1a, 1b and vertical type
1a, 1b, 2 and 3, and thus a modal analysis is
triggered for those structures.
14) Accidental Torsion
In addition to inherent torsion, accidental
torsion must be applied. This is to prevent
weak torsional resisting arrangements, as well
as account for unexpected distribution of live
load and unexpected stiffness of structural
and non-structural elements. This provision
applies to non-building structures, as well as
buildings. For torsionally irregular buildings,
amplification of the accidental torsion may
be required as per [12.8.4.3]. See [12.8.4.2].
15) Drift Check
Results from the elastic analysis must be
amplified by Cd to render expected deflections. Note that Cd is a very large value,
typically a factor of about 4 or 5. The drift
is then divided by Ie, because the allowable
drifts are organized into a table that considers
risk category. One should be careful when
using ASD load combinations not to apply
the 0.7E to drift calculations. See [12.8.6],
[12.12], and [Table 12.12-1].
16) Diaphragm Forces
Forces at lower floor diaphragms may be
higher than those used for the lateral force
resisting system [Equation 12.8-12]. This
is due to higher mode effects (i.e., modes
higher than the first mode) where the lower
floors may be accelerating higher than calculated. Note that Fpx minimums of [Equation
12.10-2] often govern for the lower floors.
See [12.10.1.1].
17) Non-structural Components
Non-structural components may also experience higher local accelerations due to higher
mode effects, as well as amplification of the
force within the non-structural element itself.
See [Equation 13.3.1]. Industrial structures
often feature very large forces. It is unlikely
that the forces on two different floors would
occur at the same point in time. Therefore,
one method of accounting for the forces in a
computer model is to evaluate two conditions.
1) Run a load case with the weight
of the equipment included in the
seismic weight of the floor and the
base shear, V, distributed over the
height as per [Equation 12.8-12].
2) Run a load case with only the nonstructural component force for one
piece of equipment, so as to verify
an adequate load path to the vertical
system and/or foundation.
Note that it is necessary to apply Ev
to load combinations with nonstructural component forces. The
factor Ωo does not apply to such load
combinations, except in some ACI
318-11 Appendix D calculations.
Note also that when non-structural
components get very large – i.e.,
25% or more of total structure mass
– then [15.3] provisions apply. For
these heavy components, the stiffness
and design coefficients of both the
component and the primary structure
must be considered together in a
computer model.
18) Wall Design
Connections to wall panels made of concrete
and concrete masonry units (CMU) have
performed poorly in past earthquakes. The
equations of [12.11.1] and [12.11.2.1] should
be implemented, as well as ACI 318-11
Appendix D for anchorage.
19) Foundation Ties
Foundation ties are required as per [12.13.6.2]
in order to ensure that the foundation system
acts as an integral unit, not permitting one
column or wall to move appreciably relative
to another. This applies to pile caps in SDC
C, D,E and F, and spread footings for SDC
E and F.
20) Reduction of Foundation
Overturning
[12.13.4] allows for a reduction of the bearing pressures at the soil-foundation interface.
STRUCTURE magazine
40
September 2015
Forces may be reduced by 25% in recognition
that the first mode triangular force distribution will likely not occur without higher mode
effects occurring and negating the direction of
the first mode, resulting in reduced maximum
overturning moments.
21) Errata
The ASCE/SEI 7-10 and IBC 2012 websites
have the latest errata for those documents.
Significant entries due to typographical mistakes or unintended consequences of revisions
are corrected in the errata.
22) IBC Overrides
IBC 2012 contains amendments to ASCE/
SEI 7-10. See [IBC 1613], [IBC 1613.5],
and [IBC Chapters 18 through 23]. ASCE/
SEI 7 is on a six-year update cycle, and IBC
is on a three-year cycle. Technical changes
to IBC often have to be approved well
before the issue date. Inevitably, coordination between ASCE 7, IBC and referenced
material standards (e.g. ACI, AISC, etc.)
often occur through errata, supplements
or IBC-published amendments. It is essential to check for these changes periodically.
Individual state and local governments may
also adopt amendments that affect projects
located within their jurisdiction.
23) ASCE/SEI 7-10 Third Printing
It is recommended that the user make use
of the ASCE/SEI 7-10 Expanded Seismic
Commentary, which provides 135 pages
of valuable background information. It is
incorporated in the third printing of ASCE/
SEI 7-10 only. For those who own a first or
second printing, you may download a PDF
file of the commentary for free from the
ASCE website. This Commentary was developed by the National Earthquake Hazard
Reduction Program/Building Seismic Safety
Council/Provisions Update Committee
(NEHRP/BSSC/PUC) and describes the
reasons for the individual provisions of
ASCE/SEI 7-10.
Conclusion
A concerted effort to avoid errors is essential. Errors can be minimized by applying
knowledge and experience. This article is
intended to assist in that effort. The above
listing of common errors was developed
by the author during frequent reviews of
other engineers’ work. It is based upon the
author’s experience and should not be construed as a consensus document prepared or
endorsed by the ASCE/SEI 7-10 or NCSEA
Seismic Committees.▪
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Take Your Practice to New Heights at the
2015 Structural Engineering Summit
National Council of Structural Engineers Associations
September 30 – October 3rd
Red Rock Resort Las Vegas, NV
th
STAY CONNECTED BY USING THE HASHTAG #NCSEASummit
Wednesday, September 30
8:00 – 5:00
8:00 – 12:00
5:30 – 6:30
6:30 – 8:30
evacuation refuge structures, based on the new ASCE 7-6 chapter Tsunami
Loads & Effects.
Gary Chock is Chair of the ASCE 7 Tsunami Loads and Effects Subcommittee that in
2015 completed the first national standard for tsunami-resistant design for the upcoming
2016 edition of the ASCE 7 Standard.
Committee Meetings
NCSEA Board of Directors Meeting
Young Engineer Reception
SECB Reception
B.) Effective Communication: Tips for
Improving Your Skills
Thursday, October 1
7:00
8:00
Delegate Interaction Meeting
Welcome & Introduction
Kirsten Zeydel, S.E., President, ZO Consulting and
Annie Kao, P.E., Field Engineer, Simpson Strong-Tie
8:15 – 9:30
Keynote
STRUCTURAL ENGINEERING:
The Profession, The Grandeur, and The Glory
Ashraf Habibullah, S.E., President & CEO,
Computers & Structures, Inc.
Ashraf brings into focus the invaluable socio-economic contributions of
structural engineering by recognizing its unmatched impact on humanity.
He will highlight the ways in which the intellect and talent of structural
engineers have literally saved hundreds of millions of lives, spared us from
death and destruction, and preserved and protected progress and property.
Ashraf Habibullah is a registered Civil and Structural Engineer who founded CSI in 1975
and has led the development of CSI’s products, including SAP2000 and ETABS, for the last
four decades. CSI’s software is used by thousands of engineering firms in over 160 countries.
9:45 – 11:00
Basis for ASCE 7 Seismic Design Maps
ASCE 7-10 and IC-2012 introduced the concept of risk-adjusted Maximum
Considered Earthquake (MCE-R) shaking derived to produce a 1% chance
in 50 years that buildings will experience earthquake-induced collapse. As
compared with older MCE definitions, this resulted in reduction of design
ground motions in much of the U.S. while assuring design risk comparable
to that already accepted in the Western U.S. The basis for this change and
its significance are presented.
NCSEA Past President and Past Code Advisory Committee chair, Ron Hamburger,
is Senior Principal with Simpson Gumpertz and Heger in San Francisco and the current chair of the ASCE-7 Committee. He is presently chairing a joint USGS-BSSC
planning committee, formalizing plans to develop a new generation of seismic risk maps
for the building codes.
11:00 – 12:00
Building Rating, Retrofit Ordinances, and
Community Resilience
A.) Wood & Cold-Formed Light Steel
Frame Construction – Deficiency in
IBC Special Inspections
The session will compare light frame construction inspection
requirements to other structural systems, identify the areas of deficiency in
the Code, and present strategies to address these deficiencies.
Kirk Harman is President and Managing Principal of The Harman Group, headquartered in Philadelphia, PA. He served for 10 years as Chairman of the NCSEA
Code Advisory Committee’s sub-committee on Special Inspections.
B.) Find the Lost Dollars:
6 Steps to Improve Profits
June Jewell, CPA, AEC Business Solutions
Learn to get the most from people, processes and technology
to gain a competitive edge. June Jewell will show you how to
improve your firm’s performance and prepare the firm’s future leaders to
successfully take the reins.
June Jewell is a speaker and business management consultant to the A&E industry, and
author of Find The Lost Dollars: 6 Steps to Increase Profits in Architecture, Engineering,
and Environmental Firms.
Concurrent Sessions 4:00 – 5:00
Panel from Structural Engineers Association of California
Moderator: Ryan A. Kersting, S.E., Associate Principal
Buehler & Buehler Structural Engineers, Inc.
A.) Changes to Wind Loading in ASCE 7-16
Don Scott, S.E., PCS Structural Solutions
The panel will discuss building rating systems, performance based design,
renewed efforts for retrofit ordinances, and emerging concepts of community resilience that have launched a wave of discussions, innovations,
and political involvement by California’s structural engineering community.
Concurrent Sessions 1:00 – 2:15
A.) The ASCE 7-16 Tsunami Loads Design Standard
The session will provide an overview of the technical basis
and methodology for tsunami-resilient design of critical
and essential facilities, taller building structures and tsunami
STRUCTURE magazine
Concurrent Sessions 2:45 – 3:45
Kirk Harman, P.E., S.E., SECB, President, The Harman Group
Ron Hamburger, P.E., S.E., SECB, Senior Principal,
Simpson Gumpertz & Heger
Gary Chock, S.E., President, Martin & Chock
Instant communication – email, Facebook, LinkedIn, Twitter,
Snapchat, and more – doesn’t mean that we are communicating effectively.
You will hear concrete tips to improve your written, verbal, and non-verbal
communication skills.
Kirsten Zeydel has over 15 years of experience leading over 200 projects and is the
President of ZO Consulting, Inc. located in Orange, CA. ZO Consulting specializes in
cold-formed steel and evaluating/coordinating exterior facades .
Annie Kao is a field engineer for Simpson Strong-Tie, where she connects with and educates
engineers, architects, building officials, and contractors on design and product solutions
for wood, concrete, steel, and masonry construction in the Southwest region of the U.S.
This session will identify significant changes to the wind load
provisions of ASCE 7-16 and the rationale for these changes.
These include new wind speed maps, changes to component
and cladding pressure coefficients, expanded commentary on tornado design,
and more.
Don Scott has been a member of the ASCE 7 Wind Load Committee since 1996 and currently serves as chair, shaping future IBC provisions for wind design. He is also a member of
the ASCE 7 General Provisions committee and the ASCE 7 Steering Committee, Chairman
of the NCSEA Wind Committee and Past-Chair of the SEAW Wind Load Committee.
42
Register today at www.ncsea.com!
September 2015
B.) BIM and Structural Engineering
Desiree Mackey, P.E., S.E., BIM Manager, Martin/Martin
What is the future of Building Information Modeling (BIM) in
structural engineering? This session will cover the processes,
collaboration, and coordination with clients and other project
participants, with an open forum for questions.
Desirée (Dezi) Mackey is the BIM Manager at Martin/Martin, Inc., in Denver. Dezi
has been using Revit for most of her career, and she is extremely active in the BIM community as a regular speaker at conferences, co-founder of the Rocky Mountain Building
Information Society, and Chair of SEAC’s BIM Committee.
Welcome Reception on Trade Show Floor
(Red) Rock ‘n’ Bowl with NCSEA
6:30 – 8:30
8:30 – 11:30
Friday, October 2
8:00 – 10:00
8:00 – 10:00
Member Organization Reports
Vendor Product Presentations
Cliff Schwinger is a Vice President and Quality Assurance Manager at The Harman
Group. He serves on the AISC Manuals Committee and has over 30 years of experience
designing building structures.
Concurrent Sessions 2:45 – 3:45
A.) Concrete & CMU Elements in
Bending + Compression
John Tawresey, S.E, retired, KPFF Consulting Engineers
John Tawresey will present the applied mechanics equations
for cracked elements subject to bending plus compression in
a form more understandable for the practicing engineer and will then relate
these to the latest masonry and concrete code requirements.
JohnTawresey is a past president of The Masonry Society, past president of the Structural
Engineers Risk Management Council (SERMC), past chair of the SERMC Claims
Committee, past president of SEI and current member of the ASCE 7 Main Committee
and TMS 402/602 Main Committee.
B.) The Decline of Engineering Judgment
Jon Schmidt, P.E., SECB, Associate Structural Engineer,
Burns & McDonnell
Concurrent Sessions 10:15 – 11:30
A.) Lateral Design of Buildings with
Sloped Diaphragms
Steven Call, P.E., S.E., Call Engineering
Buildings constructed with slope roof diaphragms are often
designed as if they had a flat roof diaphragm. The significant
differences between the lateral designs of sloped vs. flat diaphragms will be
presented, including the proper diaphragm depth, the effect on the wall-todiaphragm connection, and the effect on the design of shear walls with a
sloped connection to the diaphragm.
Steven Call has over 25 years of experience in structural design of buildings, including
17 years as the president of Call Engineering, and is an instructor on design and analysis
of diaphragms for Boise State University.
Modern society increasingly embraces theoretical knowledge
and technical rationality – i.e., science and technology – while
downplaying practical judgment. For structural engineers, this is especially
evident in the constantly growing size and complexity of the codes and standards. Jon Schmidt will discuss the implications, unintended consequences,
and potential alternatives.
Jon Schmidt is an associate structural engineer at Burns & McDonnell. He chairs the
editorial board for STRUCTURE magazine and authors a bimonthly “InFocus” column
in which he often explores the relationship between philosophy and engineering.
Concurrent Sessions 4:00 – 5:00
A.) Creative Problem Solving for Repairing
Wood Structures
B.) Working with Multiple Generations
Panel Discussion with the NCSEA Young Member Group
Support Committee
Moderator: Emily Guglielmo, S.E., Associate,
Martin/Martin Inc.
Structural engineering firms find themselves managing four generations of
employees, while working to attract, train and retain staff. This session will
explore differences and similarities between generations, ways to leverage
their uniqueness, and suggestions for successful integration of a multigenerational workplace.
Kimberlee McKitish, P.E., Nutec Group
Kimberlee McKitish will showcase four mini-case studies with creative solutions to wood repair issues. The
case studies will look at the problems encountered, alternative repair
options, and the thought process that led to the chosen solutions.
Kim McKitish is a structural engineer with NuTec Design Associates, Inc. A licensed
professional engineer, her area of expertise is in the design, repair, and reuse of manufacturing and industrial buildings.
B.) Business Ownership Transfer
Craig Barnes, P.E., SECB, Founding Principal, CBI Consulting
Concurrent Sessions 1:00 – 2:30
A.) Lateral Analysis: Right Way/Wrong Way
with Software
Sam Rubenzer, P.E., S.E., Structural Engineer, FORSE Consulting
Lateral load requirements and corresponding analysis methods
continue to increase. Sam Rubenzer will discuss the key points
in lateral analysis when using different software, and will guide engineers
regarding what is right and what is wrong in modeling loads.
Sam Rubenzer founded FORSE Consulting in 2010 and has been assisting other
structural engineers with, and comparing the attributes of, an assortment of structural
engineering design software.
B.) Quality Assurance for Structural
Engineering Firms
Craig Barnes and a likeminded structural engineer started CBI
Consulting Inc. in 1984. In 2002 he designed and implemented
a detailed buyout transition program with two of his long-term
employees, to enable them to continue operations of what is now a multidiscipline engineering consulting firm. This presentation will be of benefit
to attendees looking toward, or involved in, ownership transfer.
