PCI- Chapter One
Content
1.1 General
1.1.1 History of Precast, Prestressed Concrete in North America
The growth of precast and prestressed concrete is a story of the vision and
daring of a few notable people. These people took a new idea and
maximized its potential by modifying and improving existing methods,
conceiving new methods, and inventing new devices, all with a focus on
mass production. An excellent portrayal of the beginnings and the growth of
precast and prestressed concrete in North America and the early pioneers is
given in a series of papers1 that were developed to commemorate the 25year silver jubilee of the founding of the Prestressed Concrete Institute. A
similar publication2 was developed at the 50-year golden anniversary of the
Institute, which is now known as the Precast/Prestressed Concrete Institute
(PCI).
The most important event leading to the launching of the precast/prestressed concrete
industry in North America was the construction in 1950 of the famed Walnut Lane
Memorial Bridge in Philadelphia, Pa. (Fig. 1.1.1). From technical and historical
perspectives, it is both surprising and fascinating that the Walnut Lane Memorial Bridge
was constructed of prestressed concrete. There was very little published information on
the subject and there was a total lack of experience with linear prestressing in this
country at that time. Furthermore, the length of the bridge span (the main span of the
structure was 160 ft long) involved would have been a daring venture in the late 1940s
anywhere in the world. The bridge became a reality through a fortunate sequence of
events and the vision, courage, and persistence of a few extraordinary individuals.
Following completion of the Walnut Lane Memorial Bridge, American engineers and the construction
industry enthusiastically embraced prestressed concrete. While many of the early applications remained
in bridge construction, such as the lower Tampa Bay crossing now known as the Sunshine Skyway,
American engineers and contractors were simultaneously conceiving new devices, improving techniques,
and developing new materials for all types of structures.
The 1950s were the years that brought into focus the sevenwire strand, longline beds (Fig. 1.1.2),
admixtures, highstrength concrete, vacuum concrete, steam curing, and many other innovations. With
these developments, coupled with the technical and logistical support provided by PCI (chartered in
1954), the industry grew, and the applications of precast and prestressed concrete began to appear in an
impressive variety of structures. See chapter 9 for information related to materials used in the precast,
prestressed concrete industry.
Development of standard products was one of the major activities through the 1950s and the 1960s. Early
in the 1960s, the federal government–sponsored program Operation Breakthrough led to the introduction
of different highrise, precast concrete building types for housing. As part of this program, a significant
testing program was conducted by the Portland Cement Association to establish design principles to
prevent progressive failure and to ensure the safety of highrise precast buildings. These rules were
adopted into the ACI 318 building code as early as 1963 and have been expanded upon since. The basis
for this handbook is ACI 31805.3
In the late 1970s, lowrelaxation strand was introduced, which reduced the loss of prestress force due to
relaxation in the strand, thus allowing more efficient use of prestressing and resulting in longer spans and
smaller sections. Larger strand sizes have been made available as well, such as 0.6in.diameter strand.
In the field of bridges, there was the development of spliced girders, segmental
bridges (Fig. 1.1.3), cable-stayed bridges (Fig. 1.1.4), and cantilevered girder
bridges.
During the 1980s, both engineers and owners recognized that durability is an
important aspect of a structure. The precast and prestressed concrete industry
responded by taking advantage of one of its natural strengths. Plant-cast concrete is
more durable than site-cast concrete because it can be cast with lower water–
cementitious materials ratios and under controlled conditions. This natural durability
was enhanced
with the development of admixtures that make the concrete matrix more impermeable, which inhibits
steel corrosion. Pretopped doubletees were developed for parking structures to maximize the benefits of
the durability of precast, prestressed concrete at the wearing surface.
The past few decades have seen the development of more efficient structural sections and more
complex architectural shapes and surface treatments. The increasing demands of owners and architects for
quality finishes has led to the development of new surface textures and surface treatments. Thinset brick
and stonefaced panels, as well as textures and colors of infinite variety, have been developed. Emerging
material technologies using ultrahighstrength concrete, selfconsolidating concrete, polymers, carbon
fibers, and highstrength steels continue to improve the capabilities of the industry.
With the consolidation of the model building codes and the incorporation of the
National Earthquake Hazard Reduction Program (NEHRP) provisions into the
International Building Code and the ASCE 7 load standard, design of precast
concrete structures for earthquake loading has become a new priority in much of
the United States. PCI and its producer members have met this challenge with a
sustained program of seismic research and the development of seismic systems and
connections that recognize the unique characteristics of precast construction.
1.1.2 Features and General Principles
Precasting concrete in PCI-Certified Plants ensures the manufacture of high-quality
architectural and structural products. Precasting also facilitates production of a wide
variety of shapes and sizes, and the use of prestressing substantially extends the
span capability of the products. Similarly, prestressing, defined by ACI 318-05 as
“concrete in which internal stresses have been introduced to reduce potential
tensile stresses in concrete resulting from loads,” can be used to enhance the
structural capabilities of a concrete component. These capabilities enable architects
and engineers to achieve highly innovative and economically competitive buildings
and other structures.
This handbook serves as the primary reference for the design and use of precast
and prestressed concrete structures. This chapter enumerates some of the
important and unique features and benefits of precast and prestressed concrete.
These include the following:
• Speed of construction resulting from the ability to begin casting components for
the superstructure while foundation work is in progress, and being able to erect the
superstructure year round without delays caused by harsh weather or additional
curing requirements.
• Design flexibility from the long-span capabilities result in larger open areas in
buildings and fewer piers in bridges.
• Fire resistance, which provides improved safety and reduced insurance premiums.
• Durability, which allows the material to have a long service life, in some cases
more than 100 years, and reduced life cycle costs.
• With prestressing, components have greater span-to-depth ratios, enhanced
performance, and less material usage.
• Aesthetic flexibility, achieved by the variety of textures, colors, finishes, and inset
options that are available and can mimic granite, limestone, brick, and other
materials in virtually any shape and configuration.
• Acoustical control, which results in pleasant work and living conditions for
inhabitants and users.
• Thermal and energy efficiency, due to the material’s high thermal mass, which
can be enhanced further with the use of insulated sandwich panels.
• Sustainability by efficiently using materials and energy resources to minimize their
depletion.
• Improved quality control resulting from being manufactured under plant-controlled
conditions.
• Modular construction and design capabilities lending well to future reuse of
systems for a variety of functions.
• Ability to design redundancy into the building systems to provide blast resistance
and structural integrity.
To fully realize these benefits and gain the most economical and effective use of the
material, the following general principles are offered:
• Precast concrete is basically a simple-span material. However, continuity can be,
and often is, effectively achieved with properly engineered connection details with
and without the use of field-cast concrete.
• Sizes and shapes of components should consider production, hauling, and erection
techniques.
• Concrete is a massive material. This is an advantage for such matters as stability
under wind and seismic loads, thermal changes, vibration, and fire resistance.
• Maximum economy is achieved with maximum repetition. Standard or repetitive
sections should be used whenever possible.
• The most efficient and economical use is largely dependent on an effective
structural layout and carefully conceived connection details.
• The effects of volume changes caused by creep, shrinkage, and temperature
change and the potential restraint of these effects must be considered in every
structure.
• Architectural precast concrete panels can be used as cladding as well as loadbearing components. They can be used to support both gravity and lateral loads.
• Prestressing improves the economy and performance of precast concrete
components, but is usually only economically feasible with standard shapes that are
capable of being cast in long-line beds.
1.1.3 Sustainability and LEED Considerations
Precast concrete components can contribute to sustainable designs and in meeting
standardized requirements for environment-friendly designs. Sustainability and
other terms such as “environmental friendliness” and “green buildings” have
become watchwords for owners and architects when designing new buildings to
attain several of the rating criteria incorporated into the Leadership in Energy and
Environmental Design (LEED) standards4 from the U.S. Green Building Council
(USGBC). In general, sustainability is considered to mean “development that meets
present needs without compromising the ability to meet the needs of future
generations.”5 This can be interpreted many ways, but in general most would agree
that this translates to reducing the amount of virgin raw materials used and that
buildings and components are durable, have long life cycles and are environmentally sensitive.
Today’s approach to sustainable design extends beyond the ability to use renewable or recycleable
resources to examine all environmental flows (materials and energy requirements) for the entire life cycle
of a component or building. This environmental accounting practice (known as lifecycle assessment or
LCA) encompasses all the energy and materials necessary to manufacture, deliver, install, and use the
product, including fuel to extract materials, finish them, and transport them to the site, for its entire life
cycle (cradle to grave).
Precast concrete’s inherent durability contributes greatly to its sustainable
attributes. For more information, on precast concrete’s contributions to the LEED
systems, consult "Sustainability" in PCI's Designer’s Notebook Series.6
1.1.4 Common Products
While precast and prestressed concrete components can be manufactured in a variety of customized
sizes and shapes, maximum economy is achieved by using the common products that have evolved in the
industry. Among the more prevalent of these products are doubletees (Fig. 1.1.5) and hollowcore slabs
(Fig. 1.1.6). Doubletees are efficient for spans in the range of 40 ft to 80 ft using depths of 24 in. to 34
in., respectively, although longer spans are possible with deeper sections. Hollowcore slabs are available
in a variety of widths ranging from 16 in. to 12 ft, and are used for spans up to about 40 ft. Figure 1.1.7
shows these and other commonly used products. The Ibeam, box beam, and bulbtee are used in bridge
construction. The invertedtee and ledger beam are used for structural framing to support deck
components.
