Research on Seismic Rehabilitation of RC Structures
Content
Research on Seismic Rehabilitation of RC Structures—Past and Future
James O. Jirsa University of Texas at Austin USA
ABSTRACT Ten years ago a similar symposium was held on the occasion of the completion of a large national program in Japan on the seismic rehabilitation of concrete structures. The symposium featured summary presentations of research and practice on rehabilitation of buildings and civil structures. This workshop provides an opportunity to once again exchange information on research and practice advances that have occurred in the past decade. Some of the past collaborative efforts will be reviewed, various research programs will be described, and the influence of the research on design guidelines and standards will be discussed.
US-JAPAN SYMPOSIUM, JUNE 2000 The Symposium held in 2000 was organized to assess the state of seismic rehabilitation. Sixteen overview papers were presented on a variety of topics. Through the dedicated work of Dr. Shunsuke Sugano and other JCI members, the presentations at the symposium as well as a number of additional papers were translated into English and were compiled to develop IPS-2 Seismic Rehabilitation of Concrete Structures following the symposium. IPS-2 made important research on seismic rehabilitation in Japan available to designers and researchers in the US and worldwide. The topics included: State of seismic rehabilitation Target performance for rehabilitation Rehabilitation of members by jacketing Rehabilitation of frame structures Response control rehabilitation New seismic rehabilitation techniques The field of rehabilitation has advanced substantially in the past decade. It is an opportune time to meet again to share knowledge and renew acquaintances and I am pleased to have the opportunity to open this workshop to reflect on the state of rehabilitation research and practice.
PREVIOUS US-JAPAN COLLABORATIVE ACTIVITIES There have been collaborative efforts in rehabilitation or structures between US and Japanese practitioners and engineers since the 1970’s when a program of large -scale building research was initiated under US-Japan Cooperative Program in Natural Resources (UJNR). The UJNR Panel on Wind and Seismic Effects organized the
Page 1 of 11
program to utilize the then newly-constructed Building Research Institute (BRI) facilities at the Tsukuba Science City. In connection with the UJNR program, a series of seminars and workshops began in the 1980’s. In 1980-1982, three seminars organized by the University of Michigan were held in Los Angeles, Tsukuba, and San Francisco. Funding was provided the National Science Foundation. The workshops were intended to- Compare US and Japanese procedures Solicit problems encountered in developing repair and retrofit designs and construction Focus attention on practical repair and retrofit techniques Develop data on rehabilitation techniques and methods to evaluate their effectiveness That series was followed by second group of workshops from 1983-1885 organized by Cornell University and held in Tsukuba, Berkeley, and Tokyo. It should be noted that the first large structure in the UJNR program, a seven-story reinforced concrete building, was tested in the BRI facility in Tsukuba. Since micro-computer based evaluation methods were considered to become increasingly important in the near future, the emphasis in these workshops was on evaluation techniques for existing structures. The objective was to assess- What types of structures can be evaluated by a given method? What is level of safety implied by method and what is acceptance/rejection criterion? How much effort is needed to conduct evaluation? To calibrate evaluation procedures, instrumented benchmark structures were needed. Two structures were selected—an instrumented hotel damaged in the 1971 San Fernando earthquake (Fig. 1) and the seven-story RC building tested in Tsukuba
Holiday Inn, Southern Callifornia Fig. 1 Selected benchmark structures
Page 2 of 11
In 1987, a seminar was held in Tsukuba on the “Repair and Retrofit of Structures.” Presentations emphasized concerns related to performance of elements and connections, need for quality control, and cost of construction. Similarities of current techniques for repair and strengthening indicated that there were significant opportunities for exchanges between the two countries. The most pressing research needs were determined to be experimental verification of repair and strengthening techniques in the following areas: Use of new materials Development of innovative techniques Evaluation of foundation effects Influence of member response on structure response Implementation of analytical techniques calibrated from experimental results The participants concluded that there was a need to continue efforts to develop a common understanding of the performance, design, and construction data. Studies related to damage control for prevention of environmental hazards and for maintenance of operations in existing structures were also felt to be needed. The importance of benchmark structures was discussed. Several benchmark buildings (Fig. 2) in Japan were discussed. While there was agreement that similar workshops should be organized periodically, none were held until the 2000 Symposium described above