Craig Barnes worked for a structural engineering firm, an architectural firm, and a national
multi-disciplined consulting firm before joining with a fellow engineer to start and grow a
new firm to an engineering architectural company with 35 employees.
6:00 – 7:00
7:00 – 10:00
Cliff Schwinger, P.E., SECB, Vice President & Quality
Assurance Manager, The Harman Group
BIM modeling, sophisticated analysis and design software,
increasingly complex building codes and young engineers taking on more
responsibility earlier in their careers, all emphasize the need for a formal inhouse Quality Assurance program. This seminar reviews the components
of a model Quality Assurance program, as well as the methodologies for
performing in-house Quality Assurance reviews.
STRUCTURE magazine
Awards Reception
(formal attire encouraged, but not required)
NCSEA Banquet & Awards Presentation,
featuring the NCSEA Excellence in Structural
Engineering Awards and the NCSEA Special
Awards (see pages 76 – 77 for honorees)
Saturday, October 3
8:00 – 12:00
12:30 – 2:00
43
NCSEA Annual Business Meeting
NCSEA Board of Directors Meeting
September 2015
Take Your Practice to New Heights at the
2015 Structural Engineering Summit
Trade Show Hours: Thursday, October 1st – 10 a.m. to 3:30 p.m. & 6:30 to 8:30 p.m.
Friday, October 2nd – 7 a.m. to 12 p.m.
(###) Booth number
Denotes NCSEA membership
(138) AISC
(114) Simpson Strong Tie
(135) Alpine ITW
(106) Star Seismic
www.aisc.org
www.strongtie.com
www.trussteel.com
www.starseismic.net
www.concrete.org/
www.sdi.org/
www.armadillonvinc.com
www.steeljoist.org
www.atlastube.com
www.steeltubeinstitue.org
www.azzgalv.com
www.strand7.com
www.bekaert.com/building
www.cscworld.com
www.herculesbolt.com
www.usg.com
www.castconnex.com
www.valmonttubing.com
www.corebrace.com
www.vector-corrosion.com
www.dlubal.com
www.nucor.com/products/products/matrix/
www.euclidchemical.com
www.vulcraft.com
www.fabreeka.com
www.vulcanmaterials.com
(120) Steel Deck Institue
(143) American Concrete Institute
(119) Steel Joist Institute
(134) Armatherm (armadillo)
(140) Steel Tube Institute
(126) Atlas Tube
(144) Strand7 PTY LTD
(125) AZZ Galvanizing
(149) TEKLA/CSC Inc
(108) Bekaert
(141) USG
(146) Blind Bolt
(131) Valmont Tubing
(129) Cast Connex Corporation
(130) Vector Corrosion Technologies
(137) CoreBrace Buckling Restrained Braces
(136a) Verco Decking, A Nucor Co.
(117) Dlubal Software, Inc
(136b) Vulcraft-Nucor
(128) Euclid Chemical
(139) Vulcan Materials Company
(127) Fabreeka International INC
(123) Fyfe Co./Fibrwrap Construction
Please visit www.ncsea.com for the most current list of exhibitors.
www.fyfeco.com
(115) Geopier Foundation Company/TENSAR
www.geopier.com
Reserved
(122) Hilti
www.us.hilti.com/engineering
100
101
102
Available
103
104
105
106
107
(133) Holcim Inc
www.holcim.us
113
112
111
110
109
108
114
115
116
117
118
119
(121) Lindapter
125
124
123
122
121
120
(118)Meadow Burke LLC
126
127
128
129
130
131
(116) Independence Tube Corporation
www.independencetube.com
(124) ITW Red Head, Ramset and Buildex
www.itwredhead.com
www.lindapterusa.com
133
Entrance
www.meadowburke.com
132
(107) MiTek, USP Connectors, Hardy Frame
www.mitekbuilderproducts.com
141
(132) Nemetschek Scia
140
134
www.nemetschek-scia.com
149
(147) New Millennium Building Systems
148
147
146
142
139
www.NEWMILL.com
135
(142) Powers Fasteners
www.powers.com
(148) RISA
www.risa.com
143
138
144
137
136a
(145) Side Plate Systems
www.sideplate.com
145
STRUCTURE magazine
44
September 2015
136b
BAR
National Council of Structural Engineers Associations
September 30th to October 3rd
Red Rock Resort Las Vegas, NV
Sponsors
NCSEA extends its appreciation to the sponsors
of the NCSEA Annual Conference.
Platinum
Gold
Copper
Registration
Contributing
Full conference registration includes:
AZZ Galvanizing Services
• 17 educational sessions & resources on 2 tracks, geared
toward the practicing structural engineer
• Wednesday evening receptions
• Thursday’s Gala Opening Reception
• All breakfasts, lunches & refreshment breaks
• Access to the NCSEA Trade Show
• The NCSEA Awards Banquet, featuring the
Excellence in Structural Engineering Awards and
NCSEA Special Awards
Conference Hotel
The Red Rock Resort is located just 10 miles from the
Las Vegas strip. Enjoy 4-diamond accommodations,
the unmatched combination of comfort, extravagance
and value for just $180/night + the discounted resort fee
of $15. Reserve your room online at www.ncsea.com
to take advantage of the group rate. Please contact
NCSEA if you have trouble securing a room.
Transportation to Hotel
There will be plenty of opportunities to network with
structural engineers from across the country at the
sessions and these special events:
The hotel is accessible by shuttle from the McCarran
Airport. The complimentary shuttle is included in
your $15 resort fee.
• Young Engineer Reception
• SECB Reception
• NCSEA Red Rock ‘n Bowl Event on Thursday
More than just a conference hotel!
Whether you like gambling, entertainment, shopping
or outdoor activities, the Red Rock area of Las Vegas
has you covered!
The host hotel, Red Rock Resort & Casino, features
restaurants, lounges, a movie theatre and bowling alley,
and a walkway to Downtown Summerlin, with shops,
dining and entertainment options. If you want to check
out The Strip, the hotel has a shuttle to take you there.
If you prefer outdoor options, a high desert wonderland
is located just minutes from the hotel.
Special Offers!
Engineers 35 years of age or younger pay only $250 for complete
registration, which also includes special Young Engineer activities.
First-Time Attendees to the NCSEA Annual Conference pay only $600.
STRUCTURE magazine
REGISTER TODAY!
Reservation information is available at www.ncsea.com.
45
September 2015
606
West 57th street,
New York
Design of Structurally-linked
Multiple Tower Structures
By Sunghwa Han, P.E., S.E., LEED AP
T
he behavior of structurally-linked multiple tower structures is largely affected by the effectiveness of the rigid
links made between towers at the bases or at the tops.
These links have a strong influence on the distribution of
wind and earthquake loads. Depending on the interactive dynamic
behavior of the adjacent building parts with one another, a separation may or may not be needed. If the links are rigid enough, then
two linked towers can be considered to be one integral structure.
But if the links cannot be made strong enough, one might consider
placing a separation joint.
Project Description
The project consists of a shared base with two levels below grade and
two residential towers (1.2 million square feet of gross building area
holding 1,028 apartments): a 42-story tall tower on the east and a
17-story tall tower on the west side of the site. The two towers are
connected by a shared podium below the 7th floor, and the podium
footprint is enlarged below the 2nd floor. These two towers are structurally separate above the 7th floor. However, the occupants of the two
towers require access between the two at every floor. Therefore, there
is a separate, 10-story tall, 7-foot wide and 30-foot long cast-in-place
concrete “bridge” structure (the west bridge) between two towers.
This bridge structure will provide a continuous means of egress for
each floor of the 17-story west tower.
STRUCTURE magazine
Figure 1. Building perspective (south elevation).
The 42-story east tower is comprised of three sections (Figure 1).
Two towers emanate from the 2nd floor, and each rises up to the 28th
floor on the east side of the site. On top of these two towers, there
is an additional 13-story tall building section rigidly connecting
the two towers above the 28th floor. The two eastern towers are 30
feet apart below the 28th floor and have another seven-foot wide
46
September 2015
Figure 2. Site plan.
and 14-inch thick concrete slab pedestrian corridor-bridge (the
east bridge) connecting them at every floor from the 3rd floor to
the 28th floor. The corridor bridges are fixed to one tower but rest
on sliding bearing pads on the other tower. This allows the two
eastern towers to sway independently of one another from the 3rd
floor to the 28th floor.
The ground level gently slopes down to the west in the site. Thus, a
portion of the ground floor is exposed above grade at the southwest
corner of the site. Top of rock elevation gradually slopes to the west,
but drops drastically at the northwest corner of the site. Spread footings
or excavated piers resting on an allowable bearing capacity of 40 tons
per square foot (tsf ) bedrock was recommended in the eastern portion
of the site. The site is surrounded by the existing low-rise buildings
ranging in height from three to seven stories tall. Most of the existing
buildings are planned to be underpinned except the relatively newer
buildings at the west end of the site. These buildings were found to
be supported by caissons. The structure will also have caissons in this
western portion of the site, where the top of rock elevation is low.
Structural System of Towers
A combination of cast-in-place concrete (CIP) shear walls and 10-inch
thick flat plates supported by CIP columns and shear walls is utilized
to resist gravity loads, wind loads and earthquake loads. Some of the
tower columns need to be transferred to accommodate a variation in
the architectural layouts.
The main elevator core located in the middle of the site (one of two
eastern towers – Figure 2) provides vertical transportation for occupants
of other towers. This main core is constructed with concrete shear walls.
It is the primary source of the overall building stiffness, resisting the
lateral loads and reducing the calculated displacements of the east tower.
The seismic load resisting system of the buildings is defined to be a
“Shear wall-Frame Interactive System with Ordinary Moment Frames
and Ordinary Reinforced Concrete Shear walls” per the New York City
Building Code (NYCBC) 2008. This system allows utilizing frame
elements as a part of the seismic load resisting system for a building
with a seismic design category B rating. It was beneficial to consider
contribution of frames in the seismic load resisting system to reduce
the calculated building displacements.
STRUCTURE magazine
Structural System of Two Bridges
and Separation Joints
Originally, both bridges (west and east) were designed as a concrete
slab pedestrian corridor-bridge fixed to one tower and supported on a
sliding connection resting on the other tower at every floor. The lateral
displacements of each tower were calculated, and the largest relative
displacement was used to determine the distance of the separation
joint for these elements shared by the adjacent towers.
The displacements due to wind loads were calculated using the results
from the wind tunnel test performed by Rowan Williams Davies &
Irwin Inc. (RWDI). The elastic displacements due to the seismic loads
were also calculated based on the elastic dynamic analysis (response
spectrum analysis). These calculated displacements were magnified
using the deflection amplification factor of Cd = 5 for Shear Wall-Frame
Interactive System to compute the inelastic maximum displacements
as per ASCE 7. These calculated inelastic maximum displacements
were significantly larger than the displacements due to the wind loads.
The required distance of separation joints was calculated to be 2
inches at the sliding connection of the east bridge and approximately
9 inches at the sliding connection of the west bridge, assuming
two towers can be moving in opposite directions at the same time.
The 2 inches of movement can be easily accommodated, but the
9 inches seismic separation requirement became a critical issue to
the cladding design.
Code Requirements for Building Separation
The building code allows the use of alternate methods to compute
the distance of separation gaps which generally produce preferable
results. When considering a seismic separation at the lot line, it is
acceptable to set back structure from the property line by 1 inch for
every 50 feet in height according to the NYCBC 2008 for structures
assigned to seismic design category A, B or C (the project building
is assigned to Seismic Design Category B). This section of the code
may be applied to separate structures, assuming that the provided
separation is sufficient enough to avoid significant damage to the
adjoining structures.
47
continued on next page
September 2015
The design team has adopted a more advanced analysis method
(Nonlinear Response History Analysis – NLRHA) to ensure the
sufficient separation gap between adjacent structures. The structural system of the west bridge was modified to become a separate
ten story tall structure consisting of a 14-inch thick flat plate and
four corner columns supported by the transfer beams at the 7th
floor. This independently supported west bridge structure, with
separation gaps at both ends, would be able to accommodate
larger differential movements of two adjacent towers than the
previously considered system (a flat plate supported on a sliding
connection at one end).
A 6-inch seismic gap (magnified by less than Cd) is tentatively
provided at both ends of the west bridge. This will allow 3½ inches
of movement of the buildings, after the compressible material in the
gap joints is fully compressed. This net 3½ inches of separation has
been verified through the recent NLRHA.
1
Period Range
of Interest
(0.72 sec – 5.4 sec)
Spectral Acceleration (g)
0.1
0.01
Development of
Ground Motion Time Histories
Initially, the site-specific seismic design spectra were developed for
design of the structures. For NLRHA, three sets of ground motion
time histories consisting of two horizontal components were provided by Amec Foster Wheeler, Environment & Infrastructure,
Inc. Three sets of seed time history (1999 Chi-Chi Earthquake)
were selected. Then, these time histories were scaled to match
their response spectra with the site-specific design response spectrum as per Section 16.1.3.2 of ASCE 7-10 Chapter 16. This
design spectrum (Figure 3) represents the Maximum Considered
Earthquake (MCE) with a mean recurrence interval of 2475 years
(2% probability of exceedance in 50 years).
606 West 57th Street
Target
Average of SRSS
GRN180
GRN270
KAU078N
KAU078W
TAP078N
TAP078W
0.001
0.01
0.1
Period (Sec)
1
Figure 3. Comparison of response spectra and 3 sets of scaled time histories
prepared by Amec.
Estimating Required Seismic Separation
The Nonlinear Time History Analyses were performed using Perform
3D, a commercial analysis software which considers material nonlinearity. The analysis model on Perform 3D includes the cellar floor
excluding foundation walls. The flat plates were modelled as slab-beam
elements with an effective width reduced from a full panel width as
recommended in ASCE 41. Stiffness of slab-beam elements and columns was further reduced in consideration of nonlinear behavior of
structural members. Shear walls were modelled using fiber sections,
and link beams are modelled using beam elements with an inelastic
hinge at both ends of the link beams.
Figure 4. Wind load cases maximizing differential loading between towers.
Wind Loads on Structurally Linked Structures
SUBSTRUCTURE 1
In general, for a typical single tower, the wind tunnel testing results
are combined with the local climate data and the dynamic properties
of the structure to generate the design wind loads. Wind loads are
provided in the form of static point loads applied at each floor, along
with the multiple load cases representing loading that imposes the
maximum effect on the structural members. Each set of wind loads is
represented by the corresponding load combination factors for each
component (X, Y and Torsion) which are applied simultaneously to
the tower to determine the internal forces acting in each member of
the lateral load resisting system.
For buildings with rigid links or shared components, additional
loading scenarios must be considered. Load cases maximizing their
effects on each tower will be separately generated first. When the
foundation, podium or the linked portions such as a bridge between
STRUCTURE magazine
SUBSTRUCTURE 3
SUBSTRUCTURE 4
SUBSTRUCTURE 2
Figure 5. Multi-blocks (substructures) approach used in wind tunnel study.
48
September 2015
10
Figure 6. Sample displacement time history (at top of the west tower in E-W direction).
towers are involved, additional simultaneous loading conditions maximizing differential loading between linked towers can be generated.
These load cases (Figure 4) were used to design the two bridges and
the 29th floor slab, which is the lowest rigid link of the top 13-story
tall section spanning the two towers rising up to the 28th floor in the
east tower. The differential movements of the adjacent towers were
calculated using these load cases, and compared with the maximum
calculated displacements for the seismic loads to finalize the distance
of separation gaps.
For an appropriate analysis of the wind tunnel data and accurate
assessment of wind-induced responses, the entire building was
“divided” into five blocks or “sub-structures” as shown in Figure
5 and presented in the RWDI’s wind study report. Diaphragms
assigned in the analysis model, using ETABS®, are matched with this
substructure configuration.