Square or rectangular columns, with or without corbels, are an integral part of the precast concrete
columnbeamdeck framing that makes rapid, allweather erection possible. Precast concrete piles are
manufactured in a variety of shapes, including round, square, hexagonal, and octagonal, as well as
rectangular sheet piles. Channel slabs are used to support heavy floor or roof loads in short and medium
span ranges. Stadium riser units (Fig. 1.1.8) and raker beams (Fig. 1.1.9) have gained prominence during
the past two decades in stadium/arena construction. These risers are typically cast as single, double, or
triple step units and offer spans up to 60 ft, depending on their depth. Precast concrete modular products
have also established a strong presence in the construction industry, most noticeably as cell units for
correctional facilities (Fig. 1.1.10). Single, double, and quadcell modules can be manufactured,
finished, and furnished at a precaster’s facility, significantly reducing onsite labor and schedule
demands. Additionally, precast concrete pavements have been introduced as a material for rapid
construction in transportation systems (Fig. 1.1.11).
Quality precast and prestressed products are assured when products are designed in accordance with the
latest engineering standards and produced in plants where PCI’s Plant Certification Program is an integral
part of plant production. The program assures specifiers of a manufacturing plant’s audited capability to
produce quality products. A minimum of two unannounced plant inspections are performed each year by
specially trained engineers of PCI’s independent quality auditing agency to evaluate and grade
compliance with current performance standards. These performance standards can be found in PCI
qualitycontrol manuals Manual for Quality Control for Plants and Production of Structural Precast
Concrete Products (MNL1161999)7 and Manual for Quality Control for Plants and Production of
Architectural Precast Concrete Products (MNL1171996).8 These manuals are considered industry
standards for quality assurance and control. A plant that does not achieve a minimum required quality
audit score loses certification. Plant certification is a prerequisite for PCI producer membership. Plants in
Canada subscribe to a similar plant certification program based on the Canadian Standards Association
(CSA) A251 Standard. For more information on the PCI Plant Certification Program, see Section 14.4.
The high-quality standard products noted previously form the basis for configuring a
wide variety of systems for buildings, bridges, parking structures, and other
structures. The following pages provide an overview of some of the applications. For
other applications and also for products and practices suitable in different
geographical zones, contact with the regional producers is highly recommended. A
list of PCI producer members as well as other information pertinent to the industry
can be obtained by contacting PCI or accessing the PCI website at www.pci.org.
Design of precast and prestressed concrete products and structures for the building
industry is usually based on ACI 318-05.
Section 1.4 of ACI 31805 specifically allows variances when analysis, research, or testing demonstrates
structural adequacy. PCI publishes "PCI Standard Design Practice," included in Section 14.1 of this
handbook, that identifies many of the variations commonly encountered in precast/prestressed concrete
construction. This is regularly updated to reflect code changes, the latest research results, and new
experience. The longterm objective is to augment ACI 31805 building code with proven industry
practices to develop the best designs that take advantage of the many special features of precast and
prestressed concrete.
Design of precast and prestressed concrete products and structures for the
transportation sector is usually based on the AASHTO LRFD Bridge Design
Specifications.9 While these specifications encompass the entire range of
substructure and superstructure types, PCI publishes the Bridge Design Manual10 for
guidance with examples specific to precast, prestressed concrete systems.
1.2 Applications
The developments in products, materials, and techniques noted in the previous section have made
precast/prestressed concrete competitive in a variety of residential, commercial, institutional, industrial,
transportation, and other types of structures. A few examples of applications for different types of
structures are given in this section.
1.2.1 Building Structures
Owners, developers, and designers recognize the many inherent qualities of precast and prestressed
concrete that make it suitable for many types of building structures. Precast and prestressed concrete
building structures, assembled from highquality, plantproduced products, provide superior flexibility for
achieving the required degrees of fire resistance, sound control, energy efficiency, sustainability, and
durability. The availability of various materials and finishes makes it possible to render almost any
desired aesthetic character. The speed of construction that is possible with precast and prestressed
concrete minimizes onsite labor costs and reduces the cost of interim financing, providing important
overall economy to the owner and developer.
1.2.1.1 Total-Precast-Concrete Systems
Totalprecastconcrete solutions have been provided by the precast concrete industry for many years.
The ability for a building’s structural solution to be completely prefabricated and erected by a single
source precast concrete manufacturer continues to be of more and more value to the owner, the con
tractor, and the design team in today’s fastpaced environment. Support systems can be typical beam and
column framing with doubletee decks (Fig. 1.2.1), precast concrete loadbearing walls, loadbearing
architectural precast concrete exterior panels (Fig. 1.2.2), special framing systems, and any combination
of these vertical loadbearing components. Floor slabs and roof slabs for totalprecastconcrete buildings
are typically either doubletees or hollowcore slabs. The single source of responsibility makes project
management and construction of these buildings much easier and eliminates the cost and schedule risk
created by having many different material suppliers all working on the site at one time. While site work is
being performed and foundations are being built, the precast concrete engineering, drawing coordination,
and production are simultaneously taking place so that, when the site is ready, the total structure can be
erected without interruption. The ability to overlap many of the critical path items makes totalprecast
concrete systems one the fastest building systems available. Figures 1.2.3 and 1.2.7 illustrate another
example of totalprecastconcrete systems.
1.2.1.2 Precast Concrete Cladding
Architectural precast concrete cladding, illustrated in several figures in this chapter (Fig. 1.2.4 through
1.2.6), provides significant flexibility for architectural expression with the economy of mass production
of precast concrete components. The cladding may serve only as an enclosure for the structure or may be
designed to support gravity loads. Cladding may also be designed to contribute to the resistance of lateral
loads.11
Architectural precast concrete can be cast in almost any color, form, or texture to meet aesthetic and
functional requirements (Fig. 1.2.8 through 1.2.11). Special sculptured effects can provide such visual
expressions as strength and massiveness or grace and openness (Fig. 1.2.12). Aesthetic versatility is
possible in both color and texture by varying aggregate and matrix color, size of aggregates, finishing
processes, and depth of aggregate exposure. Architectural precast concrete can also be designed to match
existing systems, benefiting historical renovation and expansion projects.
PCI has developed a guide to assist designers in selecting colors and textures for architectural precast
concrete.12 Additional flexibility of aesthetic expression is achieved by casting various other materials,
such as veneers on the face of precast concrete panels. Natural stone, such as polished and thermal
finished granite, limestone, marble, and clay products, such as brick, tile, and terracotta, have been
frequently used as veneer materials.13
In addition to the freedom of aesthetic expression achievable with loadbearing or nonloadbearing
architectural precast concrete, there are a number of other important functional and construction
advantages. Insulated wall panels consist of two concrete wythes with a continuous layer of rigid
insulation sandwiched between them. These types of panels contribute substantially to the overall thermal
efficiency of a building. In castinplace concrete construction, precast concrete cladding panels are
sometimes used as permanent concrete formwork, thus becoming an integral part of the structure. Offsite
preassembly of all components comprising a total wall system, including window sash and glazing, can
also be very cost effective. For more comprehensive information about the possibilities available with
architectural precast concrete, see Architectural Precast Concrete, MNL12207.13
Glass-fiber-reinforced concrete (GFRC) has been adopted for use in producing
strong, thin, light–weight architectural cladding panels. GFRC is a portland cement–
based composite reinforced with randomly dispersed, alkali-resistant glass fibers.
The fibers serve as reinforcement to enhance flexural, tensile, and impact strength
of concrete. A major benefit of GFRC is its light weight, which provides for
substantial economy resulting from reduced costs of product handling, transportation, and erection, and also results in lower seismic loads.
1.2.1.3 Residential Buildings
Precast and prestressed concrete has broad acceptance in lowrise and midrise apartment buildings
(Fig. 1.2.13 and 1.2.14), hotels, motels, condominiums, dormatories, retirement housing, and nursing
homes. The superior fire resistance and soundcontrol features are specifically recognized by owners and
developers.
Twohour fire containment within each living unit provides a high level of safety for adjacent units.
With this type of highquality precast concrete housing, fire insurance rates are reduced and often higher
incomes can be generated because of the safer, more soundproof, higher quality environment and lifestyle
offered.
1.2.1.4 Justice Facilities
Justice facilities encompass many types of building occupancies. These include jails, prisons, police
stations, courthouses, juvenile halls, and special mental health or drugabuse treatment centers (Fig.
1.2.15).
Precast concrete has proven to be the favored system for justice facilities because it has many inherent
benefits that are important to these building types. In addition to the benefits noted previously, precast
and prestressed concrete is ideal for building in the desired level of physical security coupled with
efficient accommodation of security hardware and communication systems. The thickness and
reinforcement of typical precast concrete wall and slab systems, when designed for gravity and lateral
loads, are sufficient even for maximum security requirements. Typical precast concrete products such as
loadbearing insulated wall panels, cell walls, and floor slabs are employed frequently in justice facilities.
Also, the modular nature of precast and prestressed concrete products facilitates preinstallation of
necessary security and communication hardware in the plant, greatly simplifying field installation work as
well as saving valuable time on the project’s critical path.