Namioka Town Hospital
Page 3 of 11
Hachinohe Technical College Fig. 2 Benchmark Buildings in Japan
SEISMIC REHABILITATION OF RC STRUCTURES Progress in the art of rehabilitation seems to follow major events. The earthquakes listed below triggered the development of design requirements and an increase in rehabilitation projects. • Long Beach 1933 • Tokachi-oki 1968 • San Fernando 1971 • Mexico City 1985 • Loma Prieta 1989 • Northridge 1994 • Hyogoken-Nambu (Kobe) 1995 Damage to schools and hospitals made both the public and policy-makers aware of the risks posed by inadequate buildings (Fig. 3). The 1933 Long Beach earthquake resulted in passage of the Field Act for school safety in California. The 1968 Tokachi-oki event resulted in similar measures in Japan for school buildings. The 1971 San Fernando earthquake led to hospital safety measures in California and the US Veterans Administration began a program to upgrade veteran’s hospitals. The 1985 Mexico City earthquake devastated hospital facilities and other government buildings and caused widespread damage to mid-rise office and apartment buildings. Following the earthquake, many buildings were repaired and strengthened. The activity in Mexico City provided valuable experience regarding problems associated with the management of a major rehabilitation and repair effort. The experience gained from collaboration with Mexican engineers and researchers emphasized the need for the US to develop procedures for mitigating the risk of existing buildings before an emergency arose. Interest in research related to hazard mitigation was stimulated and a number of research projects were funded by the National Science Foundation.
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Damage to school— Long Beach 1933
Damage to school—Tokach-oki 1968
Olive View Hospital— San Fernando 1971
Veteran’s Administration Hospital— San Fernando 1971
General Hospital-- 1985 Mexico City Juarez Hospital—1985 Mexico City Fig. 3 Damage to schools and hospitals
Page 5 of 11
In Mexico City, a wide variety of different techniques were used to rehabilitate buildings. An overview of some of the techniques is shown in Fig. 4.
Beam and column jacketing
New walls
Cable bracing systems
Page 6 of 11
Steel bracing systems Fig. 4 Strengthening techniques used in Mexico City
REPAIR AND REHABILITATION RESEARCH IN THE UNITED STATES During the 1980’s, the National Science Foundation and other governmental agencies provided support for research on buildings and bridges. In 1990, NSF funded an initiative on repair and rehabilitation that was guided by a steering committee of researchers and practitioners that proposed a research agenda for each of the three years of the initiative. The program was coordinated with programs at the National Center for Earthquake Engineering Research (NCEER at Buffalo), the California Department of Transportation (CALTRANS), the National Institute of Standards and Technology (NIST), and the California Seismic Safety Commission. A number of projects related to reinforced concrete structures were funded. • Evaluaton of Existing RC Columns— University of California, Berkeley • Evaluation and Repair of Tilt-Up Systems--University of Illinois • Seismic Rehab of Unreinforced Buildings using Post-Tensioned Steel Braces-Nabih Youssef & Associates • Retrofit Strategies for Non-ductile RC Flat Slab Buildings--Rice University • Innovative Techniques for Strengthening RC Frame Buildings— University of Texas at Austin • Evaluation of Seismic Retrofit Strategies for Non-Ductile Concrete Frame Structures— Lehigh University • Retrofit of Tilt-Up Construction— University of California, Irvine and Dames and Moore
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With the development of the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES), a number of projects were funded in the area of rehabilitation since 2004. The projects are multi-year and multi-institutional and involve the experimental facilities developed under NEES. The common theme is the use of cutting-edge experimental simulation tools and facilities to reduce earthquake risk. Most studies have been conducted at large scale to better replicate nonlinear behavior and simulate collapse . Several of the projects that include rehabilitation procedures are listed below. Development of a Seismic Design Methodology for Precast Floor Diaphragms The project is being conducted at the University of