Currently, the foundation is under construction and the
super-structure is scheduled to be completed by 2017. Danny
Jadeja, P.E., Senior Associate, was the project manager and
Ben Pimentel, P.E., President, was the engineer of record.▪
Sunghwa Han, P.E., S.E., LEED AP, is a senior associate at
Rosenwasser/Grossman Consulting Engineers, P.C. and in
charge of conceptual structural design and analyses, including a
nonlinear response history analysis. She can be reached by email
at [email protected].
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Design Architect: Arquitectonica
Architect of Record: SLCE Architects, LLP
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Geo-seismic Engineering Consultant: Amec Foster Wheeler,
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Wind Engineering Consultant: Rowan Williams Davies &
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September 2015
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The site is approximately 550 feet in the east-west direction by 200
feet in the north-south direction. The base of the towers is designed
as one single structure without any expansion joint. In order to
minimize shrinkage cracks, one 4-foot wide control strip is placed
between the west tower and the east tower in the podium floors. It
is located at approximately 2/3 of the building length in east-west
direction (Figure 2).
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A Need for Speed
Coordinating
Fast PaCed
Urban
ConstrUCtion
By Ramon Gilsanz, P.E., S.E., F.SEI,
Phil Murray, P.E.,
Gary Steficek, P.E.
and Petr Vancura
F
Figure 1. Avalon West Chelsea. View from High Line Park.
ast-paced construction within a dense urban environment like
New York City has several distinctive rationales, approaches,
constraints, and requirements that necessitate careful coordination. The fundamental principle that drives the need
for speed in construction is economic. The sooner a new building is
completed and put into operation, the lower are the carried financing costs and the sooner the project can recapture generated revenue
streams. There are numerous approaches and structural systems that
can speed up the construction process. This article focuses on characteristics of flat plate concrete systems which, when floor plates are
repetitious and identical, can achieve fast superstructure builds by
using a 2-day concrete placement cycle. However, in tight urban
locations, spatial constraints for staging, installation, material, and
labor, as well as complexity of architectural/design coordination, can
potentially interrupt the cycle and cause delays. Instant communication and in-the-field coordination are keys to maintaining the fast
paced schedule and to minimizing mistakes. The structural engineer
needs to be fully immersed in the day-to-day construction process to
ensure successful and timely completion of the project.
Three projects in New York City are presented to illustrate coordination issues that are particular to this type of construction: Avalon
West Chelsea, 41-42 24th Street (aka “QLIC”), and 150 Charles
Street. These developments are primarily multi-family residential,
but also feature street-level retail, at- and below-grade parking, and
amenity features at upper levels including planted green roofs and
terraces. Both Avalon West Chelsea and QLIC are rental buildings
that required high-speed construction. In contrast, 150 Charles
Street is a luxury condominium development.
Avalon West Chelsea
Avalon West Chelsea is a recently completed 588,000 square-foot
“L-shaped” building located in the prime Chelsea Arts District of
STRUCTURE magazine
Manhattan (Figure 1). Programmatically, this building consists of
two distinct components: a 31-story tower featuring 309 luxury
apartments, and a 14-story mid-rise that extends from the tower
at the west to the elevated rail structure, now known as High
Line Park, at the east, housing 405 units geared toward a younger
demographic. The LEED Silver certified property also includes 142
affordable housing units, roof-top terraces, green roofs, rear yards,
a fitness center, lounge areas, a 140-car parking garage, and retail
space at street level.
QLIC
QLIC, a 400,000 square-foot development at Queens Plaza North in
Long Island City, is nearly complete (Figure 2). The 21-story tower
holds 421 rental units, double-height retail at grade and parking for
120 cars below grade. The building’s 28,000 square feet of amenity
space includes a rooftop pool, cabanas, a roof deck with an open-air
theater and barbecue, a landscaped courtyard with a fire pit, media
lounge, game room, fitness center, and other amenities on an accessible terrace.
150 Charles Street
This 300,000 square-foot, 16-story luxury residential development in
Manhattan’s West Village consists of 98 condominium units (Figure
3). The project incorporates the façade structure of an existing 4-story
warehouse for the lower podium floors. Above, two corner towers flank
a mid-block volume and each floor steps back, forming a cascade of
terraces toward the Hudson River. The superstructure accommodates
high gravity loads due to precast façade assemblies as well as 40,000
square feet of landscaped courtyards, green-roofs and planted terraces
with up to five feet of soil cover. The building’s total landscaped area
is equivalent to the combined areas of four small neighboring parks.
continued on next page
51
September 2015
Figure 2. QLIC – architect’s rendering.
Structural Systems
The structural systems of the three buildings consist of reinforced
cast-in-place concrete flat plates, which is the most common slab
structural system for high-rise residential construction in New York
City (Figure 4). Compared to other structural systems, flat-plate
construction maximizes usable floor-to-ceiling space (no beams or
suspended ceilings) and also provides flexibility in the architectural
layout of interiors since columns are not constrained to gridlines. This
type of construction affords both lower costs and, depending on the
uniformity of design, faster erection. Concrete construction is also
inherently fireproof and, with sufficient slab thickness, is minimally
susceptible to vibration and noise transmission between floors.
At Avalon West Chelsea, floor slabs are supported by almost
200 columns that range from one story to thirty-one stories, and
seven shear wall configurations around two vertical cores. QLIC
employs 120 columns and four cores. Despite its smaller size,
150 Charles Street has over 300 columns, though few of these
extend the full height of the building. Columns are transferred
from level to level, because each floor has a distinct architectural
layout (Figure 5, page 54). For contrast: 1) QLIC included 10
column sizes and 4 transfers, 2) Avalon West Chelsea had 14
column sizes and approximately 20 transfers, primarily at the
13th floor connection between the tower and the mid-rise, and 3)
150 Charles included 41 various column sizes and 250 transfers,
whereby columns substantially changed location, size/shape, or
orientation between floors. Shear walls are located around building cores that house elevator shafts and egress stairs to provide a
structural and fireproof enclosure of these spaces and to minimize
the architectural impact of the walls. The 8-inch slabs used at each
of these buildings accommodate multiple in-slab mechanical and
plumbing services, as well as electrical conduits.
The smaller-footprint repetitious upper floors of Avalon West Chelsea
and QLIC were erected using one concrete pour on a two-day cycle (see
below for explanation), whereas the larger lower levels required several
pours. At 150 Charles, due to the irregular and constantly changing
floor layouts, slab elevation steps, and the larger quantity of column
sizes (requiring differently sized formwork), concrete placement took
16 days on average per floor. At QLIC, the locations of construction
Figure 3. 150 Charles Street – architect’s rendering.
STRUCTURE magazine
52
September 2015
joints between the two or three pours at the 27,000 square-foot
horseshoe-shaped lower eight floors were assessed and determined
in the field by the inspector-engineer. In-house Special Inspections
therefore served to expedite this coordination in the field. At Avalon
West Chelsea, however, the 575-foot-long floor slabs of the lower
14 floors demanded an advanced construction sequence analysis to
understand changes in temperature and shrinkage of concrete. The
structural design thus enabled a four-part pour sequence without
the need for any expansion joints. All three projects incorporated
crack-control reinforcing at column exteriors, shear wall corners,
and re-entrant corners.
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Coordination
During superstructure erection of highrise buildings, materials and equipment
must be lifted to the top level using a
tower crane, which all trades share. If a
delay in delivery or staging prevents a
component’s lift, placement crews must
improvise using materials that are available
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STRUCTURE magazine
53
September 2015
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The tower portions of Avalon West
Chelsea (above the 14th floor) and QLIC
(above the 16th floor) were built using a
2-day cycle whereby an entire floor slab
is poured every two days (Figure 6 ). The
maximum feasible floor size that can
achieve a 2-day cycle is around 20,000
square feet, with floor plates around 65
feet wide. This dimension is typical of
multifamily rental buildings organized
around double-loaded corridors, and
was the case for both buildings. Only
a skilled labor force, experienced with
this method of construction, can execute
the cycle because it requires a specific
sequence of tasks before crews can proceed to subsequent floors. These tasks
include installation of: deck slab formwork, bottom mats, MEP duct/conduit/
pipe & blockouts, top mats, concrete for
deck slab, column/shear wall formwork,
reinforcing steel, and concrete for columns/shear walls. Therefore, a setback of
any single step of the process can potentially “domino” into a delay of an entire
work day.
With the advent of computer aided
analysis and design, buildings are more
complex, less repetitive, and less conservative than they were in the 1950s, when
this technique was developed. Highperformance buildings today also hold
many more systems and services, so there
are more trades and more congestion on
the construction site. As a result, buildings
with a 2-day cycle today are more challenging than they were half a century ago.
on the deck, rather than wait for subsequent lifts. The engineer must
be available to assess if each ad hoc substitution is structurally acceptable. Moreover, at dense urban construction sites that have limited
space for staging and storage, contractors may request temporary
slab openings in order to reposition materials and equipment, or
achieve clearance for installation. These logistics are not included
on construction documents and are typically decided in the field.
In the event that the designed slab reinforcement gets displaced as a
result, the structural engineer is on-hand to coordinate its relocation.
Coordination of mechanical, electrical and plumbing (MEP)
trades typically occurs during shop drawing review, and layouts of
these systems remain schematic until finalization of construction
documents. MEP subcontractors often respond to field conditions
Figure 4. Flat plate concrete construction at QLIC.
by proposing amendments to sizes or locations of slab penetrations,
which may impact the structural design. Such substitutions require
the structural engineer’s review to confirm that the integrity of
the slab is not compromised.
Foundations
The foundation of QLIC is a combination of spread footings and a
3-foot mat foundation over rocky geology. The columns and shear
walls at Avalon West Chelsea are supported by more than 1,000 piles
within a 67,000 square-foot site containing varying rock and soil
conditions. Here, the underlying rock stratum was found to be so
shallow in about one-third of the site that the piles were too short to
achieve substantial lateral resistance capacity. However, the remaining
piles were able to provide sufficient lateral resistance to eliminate the
need for footings or additional foundation elements. A foundation
slab ties all the piles together. As the floor slabs are designed without
an expansion joint, the structure engages all the piles jointly. The
stiffness of the slab without expansion joints enables the 14-story
mid-rise structure to laterally support the tower.
Envelope
Avalon West Chelsea employs a standard masonry/curtain wall façade.
The building envelope system of QLIC, however, is comprised of
STRUCTURE magazine
Figure 5. Column transfer at 150 Charles. This transfer occurs at the slab edge
and uses a concrete beam segment. Transfers at slab interior employ beams or
thicker slab sections.
54
September 2015
prefabricated metal-stud-reinforced panels
with thin brick veneer. These components were
assembled on Long Island along with windows
fabricated in Buffalo, and then shipped to the
construction site in Queens. These panels with
pre-installed windows were lifted and attached
to the building using a crane. While the price
of this system is comparable to traditional
masonry façade systems, utilizing prefabricated
panels saved roughly 20% of the time required
to enclose the building.
The combination of using the pre-assembled
façade panels and just-in-time shipping (a
delivery method whereby material arrives
to the site at the time it is to be installed)
resulted in multiple benefits for the design
and construction team. By assembling the
panels in the shop, the working conditions
and consistent temperatures allowed for higher Figure 6. Avalon West Chelsea. Tower (at right) is on a 2-day cycle, with staging on mid-rise roof deck.
quality water- and air-tightness, improving
the energy efficiency of the building. Just-in-time delivery allowed
Having both structural and building envelope teams in-house
the Contractor to minimize staging and storage space while efficiently allowed communication of structural requirements internally, withenclosing the building.
out the need for time-consuming Request For Information (RFI)
While 150 Charles also used pre-fabricated panel components (in processes through the architect, thus enabling speedy communication
this case pre-cast concrete with brick exterior), the entire building and coordination of interacting structural and envelope systems.
featured additional façade systems including masonry cavity walls, Another aspect that facilitated coordination at QLIC was the use of
curtain walls, window walls, stone cladding & storefront assemblies. Building Information Modeling (BIM), whereby all trades (strucIn most locations, the 13-inch precast panels are at least as thick as tural, mechanical, electrical, etc.) could be coordinated within a single
the building frame to which they are attached (Figure 7, page 56).
Uniformity
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Uniformity of design and repetition of structural elements enables
efficiency of construction, which in turn results in economies of
scale. This approach allows installation crews to maintain consistent
work processes and reuse formwork, rather than needing to adjust
for each individual location. This speeds-up erection. At Avalon
West Chelsea and QLIC, approximately 80% of the columns have
the same cross section and reinforcing. At Avalon West Chelsea,
80% of pile caps are also typical.
The varying areas of the floor plates and architectural amenity features
at 150 Charles required a different interior layout for every floor, as
well as numerous slab elevation changes at each level. This provided
opportunities for innovative solutions to structural challenges associated with shifting and rotating columns between the floors through
slab transfers. While the structural design responds to the architectural
requirements to achieve real estate marketing objectives, such a design is
not conducive to sustaining a 2-day cycle. The complexity and variety
of floor layouts result in lathers relocating their staging at each level.
The work space is further congested by MEP trades that also deal with
offsetting mechanical shafts and plumbing risers at each floor.
Team Interconnectedness
The structural engineer’s continuous presence in the field allows for
quick responses to coordination issues. Since Gilsanz Murray Steficek
(GMS), the project’s Structural Engineer, also served as special inspector
of concrete and steel at each project, the engineer-inspector was often
on-site. A direct line of communication between the construction team
and the design team allowed challenges to be immediately resolved
with the contractor, trades and other design team members, as needed.
STRUCTURE magazine
55
September 2015
digital 3D model during design development and pre-construction.
Few unanticipated conditions remained in the design by the time
the first shovel hit the ground.
Economics
The speed of construction translates directly to cost of the project. New
York City construction projects with the scale and complexity of Avalon
West Chelsea typically employ approximately 150 union workers on
a given day of superstructure erection. According to local prevailing
wages, this project would incur a cost of over $100,000 for a delay of
a single day for labor alone. This does not include other costs associated with remobilization or equipment rentals. At the same time, the
owner continues to maintain high-interest construction loans and his
receipt of operating revenues is also delayed. As a result, field changes
after concrete placement, such as demolition/removal/re-placement
of concrete, or fiber-reinforced polymer applications for topical reinforcement or modification/repairs, while expensive, tend to be more
economical to both contractor and developer as opposed to stalling the
construction cycle for design coordination.
The impact of construction speed upon a project’s overall economics,
however, depends largely on the type of asset that is being developed.
Avalon West Chelsea and QLIC are both rental apartment buildings.
Other types of buildings, such as residential condominiums, follow
a different economic formula focused on the apartment buyer. The
target market with high sales prices demands diversity of unique units
and amenity-rich architecture which cannot be easily systematized into
repetitive workflows. Unlike rental buildings, where tenants constantly
change, condominium building design is driven by the ability to sell
the apartments. 150 Charles sold out with asking prices ranging from
$3-$35 million (or approximately $3,200 per square foot). In comparison,
Avalon West Chelsea currently rents at around $78 per square foot per
year. This translates to a property value of approximately $312 per gross
square foot, as assessed by the New York City Department of Finance.
(Note that this incorporates the building’s operating expenses).
Despite the structural design challenges at 150 Charles, the added
costs of longer construction duration are absorbed by the condominium project since returns on investment are realized immediately
upon completion and sale of the units, whereas rental revenue streams
are distributed over the course of a building’s operation.
Summary
Not all projects rely on speed to maintain profitability. Those that
do, achieve efficiencies through uniformity of design, systematized
construction methods, and the engineer’s engagement during
construction. Moreover, when members of the design and construction teams have direct mutual access to information
through all phases of project design, preconstruction
and construction, coordination conflicts during erection can be immediately resolved.▪
Team: Avalon West Chelsea
Owner/Developer: AvalonBay Communities
Structural Engineer: Gilsanz Murray Steficek
Architect: SLCE Architects
Geotechnical Engineer: Mueser Rutledge
MEP Engineer: MG Engineering
Construction: AvalonBay Communities
Concrete: SBF Construction
Team: QLIC
Owner/Developer: World Wide Group
Structural Engineer: Gilsanz Murray Steficek
Architect: Perkins Eastman
Geotechnical Engineer: Langan Engineering
MEP Engineer: MG Engineering
Construction: Lettire Construction Corp.
