Welcome

This is the coordination webpage for researchers of the Pacific Earthquake Engineering Research (PEER) Center working on the testbed program. It summarizes the testbed program; provides storage of documents such as ground-motion records, geotechnical reports, blueprints, photographs, etc.; and provides contact information.  See the attached pages for details on each testbed, on contacts and meetings, and other resources.

Special Interest

Overview of Performance-Based Earthquake Engineering

History.  Structural design comprises the selection of structural, nonstructural, and geotechnical systems, and their materials and configuration, with the goal of constructing a building, bridge, or other structure that will be safe and economical under foreseeable circumstances.    Historically, structural engineers used allowable-stress design (ASD) and load-and-resistance-factor design (LRFD), which focus on individual structural elements and connections, and seek to ensure that none will experience loads or deformation greater than it is capable of withstanding.  An emerging approach, called performance-based design (PBD), seeks to ensure that a designed facility as a whole will perform in some predictable way, in terms of safety and functionality.  Seismic aspects of PBD are referred to as performance-based earthquake engineering (PBEE).  PBEE therefore considers the seismic reliability of the elements and connections, but also directly addresses the facility's earthquake performance from the viewpoint of facility users, owners, and other stakeholders.  

PEER's PBEE effort.  The PEER Center is not alone in developing PBEE.  The Federal Emergency Management Agency (FEMA) and the American Society of Civil Engineers (ASCE) have developed a prestandard, FEMA/ASCE 356, that addresses performance in terms of facility operability, occupiability, life safety, and resistance to collapse, under four discrete levels of seismic excitation.  SEAOC's Vision 2000 document embraces this approach.  As important as these pioneering methodologies are, PEER has been able to build on them substantially in its second-generation approach. PEER’s mission is essentially to bring two new features to PBEE:

(1) Explicit calculation of system performance. We explicitly calculate performance of the whole system in terms of direct interest to stakeholders: dollars, deaths, and downtime. We are examining risk-communication issues to ensure that we calculate and express performance in terms that are the most appropriate for various stakeholder groups. By comparison, although first-generation PBEE methodologies elucidate a number of system performance levels, their analytical methodologies address system performance only indirectly. Their explicit calculations attempt to assure performance by limiting component-level forces and deformations. We refer to forces and deformations as engineering demand parameters (EDPs), and assert that they are indicative of, but are not the same as, performance. The relationship between a vector of EDP inequalities (whether the EDPs exceed prescribed limits) and a level of system performance is unclear, especially in cases where EDP limits are exceeded for only a few, possibly minor components.

(2) Rigorous probabilistic calculation. We calculate performance probabilistically, without relying on expert opinion.  We explicitly consider uncertainties in earthquake site intensity, ground motion, SFSI, structural response, physical damage, and economic and human loss. We are performing and compiling laboratory and analytical tests to quantify and reduce these uncertainties, and have produced open-source software to treat them in a rigorous fashion. Calculations in first-generation PBEE methodologies by contrast are largely deterministic. Force and deformation limits are crude and are based largely on authors’ judgment. They offer no insight into the probability of achieving system performance levels, whether or not drift and force limits are exceeded.

Our methodology is illustrated schematically below.  It includes familiar aspects of current practice (hazard analysis and structural analysis), and adds two new features: (1) Damage analysis.  This is the explicit, probabilistic calculation of physical damage (which bars have buckled, which beams have spalling, etc.); and (2) Loss analysis.  This is the explicit, probabilistic calculation of performance in terms that owners and other stakeholders care about, such as economic loss, fatalities, and loss of use ("dollars, deaths, and downtime").   

Methodology image: K Porter 2002

To emphasize: first-generation PBEE methodologies assume that if a given level of ductility demand, for example, is achieved, then the designer can be fairly assured of an associated performance level (bridge open; building operable, etc.)  PEER replaces these assumptions with explicit, probabilistic descriptions of physical damage and  system performance.  Using the PEER approach, the engineer will be able to inform the stakeholder (a bridge or building owner, for example): "Here is the probability that the bridge will be open after an earthquake of this intensity.  Here is the probability that repair costs will not exceed X dollars during the next Y years."  This is the new value that PEER brings PBEE. 

Purpose of the testbed project.  PEER's methodology is currently in development. The testbed project seeks to synthesize disparate university research products of PEER's research into a coherent methodology and to demonstrate and exercise that methodology on six real facilities: two buildings, two bridges, a campus of buildings, and a network of highway bridges.  Engineering practitioners meanwhile will compare the new PEER methodology with current practice, to identify strengths and development needs relative to FEMA and other approaches. 

Further information.  PEER's home page, containing detailed information about research participants, research projects, OpenSees, and other relevant  topics, can be found here.  The objectives and organization of the testbed effort is described in detail in Deierlein (2001).  This page is written and maintained by the testbed coordinator, Keith Porter of the California Institute of Technology.   For questions or comments, call or email me at (626) 395-4141, .