California, San Diego, University of Arizona, Lehigh University, and the Precast/Prestressed Concrete Institute. A ½ -scale model of 3-story precast parking structure was tested on the NEES outdoor shake table at UC San Diego. Mitigation of Collapse Risk in Vulnerable Concrete Buildings Axial failure of the columns is a primary cause of collapse during an earthquake. A goal of this project is the development of tools to identify vulnerable columns and to help understand how columns fail during earthquakes. The objective is improvement of seismic rehabilitation standards such as ASCE-41. NEES equipment sites and partner institutions include: University of Minnesota, UC Berkeley, UC Santa Barbara field sites, the UCLA mobile lab, Purdue University, University of Kansas, University of Puerto Rico, University of Washington, and the Concrete Coalition of EERI. Seismic Risk Mitigation for Port Systems Seismic risks faced by ports are unique. The objectives are to understand the complex soil-foundation-structure systems typical of ports and to develop geotechnical and structural mitigation strategies the will reduce risk of port systems. Large-scale tests were conducted to assess the expected performance of existing container cranes. A 1/20th scale model of a container crane was tested on the NEES shake table at the University at Buffalo. Project team includes the Georgia Institute of Technology, University of Texas at Austin, University of California-Davis, University of Washington, Massachusetts Institute of Technology, University of Illinois-Urbana-Champaign, Drexel University, and a number of practicing engineers.
More information on these and other projects can be found at the NEES Project Warehouse (https://nees.org/home) .
Page 8 of 11
EVALUATION AND DESIGN GUIDELINES AND STANDARDS IN THE US The details of various developments in evaluation and design procedures in the US will be discussed in other presentations at this workshop. A brief overview of the development of those activities is provided here. The Federal Emergency Management Agency (FEMA) initiated a program in 1985 to reduce the risks posed by the existing building inventory in the US. The first document FEMA published in 1992, FEMA 172 NEHRP Handbook of Techniques for the Seismic Rehabilitation of Existing Buildings (FEMA 1992), provided practical approaches to seismic rehabilitation. This document included all building types but was primarily directed at wood frame buildings and non-structural elements. The document did not receive much attention until after FEMA 273 NEHRP Guidelines for the Seismic Rehabilitation of Existing Buildings (FEMA 1997) was published. At that time, it was realized that FEMA 172 was inadequate in providing the design guidance needed for a variety of building types and an update of FEMA 172 was initiated under the auspices of the National Institute of Standards and Technology. The techniques were grouped by building type or elements common to various types and included results from the research activity described previously. The resulting document was published as FEMA 547 Techniques for the Seismic Rehabilitation of Existing Buildings (FEMA 2006). FEMA 172 was updated with the publication of FEMA 310 Handbook for the Seismic Evaluation of Buildings—a Prestandard (FEMA 1998). The document was standardized by the American Society of Civil Engineers (ASCE) and published as ASCE/SEI 31-03 Seismic Evaluation of Existing Buildings (ASCE 2003). FEMA 310 was intended to be consistent with FEMA 273 which was also updated and published as FEMA 356 Prestandard and Commentary for the Seismic Rehabilitation of Buildings (FEMA 2000). ASCE standardized the document and published ASCE/SEI 41-06 Seismic Rehabilitation of Existing Buildings (ASCE 2006). The chapter of ASCE/SEI 41-06 that covers concrete buildings was updated by a supplement issued in 2009 (ASCE 2009). Two additional documents for buildings with walls were published: FEMA 306 Evaluation of Earthquake Damaged Concrete and Masonry Wall Buildings (FEMA 1998) and FEMA 308 Repair of Earthquake Damaged Concrete and Masonry Wall Buildings (FEMA 1999). FEMA 306 provides guidance for evaluating earthquake damage through damage classification guides. FEMA 308 provides guidance for the repair and upgrade of earthquake-damaged wall buildings. It includes guides for typical repair procedures. It is likely that efforts to update these documents will continue as their usage increases. The results from additional research and the experience gained by engineers implementing the standards will need to be considered in such updates. In the US, there have been very few rehabilitated buildings, especially using the standards described above, that have been subjected to significant earthquake motions. When that happens, it will provide a means of calibrating and improving rehabilitation documents.