Concrete: RNC Construction
Team: 150 Charles Street
Owner/Developer: Witkoff Group
Structural Engineer: Gilsanz Murray Steficek
Architect: Cook + Fox Architects
Geotechnical Engineer: RA Consultants
MEP Engineer: Flack+Kurtz
Construction: Plaza Construction
Concrete: Navillus
Ramon Gilsanz, P.E., S.E., F.SEI, is founding partner of Gilsanz
Murray Steficek and project manager for Avalon West Chelsea.
He currently serves as Chair of the New York City Department
of Buildings’ Structural Technical Committee and Chair of
the American Council of Engineering Companies of New York
Metropolitan Section Structural Code Committee. Ramon can be
reached at [email protected].
Phil Murray, P.E., is founding partner of Gilsanz Murray
Steficek and project manager for QLIC. Phil can be reached
at [email protected].
Gary Steficek, P.E., is founding partner of Gilsanz Murray Steficek
and project manager for 150 Charles Street. Gary can be reached at
[email protected].
Petr Vancura is Director of Communications at Gilsanz Murray
Steficek and has experience in construction management, real
estate development and urban planning. Petr can be reached at
[email protected].
Figure 7. 13-inch precast façade panel at 150 Charles Street.
STRUCTURE magazine
56
September 2015
InSIghtS
new trends, new techniques and current industry issues
Creating Clarity and Scoping Profits in BIM with LOD 350
By Will Ikerd, P.E., CM-BIM, LEED AP
C
learly defined structural engineering contract scopes save engineers
time, profit, and – most importantly – the personal satisfaction
of their profession. Building Information
Modeling (BIM) can improve this scope clarity if addressed proactively, or compound the
difficulties in achieving clarity if ignored. The
construction industry has reached a point
where the use of BIM is not self-explanatory:
it could be used to create 2D shop drawings,
coordinate trades, or estimate cost. Since
BIM came into existence, the industry has
lacked a vocabulary for communicating the
Level of Development (LOD) between parties. The BIM Forum™ Level of Development
(LOD) Specification 2015 (BIMforum.org/
LOD) is an industry-changing reference that
enables structural engineers to clarify their
scope with BIM, providing the solution to
this paramount problem of vague BIM scope
definition.
Previous to this development, many model
element authors were unaware of expectations upon entering a project. The LOD
Specification now provides a way to define
the scope of detail and input minimums for
each particular component of the design. It
is simply a collection of definitions describing input and information requirements and
graphic/model examples of the different levels
of development for building elements. The
document does not outline the necessary
levels of development for different steps in
the construction process, leaving these determinations for each project team. Instead, it
gives a common vocabulary for use between
parties on a project team. It is important
to note that the document is now in its 3rd
edition, with the 2015 version released for
public comment. Key aspects of the document
are its support and input from the national
BIM Masonry (BIMforMasonry.org), Steel
Joist Institute (SteelJoist.org), Steel Deck
Institute (SDI.org), ACI (Concrete.org),
and the National Institute of Steel Detailers
(NISD.org).
LOD definitions in terms of model elements* (emphasis added):
• LOD 100 The Model Element may
be graphically represented in the
Model with a symbol or other generic
representation, but does not satisfy
A masonry wall element progression shown from LOD 200 through 400. Copyright, BIM Forum
(BIMforum.org/LOD) & IKERD Consulting (IKERD.com) 2015.
the requirements for LOD 200.
Information related to the Model
Element (i.e. cost per square foot,
tonnage of HVAC, etc.) can be derived
from other Model Elements.
• LOD 200 The Model Element is
graphically represented within the
Model as a generic system, object, or
assembly with approximate quantities,
size, shape, location, and orientation.
Non-graphic information may also be
attached to the Model Element.
• LOD 300 The Model Element is
graphically represented within the
Model as a specific system, object or
assembly in terms of quantity, size,
shape, location, and orientation.
Non-graphic information may also be
attached to the Model Element.
• LOD 350 The Model Element is
graphically represented within the
Model as a specific system, object, or
assembly in terms of quantity, size,
shape, orientation, and interfaces with
other building systems. Non-graphic
information may also be attached to
the Model Element.
• LOD 400 The Model Element is
graphically represented within the
Model as a specific system, object
or assembly in terms of size, shape,
location, quantity, and orientation
with detailing, fabrication, assembly,
and installation information. Nongraphic information may also be
attached to the Model Element.
STRUCTURE magazine
58
September 2015
It is important to note that there is no LOD
of an entire model; the model is a mixture
of different elements within different LODs.
For permit drawings, which will be
required for the foreseeable future on building projects, elements are typically only
modeled to LOD 300. However, for full
trade coordination, higher LOD is required,
short of fabrication LOD. For this reason,
the author proposed LOD 350 for bridging the gap between element development
at permit drawings and fabrication level.
LOD 300 does not include the information
necessary for full cross trade coordination,
while LOD 400 requires information that
may not yet be available.
LOD 300 represents model elements traditionally shown in the plan view of a set
of construction documents. This would
include main structural members with information such as specific location and type.
Construction Documents made from the
LOD 300 model are accompanied by 2D
information: general notes, typical details,
specific details and specifications to define
higher level information not typically shown
in 1/8-inch scale plans or modeled for permit
drawings. For coordination, model elements
with an LOD of 350 represent information generally shown with typical details
in construction drawings. This information requires trade-knowledgeable input
to model accurately. Most main structural
member elements are at LOD 300. However,
structural engineers must be mindful that
LOD 300 requires elements to be in the
correct location. For example, although the
2D plans may appear to be correct, sloping
roof members that are modeled flat are not
at LOD 300. Also, design-level open web
bar joists at LOD 300 are not acceptable
for trade coordination with MEP, as they
do not have the specific manufacturer’s web
profiles to detect conflicts. Other areas of
misunderstanding are structural elements
shared with architecture, such as tilt walls,
slabs and load bearing masonry walls.
A masonry wall element, for example, is
shown in the progression from LOD 200
through 400 (see the accompanying graphic).
Note that most structural design models would
only take the wall elements to LOD 300 to
create sealed 2D construction permit drawings. The wall at LOD 300 would specifically
identify the masonry system, and would reference typical details and project specifications
for higher levels of development details. This
higher LOD information, such as but not limited to jam conditions, bond beams, grouted
cells, dowel locations, and joints, would not
appear until LOD 350 and higher. These
higher LOD aspects would typically be modeled as part of the construction side submittal
process. LOD 400 masonry modeling is currently found on more progressive BIM projects
in limited areas of building as part of virtual
mockups for water proofing review at key
building transition areas. Situations such as this
make a compelling case for using LOD 350 as
an important step between specific assemblies
and detailed assemblies for coordination with
manufacturer’s specific content. The structural engineer’s scope should address who is
responsible for modeling such information
at higher LOD, as owner and lead designers
begin requesting higher LOD model elements.
As more projects require detailed 3D coordination, the need for accurate MEP models
will become even clearer to lower the risk
of the entire design team (A & E). There
is little value in above ceiling coordination
in taking the architectural and structural
model elements to LOD 300 (specific in the
actual orientation) if MEP model elements
are only at LOD 200 (generic in approximate
location). Structural engineers should consider
adding additional services in their contracts
for manual MEP coordination review if the
MEP model elements are not to LOD 300.
This represents the added time the structural
engineer will have to invest in the project
during construction administration to deal
with changes in the MEP due to lack of
model definition (and MEP design). For
instance, all gravity plumbing lines must
slope for these elements to be at LOD 300,
whereas many MEP design models do not
slope these lines. This creates the risk of failing to discover that the line will not fit below
the structure and above the ceiling if the lines
are not modeled at LOD 300 (with slopes).
The structural engineer may then be forced
to consider adding web openings in their
beams or redesigning shallower beams, losing
time and profit.
Profit is vital in the business of any profession; structural engineering with BIM is no
different. Clearly defined scopes in BIM and
LOD 350 is a key to creating clarity in the
design-to-construction process and aiding
structural engineers in the opportunity to find
profits in clearly defined project BIM scopes.▪
Will Ikerd, P.E., CM-BIM, LEED AP, is a
principal at IKERD. He currently co-chairs
both the Designers Forum of the AGC’s
national BIM Forum and the Structural
Engineering Institute’s national BIM
Committee. Additionally, he co-chairs the
AGC BIM Forum – AIA workgroup on
Structural LOD. He may be contacted at
[email protected].
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STRUCTURE magazine
59
September 2015
EnginEEr’s notEbook
aids for the structural engineer’s toolbox
Moment-Curvature and Nonlinearity
A Fundamental Discussion
By Jerod G. Johnson, Ph.D., S.E.
N
early every day in our careers as
structural engineers, we consider
the following equations:
Mn = As fy(d-a/2), Mn = Fy Z x
Readers will no doubt recognize these as the
nominal flexural strengths utilized in beam
designs for reinforced concrete and steel, also
known as (among other things) the flexural
limit state. While there are variations reflecting
unbraced lengths, the presence of compression
reinforcement, axial loads and other considerations, these are the fundamental relationships.
What exactly does this mean?
Structural engineers understand that the
capacities represented by these equations do
not correspond to the loads that we actually
expect the members to see during a typical service condition. Rather, these are the approximate
magnitudes of loads that the members would
experience in the unlikely event that they are
pressed toward ultimate failure. This will hopefully never occur for members that are part of
the ‘gravity’ system. Likewise, this will hopefully not occur for a large but rare transient
event in members that are part of the ‘lateral’
system. Either way, the fundamental objective
is to ensure that designs have φMn greater than
Mu, the maximum flexural factored load effect.
Now consider the ‘middle ground’ in this
scenario – the flexural behavior that occurs
between zero load and a condition where Mu
equals Mn. Doing so offers a glimpse of basic
nonlinear behavior and the formation of flexural mechanisms that hopefully reflect stable
and ductile performance.
For the concrete beam scenario, at a load
equal to Mn it is assumed that the reinforcement has yielded in tension following
the idealized elastic-to-plastic relationship,
with a constant stress equal to yield stress
(fy) with a strain somewhere beyond the
yield strain of approximately 0.00207 (for
Grade 60 bars). It is also assumed that the
concrete acting in compression has reached
a strain of 0.003 and that at this point, it
is theoretically being crushed at its extreme
compressive surface. To understand what
has happened in the beam while reaching this point requires developing a series
of calculations reflecting various levels of
reinforcement strain, from zero all the way
Moment vs. curvature relationship for reinforced concrete beam.
up to the net tensile strain (εt) which occurs
at a theoretical load of Mn.
For each one of these calculations, it is possible to develop resultant forces based on
relative strains in the tension steel and the
concrete compression zone, and a momentcouple relationship based on the distance
between the resultant forces. This relationship
is relatively simple, since we know from statics
that the resultants of tension and compression
must always be equal in magnitude and opposite in direction. While many theories have led
to the development of models reflecting the
distribution of stress in the concrete compression zone, assuming a uniform compression
zone as prescribed by ACI 318 is valid and
greatly simplifies the calculation, enabling the
a/2 portion of the equation previously shown.
For each series of calculations, the curvature
value is simply taken as the strain in flexural
reinforcement divided by its distance from the
theoretical neutral axis. Plotting the values of
Mn and curvature yields a load-deformation
(curvature) relationship, an example of which
is shown in the Figure.
Among the interesting things observable in
this figure is that nominal moment capacity
is nearly reached at the point where the tensile reinforcement first yields – long before the
member reaches is ultimate capable curvature
at Mn. What does this mean in a practical sense?
Observe that the nominal flexural strength is
approximately 240 kip-ft and that this particular
member reached this capacity at a curvature just
beyond 0.0002/in. However, the member was
able to sustain this load to a curvature nearly five
times this value, thereby demonstrating the ductile behavior toward which the codes are geared.
This exercise demonstrates that failure of this
member would be preceded by deformations
STRUCTURE magazine
60
September 2015
likely to present a serviceability issue, thus giving
occupants warning of trouble.
As an interesting exercise, consider increasing the area of reinforcement to the balanced
or over-reinforced condition. The results will
demonstrate a smaller ratio of maximum capable curvature vs. yield curvature, which grows
ever smaller as the amount of reinforcement
increases. This demonstrates the pitfall of simply
adding reinforcement to improve strength.
It is also worthwhile to consider seismic
response. The Figure demonstrates the potential for favorable hysteretic behavior as the area
under the curve is proportional to the energy
release occurring through each cycle of flexural
load and rotation. If the reinforced concrete
is detailed correctly, this is a favorable, stable
and controlled method for dissipating energy
during an earthquake, thereby preventing it
from becoming manifest elsewhere. The same
holds true for steel beams, provided that they
are appropriately sized and detailed to promote
fundamental material nonlinearity, as opposed
to other forms of ‘macro’ nonlinearity such as
global or local buckling.
Observations of the projected theoretical
behavior of mechanisms such as this are worthwhile. They offer a glimpse into the basis for
code provisions that we often take for granted.▪
Jerod G. Johnson, Ph.D., S.E.
([email protected]), is a principal
with Reaveley Engineers + Associates in
Salt Lake City, Utah.
A similar article was published in the
Structural Engineers Association-Utah
(SEAU) Monthly Newsletter (September
2011). Content is reprinted with permission.
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CASE BuSinESS PrACtiCES
Strategic Planning: A Comprehensive Approach
By Dilip Choudhuri, P.E.
M
ost high-performing firms that
are successful over the long
term are those which truly
embrace strategic planning.
If you have been part of a strategic planning
process in your firm and are still skeptical
about the importance of such a process, you
should revisit the goals of your firm’s last two
strategic planning sessions and assess how
your firm has changed as a result. You will
likely be amazed!
Walter P Moore has been in business for 84
years; its latest comprehensive strategic plan
was developed in 2012 and is currently being
implemented. The firm has the benefit of the
historical perspective of the last five strategic
plans that outlined its trajectory and validated
the importance of building upon previous
strategies. Walter P Moore’s successful strategic planning under the author’s leadership
is the basis for this article.
people “outside the room” should be engaged
for various efforts, increasing engagement
and buy-in.
Deciding on an Approach
There are many approaches that can be
used for comprehensive strategic planning.
For example, you could chose to conduct
a vision-based, goal-based, issue-based, or
scenario-based planning session. Some of the
most widely used books which should be
read prior to deciding on a strategic planning
approach include The Balanced Scorecard by
Kaplan and Norton, Blue Ocean Strategy by
Kim and Mauborgne, and Good to Great by
Collins. Each approach has its special nuance
and benefit. However, whichever approach is
ultimately chosen, the successful implementation of the resulting initiatives requires a
strong commitment from the core strategic
planning team.
Hiring a Facilitator
Planning Framework
Getting Started
Ideally you want to start the process by having
the firm’s senior leadership team agree on the
need for a new strategic plan. This should be
followed by hiring the strategic planning consultant, providing the selected consultant with
necessary firm background and deciding on
two important facets of the proposed strategic
planning work – (i) the ideal number of core
team members and (ii) the methodology for
the strategic planning session. You want to
have the largest number of people in the room
that the facilitator is comfortable including,
without any adverse effects on sessions for
the chosen strategic planning approach. This
will afford you greater flexibility on the issue
of being inclusive with team members from
across the firm who are at different stages of
their professional career.