The use of precast concrete box modules in single, double (Fig. 1.2.16), and quadcell (Fig. 1.2.17)
configurations has greatly reduced field labor, erection time, overall construction time, punch list
problems, multitrade confusion and, ultimately, cost and schedule risk. These units can be quickly stacked
and can be substantially completed with outfitted materials (bunks, plumbing, desks, and the like) (Fig.
1.2.18) in the precasting plant requiring little finishing work in the field, thereby enhancing the quality
and improving the schedule (Fig. 1.2.19).
Given the serious shortage of justice facilities, savings in total project time is often a critical consideration
in selection of a structural material and system for these projects. Case histories show that totalprecast
concrete projects have resulted in saving one to two years of construction time over the estimated sched
ule for competing systems. These experiences and the other considerations discussed have led to rapid
growth in the use of precast and prestressed concrete in justice facilities projects.
1.2.1.5 Office Buildings
There are many uses of precast and prestressed concrete in officebuilding construction, from total
building systems to single products like precast concrete stairs. Precast and prestressed concrete beams,
columns, and floors are used in framing systems; shear walls can be used alone or in conjunction with
beams and columns to resist lateral loads. Precast concrete stairs, along with being economical, provide
immediate safe use of stairwells during construction. Architectural precast concrete is used with all types
of framing systems. It provides an economical, fireresistant, soundproof, durable, maintenancefree
cladding that allows the architect much freedom of expression and results in beautiful facades. Archi
tectural precast concrete cladding is discussed more fully in Section 1.2.1.2 and in Chapter 7 of this
handbook. Also see Reference 13.
Significant time savings in both design and production usually result from the choice of a totalprecast
concrete structure. The superstructure is prefabricated while the onsite foundations are being built. Details
of this type of construction are shown in Fig. 1.2.1. Potential construction delays are reduced with the
complete building system being supplied under one contract. Erection of large, precast concrete
components can proceed even during adverse weather conditions to quickly enclose the structure. Load
bearing, architectural precast concrete panels provide a finished exterior as the superstructure is erected.
The prestressed floors provide an immediate working platform that allows the interior workers to get an
early start on the mechanical, electrical, and interior finishing work. The quality finishes and fast
production and erection schedules result in early occupancy, increased tenant satisfaction, and reduced
financing costs, making precast and prestressed concrete buildings very suitable for office buildings.
1.2.1.6 Warehouses and Industrial Buildings
The ability of prestressed concrete to span long distances with shallow depths and carry heavy loads is
particularly suitable for warehouses and industrial buildings (Fig. 1.2.20 and 1.2.21). Standard prestressed
concrete walls, insulated or noninsulated, are very economical for warehouse and light manufacturing
applications. Totalprecastconcrete systems with prestressed roof diaphragms and precast concrete shear
walls can provide owners with a complete structural package. In heavy industrial projects, prestressed
floor units capable of carrying the heavy floor loads typical of industrial facilities (Fig. 1.2.22) can
be combined with other precast concrete components to construct versatile, low
maintainence, and corrosion-resistant structural systems. The precast and
prestressed concrete framing can be designed to accommodate a variety of
mechanical systems and to support bridge cranes for industrial uses. High-quality
precast concrete provides improved protection against fire, dampness, and
resistance to a variety of chemical substances. The smooth surfaces achievable in
precast concrete make it ideal for food processing, wet operations, computercomponent manufacturing, and many other types of manufacturing and storage
operations where cleanliness is a critical concern. Clear spans of 40 ft and 80 ft are
possible using hollow-core and double-tees, respectively. Even longer spans to
about 150 ft can be obtained with bridge-type girders or special double-tees.
1.2.1.7 Educational Facilities
Both students and taxpayers benefit immensely when educational facilities are built using
precast/prestressed concrete systems. The natural and inherent benefits of the material are realized as well
as many that are unique and of special value to educational facilities (Fig. 1.2.23 through 1.2.25).
While fire safety is important in all educational facilities, it is particularly important in elementary
schools and middle schools where younger children are present. Precast concrete floors and walls do not
burn, and, therefore, do not add fuel to a fire, providing overall improved fire safety. School structures
can also be compartmentalized, easily containing a fire to a limited area.
Precast concrete contributes significantly to energy conservation and sustainability. Insulated sandwich
wall panels provide better overall thermal resistance or a higher Rvalue for a wall assembly than other
materials. The massive nature of precast concrete structures provides a thermal lag that reduces overall
heating and cooling expenses and provides a high comfort level for the occupants.
Most education facilities need to be completed on a fast track schedule to satisfy opening day. Precast
concrete is a perfect material for these tight schedules, since many of the critical path items can be
overlapped. Building superstructure components are all cast offsite while upfront coordination, site
preparation, and foundations are completed at the same time.
Several educational facilities have been confronted with mold that has been deemed dangerous to the
occupants, and remedial cleanup procedures have resulted in these facilities being closed for an entire
school year. Precast concrete provides water tight, quality vapor barriers and eliminates the water and
moisture that contribute to the growth of mold. Precast concrete insulated wall panels, architectural
precast concrete exterior walls, and precast concrete floor slabs are also free of the organic material that is
required for mold to grow.
The density that precast concrete floors and walls inherently have also provides
improved acoustical qualities that provides students with a quiet environment that
promotes learning.
1.2.1.8 Other Building Structures
The many benefits of precast and prestressed concrete make it suitable for many other types of
buildings in addition to residential, justice facilities, office buildings, industrial buildings, and educational
facilities. Applications abound in commercial buildings such as shopping malls, and public buildings,
including hospitals, libraries, museums (Fig. 1.2.26) and airport terminals. Precast and prestressed con
crete has also been effectively used in numerous retrofit projects.
1.2.2 Parking Structures
Architects, engineers, developers, and owners have made precast and prestressed concrete the material
of choice for their commercial, municipal, and institutional parking needs. Though classified and
constructed as buildings, parking structures are unique; in some ways, they may be compared with
bridges with multiple decks. They are subjected to moving loads from automobile traffic, and the roof
level of a parking structure is exposed to weather in much the same way as a bridge deck. In addition,
they are usually openair structures and, thus, the entire structure is subjected to ambient weather
conditions. Also, exposure to deicing salts in northern climates or to saltladen atmospheres in coastal
regions requires special consideration of durability to ensure longterm performance.
The controlled conditions in a precast concrete plant assures the parkingstructure owner of both the
quality concrete and workmanship that provides longterm durability. The low water–cementitious
materials ratio concrete that precast concrete manufacturers use has been proven to increase resistance to
deterioration as compared with other materials. Studies 14 have also shown that accelerated curing makes
precast concrete more resistant to chloride penetration than fieldcured concrete.
These inherent, enhanced durability characteristics, along with lowcost, rapid erection in all weather
conditions, unlimited opportunities for architectural expression, and long clear spans make precast
concrete the natural choice for parking structures. Through surveys of existing structures and other
experiences, and through PCIfunded and private research and development, significant improvements
have been achieved in engineering stateoftheart parking structures. This accumulated experience and
knowledge has been assembled in a comprehensive publication, Precast, Prestressed Parking Structures:
Recommended Practice for Design and Construction,15 that includes recommendations on planning,
design, construction, and maintenance.
Figures 1.2.27 and 1.2.28 show typical precast concrete parking structures. Longspan doubletees are
shown in Fig. 1.2.29, and Fig. 1.2.30 shows doubletees bearing on an innovative litewall that adds
openness and enhances both the perceived and actual security. Figure 1.2.31 shows a precast, prestressed
spandrel beam being erected into pockets of a precast concrete column. This same figure also shows a
doubletee bearing on an interior, invertedtee beam spanning from column to column. Interior spandrel
beams can also serve as bumpers for automobile traffic (Fig. 1.2.32).
Vertical expansion of precast concrete parking structures can be accomplished with special erection
methods that allow for erection of new components over erected decks (Fig. 1.2.33). This erection
method also allows precast concrete to be considered for expansion of nonprecast concrete structures.
1.2.3 Stadiums/Arenas
Large stadiums and arenas (Fig. 1.2.34 and 1.2.35) are complex structures that can benefit significantly
from the applications of precasting technology. Often these projects are built on tight schedules to
accommodate a specific sporting event. Because of both the constructionperiod advantages and the long
term, lowmaintenance characteristics, precast and prestressed concrete has been the overwhelming
choice for many of these projects. For the same reasons, precast/prestressed concrete systems are also
beneficial for smaller facilities such as high schools and small arenas (Fig. 1.2.36).
Massproduced seating units have been manufactured in a variety of configurations and spans to provide
for quick installation and longlasting service. Local producers can provide the best advice regarding
readily available riser sections.
Longspans and the ability to eliminate costly field formwork makes precast, prestressed concrete the
best choice for many components of stadium construction, especially for seating that can be standardized
to take advantage of repeated form utilization. Construction of components that would require tall
scaffolding towers to fieldform, such as raker beams and ring beams, can be simplified by precasting
these units in a plant, delivering them to the site, and lifting them into place (Fig. 1.1.8 and 1.1.9).
Pedestrian ramps, mezzanine floors, concession, toilet, and dressingroom areas can all be efficiently
framed and quickly constructed using precast, prestressed concrete components.
The technique of posttensioning precast concrete segments together has made complex cantilever arm
and ring beam construction possible, which can efficiently support the roofs of these structures. Post
tensioning can be employed to minimize the depth of precast concrete cantilevered raker beams, which
carry the seating and provide unhindered viewing of the playing surface.