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CHALLENGES In the US, there is no impetus for rehabilitation on a broad basis. While excellent experimental facilities have been developed through the NEES program, there has not been a commensurate commitment to conduct research using those facilities. The current economic difficulties at all levels of government do not bode well for research activity. Considerable research has already been conducted on rather simple test specimens or assemblages. More realistic tests on large-scale structures and on shake-tables is needed but will be very expensive. The rehabilitation of structures that are most vulnerable and lead to most fatalities and injuries is needed. Although the experience in Haiti is an extreme example, vulnerable systems have been identified in every country. The will of governments, lenders, and insurers to reduce the risks posed by such buildings is lacking. Investment in seismic rehabilitation will continue to lag even for critical structures such as hospitals. To make rehabilitation a more viable option, the cost of rehabilitation must be reduced. New materials that are inexpensive, easily installed, lightweight, and durable offer opportunities for development of innovative rehabilitation techniques. The use of industrial techniques to produce rehabilitation elements that can be quickly and conveniently installed with a minimum of disruption to the occupants of the building should also reduce the cost of rehabilitation. Finally the education of stakeholders affected by the risk of inadequate buildings must be accelerated so that they are aware of developments in rehabilitation design and technology. Associated with this is a need to develop methods to assure quality in the construction processes associated with rehabilitation.
CONCLUSIONS While developments in evaluation and rehabilitation of existing buildings in the ten years since the previous meeting between JCI and ACI have been significant, much remains to be done. The opportunity to meet and exchange views and share experience gained is an important activity that will be of value to both organizations and the profession.
ACKNOWLEDGEMENTS I would like to close by thanking the organizers, Profs. Shunsuke Sugano and Kenneth Elwood, for their efforts to make this workshop possible and successful. NEES support enabled several of the participants to attend the workshop and is greatly appreciated.
Page 10 of 11
REFERENCES American Society of Civil Engineers (ASCE), 2002. Seismic Evaluation of Existing Buildings, ASCE 31-03, Reston, VA. ASCE, 2007, Seismic Rehabilitation of Existing Buildings , ASCE/SEI Standard 41-06, Reston, VA. ASCE, 2009, Supplement to ASCE 41-06, Reston, VA Federal Emergency Management Agency (FEMA). 1985, An Action Plan For Reducing Earthquake Hazards of Existing Buildings (FEMA 90), Washington, D.C. FEMA, 1992 NEHRP Handbook of Techniques for the Seismic Rehabilitation of Existing Buildings (FEMA 172), Washington, D.C. FEMA, 1997, NEHRP Guidelines for the Seismic Rehabilitation of Existing Buildings (FEMA 273), Washington, D. C. FEMA, 1998, Handbook for the Seismic Evaluation of Buildings —A Prestandard (FEMA 310), Washington, D. C. FEMA, 1998, Evaluation of Earthquake Damaged Concrete and Masonry Wall Buildings (FEMA 306), Washington, D. C. FEMA 1999Repair of Earthquake Damaged Concrete and Masonry Wall Buildings (FEMA 308) Washington, D. C. FEMA, 2000 Prestandard and Commentary for the Seismic Rehabilitation of Buildings (FEMA356), Washington, D. C. FEMA, 2006, Techniques for the Seismic Rehabilitation of Existing Buildings, FEMA 547, Federal Emergency Management Agency, Washington, DC.