Selection of the core group should be well
thought out and incorporate new leaders
within the firm as well as senior leadership
for a balanced perspective. Preferably, these
core strategic planning team members are
either principals or senior project managers. Consistent communication firm-wide
about the ongoing process can build excitement, especially among those not actively
involved in the planning sessions. These
Working with an expert facilitator knowledgeable about your selected approach, and one
who is intimately familiar with firms in the
A/E/C space, is critical. Indeed, most successful
strategic planning efforts require firms to hire
an outside specialty consultant to facilitate the
process. The external facilitator, by virtue of
being an outsider, has tremendous freedom
of expression and inquiry, and can maintain
objectivity, which is understandably difficult
to do from an insider perspective.
At Walter P Moore, the external facilitator
who was selected used The Balanced Scorecard
approach to guide five strategic planning sessions that spanned a 12-month period for the
2012 strategic planning. The session was a
goal-based strategic planning session which
was tested for alignment with the firm’s overall vision. The core strategic planning group
of twenty-two leaders met for two days for
each of the five sessions. These meetings were
held within Walter P Moore’s facilities, which
made it efficient from a logistics point of view
and also signaled to others in the office that
the firm’s leaders were planning the future
of the firm in plain view. When working in
your own facilities, it is even more important
to stay focused and observe the ground rules.
There were always assignments between the
sessions for the entire group of twenty-two.
The facilitator was very successful in making
STRUCTURE magazine
63
September 2015
Culture and strategy are intertwined.
sure that the conversations at these sessions
were not dominated by a few of the most
outspoken in the room.
Assessing Firm Culture
For strategic initiatives to be successful, a
supportive cultural environment is a must.
It is critically important to seek the answer
to “How are things done within the firm?”
Personal mastery guru David Aitken of the
Aitken Leadership Group says, “Any good
strategy is going to depend on culture to
support it. So culture and strategy become
synergistic, part of a system diagram.” Hence,
knowing the cultural predisposition of your
firm is an important first step in a successful
strategic planning process.
Conducting a cultural scan at the early
stages of the strategic planning process is also
a great way to engage all members of your
firm. Typically, your strategic planning consultant will need to depend on a specialized
personal mastery expert to develop the parameters of a cultural scan and then interpret the
findings. There are well-established ways in
which organizational behavior experts collect
valuable qualitative data through employee
surveys with respect to the cultural aspects
of a given firm.
At Walter P Moore, all employees responded
to a confidential survey that helped develop
the cultural scan for the firm. From the data,
the firm recognized the collective wisdom of
how employees viewed what made Walter P
Moore successful in the past, how things get
done, and how they envisioned the firm’s future
– very valuable insight for all involved. It was
also recognized that, as a firm, organic growth
continued on page 65
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was preferred over growth through mergers and
acquisitions because it allows maintenance and
reinforcement of its culture across the firm.
Walter P Moore has made just four acquisitions
in its history, so an acquisition is rare. Culture
is important; hence, the firm is much more
deliberate about determining the cultural fit in
the due diligence process as it approaches any
acquisition opportunities for growth.
Four Basic Steps
to Strategic Planning
Steps for strategic planning.
Expecting linearity in the strategic planning
process is unrealistic. The overall process is
highly non-linear; hence, having a high level
of comfort and trust in the selected facilitator is of utmost importance. The facilitator
must guide the sessions while retaining the
flexibility to modify the direction of the
sessions to elicit open dialogue concerning
the four basic steps to strategic planning –
Current State Analysis, Desired Future State,
Understanding of Barriers, and Development
of a Strategic Plan. These steps do not necessarily occur in sequence.
Rod Hoffman, CEO of S&H Consulting,
a strategic planning firm, likes to use The
Balanced Scorecard as a framework for strategic
planning sessions. Hoffman says, “Strategic
planning is about connecting the dots so
that everyone can see the picture.” A comprehensive strategic planning exercise typically
requires multiple sessions over multiple days.
The benefit of having the core team attend all
of these sessions is the continuity component,
and the team building that happens through
group exercises during the sessions and informal conversations outside of the sessions.
1.0 Current State Analysis
Context for the current state analysis is
established by restating the vision, mission, and core values, and by sharing the
updated firm-wide cultural scan with the
core strategic planning group. It is critical
for any strategic planning exercise to do a
deep dive into the current state of the firm,
and the current internal environment as
perceived by the internal core team, members of the firm, and clients of the firm. To
understand the current state of the firm, a
basic Strengths, Weaknesses, Opportunities,
Threats (SWOT) analysis should be conducted by the core team. In addition, key
production leaders who may not be part of
the core strategic planning group can be
surveyed for additional SWOT data points.
A select group of the firm’s clients can be
surveyed, via a series of prepared questions,
on their thoughts on Social, Technological,
Environmental, Economic, and Political
trends affecting their industry (STEEP
analysis) in the next five years. These client
response data sets can then be aggregated to
enhance the current state analysis. This is
yet another example of where others can be
engaged who may not be part of the core strategic planning group to improve the overall
process. The core strategic team can then be
engaged to see what trends are working in
the firm’s advantage (also known as tailwinds)
and those that are working against the firm
(headwinds). During the strategic planning
process at Walter P Moore, the firm confidentially turned to about 40 trusted clients
across market sectors to provide answers for
the STEEP analysis. These were very useful
client touches in that they educated the firm
about their client’s business realities in their
specific sector while showing Walter P Moore’s
interest in them. The data collected was sorted
by the various categories to understand the
impact of these client-specific realities. Some
created opportunities and some required the
strategic direction as a firm to be altered.
2.0 Desired Future State
This desired future state analysis should not
be limited to business growth opportunities,
but should also examine internal and cultural
aspects of the firm’s future. This goes back to
the central idea that business strategic growth
is very much intertwined with culture. The
growth opportunities can be categorized as
those that can be achieved through an increase
in market share, change of portfolio, and
through acquisition of new lines or divesting from a current line of business. There are
many exercises that can be developed by the
facilitator to have a dialogue within the core
group about these topics, and also engage the
group members in smaller working groups
with a report out process.
In Walter P Moore’s 2012 strategic planning process, the core team of twenty-two
leaders each had five votes to endorse various growth and cultural strategies that were
the result of the planning work. In addition,
the full corporate Board of Directors had an
STRUCTURE magazine
65
September 2015
opportunity to vote on each of the stated
growth and internal/cultural initiatives. This
was another way to formally get the board
as a group to review selected initiatives and
provide their wisdom with respect to prioritization of the strategic initiatives. The votes
from the Board of Directors were weighted
and then tabulated in addition to those of
the core strategic planning group. Corporate
boards tend to like to weigh in on strategic
initiatives because they, as a group, do have
strategic thinkers who have taken on the
responsibility. It is also much easier for the
board to support the CEO when they are
implementing the strategy, because they are
familiar with it and have provided a voice to
the plan. Walter P Moore’s core team settled
on thirteen initiatives – seven growth initiatives and six internal/cultural initiatives.
3.0 Understanding of Barriers
This phase of strategic planning builds on the
current state analysis described in Step 1 and
the desired future state analysis described in
Step 2. There is clearly a need to have an open
and robust discussion about the culture of the
firm and the current state of the external barriers that impact the attainment of the desired
future state. If you have a large core strategic
planning team (20-24 people), you can use
group work and a voting process to continue
engagement and maintain focus. This phase of
planning provides insight into potential cultural initiatives needed for success, and can test
the durability of your core practice areas. Such
informative insights into the firm likely would
not have been discovered without having gone
through this comprehensive process.
4.0 Development of a Strategic Plan
Potential growth and cultural strategies should
be voted on by the core group and the Board
of Directors of the organization. Each strategy
should be associated with a weighting system
to allow ranking by levels of importance. The
development of the final strategic plan requires
the core team to consider three horizons or
time-frames of growth. Horizon 1 includes
strategies that affect the core business and are
things that need to be addressed immediately.
Horizon 2 contains those strategies that need to
be addressed in three to five years and are about
building emerging practice areas. Horizon 3
strategies are those that are very ‘blue-sky’
growth opportunities achievable further out
– five years plus into the future. In general,
there should be more initiatives in Horizons
1 and 2 than in Horizon 3.
Stair-step to growth – starting a new practice while limiting risk.
Strategic Implementation
Once a strategic direction is identified, the
final step and bigger task is to develop a
preliminary schedule of implementation for
each strategic initiative adopted. Once implementation plans are developed, they should
be reviewed by the Board or a subset of the
Board for acceptance and authorization. The
strategies for Horizon 2 or 3 require better
risk management since they are considered
relatively uncharted territory compared to
the core business strategies. The CEO should
create a detailed communication plan to share
the strategic direction with firm members
who were external to the process. He or she
should regularly communicate updates of the
strategic plan’s implementation as items are
completed or revised. This keeps the strategic
plan front and center for the entire firm.
One can consider a stair-step implementation
process for those initiatives in Horizon 2 and 3.
The first step is to conduct small-scale experiments of a service or practice area, followed by
a validation of the service or practice area – is it
profitable? Is it something that fits our firm well?
Once the service or practice area is validated,
one can replicate and then scale the practice
area within the firm. Think carefully about key
performance indicators for each of the strategies
being implemented. As it is said, “what cannot
be measured cannot be improved.”
Once a firm-wide implementation plan is
developed, individual business units or groups
within a firm need to develop complementary
implementation plans that are shorter-term
and co-exist with firm-wide strategic direction.
Walter P Moore’s 2012 plan outlined several
strategic growth initiatives that were specific to
select individual business units (business unit =
a group of complementary practice areas with
service offerings). It was then the responsibility
of each business unit to develop the strategic
implementation plans for the growth initiative.
The implementation plan was then reviewed
by a review committee consisting of members
from across the firm. Seventy-five percent of
the review committee membership consisted
of people within the business unit for the specific growth initiative and the remainder from
outside the business unit. In 2014, a Strategy
Council was created as part of the organizational structure which is chaired by the CEO
and has the business unit leaders from each
operating group and two additional members
that are appointed by the CEO. The Strategy
Council meets on a quarterly basis to focus on
the strategic agenda of the firm. The implementation plans are subsequently submitted to the
Strategy Council and the Board of Directors
for formal authorization and approval.
Achieving Results
Team members within high-performing firms
will want to see results of the strategic planning process. Results primarily depend on
solid execution of the strategic plan. The old
project management adage that you have to
“plan the work and then work the plan” is
true for strategic initiatives, too.
In a multi-discipline firm, the number of concurrent strategic initiatives can be numerous and
overwhelming. It may be acceptable to have
multiple growth and internal/cultural strategic
initiatives, as long as the implementation team
5 Key Takeaways
1) Use an external facilitator familiar
with the A/E/C industry for your
strategic planning.
2) Conduct a cultural scan of your entire
firm and try to communicate the
importance of the survey for a high
response rate.
3) A long-range view of the strategic
planning process is important. This
allows you to make sure that you focus
on the progress and not worry about
small delays that are bound to occur.
4) Communicate the final strategic plan
widely with your entire team. Strategic
implementation happens both from
the top down and the bottom up.
5) Devote ample time to developing
actionable implementation plans. The
goals of the implementation plans
should be revisited at least quarterly to
ensure their achievement.
STRUCTURE magazine
66
September 2015
members are selected from across the organization and also across various practice areas of the
firm. There are many reasons for this: implementers bring passion to their initiative of choice
(ask for volunteers for some initiatives), they
bring subject matter expertise, their service to
the firm should be linked to their personal action
plans and annual performance goals. When
leaders stop going to the same ‘four’ people for
all strategic implementation needs, you have the
unintended and beneficial consequence of getting broad based buy-in for the implementation
of the strategic plan. For a multidiscipline firm
or firms in multiple geographies, it becomes
vital to energize some of the non-core practice
areas or emerging offices that have the potential
to blossom in the near future.
Conclusion
A comprehensive strategic planning process
requires a huge commitment of resources
for any professional services firm, but yields
incredible benefits. Having the entire senior
leadership team support the effort, without any
questions, is critical since the strategic planning
process will intrude on your firm’s immediate needs and other tasks that are critically
important today. A comprehensive strategic
planning and implementation process is akin to
a marathon rather than a sprint. To succeed, we
must maintain collective focus on the critically
important initiatives for the three horizons –
short, medium and long-term.
Walter P Moore implemented a new organizational structure as a direct result of one
of the strategic planning initiatives from the
firm’s 2012 Strategic Plan. Operating under
a new organizational paradigm for the firm
for just over a year now, Walter P Moore has
successfully deployed a flat, responsive organizational structure to address the challenges
of a changing marketplace and client needs.▪
Dilip Choudhuri, P.E., is President and CEO
of Walter P Moore. Dilip can be reached
at [email protected] and
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downtown Chicago. The class is also fully
accessible on the Web.
and SEAOI for offering it on the
Web.”
Participants can take the entire course or
focus on specific areas.
5432 Any Street West
Townsville, State 54321
Phone 555.543.5432
Fax 555.543.5433
core requirements and lifelong learning for structural engineers
Education issuEs
Structural Education Deficiencies
Timber and Masonry
By Kevin Dong, P.E., S.E. on behalf of the Basic Education Committee
O
ne of the concerns of professionals in the structural engineering
community is the limited exposure to timber and masonry
design for graduating civil/structural engineering majors. A majority of smaller scale
structures are constructed using timber/
masonry separately or a combination of these
materials; yet most civil/structural engineering
curriculums emphasize steel and concrete as
building materials and provide less of a focus
on timber and masonry design. Additionally,
the timber industry has evolved beyond the
typical traditional stick-framed construction
Suggested Timber/Masonry
Module One
1) Wood Buildings and Design Criteria
using allowable stress design (ASD)
2) Properties of Wood & Lumber Grades
3) Beam & Joist Design – Sawn
Lumber, Glued Laminated Timber,
Manufactured Lumber
4) Stud & Column Design – Axial
members (buckling versus crushing)
and combined axial and bending
5) Shear Wall Design – Segmented and
perforated wall concepts. Calculations
for segmented wall method only
6) Diaphragm Design – Sheathing,
chords and collectors for flexible
diaphragms
7) Connector capacity – Behavior and
capacity of nails and bolts
8) Masonry Buildings and the history
of masonry as a building material,
ASD versus LRFD
9) Construct-ability, sequencing, and
terminology for masonry construction,
material strengths and lab testing
10) Beam Design (LRFD) – flexural
model, failure modes, shear
requirements, deflections using
cracked section properties
11) Column/Pilaster Design – role of
longitudinal and transverse, pure axial
and combined axial and bending
12) Shear Wall design – in-plane design
for shear, flexure, and introduction
of the axial-moment relationship
13) Wall Design – out of plane design,
including second order effects
to a more advanced and innovative building
material, and many students will be unprepared to design buildings without this as
part of their curriculum. As noted in prior
STRUCTURE® articles, the National Council
of Structural Engineers Associations (NCSEA)
promotes a varied curriculum that includes a
balance of analysis, design, and other technical skills. Timber and masonry design are an
integral part of the recommended curriculum.
And although NCSEA believes timber and
masonry should each be provided as its own
course, a timber/masonry material design curriculum can be organized into two modules:
element design and building systems design.
In the first module, the basics are introduced,
such as: the properties of a given material,
advantages and limitations of a given building
material, design of beams (flexural), columns
(axial and combined axial and bending), shear
walls or structural panels, and diaphragms
Suggested Timber/Masonry
Module Two
1) Building configuration
2) IBC load requirements (gravity
and lateral)
3) Selection of roof and floor systems
4) Preliminary design process
5) Structural design computations using
allowable stress design (ASD) for
timber and LRFD for masonry, then
develop working drawings (notes,
plans, elevations, details) for structural
systems including:
a. floor framing – sawn lumber,
I joists, manufactured lumber,
glulams, etc.
b. roof framing – sheathing, stick
framing, prefab trusses, tiebacks/
anchorage etc.
c. wall framing – sheathing, studs,
posts, headers, masonry, trim
requirements at openings etc.
d. shear walls – sheathing/block
selection, chords, connections,
segmented, perforated (optional) for
plywood and masonry, etc.
e. diaphragms – sheathing, chords,
collectors, sub-diaphragms, cross-ties,
flexible vs. rigid, cantilever, etc.
