Advancing Performance-Based Earthquake Engineering

Helmut Krawinkler
Professor of Civil and Environmental Engineering
Stanford University

The Pacific Earthquake Engineering Research Center (PEER) has set the lofty goal of developing and disseminating urban earthquake risk-reduction technologies. This goal is to be achieved through a research program that is organized to promote an integrated, multidisciplinary systems approach to performance-based earthquake engineering (PBEE). PEER has taken on a major challenge by pursuing this approach. "Multidisciplinary" and "systems" imply collaboration and teamwork, and the term "performance-based" raises responses ranging from "nothing new, we are doing it already" to "it cannot be implemented." This short article rationalizes PBEE, provides arguments why PEER's emphasis on PBEE is the right course, and presents basic issues that need to be addressed to make PBEE an effective concept for urban earthquake risk reduction.

PBEE Defined

Performance-based earthquake engineering implies design, evaluation, and construction of engineered facilities whose performance under common and extreme loads responds to the diverse needs and objectives of owner-users and society. PBEE is based on the premise that performance can be predicted and evaluated with sufficient confidence for the engineer and client jointly to make intelligent and informed decisions based on building life-cycle considerations rather than on construction costs alone. Implementation of such a design decision process necessitates a shift away from the dependence on empirical conventions, and toward a design and assessment process more firmly rooted in the realistic prediction of structural behavior under the realistic description of the spectrum of loading environments the structure is likely to experience in the future. This process implies a shift toward a more scientifically oriented design approach, with an emphasis on accurate characterization and prediction that employs a higher level of technology than has been used in the past.

Why PBEE Is the Desirable Approach

Earthquake engineering practice is undergoing drastic changes triggered by a variety of reasons. These include improved knowledge about earthquake occurrences, ground motion, and structural response characteristics. They also include the realization gained from recent earthquakes in the U.S. and Japan that monetary damage can greatly surpass expectations. Perhaps most important is the recognition that present code design procedures often cannot be rationalized sufficiently by first principles to satisfy (1) the designer's desire for a logical explanation of the rules on which decision making is based; (2) the owner's desire for sound judgment on the costs and benefits of earthquake protection; and (3) society's needs for informed decision making in the face of random (and often highly uncertain) seismic demands imposed by ground shaking, and uncertain seismic capacities of existing and new construction. Another strong argument for a focus on PBEE is the need to encourage innovative techniques for performance enhancement. Presently employed prescriptive codes have stifled innovation because new concepts are difficult to fit into the rigid framework of such codes. The history of base isolation, which covers about 20 years from conception to implementation, is a good example of how slowly new technology is adopted within the current building code framework.

Challenges to Implementing PBEE

The implementation of PBEE will necessitate radical changes in engineering/construction practices and a redirection of research and development. Architects, engineers, and contractors will have to work together and resist taking adversarial positions. Academic researchers will have to interact, much more than in the past, with practitioners, who will lead the implementation process. Society will set the performance objectives, and in the design process researchers and practitioners will have to find ways to fulfill them. Complexity in the design process must be confined to important structures for which it can be justified. For widespread acceptance of PBEE it will be necessary to develop simple prescriptive procedures that are derived from rigorous performance-based concepts but are easy to implement. Each of these aspects poses a major challenge to be overcome in developing and implementing performance-based earthquake engineering.

Who Should Be Involved

PBEE has no future unless it becomes an attractive process for all stakeholders. In addition to architecture, engineering, and contracting practitioners, stakeholders include, among others, planners, building officials, facility managers, owners, lenders, and insurers. Identification and involvement of all stakeholder groups early in the research and development effort is critical.

A Global Framework for PBEE

Several conceptual frameworks for PBEE have been developed in recent professional efforts (SEAOC Vision 2000, FEMA 273, ATC-40). They differ in details but not in concepts. The chart illustrates a global framework which identifies processes, concepts, and major issues that need to be addressed in this context.


Chart


The issues encompass seismological, geotechnical, structural, architectural and MEP (nonstructural), and socioeconomic considerations. Each issue is associated with an extensive research agenda that covers much more than PEER can address. What distinguishes this research agenda from a general shopping list is the focus on a single objective, which is the common one of providing knowledge, methods, tools, and data for development and implementation of PBEE. The challenge for PEER is to select subsets of this comprehensive research agenda that will result, by a specified target date, in substantial and measurable progress on critical aspects that bring PBEE much closer to realization.

PEER's Research Agenda for PBEE

PEER is sponsoring research on all concepts and most of the issues, identified in the figure, with emphasis on striking a balance between engineering and socioeconomic issues, and on maintaining a focus that will lead to substantial progress in a few critical areas. At this time the research agenda for Year 2 is still under discussion, but it is likely that the focus will be on sponsoring coordinated research that addresses global aspects to

A Personal Perspective

PBEE is a noble concept, but its full implementation has a long way to go. Legal and professional obstacles pose challenges as do many questions about whether PBEE will be able to deliver on its promises. There are, nevertheless, compelling reasons to advocate PBEE as a critical area for research and implementation. Chief among these is that the objective of seismic engineering is to design and build better and more economical facilities. Both terms are relative to the current practice of earthquake engineering. In the writer's opinion, significant improvements beyond the status quo will not be achieved without a new and idealistic target to shoot for. We need to set this target high and then strive toward its accomplishment. We may never fully achieve everything we set out to, but the benefits that successful implementation of PBEE offers make it worthy and demanding of our attention.

References
Applied Technology Council. 1989. ATC 20 Procedures for Postearthquake Safety Evaluation of Buildings. Redwood City, Calif.: Applied Technology Council.

FEMA. 1997. NEHRP Guidelines for the Seismic Rehabilitation of Buildings. Prepared by the Applied Technology Council. [Washington, D.C.: Federal Emergency Management Agency]. FEMA 273.

Structural Engineers Assn. of California (SEAOC), Vision 2000 Committee. April 3, 1995. Performance Based Seismic Engineering of Buildings. J. Soulages, ed. 2 vols. [Sacramento, Calif.]