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James O. Jirsa University of Texas at Austin USA
ABSTRACT Ten years ago a similar symposium was held on the occasion of the completion of a large national program in Japan on the seismic rehabilitation of concrete structures. The symposium featured summary presentations of research and practice on rehabilitation of buildings and civil structures. This workshop provides an opportunity to once again exchange information on research and practice advances that have occurred in the past decade. Some of the past collaborative efforts will be reviewed, various research programs will be described, and the influence of the research on design guidelines and standards will be discussed.
US-JAPAN SYMPOSIUM, JUNE 2000 The Symposium held in 2000 was organized to assess the state of seismic rehabilitation. Sixteen overview papers were presented on a variety of topics. Through the dedicated work of Dr. Shunsuke Sugano and other JCI members, the presentations at the symposium as well as a number of additional papers were translated into English and were compiled to develop IPS-2 Seismic Rehabilitation of Concrete Structures following the symposium. IPS-2 made important research on seismic rehabilitation in Japan available to designers and researchers in the US and worldwide. The topics included: State of seismic rehabilitation Target performance for rehabilitation Rehabilitation of members by jacketing Rehabilitation of frame structures Response control rehabilitation New seismic rehabilitation techniques The field of rehabilitation has advanced substantially in the past decade. It is an opportune time to meet again to share knowledge and renew acquaintances and I am pleased to have the opportunity to open this workshop to reflect on the state of rehabilitation research and practice.
PREVIOUS US-JAPAN COLLABORATIVE ACTIVITIES There have been collaborative efforts in rehabilitation or structures between US and Japanese practitioners and engineers since the 1970’s when a program of large -scale building research was initiated under US-Japan Cooperative Program in Natural Resources (UJNR). The UJNR Panel on Wind and Seismic Effects organized the
Page 1 of 11
program to utilize the then newly-constructed Building Research Institute (BRI) facilities at the Tsukuba Science City. In connection with the UJNR program, a series of seminars and workshops began in the 1980’s. In 1980-1982, three seminars organized by the University of Michigan were held in Los Angeles, Tsukuba, and San Francisco. Funding was provided the National Science Foundation. The workshops were intended to- Compare US and Japanese procedures Solicit problems encountered in developing repair and retrofit designs and construction Focus attention on practical repair and retrofit techniques Develop data on rehabilitation techniques and methods to evaluate their effectiveness That series was followed by second group of workshops from 1983-1885 organized by Cornell University and held in Tsukuba, Berkeley, and Tokyo. It should be noted that the first large structure in the UJNR program, a seven-story reinforced concrete building, was tested in the BRI facility in Tsukuba. Since micro-computer based evaluation methods were considered to become increasingly important in the near future, the emphasis in these workshops was on evaluation techniques for existing structures. The objective was to assess- What types of structures can be evaluated by a given method? What is level of safety implied by method and what is acceptance/rejection criterion? How much effort is needed to conduct evaluation? To calibrate evaluation procedures, instrumented benchmark structures were needed. Two structures were selected—an instrumented hotel damaged in the 1971 San Fernando earthquake (Fig. 1) and the seven-story RC building tested in Tsukuba
Holiday Inn, Southern Callifornia Fig. 1 Selected benchmark structures
Page 2 of 11
In 1987, a seminar was held in Tsukuba on the “Repair and Retrofit of Structures.” Presentations emphasized concerns related to performance of elements and connections, need for quality control, and cost of construction. Similarities of current techniques for repair and strengthening indicated that there were significant opportunities for exchanges between the two countries. The most pressing research needs were determined to be experimental verification of repair and strengthening techniques in the following areas: Use of new materials Development of innovative techniques Evaluation of foundation effects Influence of member response on structure response Implementation of analytical techniques calibrated from experimental results The participants concluded that there was a need to continue efforts to develop a common understanding of the performance, design, and construction data. Studies related to damage control for prevention of environmental hazards and for maintenance of operations in existing structures were also felt to be needed. The importance of benchmark structures was discussed. Several benchmark buildings (Fig. 2) in Japan were discussed. While there was agreement that similar workshops should be organized periodically, none were held until the 2000 Symposium described above