1.2.4 Bridges
Bridge construction gave the prestressing industry its start in North America. Precast and prestressed
concrete is now the dominant structural material for short to mediumspan bridges. With its inherent
durability, low maintenance, performance, and assured quality, precast and prestressed concrete is a
natural product for bridge construction. The ability to quickly erect precast concrete components in all
types of weather with little disruption of traffic adds to the economy of the project. For short spans (spans
to 100 ft), use of box sections and doubletee sections have proven economical. However, the most
common product used for short to mediumspans is the Igirder. Spans to 150 or 160 ft are not
uncommon with Igirders and bulbtees. Spliced girders allow spans as much as 300 ft. 16 Even longer
spans (300 ft and up) can be achieved using precast concrete box girder segments, which are then post
tensioned together in the field. Using cable stays, the spanning capability of precast and prestressed
concrete has been increased to over 1000 ft.
An important innovation in bridge construction has been the use of precast concrete in horizontally
curved bridges. A study17 commissioned by PCI documents the technical feasibility and the economic
viability of this application.
Another application of precast and prestressed concrete in bridge construction is the use of precast
concrete deck panels.18 Used as stayinplace forms, the panels reduce field placement of reinforcing steel
and concrete, resulting in considerable savings in both cost and schedule. The panels become composite
with the fieldplaced concrete for live loads.
Through PCI’s commitment to provide quality bridges for the transportation infrastructure, the Bridge
Design Manual was published to provide guidance to engineers and owners on the design of precast
concrete bridges. Precast concrete not only is the choice material for highway bridges, but also finds
tremendous use in railway bridges.
Figures 1.2.37 through 1.2.42 show some of these applications that have been
discussed.
1.2.5 Other Structures and Applications
The inherent qualities of precast and prestressed concrete noted in previous sections and the high degree
of design flexibility also make it ideal for a wide variety of special applications. Properties such as
corrosion resistance, fire resistance, durability, and fast installation have been used to good advantage in
the construction of poles (Fig. 1.2.43), piles, railroad ties (Fig. 1.2.44), storage tanks (Fig. 1.2.45 and
1.2.46), monorails (Fig. 1.2.47), retaining walls, highway and runway pavements, and sound barriers (Fig.
1.2.48).19–25 Where repetition and standardization opportunities exist, precasting components can
economically provide the quality of plantmanufactured products while eliminating expensive and risky
field procedures. Precast, prestressed concrete can also be used efficiently in customized applications,
blending function and form to suit any contextsensitive environment. These applications are too
numerous to categorize here separately but examples are illustrated in the figures in this chapter.
1.3 Production Process
The methods used to produce precast concrete components vary with the type of component being
manufactured. Among the factors influencing the production process are:
• Structural components versus architectural components
• Longline, multipiece forms versus singlepiece forms
• Prestressed components versus nonprestressed components
• Pretensioned components versus posttensioned components
• Production facility limitations
Discussions with regional precasters during project development will allow these factors to be
considered in the design of the precast concrete components and structures. See Fig. 1.3.1 through 1.3.5
for various aspects of production.
1.3.1 Structural Components versus Architectural Components
Structural precast concrete components are traditionally produced in a process aimed toward high
volume and high efficiency. Emphasis is placed on using standard shapes so that forms can be reused
multiple times. These forms are usually long steel forms designed to produce a number of components
with each casting. Products commonly considered to be structural components include doubletees, bridge
girders, interior beams, hollowcore units, and interior walls. Precast concrete producers certified by PCI
as structural or commercial fabricators must comply with the requirements of PCI 's MNL11699.
The flexibility of architectural precast concrete allows designers to incorporate a wide array of shapes,
colors, and textures into a project’s appearance. This demands that the precast producer be capable of
constructing complex forms, using a variety of concrete mixtures and offering an assortment of surface
treatments such as sandblasting, acid etching, or veneers of brick, stone, or other decorative material.
Architectural precast concrete components are fabricated under the guidelines of PCI's MNL11796.
Components manufactured in accordance with these guidelines must satisfy stringent dimensional
tolerances and offer consistent appearances to match finish samples accepted by the architect. These
requirements commonly demand that the product be poured on custommade forms with special attention
given to true, flat surfaces, clean edges and consistent concrete color and texture. Fiberglasscoated forms
are often used to achieve the desired surface quality, and all form joints are sealed to ensure clean edges.
Reinforcement is hung from prestressing strands within the component or stiff assemblies spanning
across the form. This eliminates the need for reinforcing chairs, which might become visible on the
exposed face of the component. Special care must be taken to maintain adequate cover over the
reinforcement, not only to maintain durability but also to prevent reinforcement patterns from shadowing
through to the face of the component.
In instances where exacting tolerances and ornate shapes are not needed but special surface treatment or
colors are desired, consideration should be given to using a PCICertified commercial producer capable
of providing such services. These producers are designated with an A suffix on their classification (for
example, C3A), and have demonstrated their ability to apply special finishes to their structural products.
Additional information regarding plant certification categories can be found in Section 14.4 of this
handbook.
1.3.2 Long-Line, Multi-Piece Forms versus Single-Piece Forms
When producing large quantities of a standard shaped component, precasters will commonly use a long
line form approach. These longline forms may be several hundred feet long and are designed to produce
a number of pieces with each casting. In most instances, the components produced in this fashion are
pretensioned, prestressed components. Products such as beams and doubletees use bulkheads at the end
of each unit in the form while extruded products such as hollowcore are placed as one continuous piece
of concrete and then cut to the prescribed component lengths after curing.
Singlepiece forms are used with the intent of making one piece with each casting. This type of forming
system readily accommodates nonprestressed or posttensioned products, and is commonly used for
architectural precast concrete components. It can also be used to create custom structural and architectural
applications.
1.3.3 Prestressed Components versus Non- Prestressed Components
Where a component’s dimensions and applied loads will allow, a precaster may elect to use reinforcing
bars or welded wire to reinforce the product. In these cases, a reinforcing cage or mat is usually
assembled and placed in the form. Concrete is then placed and vibrated around the assembly. Care must
be taken by the designer to check crack control and deflections when using this type of design.
Concrete components are prestressed to achieve higher spantodepth ratios and provide resistance to
cracking. Prestressing is incorporated into a component in the form of pretensioned or posttensioned
strands. Prestressing is generally used as the primary reinforcement with reinforcing bars or weldedwire
reinforcement serving as secondary reinforcement.
1.3.4 Pretensioned Components versus Post-Tensioned Components
In pretensioned components, strands are first tensioned, then supplemental reinforcing bars and other
items to be embedded in the component are secured and concrete is placed into the form. After the
concrete is allowed to cure and forms a bond with the pretensioned strands, the strands are cut
(detensioned) and the prestressing force is transferred from the strands to the concrete through bond and
mechanical interlock. At this point, the components are removed from the form and placed in storage.
Posttensioning is typically tied to a cage or mat of reinforcement, which is then placed into the form.
Mechanical anchorages are placed at each end of the tendon and secured to the form or the reinforcement.
After concrete has been placed and cured within the form, the prestressing force is applied to the post
tensioning strands and held at the mechanical anchorages. At this point, the prestress force has been trans
ferred to the component, which can then be stripped out of the mold and placed in storage.
Under some circumstances, a combination of pretensioning and posttensioning may be used. This
approach may be used where the self-stressing forms or tensioning abutments cannot
sustain the full prestressing force. In this case, the majority of the force is applied
through pretensioned strands, and post-tensioned tendons are used to introduce the
remainder of design prestressing force after the component is stripped. This
approach may also be used in prestressed panels that are poured in a flat position
but stand in an upright position in service. Occasionally, the full prestress force will
cause cracking in the panel while it is flat in the form. This cracking can be avoided
by applying a portion of the prestress by post-tensioning after the panel is stripped
and upright. Thought should be given to space restrictions at the anchorage area
and the additional cost of a two-step process.
1.3.5 Production Limitations
A wide variety of products, in a variety of shapes and sizes, are generally available. Not all products are
available in all geographical areas, and, therefore, designers should be aware of these limitations during
the project development. Contacting regional precast concrete producers in the project's area is the best
way to ensure that the design team takes maximum advantage of precast concrete elements that are
readily available.
The size of the piece may be limited by the handling equipment available in the manufacturing plant or by
the transporting and erection equipment available. In most cases, manufacturers are geared to produce
standard products that can be transported over the road with a minimum of special permits. Unusually
large pieces can be made, but the special equipment required to handle such pieces can significantly add
to the cost.
The tensioning capacity of the prestressing beds may be another limitation. Some products, such as deep,
longspan bridge girders require massive stressing abutments and beds that can handle large holddown
forces for depressed strands. These capabilities are costly and must usually be amortized over a number
of projects. For large projects with many pieces, it is sometimes economical to install special facilities
that can be written off on the single project. Selfstressing forms, which resist the large forces from the
stressing bulkheads with heavy compression members (usually steel) built into the forms, may be another
solution.
Environmental concerns may also limit the scope of a precaster’s operation. For example, in most cases,
operations like sandblasting and acid etching must be contained. The location of the facility related to
residences, businesses, streams, and the like may require special noise, dust, or runoff containment. These
are conditions that are confronted by almost all manufacturing industries, and generally are not
restrictions on the design and use of precast concrete products.