6) Configuration & design of connections
STRUCTURE magazine
69
September 2015
(where applicable). The second module links
the use of building codes and standards,
such as the International Building Code,
American Concrete Institute’s Building Code
Requirements for Structural Concrete, American
Institute of Steel Construction’s Specification
for Structural Steel Buildings, American Wood
Council’s National Design Specification for
Wood Construction, and Masonry Standards
Joint Committee’s Building Code Requirements
for Masonry Structures, with structural analysis
to design small scale (and regular) buildings.
The curriculum includes developing a framing
system for both lateral and vertical loading
to emphasize the concept of load path and
to gain exposure to building irregularities in
structural systems. Then there is determining the gravity and lateral loads to establish
loading and design criteria, followed with
designing beams, columns, structural panels,
diaphragms, collectors, and connectors to
resist gravity and lateral load requirements.
Finally, there is the development of structural drawings (plans and connection details)
to connect analytical work to the communication tool used for construction. The
last step exposes students to a critical part
of design, but also to constructability and
building sequencing. Together, Module One
and Module Two encompass the NCSEA
Core Curriculum suggestions for Timber and
Masonry. It’s envisioned that the first module
is either a combined timber/masonry course, as
currently offered at some institutions, or as two
separate timber and masonry courses. Schools
limited by a variety of constraints can implement Module One to expose students to both
materials. Module One is sufficiently intense to
provide a student with a basic understanding
of both materials so that self-teaching can raise
the student to a higher level of understanding. In either scenario, 60 (semester) lecture
hours are proposed to introduce the basics of
material design for wood and masonry. The
second module would include the design of a
regular building with the two materials, and
a comparative study of using either masonry
or wood as the lateral load resisting elements,
such as shear walls. Although this module may
be more demanding, 60 lecture or contact
hours are foreseen as a minimum to cover the
recommended material.▪
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ANCHORING GUIDE
American Wood Council
Phone: 202-463-2766
Email: [email protected]
Web: www.awc.org
Product: Special Design Provisions for Wind and
Seismic standard
Description: Provides criteria for proportioning,
designing, and detailing engineered wood systems,
members, and connections in lateral force resisting
systems. Allowable stress design (ASD) or load and
resistance factor design (LRFD). Nominal shear
capacities of diaphragms and shear walls are provided
for reference assemblies.
Bentley Systems
Phone: 800-236-8539
Email: [email protected]
Web: www.bentley.com/
Product: RAM Connection
Description: Perform analysis and design of virtually
any connection type, verify connections in seconds,
all with comprehensive calculations, including seismic
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Construction Tie Products
Phone: 219-878-1427
Email: [email protected]
Web: www.ctpanchors.com
Product: Stitch-Tie
Description: Stainless steel helical anchors for
masonry crack repair (6mm) and masonry anchors
(8mm & 10mm) for re-attaching existing brick
veneers to masonry, wood, concrete, tile and steel stud.
Replicates missing wall ties, but stronger and stiffer.
Installs easily and is concealed when completed.
Decon® USA Inc.
Phone: 866-332-6687
Email: [email protected]
Web: www.deconusa.com
Product: Anchor Channels
Description: Exclusive representative of Jordahl in
North America. Hot rolled Anchor Channels are
embedded in concrete and used to securely transfer
high loads. Their main application is for flexible
connections of glazing panels to high-rise buildings.
Anchor Channels with welded-on rebar or corner
pieces are available.
Product: Studrails®
Description: The North American standard for
punching shear enhancement at slab-column
connections. Studrails are produced to the
specifications of ASTM A1044, ACI 318-08, AND
ICC ES 2494. Decon Studrails are increasingly used
to reinforce against bursting stresses in banded posttension anchor zones.
All Resource Guide forms for the 2015 & 2016
Editorial Calendar are now available on the
website, www.STRUCTUREmag.org.
Anchor Bolts, Concrete, Façade, Geotechnical, Masonry, Post-Tensioning,
Reinforcing and Utility Anchors, and General Hardware & Ties
Gripple Inc.
Powers Fasteners
Halfen USA, Inc.
Product: Powers Submittal Generator (PSG)
Description: PSG is a submittal and substitution
online tool that helps contractors create submittal
packages in just minutes. In only a few simple steps
users can include all applicable code reports and
technical details. Contact us for a free demonstration.
Phone: 630-952-2113
Email: [email protected]
Web: www.gripple.com
Product: Anchor Hanger Kits for Suspended Services
Description: Cable hanger kits suspend
mechanical & electrical services like HVAC,
lighting, conduit racks, and cable basket. Spider
Kit is a cast-in-place concrete insert hanger kit
that’s ready-to-use, has a safe working load of up to
200 lbs, and includes a Spider insert, cable hanger,
and a Gripple fastener.
Phone: 800-423-9140
Email: [email protected]
Web: www.halfenusa.com
Product: HALFEN HCW Curtain Wall System
Description: Designed to anchor curtain wall façade
elements quickly, securely, and economically to the
main structure. Offers various configurations for ‘top
of slab’ and ‘edge of slab’ applications. Utilized to
ensure quick, efficient, and adjustable connections
to account for on-site conditions and engineered to
resist any load combination (horizontal, vertical, and
longitudinal) as required by the project.
Product: HALFEN HSD-LD Lockable Dowel System
Description: For temporary movement joints,
commonly found in post-tensioned concrete slabs.
Dowels allow initial shrinkage of the concrete to
take place and are then locked in position with a
mechanical plate and a controlled amount of epoxy
resin. The locked dowels continue to transfer shear,
but pervert further movement.
Product: HALFEN HGB Handrail Anchor Channels
Description: HALFEN HGB Anchor Channels for
handrail connections enable safe anchoring of railing
posts to the edge of thin concrete slabs. These Anchor
Channels allow strong connections to the edge of
concrete slabs as thin as 4 inches (100mm).
Hardy Frame
Phone: 800-754-3030
Email: [email protected]
Web: www.hardyframe.com
Product: Hardy Frame Shear Walls
Description: Hardy Frame now offers pre-engineered
anchorage solutions that drastically reduce large pad
footings that can be associated with pre-fabricated
Shear Wall Panels; standard details are available for
inclusion with plan submittals.
IES, Inc.
Phone: 800-707-0816
Email: [email protected]
Web: www.iesweb.com
Product: IES VisualAnalysis
Description: VisualAnalysis offers ACI Anchor
Design checks with the base plate design feature
included in VAConnect. Use VisualAnalysis for a wide
variety of analysis and design projects. It is simple,
productive and versatile.
STRUCTURE magazine
71
September 2015
Phone: 845-230-7533
Email: [email protected]
Web: www.powers.com
Product: Powers Design Assist (PDA)
Description: Anchor design software provides
calculations in accordance with ACI 318-11 and CSA
A23.3 for mechanical, adhesive and cast-in place
anchors. Includes seismic provisions and concrete-filled
metal deck profiles. Download or update to version
2.3 for free today to take advantage of the most current
code standards.
RISA Technologies
Phone: 949-951-5815
Email: [email protected]
Web: www.risa.com
Product: RISABase
Description: Uses an automated finite element
solution to provide exact bearing pressures, plate
stresses, and anchor bolt pull out capacities,
eliminating the guess work of hand methods. Define
bi-axial loads and eccentric column locations.
Choose from several connection types and specify
custom bolt locations.
S-FRAME Software Inc.
Phone: 203-421-4800
Email: [email protected]
Web: www.s-frame.com
Product: S-FOUNDATION
Description: Quickly design, analyze and detail your
structure’s foundations with a complete foundation
management solution. Run as a stand-alone application,
or utilize S-FRAME Analysis’ powerful 2-way integration
links for a detailed soil-structure interaction study.
Automatically manages the meshed foundation model
and includes powerful Revit and Tekla BIM links.
continued on next page
CADRE Pro 6 for Windows
Solves virtually any type of structure for
internal loads, stresses, displacements,
and natural modes. Easy to use modeling
tools including import from CAD. Much
more than just FEA. Provides complete
structural validation with advanced
features for stability, buckling, vibration,
shock and seismic analyses.
CADRE Analytic
Tel: 425-392-4309
www.cadreanalytic.com
Modeling Software for
Structural Engineering
Achieve the highest quality of
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Tekla provides a BIM (Building Information Modeling) software that enables engineers to coordinate and deliver the structural
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engineers can:
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- Model steel and connections plus concrete and rebar
- Create high quality engineering drawings
- Integrate with analysis software
- Collaborate more closely with contractors / fabricators to speed up construction
a http://tek.la/ch
ANCHORING GUIDE
Product: S-CONCRETE
Description: Easily view instantaneous results
as you optimize and design reinforced concrete
walls, beams and columns. Automate workflow
by checking thousands of concrete section designs
in one run. With comprehensive ACI 31811 code support plus additional design codes,
S-CONCRETE produces detailed reports that
include clause references, intermediate results
and diagrams.
Simpson Strong-Tie
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Anchor Bolts, Concrete, Façade, Geotechnical, Masonry, Post-Tensioning,
Reinforcing and Utility Anchors, and General Hardware & Ties
Standards Design Group
Phone: 806-792-5086
Email: [email protected]
Web: www.standardsdesign.com
Product: Wind Loads on Structures 4
Description: Performs computations in ASCE 7-98,
02 or 05, Section 6 and ASCE 7-10, Chapters 26-31
computes wind loads by analytical method rather than
the simplified method, provides basic wind speeds from
a built-in version of the wind speed, allows the user to
enter wind speed. Has numerous specialty calculators.
Phone: 800-999-5099
Email: [email protected]
Web: www.strongtie.com
Product: Adhesive Piston Plug Delivery System
Description: Offers an easy-to-use means to
dispense adhesive into drilled holes for threaded rod
and rebar dowel installations at overhead, upwardly
inclined and horizontal orientations. The matched
balance design between the piston plug and drilled
hole virtually eliminates the formation of voids and
air pockets during adhesive dispensing.
Strand7 Pty Ltd
Product: Titen HD® Screw Anchor
Description: The patented, high-strength Titen
HD screw anchor for concrete and masonry offers
optimum performance in both cracked and uncracked
concrete, as required by the 2012 IBC for postinstalled anchors. Newly redesigned, this anchor now
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Tekla, Inc.
Phone: 252-504-2282
Email: [email protected]
Web: www.strand7.com
Product: Strand7
Description: An advanced FEA system used worldwide
by engineers for a wide range of structural analysis
applications. It comprises preprocessing, a complete
set of solvers and post processing. It includes a range of
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for simulations of the complete soil/structure system.
Phone: 770-426-5101
Email: [email protected]
Web: www.tekla.com
Product: Tedds
Description: Automating your everyday structural
designs, Tedds’ broad library includes anchor bolt
design per ACI 318 Appendix D. The calculation
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failure of anchors and is available as part of a free
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Product: Tekla Structural Designer
Description: Revolutionary software that provides
the power to analyze and design steel and concrete
buildings efficiently and profitably. Physical,
information-rich models contain all the intelligence
needed to fully automate the design and document
your project, including all end force reactions
communicated with two-way BIM integration,
comprehensive reports and drawings.
Product: Tekla Structures
Description: An Open BIM modeling software that
can model all types of anchors required to create a
100% constructible 3D model. Anchors can either be
created inside the software or imported directly from
vendors that have 3D CAD files of their products.
Williams Form Engineering Corp.
Phone: 616-866-0815
Email: [email protected]
Web: www.williamsform.com
Product: Anchor Systems
Description: Providing threaded steel bars and
accessories for rock anchors, soil anchors, high
capacity concrete anchors, micro piles, tie rods, tie
backs, strand anchors, hollow bar anchors, post
tensioning systems, and concrete forming hardware
systems in the construction industry for over 90 years.
All Resource Guide forms for the 2015 & 2016
Editorial Calendar are now available on the
website, www.STRUCTUREmag.org. Listings
are provided as a courtesy. STRUCTURE®
magazine is not responsible for errors.
2015 Annual Trade Show in Print
The definitive buyers’ guide for the practicing structural engineer
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STRUCTURE magazine
73
September 2015
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award winners and outstanding projects
Spotlight
Newport Beach Civic Center and Park
Inspiring Community through Holistic Design
By Janice Mochizuki, P.E., LEEP AP, John Worley, S.E., LEED AP and Joseph Collins, S.E.
Arup was an Outstanding Award Winner for the Newport Beach Civic
Center and Park project in the 2014 NCSEA Annual Excellence in Structural
Engineering awards program (Category – New Buildings over $100M).
A
spiring to create a civic center that
would bring the community together,
the coastal city of Newport Beach,
California chose to position the
new development in the geographic and
cultural center of the expanded population.
Newport Beach’s old city hall, built in 1948,
was no longer positioned to serve the needs
of the community. The team of architects
from Bohlin Cywinski Jackson (BCJ) aimed
to provide a civic center that would be an
inspiring place for the community to converge
and to provide a transparent civic institution.
Contributing and collaborating on this design
vision was PWP Landscape Architecture and
the Arup multidisciplinary team from the
San Francisco office consisting of structural,
mechanical, electrical, plumbing, and civil
engineering, as well as lighting, sustainability,
and telecommunications consulting services.
C.W. Driver was the general contractor.
The Newport Beach Civic Center and Park
is positioned on a narrow, 20 acre plot of land
partially inhabited by protected wetlands and
flanked by three major roads. The project
consists of a new city hall, community room,
council chambers, parking garage, parkland,
4 pedestrian bridges, and an addition to an
existing library.
Straddling the wetlands are three modest
pedestrian bridges amongst the 14 acres of
park land and picnic areas. The two separate
parcels of the site are connected with a sightline compatible, low-profile pedestrian bridge
spanning 150 feet over a main thoroughfare,
San Miguel Drive. The San Miguel Bridge has
a 52-foot observation platform that provides
views of the Santa Catalina Islands. It was
created by cantilevering steel supports off of
the concrete shear wall elevator tower and
perching the main bridge girders on those
supports to allow for longitudinal movement.
The 17,000 square-foot addition to the
existing Central Library, which was located
adjacent to the site, was built to serve the
high demand for reading room space and
the need for a children’s area and high-tech
media center. Over the new grand library
entrance, a dramatic
50-foot cantilever
faces the civic center
and provides covered
exterior spaces that
can be used as an
Courtesy of David Wakely.
entertainment stage.
A pair of built-up king post roof trusses with lighting) were carefully routed through web
tension cables provides a column free space openings in the wave roof beams to achieve
in the 150 seat council chambers. The special a clean look while exposing the structural
concentric brace frame building has a curved steel. The shape and directional placement of
and canted wall that provides support for the the roofs allows for ideal placement of future
iconic Polytetrafluoroethylene (PTFE) backlit solar panels.
exterior “sail”.