Namioka Town Hospital
Page 3 of 11
Hachinohe Technical College Fig. 2 Benchmark Buildings in Japan
SEISMIC REHABILITATION OF RC STRUCTURES Progress in the art of rehabilitation seems to follow major events. The earthquakes listed below triggered the development of design requirements and an increase in rehabilitation projects. • Long Beach 1933 • Tokachi-oki 1968 • San Fernando 1971 • Mexico City 1985 • Loma Prieta 1989 • Northridge 1994 • Hyogoken-Nambu (Kobe) 1995 Damage to schools and hospitals made both the public and policy-makers aware of the risks posed by inadequate buildings (Fig. 3). The 1933 Long Beach earthquake resulted in passage of the Field Act for school safety in California. The 1968 Tokachi-oki event resulted in similar measures in Japan for school buildings. The 1971 San Fernando earthquake led to hospital safety measures in California and the US Veterans Administration began a program to upgrade veteran’s hospitals. The 1985 Mexico City earthquake devastated hospital facilities and other government buildings and caused widespread damage to mid-rise office and apartment buildings. Following the earthquake, many buildings were repaired and strengthened. The activity in Mexico City provided valuable experience regarding problems associated with the management of a major rehabilitation and repair effort. The experience gained from collaboration with Mexican engineers and researchers emphasized the need for the US to develop procedures for mitigating the risk of existing buildings before an emergency arose. Interest in research related to hazard mitigation was stimulated and a number of research projects were funded by the National Science Foundation.
Page 4 of 11
Damage to school— Long Beach 1933
Damage to school—Tokach-oki 1968
Olive View Hospital— San Fernando 1971
Veteran’s Administration Hospital— San Fernando 1971
General Hospital-- 1985 Mexico City Juarez Hospital—1985 Mexico City Fig. 3 Damage to schools and hospitals
Page 5 of 11
In Mexico City, a wide variety of different techniques were used to rehabilitate buildings. An overview of some of the techniques is shown in Fig. 4.
Beam and column jacketing
New walls
Cable bracing systems
Page 6 of 11
Steel bracing systems Fig. 4 Strengthening techniques used in Mexico City
REPAIR AND REHABILITATION RESEARCH IN THE UNITED STATES During the 1980’s, the National Science Foundation and other governmental agencies provided support for research on buildings and bridges. In 1990, NSF funded an initiative on repair and rehabilitation that was guided by a steering committee of researchers and practitioners that proposed a research agenda for each of the three years of the initiative. The program was coordinated with programs at the National Center for Earthquake Engineering Research (NCEER at Buffalo), the California Department of Transportation (CALTRANS), the National Institute of Standards and Technology (NIST), and the California Seismic Safety Commission. A number of projects related to reinforced concrete structures were funded. • Evaluaton of Existing RC Columns— University of California, Berkeley • Evaluation and Repair of Tilt-Up Systems--University of Illinois • Seismic Rehab of Unreinforced Buildings using Post-Tensioned Steel Braces-Nabih Youssef & Associates • Retrofit Strategies for Non-ductile RC Flat Slab Buildings--Rice University • Innovative Techniques for Strengthening RC Frame Buildings— University of Texas at Austin • Evaluation of Seismic Retrofit Strategies for Non-Ductile Concrete Frame Structures— Lehigh University • Retrofit of Tilt-Up Construction— University of California, Irvine and Dames and Moore
Page 7 of 11
With the development of the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES), a number of projects were funded in the area of rehabilitation since 2004. The projects are multi-year and multi-institutional and involve the experimental facilities developed under NEES. The common theme is the use of cutting-edge experimental simulation tools and facilities to reduce earthquake risk. Most studies have been conducted at large scale to better replicate nonlinear behavior and simulate collapse . Several of the projects that include rehabilitation procedures are listed below. Development of a Seismic Design Methodology for Precast Floor Diaphragms The project is being conducted at the University of California, San Diego, University of Arizona, Lehigh