1.1.1 History of Precast, Prestressed Concrete in North America
The growth of precast and prestressed concrete is a story of the vision and
daring of a few notable people. These people took a new idea and
maximized its potential by modifying and improving existing methods,
conceiving new methods, and inventing new devices, all with a focus on
mass production. An excellent portrayal of the beginnings and the growth of
precast and prestressed concrete in North America and the early pioneers is
given in a series of papers1 that were developed to commemorate the 25year silver jubilee of the founding of the Prestressed Concrete Institute. A
similar publication2 was developed at the 50-year golden anniversary of the
Institute, which is now known as the Precast/Prestressed Concrete Institute
(PCI).
The most important event leading to the launching of the precast/prestressed concrete
industry in North America was the construction in 1950 of the famed Walnut Lane
Memorial Bridge in Philadelphia, Pa. (Fig. 1.1.1). From technical and historical
perspectives, it is both surprising and fascinating that the Walnut Lane Memorial Bridge
was constructed of prestressed concrete. There was very little published information on
the subject and there was a total lack of experience with linear prestressing in this
country at that time. Furthermore, the length of the bridge span (the main span of the
structure was 160 ft long) involved would have been a daring venture in the late 1940s
anywhere in the world. The bridge became a reality through a fortunate sequence of
events and the vision, courage, and persistence of a few extraordinary individuals.
Following completion of the Walnut Lane Memorial Bridge, American engineers and the construction
industry enthusiastically embraced prestressed concrete. While many of the early applications remained
in bridge construction, such as the lower Tampa Bay crossing now known as the Sunshine Skyway,
American engineers and contractors were simultaneously conceiving new devices, improving techniques,
and developing new materials for all types of structures.
The 1950s were the years that brought into focus the sevenwire strand, longline beds (Fig. 1.1.2),
admixtures, highstrength concrete, vacuum concrete, steam curing, and many other innovations. With
these developments, coupled with the technical and logistical support provided by PCI (chartered in
1954), the industry grew, and the applications of precast and prestressed concrete began to appear in an
impressive variety of structures. See chapter 9 for information related to materials used in the precast,
prestressed concrete industry.
Development of standard products was one of the major activities through the 1950s and the 1960s. Early
in the 1960s, the federal government–sponsored program Operation Breakthrough led to the introduction
of different highrise, precast concrete building types for housing. As part of this program, a significant
testing program was conducted by the Portland Cement Association to establish design principles to
prevent progressive failure and to ensure the safety of highrise precast buildings. These rules were
adopted into the ACI 318 building code as early as 1963 and have been expanded upon since. The basis
for this handbook is ACI 31805.3
In the late 1970s, lowrelaxation strand was introduced, which reduced the loss of prestress force due to
relaxation in the strand, thus allowing more efficient use of prestressing and resulting in longer spans and
smaller sections. Larger strand sizes have been made available as well, such as 0.6in.diameter strand.
In the field of bridges, there was the development of spliced girders, segmental
bridges (Fig. 1.1.3), cable-stayed bridges (Fig. 1.1.4), and cantilevered girder
bridges.
During the 1980s, both engineers and owners recognized that durability is an
important aspect of a structure. The precast and prestressed concrete industry
responded by taking advantage of one of its natural strengths. Plant-cast concrete is
more durable than site-cast concrete because it can be cast with lower water–
cementitious materials ratios and under controlled conditions. This natural durability
was enhanced
with the development of admixtures that make the concrete matrix more impermeable, which inhibits
steel corrosion. Pretopped doubletees were developed for parking structures to maximize the benefits of
the durability of precast, prestressed concrete at the wearing surface.
The past few decades have seen the development of more efficient structural sections and more
complex architectural shapes and surface treatments. The increasing demands of owners and architects for
quality finishes has led to the development of new surface textures and surface treatments. Thinset brick
and stonefaced panels, as well as textures and colors of infinite variety, have been developed. Emerging
material technologies using ultrahighstrength concrete, selfconsolidating concrete, polymers, carbon
fibers, and highstrength steels continue to improve the capabilities of the industry.
With the consolidation of the model building codes and the incorporation of the
National Earthquake Hazard Reduction Program (NEHRP) provisions into the
International Building Code and the ASCE 7 load standard, design of precast
concrete structures for earthquake loading has become a new priority in much of
the United States. PCI and its producer members have met this challenge with a
sustained program of seismic research and the development of seismic systems and
connections that recognize the unique characteristics of precast construction.
1.1.2 Features and General Principles
Precasting concrete in PCI-Certified Plants ensures the manufacture of high-quality
architectural and structural products. Precasting also facilitates production of a wide
variety of shapes and sizes, and the use of prestressing substantially extends the
span capability of the products. Similarly, prestressing, defined by ACI 318-05 as
“concrete in which internal stresses have been introduced to reduce potential
tensile stresses in concrete resulting from loads,” can be used to enhance the
structural capabilities of a concrete component. These capabilities enable architects
and engineers to achieve highly innovative and economically competitive buildings
and other structures.
This handbook serves as the primary reference for the design and use of precast
and prestressed concrete structures. This chapter enumerates some of the
important and unique features and benefits of precast and prestressed concrete.
These include the following:
• Speed of construction resulting from the ability to begin casting components for
the superstructure while foundation work is in progress, and being able to erect the
superstructure year round without delays caused by harsh weather or additional
curing requirements.
• Design flexibility from the long-span capabilities result in larger open areas in
buildings and fewer piers in bridges.
• Fire resistance, which provides improved safety and reduced insurance premiums.
• Durability, which allows the material to have a long service life, in some cases
more than 100 years, and reduced life cycle costs.
• With prestressing, components have greater span-to-depth ratios, enhanced
performance, and less material usage.
• Aesthetic flexibility, achieved by the variety of textures, colors, finishes, and inset
options that are available and can mimic granite, limestone, brick, and other
materials in virtually any shape and configuration.
• Acoustical control, which results in pleasant work and living conditions for
inhabitants and users.
• Thermal and energy efficiency, due to the material’s high thermal mass, which
can be enhanced further with the use of insulated sandwich panels.
• Sustainability by efficiently using materials and energy resources to minimize their
depletion.
• Improved quality control resulting from being manufactured under plant-controlled
conditions.
• Modular construction and design capabilities lending well to future reuse of
systems for a variety of functions.
• Ability to design redundancy into the building systems to provide blast resistance
and structural integrity.
To fully realize these benefits and gain the most economical and effective use of the
material, the following general principles are offered:
• Precast concrete is basically a simple-span material. However, continuity can be,
and often is, effectively achieved with properly engineered connection details with
and without the use of field-cast concrete.
• Sizes and shapes of components should consider production, hauling, and erection
techniques.
• Concrete is a massive material. This is an advantage for such matters as stability
under wind and seismic loads, thermal changes, vibration, and fire resistance.
• Maximum economy is achieved with maximum repetition. Standard or repetitive
sections should be used whenever possible.
• The most efficient and economical use is largely dependent on an effective
structural layout and carefully conceived connection details.
• The effects of volume changes caused by creep, shrinkage, and temperature
change and the potential restraint of these effects must be considered in every
structure.
• Architectural precast concrete panels can be used as cladding as well as loadbearing components. They can be used to support both gravity and lateral loads.
• Prestressing improves the economy and performance of precast concrete
components, but is usually only economically feasible with standard shapes that are
capable of being cast in long-line beds.
1.1.3 Sustainability and LEED Considerations
Precast concrete components can contribute to sustainable designs and in meeting
standardized requirements for environment-friendly designs. Sustainability and
other terms such as “environmental friendliness” and “green buildings” have
become watchwords for owners and architects when designing new buildings to
attain several of the rating criteria incorporated into the Leadership in Energy and
Environmental Design (LEED) standards4 from the U.S. Green Building Council
(USGBC). In general, sustainability is considered to mean “development that meets
present needs without compromising the ability to meet the needs of future
generations.”5 This can be interpreted many ways, but in general most would agree
that this translates to reducing the amount of virgin raw materials used and that
buildings and components are durable, have long life cycles and are environmentally sensitive.
Today’s approach to sustainable design extends beyond the ability to use renewable or recycleable
resources to examine all environmental flows (materials and energy requirements) for the entire life cycle
of a component or building. This environmental accounting practice (known as lifecycle assessment or
LCA) encompasses all the energy and materials necessary to manufacture, deliver, install, and use the
product, including fuel to extract materials, finish them, and transport them to the site, for its entire life
cycle (cradle to grave).
Precast concrete’s inherent durability contributes greatly to its sustainable
attributes. For more information, on precast concrete’s contributions to the LEED
systems, consult "Sustainability" in PCI's Designer’s Notebook Series.6
1.1.4 Common Products
While precast and prestressed concrete components can be manufactured in a variety of customized
sizes and shapes, maximum economy is achieved by using the common products that have evolved in the
industry. Among the more prevalent of these products are doubletees (Fig. 1.1.5) and hollowcore slabs
(Fig. 1.1.6). Doubletees are efficient for spans in the range of 40 ft to 80 ft using depths of 24 in. to 34
in., respectively, although longer spans are possible with deeper sections. Hollowcore slabs are available
in a variety of widths ranging from 16 in. to 12 ft, and are used for spans up to about 40 ft. Figure 1.1.7
shows these and other commonly used products. The Ibeam, box beam, and bulbtee are used in bridge
construction. The invertedtee and ledger beam are used for structural framing to support deck
components.