The building is stabilized against wind and
Located between the council chambers and seismic loads by buckling restrained braced
the city hall is a double-height, 4,500 square- frames (BRB). Due to the discontinuity of the
foot community. It is a continuation of the city roof diaphragm resulting from the repeating
hall’s architectural expression with large sliding- wave roof layout, each 20-foot wave roof bay
door facades that allow for the room to open functions as its own local diaphragm. Two
up to the park and sheltered outdoor spaces. horizontal lines of pinned-ended, round HSS
The 89,000 square-foot city hall building collectors pick up the lateral force from the
is a two-story architecturally exposed struc- wave roofs to deliver it to the BRBs located
tural steel (AESS) building clad with a glass in the cores and the ends of the building.
curtain wall, envisioned by BCJ as an expresThe aesthetic of the pinned-ended, round
sion to the public of a transparent structure HSS members is carried throughout the
and civic institution. Wave roofs, one of project. Double-height exterior axial-only colthe most multi-functional design elements umns that support the overhanging wave roofs
of the project, top the second floor of the are round HSS members with a pinned base
city hall and pay homage to the marine sur- connection. The exposed BRBs, provided by
roundings. North facing operable clerestory CoreBrace, have meticulously crafted pinnedwindows that are equipped with automated ends and a round HSS casing with a custom
motorized dampers provide natural ventila- made collar to conceal the cruciform core.
tion and lighting. Wide flange beams were
Through holistic decisions and collaboration
sculpted into their double radiused form by of the entire project team from design through
SME Steel. The higher elevation side of the construction, the Civic Center earned a
wave sits on top of a vierendeel truss created LEED Gold Certification while creating a
from commonly available wide flange chords place for the community to enjoy.▪
and vertical members. By using the vierendeel truss layout, the window elements and
Janice Mochizuki, P.E., LEEP AP
lighting fixtures are nicely nestled within the
([email protected]), is a
structure. The wave roofs extend beyond the
Senior Engineer in Arup’s structural buildings
curtain wall facades to create sunshade for the
group. John Worley, S.E., LEED AP
building and exterior spaces surrounding the
([email protected]), is a Principal
structure. A result of implementing a raised
in the structural buildings group. Joseph
floor system, and early design coordination
Collins, S.E. ([email protected]),
between Arup and BCJ, was concealing many
is an Associate in the structural buildings
of the distribution services. The few required
group. All three are located in Arup’s San
overhead services (fire sprinklers and overhead
Francisco office.
STRUCTURE magazine
75
September 2015
GINEERS
ASS
O NS
STRUCTU
OCIATI
RAL
EN
COUNCI L
NCSEA News
News form the National Council of Structural Engineers Associations
NATIONAL
The 2015 NCSEA Special Awards Honorees
The following awards will be presented at the Awards Banquet on October 2 nd during the 2015 NCSEA Structural Engineering
Summit in Las Vegas. For more information on the Annual Conference, see pages 42 – 45.
The James M. Delahay Award
The James M. Delahay Award is presented at the recommendation of the NCSEA Code Advisory Committee to recognize outstanding
individual contributions towards the development of building codes and standards. It is given in the spirit of its namesake, a person
who made a long and lasting contribution to the code development process.
Donald R. Scott, S.E., F.SEI, F.ASCE
Donald R. Scott is the Vice President and Director of Engineering at PCS Structural Solutions, a 50-person
firm with offices in both Tacoma and Seattle, Washington. He has been a Principal of the firm since 1986 and
has led many of the firm’s educational, commercial, institutional and private projects for new and renovated
construction. Don is a civil and structural engineering graduate of the University of Idaho with civil and
structural engineering licenses in Washington and seven other states.
Don has authored many technical publications and has presented numerous seminars and NCSEA webinars
on wind design throughout the country. He has been a member of the ASCE 7 Wind Load Committee since
1996, shaping future IBC provisions for wind design, and currently serves as Chairman. He is also a member of the ASCE 7
General Provisions committee, a member of the ASCE 7 Steering Committee, Chairman of the NCSEA Wind Committee,
and a former Chair of the SEAW Wind Load Committee.
The NCSEA Service Award
The NCSEA Service Award is presented to an individual or individuals who have worked for the betterment of NCSEA to a degree
that is beyond the norm of volunteerism. It is given to someone who has made a clear and indisputable contribution to the organization
and therefore to the profession.
Craig Barnes, P.E., SECB
Craig Barnes founded CBI Consulting Inc. in 1984 and is licensed in 20 states. Craig helped establish the
National Council of Structural Engineers Associations (NCSEA) in 1993, was President of NCSEA from
1995-1996, and received the NCSEA Robert Cornforth Award in 2005. He is a member of STRUCTURE
Magazine’s Editorial Board, as well as a continuing contributor to the publication. Craig is a Past President of
the Boston Association of Structural Engineers, as well as the Structural Engineers Association of Massachusetts.
He chaired NCSEA’s Basic Education Committee for several years, where he was instrumental in creating a
highly-recognized list of Basic Education requirements for students in the structural engineering field. Craig
has provided consulting services for exhibits at Boston’s Museum of Fine Arts and their affiliates abroad, and he spent two weeks
in Port-au-Prince following the catastrophic earthquake in 2010, reviewing and commenting on reports prepared by Haitian
consultants to determine if buildings were safe for occupancy.
The Robert Cornforth Award
This award is presented to an individual for exceptional dedication and exemplary service to a Member Organization and to the
profession. Nominees are submitted to the NCSEA Board by the Member Organizations.
Carl Josephson, S.E., SECB
Carl Josephson is a Principal Structural Engineer with Josephson-Werdowatz & Associates, a structural
engineering firm located in San Diego, California with additional offices in Sacramento, Las Vegas, and
Scottsdale. Carl is a licensed Professional or Structural Engineer in twelve states.
He has served as Convention Chair, Director, and President of SEAOC. He is currently Chair of SEAOC’s
Professional Licensing & Certification Committee and SEAOC’s recently reestablished Legislative Committee.
He was elected to the SEAOC College of Fellows in 2007. He is a member of NCSEA’s Professional Licensing
Committee and is a member of SEI’s Professional Activities Committee. In 2010, Carl was appointed by
former Gov. Schwarzenegger as the SE member of the California Board for Professional Engineers, Land Surveyors and Geologists,
(BPELSG), and he now serves as an Emeritus member of, and consultant to, BPELSG. He is active in the National Council
of Examiners for Engineers and Surveyors (NCEES) and has served on their SE Exam Committee and Mobility Task Force.
STRUCTURE magazine
76
September 2015
The Susan M. Frey NCSEA Educator Award is presented to an individual who has a genuine interest in, and extraordinary talent for,
effective instruction for practicing structural engineers. The award was established to honor the memory of Sue Frey, one of NCSEA’s
finest instructors. Nominees are submitted to the NCSEA Board.
Emily Guglielmo, S.E.
Emily Guglielmo is an Associate with Martin/Martin, Inc. and also serves as manager of the Northern
California office. Emily is deeply committed to assisting structural engineers in solving real world engineering
problems with simple, reasonable solutions. Toward that goal, she has served as a frequent lecturer for several
Structural Engineering Associations on topics ranging from wind and seismic loads to serviceability design.
Emily is a member of the ASCE 7 Seismic Committee and the NCSEA Publications Committee, and is a
founding member and current Chair of the NCSEA Young Member Group Support Committee. Outside of
the profession, Emily enjoys hiking and traveling with her husband and three children. Deeply honored by her
receipt of the prestigious Sue Frey Educator Award, Emily’s goal is to contribute to Sue’s legacy through her educational efforts.
NCSEA News
The Susan M. Frey NCSEA Educator Award
More information on the NCSEA Structural Engineering Summit can be found on pages 42 – 45.
NCSEA Awards Six Young Member Scholarships to Annual Conference
Thomas Mendez, S.E.
A Structural Engineer with Halvorson and
Partners, Chicago, Illinois, Thomas is a member
of the Structural Engineers Association of Illinois.
Matthew McCarty, S.E., P.E.
A Project Structural Engineer with Whitman,
Requardt & Associates, Monrovia, Maryland,
Matthew is a member of the Virginia Structural
Engineers Council.
Matthew Ernst, E.I.
A Structural Staff Engineer with Engineering
Ventures, PC, Burlington, Vermont, Matthew is
a member of the Structural Engineers Association
of Vermont.
Greg McCool, P.E.
A Structural Engineer with Ericksen Roed &
Associates, St. Paul, Minnesota, Greg is a member
of the Minnesota Structural Engineers Association.
Yasmin Chaudhry
A graduate student at Montana State University
and an intern at Morrison-Maierle, Inc., Bozeman,
Montana, Yasmin is a member of the Structural
Engineers Association of Montana.
NCSEA Webinars
News from the National Council of Structural Engineers Associations
For the third year, NCSEA awarded Young Member
Scholarships for the NCSEA Structural Engineering Summit.
The scholarship competition was open to any current member of
an NCSEA Member Organization who was under 36 years old.
Applicants were asked to compose an essay or video answering
one of three questions, as well as write a brief essay upon attending the Summit. Scholarships included Summit registration
and a travel stipend. The winners of this year’s scholarships are:
Michelle Quinn, P.E.
A Design Engineer with Ensign Engineering,
Sandy, Utah, Michelle is a member of the
Structural Engineers Association of Utah.
October 27, 2015
GINEERS
RAL
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IN
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STRUCTURE magazine
77
September 2015
O NS
NATIONAL
OCIATI
Diamond
Reviewed
Non-CalOES courses award 1.5 hours of continuing
education. Approved for CE credit in all 50 States
through the NCSEA Diamond Review Program.
ASS
UIN
N
NCSEA
STRUCTU
RS
EE
GIN
UR
AL
More detailed information on the webinars and a registration
link can be found at www.ncsea.com. Subscriptions are available!
EN
Observations & Reflections on the 2014 South
Napa Earthquake
Five speakers from Degenkolb Engineers: David Bonneville, S.E.;
John Dal Pino, S.E.; Mahmoud Hachem, S.E.;
Kirk Johnston, S.E., LEED AP; Roger Parra, S.E.
Calculating & Applying Design Wind Loads on Buildings
Using the Envelope Procedure in ASCE 7
T. Eric Stafford, P.E., President, T. Eric Stafford & Associates
RU
CT
October 22, 2015
November 3, 2015
ST
What You Need to Know About the Seismic Peer
Review Process
Farzad Naeim, Ph.D., S.E., Esq., President, Farzad Naeim, Inc.
G
October 6, 2015
Significant Changes to the Wind Provisions
of ASCE 7-10
T. Eric Stafford, P.E., President, T. Eric Stafford & Associates
COUNCI L
Second ATC-SEI Conference on Improving the Seismic
Performance of Existing Buildings and Other Structures
Structural Columns
The Newsletter of the Structural Engineering Institute of ASCE
December 10 – 12, 2015, San Francisco, California
REGISTRATION NOW OPEN
The ATC-SEI Conference on Improving the Seismic Performance
of Existing Buildings and Other Structures is an opportunity
for structural engineers, business owners, and users of ASCE
seismic standards to learn the latest in seismic evaluation and
rehabilitation.
Earn up to 14 Professional Development Hours (PDHs)
The conference technical program offers a wide variety of
valuable sessions, including:
• Seismic Resilience–Lessons from the Field
• Performance-Based Seismic Evaluation of Reinforced
Concrete Structures, in Conjunction with ASCE/SEI 41
• Innovative Approaches and Codes for Historic Structures
• Performance Assessment of Tall Buildings
• Recent Legal Developments Affecting Owners and
Designers: Using Performance Targets to Manage Seismic
Risk in the Legal Arena
• Multiple case studies on Evaluation and Retrofit of
Existing Buildings
Each day will begin with two compelling Keynote Speakers
and will include multiple opportunities for networking with
colleagues and leaders in the field. Don’t miss the Champions
of Earthquake Resilience Awards Dinner benefiting the ATC
Endowment Fund and the SEI Futures Fund.
Visit the conference website at www.atc-sei.org for complete
information and to register.
Young Professional Scholarship Forensic Engineering
th
Congress
Apply for the SEI Young Professional (age 35 and younger) 7
Scholarship to the Geotechnical & Structural Engineering
Congress, February 14 – 17, 2016, in Phoenix, Arizona. SEI
is committed to the future of structural engineering and offers
a scholarship for Young Professionals to participate and get
involved at the annual Congress. Many find this event to be a
career-changing and energizing experience, opening up networking opportunities and expanding horizons to new and emerging
trends. Applications are on the SEI website at www.asce.org/
structural-engineering/sei-young-professionals-scholarshipapplication/ and are due November 2.
Registration Now Open
Advance to SEI Fellow
ASCE’S “Game Changers”
Highlights Innovative Infrastructure
The SEI Fellow grade of membership recognizes accomplished SEI members as leaders
and mentors in the structural engineering
profession. The benefits of becoming an SEI
Fellow include recognition via SEI communications and at the annual Structures Congress
along with a distinctive SEI Fellow wall plaque
and pin, and use of the F.SEI designation. SEI members
who meet the SEI Fellow criteria are encouraged to submit
application packages online by November 1 to advance to
the SEI Fellow grade of membership and be recognized at the
Geotechnical & Structural Engineering Congress, February
14–17, 2016 in Phoenix, Arizona. Visit the Fellows webpage
at www.asce.org/structural-engineering/sei-fellows/ to
learn more.
STRUCTURE magazine
78
Registration is now open for the ASCE Forensic Engineering 7th
Congress, November 15 – 18, 2015, in Miami, Florida. Learn
alongside professionals who share the same challenges in their
work to identify and address the root causes and consequences
of design errors and construction defects. Register today at
www.forensiccongress.org/.
Americans are all too
aware of infrastructure challenges, yet
many states and communities are finding and implementing
innovative solutions that deserve wider recognition. ASCE
recently released Infrastructure #GameChangers, a report and
associated website identifying top trends in energy, freight,
transportation, and water, and the ways they are transforming
how infrastructure is designed, planned, and built. Explore more
than 30 examples at http://ascegamechangers.org/.
September 2015
February 14 – 17, 2016, Phoenix, Arizona
• Structural Wall Research: Recent Research &
International Collaboration
In addition several sessions explore topics that include both
structural and geotechnical engineering. Joint sessions include:
The Geo-Institute (G-I) and Structural Engineering Institute
• Bridge Scour & Erosion: Th
e Way Forward
(SEI) of the American Society of Civil Engineers (ASCE) are
• Novel Methods of Educating Geotechnical & Structural
coming together to create this fi rst-of-its-kind event. By comEngineers
bining the best of both Institutes’ annual conferences into one
• Managing Risk in Geotechnical & Structural Analysis &
unique conference, you will profit from unmatched networking
Design
opportunities with colleagues within and across disciplines.
• Foundations for Specialized Structures
With a large and varied technical program, the joint congress
• Structural Design of Deep Foundations
will offer structural engineers ample educational opportunities.
These structural sessions include:
Join the conversation: #GeoSEI2016
• Experimental & Analytical Investigation of Robustness
Visit the Joint Congress website at www.Geo-Structures.org
of Structures
for complete information and to register.
• Seismic Performance of Tall Buildings
• Lifecycle Analysis & Carbon Calculation: Parts 1 & 2
• Alternative Approaches to Multi-Hazard Analysis &
Design of Structures
WITH SEI SUSTAINING ORGANIZATION MEMBERSHIP
• Bridge Analysis
• Analysis of Nonbuilding Structures
REGISTRATION NOW OPEN
Connect | Collaborate | Build
REACH SEI MEMBERS
Errata
SEI posts up-to-date errata information for our publications at
www.asce.org/SEI. Click on “Publications” on our menu, and
select “Errata.” If you have any errata that you would like to
submit, please email it to Jon Esslinger at [email protected].
www.asce.org/SEI-Sustaining-Org-Membership
Electrical Transmission & Substation Structures Conference
September 27 – October 1, 2015, Branson, Missouri
REGISTRATION NOW OPEN
Can you afford to wait until 2018? This is your last chance
to register for the premier conference on transmission line
and substation structures, and foundation construction issues.
Don’t miss out on an excellent opportunity to network with
professionals in your industry.
Grid Modernization – Technical Challenges
& Innovative Solutions
The conference will feature three days of technical sessions, four
days of exhibits, a pre-conference workshop, and an exciting
construction-oriented demonstration day that will offer many
opportunities to share international knowledge on grid modernization from a structural and construction standpoint. Attendees
will experience a unique setting in which to learn and network
with peers, industry leaders, and knowledgeable suppliers.