University, and the Precast/Prestressed Concrete Institute. A ½ -scale model of 3-story precast parking structure was tested on the NEES outdoor shake table at UC San Diego. Mitigation of Collapse Risk in Vulnerable Concrete Buildings Axial failure of the columns is a primary cause of collapse during an earthquake. A goal of this project is the development of tools to identify vulnerable columns and to help understand how columns fail during earthquakes. The objective is improvement of seismic rehabilitation standards such as ASCE-41. NEES equipment sites and partner institutions include: University of Minnesota, UC Berkeley, UC Santa Barbara field sites, the UCLA mobile lab, Purdue University, University of Kansas, University of Puerto Rico, University of Washington, and the Concrete Coalition of EERI. Seismic Risk Mitigation for Port Systems Seismic risks faced by ports are unique. The objectives are to understand the complex soil-foundation-structure systems typical of ports and to develop geotechnical and structural mitigation strategies the will reduce risk of port systems. Large-scale tests were conducted to assess the expected performance of existing container cranes. A 1/20th scale model of a container crane was tested on the NEES shake table at the University at Buffalo. Project team includes the Georgia Institute of Technology, University of Texas at Austin, University of California-Davis, University of Washington, Massachusetts Institute of Technology, University of Illinois-Urbana-Champaign, Drexel University, and a number of practicing engineers.
More information on these and other projects can be found at the NEES Project Warehouse (https://nees.org/home) .
Page 8 of 11
EVALUATION AND DESIGN GUIDELINES AND STANDARDS IN THE US The details of various developments in evaluation and design procedures in the US will be discussed in other presentations at this workshop. A brief overview of the development of those activities is provided here. The Federal Emergency Management Agency (FEMA) initiated a program in 1985 to reduce the risks posed by the existing building inventory in the US. The first document FEMA published in 1992, FEMA 172 NEHRP Handbook of Techniques for the Seismic Rehabilitation of Existing Buildings (FEMA 1992), provided practical approaches to seismic rehabilitation. This document included all building types but was primarily directed at wood frame buildings and non-structural elements. The document did not receive much attention until after FEMA 273 NEHRP Guidelines for the Seismic Rehabilitation of Existing Buildings (FEMA 1997) was published. At that time, it was realized that FEMA 172 was inadequate in providing the design guidance needed for a variety of building types and an update of FEMA 172 was initiated under the auspices of the National Institute of Standards and Technology. The techniques were grouped by building type or elements common to various types and included results from the research activity described previously. The resulting document was published as FEMA 547 Techniques for the Seismic Rehabilitation of Existing Buildings (FEMA 2006). FEMA 172 was updated with the publication of FEMA 310 Handbook for the Seismic Evaluation of Buildings—a Prestandard (FEMA 1998). The document was standardized by the American Society of Civil Engineers (ASCE) and published as ASCE/SEI 31-03 Seismic Evaluation of Existing Buildings (ASCE 2003). FEMA 310 was intended to be consistent with FEMA 273 which was also updated and published as FEMA 356 Prestandard and Commentary for the Seismic Rehabilitation of Buildings (FEMA 2000). ASCE standardized the document and published ASCE/SEI 41-06 Seismic Rehabilitation of Existing Buildings (ASCE 2006). The chapter of ASCE/SEI 41-06 that covers concrete buildings was updated by a supplement issued in 2009 (ASCE 2009). Two additional documents for buildings with walls were published: FEMA 306 Evaluation of Earthquake Damaged Concrete and Masonry Wall Buildings (FEMA 1998) and FEMA 308 Repair of Earthquake Damaged Concrete and Masonry Wall Buildings (FEMA 1999). FEMA 306 provides guidance for evaluating earthquake damage through damage classification guides. FEMA 308 provides guidance for the repair and upgrade of earthquake-damaged wall buildings. It includes guides for typical repair procedures. It is likely that efforts to update these documents will continue as their usage increases. The results from additional research and the experience gained by engineers implementing the standards will need to be considered in such updates. In the US, there have been very few rehabilitated buildings, especially using the standards described above, that have been subjected to significant earthquake motions. When that happens, it will provide a means of calibrating and improving rehabilitation documents.