Square or rectangular columns, with or without corbels, are an integral part of the precast concrete
columnbeamdeck framing that makes rapid, allweather erection possible. Precast concrete piles are
manufactured in a variety of shapes, including round, square, hexagonal, and octagonal, as well as
rectangular sheet piles. Channel slabs are used to support heavy floor or roof loads in short and medium
span ranges. Stadium riser units (Fig. 1.1.8) and raker beams (Fig. 1.1.9) have gained prominence during
the past two decades in stadium/arena construction. These risers are typically cast as single, double, or
triple step units and offer spans up to 60 ft, depending on their depth. Precast concrete modular products
have also established a strong presence in the construction industry, most noticeably as cell units for
correctional facilities (Fig. 1.1.10). Single, double, and quadcell modules can be manufactured,
finished, and furnished at a precaster’s facility, significantly reducing onsite labor and schedule
demands. Additionally, precast concrete pavements have been introduced as a material for rapid
construction in transportation systems (Fig. 1.1.11).
Quality precast and prestressed products are assured when products are designed in accordance with the
latest engineering standards and produced in plants where PCI’s Plant Certification Program is an integral
part of plant production. The program assures specifiers of a manufacturing plant’s audited capability to
produce quality products. A minimum of two unannounced plant inspections are performed each year by
specially trained engineers of PCI’s independent quality auditing agency to evaluate and grade
compliance with current performance standards. These performance standards can be found in PCI
qualitycontrol manuals Manual for Quality Control for Plants and Production of Structural Precast
Concrete Products (MNL1161999)7 and Manual for Quality Control for Plants and Production of
Architectural Precast Concrete Products (MNL1171996).8 These manuals are considered industry
standards for quality assurance and control. A plant that does not achieve a minimum required quality
audit score loses certification. Plant certification is a prerequisite for PCI producer membership. Plants in
Canada subscribe to a similar plant certification program based on the Canadian Standards Association
(CSA) A251 Standard. For more information on the PCI Plant Certification Program, see Section 14.4.
The high-quality standard products noted previously form the basis for configuring a
wide variety of systems for buildings, bridges, parking structures, and other
structures. The following pages provide an overview of some of the applications. For
other applications and also for products and practices suitable in different
geographical zones, contact with the regional producers is highly recommended. A
list of PCI producer members as well as other information pertinent to the industry
can be obtained by contacting PCI or accessing the PCI website at www.pci.org.
Design of precast and prestressed concrete products and structures for the building
industry is usually based on ACI 318-05.
Section 1.4 of ACI 31805 specifically allows variances when analysis, research, or testing demonstrates
structural adequacy. PCI publishes "PCI Standard Design Practice," included in Section 14.1 of this
handbook, that identifies many of the variations commonly encountered in precast/prestressed concrete
construction. This is regularly updated to reflect code changes, the latest research results, and new
experience. The longterm objective is to augment ACI 31805 building code with proven industry
practices to develop the best designs that take advantage of the many special features of precast and
prestressed concrete.
Design of precast and prestressed concrete products and structures for the
transportation sector is usually based on the AASHTO LRFD Bridge Design
Specifications.9 While these specifications encompass the entire range of
substructure and superstructure types, PCI publishes the Bridge Design Manual10 for
guidance with examples specific to precast, prestressed concrete systems.
1.2 Applications
The developments in products, materials, and techniques noted in the previous section have made
precast/prestressed concrete competitive in a variety of residential, commercial, institutional, industrial,
transportation, and other types of structures. A few examples of applications for different types of
structures are given in this section.
1.2.1 Building Structures
Owners, developers, and designers recognize the many inherent qualities of precast and prestressed
concrete that make it suitable for many types of building structures. Precast and prestressed concrete
building structures, assembled from highquality, plantproduced products, provide superior flexibility for
achieving the required degrees of fire resistance, sound control, energy efficiency, sustainability, and
durability. The availability of various materials and finishes makes it possible to render almost any
desired aesthetic character. The speed of construction that is possible with precast and prestressed
concrete minimizes onsite labor costs and reduces the cost of interim financing, providing important
overall economy to the owner and developer.
1.2.1.1 Total-Precast-Concrete Systems
Totalprecastconcrete solutions have been provided by the precast concrete industry for many years.
The ability for a building’s structural solution to be completely prefabricated and erected by a single
source precast concrete manufacturer continues to be of more and more value to the owner, the con
tractor, and the design team in today’s fastpaced environment. Support systems can be typical beam and
column framing with doubletee decks (Fig. 1.2.1), precast concrete loadbearing walls, loadbearing
architectural precast concrete exterior panels (Fig. 1.2.2), special framing systems, and any combination
of these vertical loadbearing components. Floor slabs and roof slabs for totalprecastconcrete buildings
are typically either doubletees or hollowcore slabs. The single source of responsibility makes project
management and construction of these buildings much easier and eliminates the cost and schedule risk
created by having many different material suppliers all working on the site at one time. While site work is
being performed and foundations are being built, the precast concrete engineering, drawing coordination,
and production are simultaneously taking place so that, when the site is ready, the total structure can be
erected without interruption. The ability to overlap many of the critical path items makes totalprecast
concrete systems one the fastest building systems available. Figures 1.2.3 and 1.2.7 illustrate another
example of totalprecastconcrete systems.
1.2.1.2 Precast Concrete Cladding
Architectural precast concrete cladding, illustrated in several figures in this chapter (Fig. 1.2.4 through
1.2.6), provides significant flexibility for architectural expression with the economy of mass production
of precast concrete components. The cladding may serve only as an enclosure for the structure or may be
designed to support gravity loads. Cladding may also be designed to contribute to the resistance of lateral
loads.11
Architectural precast concrete can be cast in almost any color, form, or texture to meet aesthetic and
functional requirements (Fig. 1.2.8 through 1.2.11). Special sculptured effects can provide such visual
expressions as strength and massiveness or grace and openness (Fig. 1.2.12). Aesthetic versatility is
possible in both color and texture by varying aggregate and matrix color, size of aggregates, finishing
processes, and depth of aggregate exposure. Architectural precast concrete can also be designed to match
existing systems, benefiting historical renovation and expansion projects.
PCI has developed a guide to assist designers in selecting colors and textures for architectural precast
concrete.12 Additional flexibility of aesthetic expression is achieved by casting various other materials,
such as veneers on the face of precast concrete panels. Natural stone, such as polished and thermal
finished granite, limestone, marble, and clay products, such as brick, tile, and terracotta, have been
frequently used as veneer materials.13
In addition to the freedom of aesthetic expression achievable with loadbearing or nonloadbearing
architectural precast concrete, there are a number of other important functional and construction
advantages. Insulated wall panels consist of two concrete wythes with a continuous layer of rigid
insulation sandwiched between them. These types of panels contribute substantially to the overall thermal
efficiency of a building. In castinplace concrete construction, precast concrete cladding panels are
sometimes used as permanent concrete formwork, thus becoming an integral part of the structure. Offsite
preassembly of all components comprising a total wall system, including window sash and glazing, can
also be very cost effective. For more comprehensive information about the possibilities available with
architectural precast concrete, see Architectural Precast Concrete, MNL12207.13
Glass-fiber-reinforced concrete (GFRC) has been adopted for use in producing
strong, thin, light–weight architectural cladding panels. GFRC is a portland cement–
based composite reinforced with randomly dispersed, alkali-resistant glass fibers.
The fibers serve as reinforcement to enhance flexural, tensile, and impact strength
of concrete. A major benefit of GFRC is its light weight, which provides for
substantial economy resulting from reduced costs of product handling, transportation, and erection, and also results in lower seismic loads.
1.2.1.3 Residential Buildings
Precast and prestressed concrete has broad acceptance in lowrise and midrise apartment buildings
(Fig. 1.2.13 and 1.2.14), hotels, motels, condominiums, dormatories, retirement housing, and nursing
homes. The superior fire resistance and soundcontrol features are specifically recognized by owners and
developers.
Twohour fire containment within each living unit provides a high level of safety for adjacent units.
With this type of highquality precast concrete housing, fire insurance rates are reduced and often higher
incomes can be generated because of the safer, more soundproof, higher quality environment and lifestyle
offered.
1.2.1.4 Justice Facilities
Justice facilities encompass many types of building occupancies. These include jails, prisons, police
stations, courthouses, juvenile halls, and special mental health or drugabuse treatment centers (Fig.
1.2.15).
Precast concrete has proven to be the favored system for justice facilities because it has many inherent
benefits that are important to these building types. In addition to the benefits noted previously, precast
and prestressed concrete is ideal for building in the desired level of physical security coupled with
efficient accommodation of security hardware and communication systems. The thickness and
reinforcement of typical precast concrete wall and slab systems, when designed for gravity and lateral
loads, are sufficient even for maximum security requirements. Typical precast concrete products such as
loadbearing insulated wall panels, cell walls, and floor slabs are employed frequently in justice facilities.
Also, the modular nature of precast and prestressed concrete products facilitates preinstallation of
necessary security and communication hardware in the plant, greatly simplifying field installation work as
well as saving valuable time on the project’s critical path.