The conference features a compelling, single track program
of sessions chaired by moderators that are leaders in the field:
• Structural Analysis 1 – Mike Miller, P.E., M.ASCE
• Special Design Considerations – Marlon Vogt, P.E., M.ASCE
STRUCTURE magazine
• Managing Aging Infrastructure – Gary Bowles, P.E., F.SEI,
M.ASCE
• Structural Analysis 2 – Robert Nickerson, P.E., F.SEI,
M.ASCE
• Case Studies – Frank Agnew, P.E., M.ASCE
• Foundations – David Todd, P.E., M.ASCE
• Substation Design Issues – Jerry Wong, P.E., F.SEI, M.ASCE
• Construction Challenges – Dana Crissey, P.E., M.ASCE
• Line Design – Wesley Oliphant, P.E., F.SEI, M.ASCE
• Rerating and Upgrading – Tim Cashman, P.E., M.ASCE
• Codes and Standards – Otto Lynch, P.E., F.SEI, M.ASCE
• Conference Wrap up – Otto Lynch, P.E., F.SEI, M.ASCE
The pre-conference workshop, Panel Discussion of Storm
Hardening, Resiliency and Security Issues, gives attendees an
additional educational opportunity. All the major companies
in the industry will display their latest products and services
in the exhibit hall, one of the highlights of the conference. The
conference will close with a demonstration day offering participants unique opportunities to witness several overhead power
line construction and supplier demonstrations in a single day.
Earn up to 19 PDHs.
Visit the conference website at www.etsconference.org for
complete information and to register.
79
September 2015
The Newsletter of the Structural Engineering Institute of ASCE
Increase your exposure to more
than 25,000 SEI members through
www.asce.org/SEI, SEI Update
e-newsletter, STRUCTURE magazine,
and at SEI conferences year round.
Structural Columns
Geotechnical & Structural Engineering Congress 2016
CASE in Point
The Newsletter of the Council of American Structural Engineers
CASE Risk Management Contracts Available
CASE #1 An Agreement for the Provision of Limited
Professional Services
This is a sample agreement for small projects, or investigations
of limited scope and time duration. It contains the essentials of
a good agreement including scope of services, fee arrangement
and terms and conditions.
CASE #2 An Agreement between Client and Structural
Engineer of Record for Professional Services
This agreement form may be used when the client, e.g. owner,
contractor developer, etc., wishes to retain the Structural Engineer
of Record directly. The contract contains an easy to understand
matrix of services that will simplify the “what’s included and
what’s not” questions in negotiations with a prospective client.
This agreement may also be used with a client who is an architect
when the architect-owner agreement is not an AIA agreement.
CASE #3 An Agreement between Structural Engineer of
Record and Consulting Design Professional for Services
The Structural Engineer of Record, when serving in the role
of Prime Design Professional or as a Consultant, may find it
necessary to retain the services of a sub-consultant or architect. This agreement provides a form that outlines the services
and requirements, in a matrix so that the services of the subconsultant may be readily defined and understood.
CASE #4 An Agreement between Owner and
Structural Engineer for Special Inspection Services
Special Inspection services provided by a Structural Engineer
are normally contracted directly by the Owner of a project
during the construction phase. This agreement has a Scope of
Service that directly relates to the applicable code or industry
standard requirements. The Structural Engineer of Record or
another structural engineer providing these services may use this
agreement. The language for coordinating laboratory testing
work is also included within this agreement.
CASE #5 An Agreement for Structural Peer
Review Services
A request to perform a peer review of another structural engineer’s design brings with it a different responsibility than that
of the Structural Engineer of Record. The CASE #5 document
addresses the responsibilities and the limitations of performing
a peer review. This service is typically performed for an Owner,
but may be altered to provide peer review services to others.
CASE #6 Commentary on AIA Document C141
Standard Form of Agreement between Architect and
Consultant, 1997 Edition and AIA Document C142
Abbreviated Standard Form of Agreement between
Architect and Consultant, 2009 Edition
This document provides a form letter of agreement to be used with
adoption by reference to AIA Document C401. This Agreement
is intended for use when owner-architect agreement is an AIA
B-series. A scope of services is included. The purpose of the commentary is to point out provisions that merit special attention.
CASE #6A Commentary on AIA Document B-141
Standard Form of Agreement between Owner and
Architect with Standard Form of Architect’s Services,
1997 Edition
The purpose of this Commentary is to point out provisions
which merit special attention, or which some have found to
contain “pitfalls”.
CASE #8 An Agreement between Client and Specialty
Structural Engineer for Professional Services
When structural engineering services are provided to a contractor or a sub-contractor for work to be included in a project where
you are not the Structural Engineer of Record, but you are a
specialty structural engineer. Your contractual relationship differs
from the norm, and the typical contract forms will not suffice.
The CASE #8 document is tailored to this particular situation.
CASE #9 An Agreement between Structural Engineer
of Record and Testing Laboratory
The Structural Engineer of Record may be required to include testing services as a part of its agreement. If a testing laboratory must
be subcontracted for this service, CASE # 9 may be used. It can
also be altered for use between an Owner and a testing laboratory.
You can purchase these and the
other Risk Management Tools at
www.acec.org/coalitions/coalition-publications/.
WANTED Engineers to Lead, Direct, and Get Involved with
CASE Committees!
If you’re looking for ways to expand and strengthen your business skillset, look no further than serving on one (or more!)
CASE Committees. Join us to sharpen your leadership skills
– promote your talent and expertise – to help guide CASE
programs, services, and publications.
We have a committee ready for your service:
• Risk Management Toolkit Committee: Develops and
maintains documents such as business practices manuals
and policies for engineers under CASE’s Ten Foundations
for Risk Management.
Please submit the following information to [email protected]:
• Letter of interest
• Brief bio (no more than 2 paragraphs)
STRUCTURE magazine
80
Expectations and Requirements
To apply, you should
• be a current member of the Council of American
Structural Engineers (CASE)
• be able to attend the groups’ two face-to-face meetings
per year: August, February (hotel, travel partially
reimbursed)
• be available to engage with the working group via email
and conference call
• have some specific experience and/or expertise to
contribute to the group
Thank you for your interest in contributing to your professional association!
September 2015
III. Membership Committee – Stacy Bartoletti
([email protected])
• Preparing for membership recruitment campaign with
CASE staff members, target date September 2015
• Working on educating CASE Members about new
Community sites and how to use while updating new
benefits of membership
IV. Programs and Communications Committee –
Nils Ericson ([email protected])
• Confirmed/finalized sessions for 2016 ASCE/SEI
Structures Congress
• Working on sessions for 2016 AISC Conference and the
ACEC Annual Convention
• Putting together the 2015/2016 editorial calendar for
articles to Structure Magazine from CASE
V. Toolkit Committee – Brent White
([email protected])
• Finished updates on the following tools:
• Tool 4-3: Sample Correspondence Letters
• Tool 10-1: Site Visit Cards
• Working on the following new tools:
• Tool 1-3: Sample Office Policies
• Tool 8-3: Contract Clause Commentary
• Tool 10-3: Deferred Submittals
• Committee will be surveying CASE membership on
ideas for future tools and what would be helpful for their
business and/or risk management plan
The 2016 CASE Winter Planning Meeting is scheduled for
February 11-12 in Phoenix, AZ. If you are interested in attending the meeting or have any suggested topics/ideas from a firm
perspective for the committees to pursue, please contact Heather
Talbert at [email protected].
ACEC Fall Conference Features CASE Risk Management
Convocation and More!
October 13 – 17 ACEC is holding its Fall Conference at the You will not want to miss these additional important risk manWestin Copley Place, Boston, MA. CASE will be holding a agement sessions:
convocation on Thursday, October 15. Sessions include:
Managing Uncertainty and Expectations in Building
Design and Construction
10:45am How to Reduce Your Risk on Alternative
Clark Davis, Cameron MacAllister Group; Stephen Jones,
Delivery Projects
Dodge Data & Analytics
Moderator: Beth Larkin: HNTB
Building Resilient Infrastructure for Future Cities
Speakers: Mary Conway, HNTB; George Wolf, Shook
Terry Bennet, Autodesk Inc.; Donna Huey, Atkins Global;
Hardy & Bacon; David Hatem, Donovan Hatem
Marty Janowitz, Stantec
1:45pm Dead in the Water: A Case Study of Claims
Missouri’s Peer Review Law–Should Your State Have One?
Facing Civil Engineers
Karen Erger, Lockton Companies
Dan Buelow & Bob Stanton, Willis A/E
How to Reduce Your Professional Liability Costs
3:30pm Non-Negotiable Contracts: What’s Plan B?
Tim Corbett, SmartRisk
Karen Erger & Bob Fogle, Lockton Co.; Eric Miller,
The Conference also features:
Ice Miller; Jennie Muscarella, Kenny, Shelton, Liptak,
• General Session addresses by Pulitzer Prize-winning author
Nowak LLP
Doris Kearns-Goodwin; 2015 ACEC Distinguished
5:15pm ACEC/Coalition Meet and Greet
Award of Merit Honoree Dr. Robert Ballard
• CEO roundtables;
For more information and to register go to www.acec.org/
• Exclusive CFO, CIO, Architect tracks;
• Numerous ACEC coalition, council, and forum events; and
conferences/fall-conference-2015/registration.
• Earn up to 21PDHs
STRUCTURE magazine
81
September 2015
CASE is a part of the American Council of Engineering Companies
On August 6-7, the CASE Winter Planning Meeting took place
in Chicago, IL with over 30 CASE committee members and
guests in attendance, making this a well-attended and productive
meeting. Included in the planning meeting was a roundtable
discussion lead by Stacy Bartoletti, Degenkolb Engineers and
Brent White, ARW Engineers on Real Life Lessons Learned:
Project Claims Impacting Structural Engineers.
During the meeting, break-out sessions were held by the CASE
Contracts, Guidelines, Membership, Toolkit, and Programs &
Communications Committees. Listed below are the current
CASE initiatives being developed by the committees:
I. Contracts Committee – Ed Schweiter
([email protected])
• Finished working on revisions to the entire CASE
Contract Document library; release of updated Contract
Library prior to ACEC Fall Conference
• Will be creating a “How to” sheet educating people on
using the CASE Contract Documents
II. Guidelines Committee – John Dal Pino
([email protected])
• Finishing current revisions to the following Practice
Guideline Documents:
• CASE 962B – National Practice Guidelines for Specialty
Structural Engineers
• CASE 962-E – Self-Study Guide for the Performance of
Site Visits During Construction
• CASE 962-F – A Guideline Addressing the Bidding
and Construction Administration Phases for the
Structural Engineer
• Guide to Special Inspections and Quality Assurance
• Working on the following new documents:
• Commentary on ASCE-7 Wind Design Provisions
• Commentary on ASCE-7 Seismic Design Provisions
CASE in Point
CASE Summer Planning Meeting Update
Structural Forum
opinions on topics of current importance to structural engineers
A “Plug” for Power Line Structures
By David C. Gelder, P.E.
W
ithin the structural community, there seems to be
a lack of awareness, as well
as a growing opportunity,
regarding overhead electrical transmission and
distribution structures. In the United States
alone there are millions of miles of corridor
consisting of aging single- and double-pole
structures and lattice towers. These structures
form an impressive network, supporting high
and extra-high voltage wires (12 kV to 765
kV) and delivering power from generation
facilities to customers located hundreds of
miles away. This enormous infrastructure,
known as the electric grid, is a critical system
to society and constitutes a specialty market
for structural engineers. I wish to “put in a
plug” for power line structures to increase
awareness and interest among fellow structural engineers.
In 2011, when I graduated, it was still difficult to get an interview – let alone a job – with
a structural firm. Given the slow job market, I
pursued a master’s degree. The following year,
I graduated and found employment, though
not designing buildings as I had supposed,
but rather designing transmission structures.
Interestingly, five fellow graduate students
found similar entry-level positions designing either transmission structures or wind
turbines – all structures within energy sector
markets. In retrospect, this hiring trend may
not have been coincidence, but rather a lesson
in diversification: the energy market showed
signs of growth during the recession, while the
commercial building market all but collapsed.
I was both excited and curious about my
first engineering job in this non-traditional
field. After all, power lines are electrical systems, right? While they are indeed electrical
systems, there is also a huge civil engineering component – as well as environmental,
archeology, survey, construction, permitting,
and other disciplines. It seems obvious now,
but many fellow civil and structural engineers
have yet to realize that we are more academically prepared than any other discipline to
design transmission structures, including the
poles, towers, wires, and foundations.
While considered an eyesore by many, these
structures are undoubtedly critical to society.
When properly designed, power lines provide
an invaluable service to consumers; however,
when defective or deteriorated, power lines
may yield devastating consequences to the
public – particularly during extreme weather
and loading conditions. Transmission lines
have failed in a variety of ways. In extreme
cases, power lines have been blamed for igniting wildfires leading to loss of life, extensive
loss of property, and environmental damage.
Failure has also triggered power outages such
as the infamous Northeast Blackout of 2003,
which led to loss of life, water supply contamination, transportation system closures,
and billions of dollars in negative economic
impact. Not all failures pose equal risk, but
clearly proper design of poles and towers of all
voltages is critical to safeguard public health
and safety.
Transmission structures are typically
designed to withstand ice accumulation,
as well as extreme wind and temperature
loading using at least 50-year recurrence
intervals. Originally most wire systems were
copper; now most modern wires are aluminum, including aluminum conductor
steel-reinforced (ACSR) pulled to thousands
of pounds of tension. They are designed
to meet ground and wire-to-wire clearance
requirements at all times in accordance with
the Institute of Electrical and Electronics
Engineers (IEEE) National Electrical Safety
Code (NESC) and other codes. Loading
is of course unique from buildings. For
example, loads on a single-pole foundation
may consist of relatively light axial load
(10-30 kips) combined with heavy shear
(50-100 kips) and heavy bending moment
(1,000-3,000 kip-ft). Poles and towers
have a relatively low seismic base shear;
therefore, earthquake loads rarely govern
the design. Some additional tools used by
today’s practicing transmission engineers
include modern nonlinear finite element
software and Light Detection And Ranging
(LiDAR) data, which are widely used in all
aspects of design and analysis. ASCE/SEI
issues Standards 10 and 48 – for designing
steel towers and poles, respectively – and
hosts the triennial Electrical Transmission
& Substation Conference (this year it will
be held September 27 – October 1, 2015 in
Branson, MO).
On the business side, historically power lines
were designed, built, and maintained for the
most part in-house by electric utilities. Now,
much of the design knowledge base and workforce has transferred to consulting firms, so
many utilities rely on them to help complete
projects. Large projects are often offered as
engineer-procure-construct (EPC) contracts –
similar to design-build contracts – while many
smaller projects are simply awarded as part of
a master service agreement (MSA). Due to the
increasing demand for power, the aging infrastructure, and a retiring workforce, there is a
growing need for transmission engineers. This
poses an opportunity for structural engineers
either individually or as a firm. For example,
some structural engineers have chosen to
pursue transmission engineering as a means
of specialization. Additionally, some large civil
engineering firms have chosen to offer power
delivery services in order to diversify, though
newcomers have found the market extremely
difficult to penetrate.
In summary, power line design can be an
enjoyable and rewarding career path for
structural engineers, and the power delivery market can be a means of diversification
for their firms. The greater civil and structural engineering communities will benefit
by recognizing and promoting these poles
and towers as civil structures. Lastly, power
line structures may be viewed by some as
an eyesore, but for others, they represent
an opportunity.▪
David C. Gelder, P.E.
([email protected]), is
licensed as a professional engineer in
the State of California and works as a
Transmission Engineer for TRC
in Salt Lake City, UT.
Structural Forum is intended to stimulate thoughtful dialogue and debate among structural engineers and other participants in the design and
construction process. Any opinions expressed in Structural Forum are those of the author(s) and do not necessarily reflect the views of NCSEA,
CASE, SEI, C 3 Ink, or the STRUCTURE® magazine Editorial Board.
STRUCTURE magazine
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September 2015