Page 9 of 11
CHALLENGES In the US, there is no impetus for rehabilitation on a broad basis. While excellent experimental facilities have been developed through the NEES program, there has not been a commensurate commitment to conduct research using those facilities. The current economic difficulties at all levels of government do not bode well for research activity. Considerable research has already been conducted on rather simple test specimens or assemblages. More realistic tests on large-scale structures and on shake-tables is needed but will be very expensive. The rehabilitation of structures that are most vulnerable and lead to most fatalities and injuries is needed. Although the experience in Haiti is an extreme example, vulnerable systems have been identified in every country. The will of governments, lenders, and insurers to reduce the risks posed by such buildings is lacking. Investment in seismic rehabilitation will continue to lag even for critical structures such as hospitals. To make rehabilitation a more viable option, the cost of rehabilitation must be reduced. New materials that are inexpensive, easily installed, lightweight, and durable offer opportunities for development of innovative rehabilitation techniques. The use of industrial techniques to produce rehabilitation elements that can be quickly and conveniently installed with a minimum of disruption to the occupants of the building should also reduce the cost of rehabilitation. Finally the education of stakeholders affected by the risk of inadequate buildings must be accelerated so that they are aware of developments in rehabilitation design and technology. Associated with this is a need to develop methods to assure quality in the construction processes associated with rehabilitation.
CONCLUSIONS While developments in evaluation and rehabilitation of existing buildings in the ten years since the previous meeting between JCI and ACI have been significant, much remains to be done. The opportunity to meet and exchange views and share experience gained is an important activity that will be of value to both organizations and the profession.
ACKNOWLEDGEMENTS I would like to close by thanking the organizers, Profs. Shunsuke Sugano and Kenneth Elwood, for their efforts to make this workshop possible and successful. NEES support enabled several of the participants to attend the workshop and is greatly appreciated.
Page 10 of 11
REFERENCES American Society of Civil Engineers (ASCE), 2002. Seismic Evaluation of Existing Buildings, ASCE 31-03, Reston, VA. ASCE, 2007, Seismic Rehabilitation of Existing Buildings , ASCE/SEI Standard 41-06, Reston, VA. ASCE, 2009, Supplement to ASCE 41-06, Reston, VA Federal Emergency Management Agency (FEMA). 1985, An Action Plan For Reducing Earthquake Hazards of Existing Buildings (FEMA 90), Washington, D.C. FEMA, 1992 NEHRP Handbook of Techniques for the Seismic Rehabilitation of Existing Buildings (FEMA 172), Washington, D.C. FEMA, 1997, NEHRP Guidelines for the Seismic Rehabilitation of Existing Buildings (FEMA 273), Washington, D. C. FEMA, 1998, Handbook for the Seismic Evaluation of Buildings —A Prestandard (FEMA 310), Washington, D. C. FEMA, 1998, Evaluation of Earthquake Damaged Concrete and Masonry Wall Buildings (FEMA 306), Washington, D. C. FEMA 1999Repair of Earthquake Damaged Concrete and Masonry Wall Buildings (FEMA 308) Washington, D. C. FEMA, 2000 Prestandard and Commentary for the Seismic Rehabilitation of Buildings (FEMA356), Washington, D. C. FEMA, 2006, Techniques for the Seismic Rehabilitation of Existing Buildings, FEMA 547, Federal Emergency Management Agency, Washington, DC.
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