The use of precast concrete box modules in single, double (Fig. 1.2.16), and quadcell (Fig. 1.2.17)
configurations has greatly reduced field labor, erection time, overall construction time, punch list
problems, multitrade confusion and, ultimately, cost and schedule risk. These units can be quickly stacked
and can be substantially completed with outfitted materials (bunks, plumbing, desks, and the like) (Fig.
1.2.18) in the precasting plant requiring little finishing work in the field, thereby enhancing the quality
and improving the schedule (Fig. 1.2.19).
Given the serious shortage of justice facilities, savings in total project time is often a critical consideration
in selection of a structural material and system for these projects. Case histories show that totalprecast
concrete projects have resulted in saving one to two years of construction time over the estimated sched
ule for competing systems. These experiences and the other considerations discussed have led to rapid
growth in the use of precast and prestressed concrete in justice facilities projects.
1.2.1.5 Office Buildings
There are many uses of precast and prestressed concrete in officebuilding construction, from total
building systems to single products like precast concrete stairs. Precast and prestressed concrete beams,
columns, and floors are used in framing systems; shear walls can be used alone or in conjunction with
beams and columns to resist lateral loads. Precast concrete stairs, along with being economical, provide
immediate safe use of stairwells during construction. Architectural precast concrete is used with all types
of framing systems. It provides an economical, fireresistant, soundproof, durable, maintenancefree
cladding that allows the architect much freedom of expression and results in beautiful facades. Archi
tectural precast concrete cladding is discussed more fully in Section 1.2.1.2 and in Chapter 7 of this
handbook. Also see Reference 13.
Significant time savings in both design and production usually result from the choice of a totalprecast
concrete structure. The superstructure is prefabricated while the onsite foundations are being built. Details
of this type of construction are shown in Fig. 1.2.1. Potential construction delays are reduced with the
complete building system being supplied under one contract. Erection of large, precast concrete
components can proceed even during adverse weather conditions to quickly enclose the structure. Load
bearing, architectural precast concrete panels provide a finished exterior as the superstructure is erected.
The prestressed floors provide an immediate working platform that allows the interior workers to get an
early start on the mechanical, electrical, and interior finishing work. The quality finishes and fast
production and erection schedules result in early occupancy, increased tenant satisfaction, and reduced
financing costs, making precast and prestressed concrete buildings very suitable for office buildings.
1.2.1.6 Warehouses and Industrial Buildings
The ability of prestressed concrete to span long distances with shallow depths and carry heavy loads is
particularly suitable for warehouses and industrial buildings (Fig. 1.2.20 and 1.2.21). Standard prestressed
concrete walls, insulated or noninsulated, are very economical for warehouse and light manufacturing
applications. Totalprecastconcrete systems with prestressed roof diaphragms and precast concrete shear
walls can provide owners with a complete structural package. In heavy industrial projects, prestressed
floor units capable of carrying the heavy floor loads typical of industrial facilities (Fig. 1.2.22) can
be combined with other precast concrete components to construct versatile, low
maintainence, and corrosion-resistant structural systems. The precast and
prestressed concrete framing can be designed to accommodate a variety of
mechanical systems and to support bridge cranes for industrial uses. High-quality
precast concrete provides improved protection against fire, dampness, and
resistance to a variety of chemical substances. The smooth surfaces achievable in
precast concrete make it ideal for food processing, wet operations, computercomponent manufacturing, and many other types of manufacturing and storage
operations where cleanliness is a critical concern. Clear spans of 40 ft and 80 ft are
possible using hollow-core and double-tees, respectively. Even longer spans to
about 150 ft can be obtained with bridge-type girders or special double-tees.
1.2.1.7 Educational Facilities
Both students and taxpayers benefit immensely when educational facilities are built using
precast/prestressed concrete systems. The natural and inherent benefits of the material are realized as well
as many that are unique and of special value to educational facilities (Fig. 1.2.23 through 1.2.25).
While fire safety is important in all educational facilities, it is particularly important in elementary
schools and middle schools where younger children are present. Precast concrete floors and walls do not
burn, and, therefore, do not add fuel to a fire, providing overall improved fire safety. School structures
can also be compartmentalized, easily containing a fire to a limited area.
Precast concrete contributes significantly to energy conservation and sustainability. Insulated sandwich
wall panels provide better overall thermal resistance or a higher Rvalue for a wall assembly than other
materials. The massive nature of precast concrete structures provides a thermal lag that reduces overall
heating and cooling expenses and provides a high comfort level for the occupants.
Most education facilities need to be completed on a fast track schedule to satisfy opening day. Precast
concrete is a perfect material for these tight schedules, since many of the critical path items can be
overlapped. Building superstructure components are all cast offsite while upfront coordination, site
preparation, and foundations are completed at the same time.
Several educational facilities have been confronted with mold that has been deemed dangerous to the
occupants, and remedial cleanup procedures have resulted in these facilities being closed for an entire
school year. Precast concrete provides water tight, quality vapor barriers and eliminates the water and
moisture that contribute to the growth of mold. Precast concrete insulated wall panels, architectural
precast concrete exterior walls, and precast concrete floor slabs are also free of the organic material that is
required for mold to grow.
The density that precast concrete floors and walls inherently have also provides
improved acoustical qualities that provides students with a quiet environment that
promotes learning.
1.2.1.8 Other Building Structures
The many benefits of precast and prestressed concrete make it suitable for many other types of
buildings in addition to residential, justice facilities, office buildings, industrial buildings, and educational
facilities. Applications abound in commercial buildings such as shopping malls, and public buildings,
including hospitals, libraries, museums (Fig. 1.2.26) and airport terminals. Precast and prestressed con
crete has also been effectively used in numerous retrofit projects.
1.2.2 Parking Structures
Architects, engineers, developers, and owners have made precast and prestressed concrete the material
of choice for their commercial, municipal, and institutional parking needs. Though classified and
constructed as buildings, parking structures are unique; in some ways, they may be compared with
bridges with multiple decks. They are subjected to moving loads from automobile traffic, and the roof
level of a parking structure is exposed to weather in much the same way as a bridge deck. In addition,
they are usually openair structures and, thus, the entire structure is subjected to ambient weather
conditions. Also, exposure to deicing salts in northern climates or to saltladen atmospheres in coastal
regions requires special consideration of durability to ensure longterm performance.
The controlled conditions in a precast concrete plant assures the parkingstructure owner of both the
quality concrete and workmanship that provides longterm durability. The low water–cementitious
materials ratio concrete that precast concrete manufacturers use has been proven to increase resistance to
deterioration as compared with other materials. Studies 14 have also shown that accelerated curing makes
precast concrete more resistant to chloride penetration than fieldcured concrete.
These inherent, enhanced durability characteristics, along with lowcost, rapid erection in all weather
conditions, unlimited opportunities for architectural expression, and long clear spans make precast
concrete the natural choice for parking structures. Through surveys of existing structures and other
experiences, and through PCIfunded and private research and development, significant improvements
have been achieved in engineering stateoftheart parking structures. This accumulated experience and
knowledge has been assembled in a comprehensive publication, Precast, Prestressed Parking Structures:
Recommended Practice for Design and Construction,15 that includes recommendations on planning,
design, construction, and maintenance.
Figures 1.2.27 and 1.2.28 show typical precast concrete parking structures. Longspan doubletees are
shown in Fig. 1.2.29, and Fig. 1.2.30 shows doubletees bearing on an innovative litewall that adds
openness and enhances both the perceived and actual security. Figure 1.2.31 shows a precast, prestressed
spandrel beam being erected into pockets of a precast concrete column. This same figure also shows a
doubletee bearing on an interior, invertedtee beam spanning from column to column. Interior spandrel
beams can also serve as bumpers for automobile traffic (Fig. 1.2.32).
Vertical expansion of precast concrete parking structures can be accomplished with special erection
methods that allow for erection of new components over erected decks (Fig. 1.2.33). This erection
method also allows precast concrete to be considered for expansion of nonprecast concrete structures.
1.2.3 Stadiums/Arenas
Large stadiums and arenas (Fig. 1.2.34 and 1.2.35) are complex structures that can benefit significantly
from the applications of precasting technology. Often these projects are built on tight schedules to
accommodate a specific sporting event. Because of both the constructionperiod advantages and the long
term, lowmaintenance characteristics, precast and prestressed concrete has been the overwhelming
choice for many of these projects. For the same reasons, precast/prestressed concrete systems are also
beneficial for smaller facilities such as high schools and small arenas (Fig. 1.2.36).
Massproduced seating units have been manufactured in a variety of configurations and spans to provide
for quick installation and longlasting service. Local producers can provide the best advice regarding
readily available riser sections.
Longspans and the ability to eliminate costly field formwork makes precast, prestressed concrete the
best choice for many components of stadium construction, especially for seating that can be standardized
to take advantage of repeated form utilization. Construction of components that would require tall
scaffolding towers to fieldform, such as raker beams and ring beams, can be simplified by precasting
these units in a plant, delivering them to the site, and lifting them into place (Fig. 1.1.8 and 1.1.9).
Pedestrian ramps, mezzanine floors, concession, toilet, and dressingroom areas can all be efficiently
framed and quickly constructed using precast, prestressed concrete components.
The technique of posttensioning precast concrete segments together has made complex cantilever arm
and ring beam construction possible, which can efficiently support the roofs of these structures. Post
tensioning can be employed to minimize the depth of precast concrete cantilevered raker beams, which
carry the seating and provide unhindered viewing of the playing surface.
