Research on Seismic Rehabilitation of RC Structures

7/27/2019 Research on Seismic Rehabilitation of RC Structures

1/11

Page 1 of 11

Research on Seismic Rehabilitation of RC StructuresPast 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 1970s 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


2/11

Page 2 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

1980s. 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 ScienceFoundation. 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, wastested 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 selectedan 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


3/11

Page 3 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


4/11

Page 4 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 veterans 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.


5/11

Page 5 of 11

Damage to schoolLong Beach 1933 Damage to schoolTokach-oki 1968

Olive View HospitalSan Fernando 1971

Veterans Administration HospitalSan Fernando 1971

General Hospital-- 1985 Mexico City Juarez Hospital1985 Mexico City

Fig. 3 Damage to schools and hospitals


6/11

Page 6 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


7/11

Page 7 of 11

Steel bracing systems

Fig. 4 Strengthening techniques used in Mexico City

REPAIR AND REHABILITATION RESEARCH IN THE UNITED STATES

During the 1980s, the National Science Foundation and other governmental agenciesprovided 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 ColumnsUniversity 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 BuildingsUniversity of

Texas at Austin

Evaluation of Seismic Retrofit Strategies for Non-Ductile Concrete FrameStructuresLehigh University

Retrofit of Tilt-Up ConstructionUniversity of California, Irvine and Dames andMoore


8/11

Page 8 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 havebeen 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 DiaphragmsThe project is being conducted at the University of California, San Diego,

University of Arizona, Lehigh University, and the Precast/Prestressed Concrete

Institute. A -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 BuildingsAxial 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 SystemsSeismic risks faced by ports are unique. The objectives are to understand the

complex soil-foundation-structure systems typical of ports and to developgeotechnical and structural mitigation strategies the will reduce risk of port

systems.Large-scale tests were conducted to assess the expected performance ofexisting 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).
https://nees.org/homehttps://nees.org/homehttps://nees.org/homehttps://nees.org/home


9/11

Page 9 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 172NEHRP 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 273NEHRP 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 bybuilding 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 Buildingsa 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 308Repair 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.


10/11

Page 10 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.


11/11

Page 11 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, 1992NEHRP 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 BuildingsA 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, 2000Prestandard 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.

Research on Seismic Rehabilitation of RC Structures

Documents

Transcript of Research on Seismic Rehabilitation of RC Structures