1.2.4 Bridges
Bridge construction gave the prestressing industry its start in North America. Precast and prestressed
concrete is now the dominant structural material for short to mediumspan bridges. With its inherent
durability, low maintenance, performance, and assured quality, precast and prestressed concrete is a
natural product for bridge construction. The ability to quickly erect precast concrete components in all
types of weather with little disruption of traffic adds to the economy of the project. For short spans (spans
to 100 ft), use of box sections and doubletee sections have proven economical. However, the most
common product used for short to mediumspans is the Igirder. Spans to 150 or 160 ft are not
uncommon with Igirders and bulbtees. Spliced girders allow spans as much as 300 ft. 16 Even longer
spans (300 ft and up) can be achieved using precast concrete box girder segments, which are then post
tensioned together in the field. Using cable stays, the spanning capability of precast and prestressed
concrete has been increased to over 1000 ft.
An important innovation in bridge construction has been the use of precast concrete in horizontally
curved bridges. A study17 commissioned by PCI documents the technical feasibility and the economic
viability of this application.
Another application of precast and prestressed concrete in bridge construction is the use of precast
concrete deck panels.18 Used as stayinplace forms, the panels reduce field placement of reinforcing steel
and concrete, resulting in considerable savings in both cost and schedule. The panels become composite
with the fieldplaced concrete for live loads.
Through PCI’s commitment to provide quality bridges for the transportation infrastructure, the Bridge
Design Manual was published to provide guidance to engineers and owners on the design of precast
concrete bridges. Precast concrete not only is the choice material for highway bridges, but also finds
tremendous use in railway bridges.
Figures 1.2.37 through 1.2.42 show some of these applications that have been
discussed.
1.2.5 Other Structures and Applications
The inherent qualities of precast and prestressed concrete noted in previous sections and the high degree
of design flexibility also make it ideal for a wide variety of special applications. Properties such as
corrosion resistance, fire resistance, durability, and fast installation have been used to good advantage in
the construction of poles (Fig. 1.2.43), piles, railroad ties (Fig. 1.2.44), storage tanks (Fig. 1.2.45 and
1.2.46), monorails (Fig. 1.2.47), retaining walls, highway and runway pavements, and sound barriers (Fig.
1.2.48).19–25 Where repetition and standardization opportunities exist, precasting components can
economically provide the quality of plantmanufactured products while eliminating expensive and risky
field procedures. Precast, prestressed concrete can also be used efficiently in customized applications,
blending function and form to suit any contextsensitive environment. These applications are too
numerous to categorize here separately but examples are illustrated in the figures in this chapter.
1.3 Production Process
The methods used to produce precast concrete components vary with the type of component being
manufactured. Among the factors influencing the production process are:
• Structural components versus architectural components
• Longline, multipiece forms versus singlepiece forms
• Prestressed components versus nonprestressed components
• Pretensioned components versus posttensioned components
• Production facility limitations
Discussions with regional precasters during project development will allow these factors to be
considered in the design of the precast concrete components and structures. See Fig. 1.3.1 through 1.3.5
for various aspects of production.
1.3.1 Structural Components versus Architectural Components
Structural precast concrete components are traditionally produced in a process aimed toward high
volume and high efficiency. Emphasis is placed on using standard shapes so that forms can be reused
multiple times. These forms are usually long steel forms designed to produce a number of components
with each casting. Products commonly considered to be structural components include doubletees, bridge
girders, interior beams, hollowcore units, and interior walls. Precast concrete producers certified by PCI
as structural or commercial fabricators must comply with the requirements of PCI 's MNL11699.
The flexibility of architectural precast concrete allows designers to incorporate a wide array of shapes,
colors, and textures into a project’s appearance. This demands that the precast producer be capable of
constructing complex forms, using a variety of concrete mixtures and offering an assortment of surface
treatments such as sandblasting, acid etching, or veneers of brick, stone, or other decorative material.
Architectural precast concrete components are fabricated under the guidelines of PCI's MNL11796.
Components manufactured in accordance with these guidelines must satisfy stringent dimensional
tolerances and offer consistent appearances to match finish samples accepted by the architect. These
requirements commonly demand that the product be poured on custommade forms with special attention
given to true, flat surfaces, clean edges and consistent concrete color and texture. Fiberglasscoated forms
are often used to achieve the desired surface quality, and all form joints are sealed to ensure clean edges.
Reinforcement is hung from prestressing strands within the component or stiff assemblies spanning
across the form. This eliminates the need for reinforcing chairs, which might become visible on the
exposed face of the component. Special care must be taken to maintain adequate cover over the
reinforcement, not only to maintain durability but also to prevent reinforcement patterns from shadowing
through to the face of the component.
In instances where exacting tolerances and ornate shapes are not needed but special surface treatment or
colors are desired, consideration should be given to using a PCICertified commercial producer capable
of providing such services. These producers are designated with an A suffix on their classification (for
example, C3A), and have demonstrated their ability to apply special finishes to their structural products.
Additional information regarding plant certification categories can be found in Section 14.4 of this
handbook.
1.3.2 Long-Line, Multi-Piece Forms versus Single-Piece Forms
When producing large quantities of a standard shaped component, precasters will commonly use a long
line form approach. These longline forms may be several hundred feet long and are designed to produce
a number of pieces with each casting. In most instances, the components produced in this fashion are
pretensioned, prestressed components. Products such as beams and doubletees use bulkheads at the end
of each unit in the form while extruded products such as hollowcore are placed as one continuous piece
of concrete and then cut to the prescribed component lengths after curing.
Singlepiece forms are used with the intent of making one piece with each casting. This type of forming
system readily accommodates nonprestressed or posttensioned products, and is commonly used for
architectural precast concrete components. It can also be used to create custom structural and architectural
applications.
1.3.3 Prestressed Components versus Non- Prestressed Components
Where a component’s dimensions and applied loads will allow, a precaster may elect to use reinforcing
bars or welded wire to reinforce the product. In these cases, a reinforcing cage or mat is usually
assembled and placed in the form. Concrete is then placed and vibrated around the assembly. Care must
be taken by the designer to check crack control and deflections when using this type of design.
Concrete components are prestressed to achieve higher spantodepth ratios and provide resistance to
cracking. Prestressing is incorporated into a component in the form of pretensioned or posttensioned
strands. Prestressing is generally used as the primary reinforcement with reinforcing bars or weldedwire
reinforcement serving as secondary reinforcement.
1.3.4 Pretensioned Components versus Post-Tensioned Components
In pretensioned components, strands are first tensioned, then supplemental reinforcing bars and other
items to be embedded in the component are secured and concrete is placed into the form. After the
concrete is allowed to cure and forms a bond with the pretensioned strands, the strands are cut
(detensioned) and the prestressing force is transferred from the strands to the concrete through bond and
mechanical interlock. At this point, the components are removed from the form and placed in storage.
Posttensioning is typically tied to a cage or mat of reinforcement, which is then placed into the form.
Mechanical anchorages are placed at each end of the tendon and secured to the form or the reinforcement.
After concrete has been placed and cured within the form, the prestressing force is applied to the post
tensioning strands and held at the mechanical anchorages. At this point, the prestress force has been trans
ferred to the component, which can then be stripped out of the mold and placed in storage.
Under some circumstances, a combination of pretensioning and posttensioning may be used. This
approach may be used where the self-stressing forms or tensioning abutments cannot
sustain the full prestressing force. In this case, the majority of the force is applied
through pretensioned strands, and post-tensioned tendons are used to introduce the
remainder of design prestressing force after the component is stripped. This
approach may also be used in prestressed panels that are poured in a flat position
but stand in an upright position in service. Occasionally, the full prestress force will
cause cracking in the panel while it is flat in the form. This cracking can be avoided
by applying a portion of the prestress by post-tensioning after the panel is stripped
and upright. Thought should be given to space restrictions at the anchorage area
and the additional cost of a two-step process.
1.3.5 Production Limitations
A wide variety of products, in a variety of shapes and sizes, are generally available. Not all products are
available in all geographical areas, and, therefore, designers should be aware of these limitations during
the project development. Contacting regional precast concrete producers in the project's area is the best
way to ensure that the design team takes maximum advantage of precast concrete elements that are
readily available.
The size of the piece may be limited by the handling equipment available in the manufacturing plant or by
the transporting and erection equipment available. In most cases, manufacturers are geared to produce
standard products that can be transported over the road with a minimum of special permits. Unusually
large pieces can be made, but the special equipment required to handle such pieces can significantly add
to the cost.
The tensioning capacity of the prestressing beds may be another limitation. Some products, such as deep,
longspan bridge girders require massive stressing abutments and beds that can handle large holddown
forces for depressed strands. These capabilities are costly and must usually be amortized over a number
of projects. For large projects with many pieces, it is sometimes economical to install special facilities
that can be written off on the single project. Selfstressing forms, which resist the large forces from the
stressing bulkheads with heavy compression members (usually steel) built into the forms, may be another
solution.
Environmental concerns may also limit the scope of a precaster’s operation. For example, in most cases,
operations like sandblasting and acid etching must be contained. The location of the facility related to
residences, businesses, streams, and the like may require special noise, dust, or runoff containment. These
are conditions that are confronted by almost all manufacturing industries, and generally are not
restrictions on the design and use of precast concrete products.
