Report - PEER - University of California, Berkeley

HAZARD, GROUND MOTIONS AND PROBABILISTIC ASSESSMENTSFOR PBSDAllin CORNELL 1ABSTRACTPerformance-based seismic design (PBSD) requires an integration of the response and behaviorof the structure itself with a representation of the seismic threat to the site and a representationof the ground motions that will excite the structure. Further PBSD should assess the likelihoodsof possible limit states and of the range of future losses, reflecting the randomness anduncertainty in all the steps in the process from the seismicity through structural response to lossestimation. This paper addresses all these issues but emphasizes the subject of representationof the ground motion for PBSD, starting from the perspective of what the structural analysisobjectives are. This subject includes a focus on the interface between the work of theseismologist and that of the structural engineer.Keywords: Seismic hazard; Ground motions; Uncertainty analysis.1. INTRODUCTIONFollowing, for example, the vision of the Pacific Earthquake Engineering Research(PEER) Center (e.g., Deierlein, 2004; Krawinkler, 2004, Miranda (2004)) it ispresumed here that the ultimate objective of seismic performance assessment ofstructures (whether existing or designs for proposed structures) is the determination ofdecision metrics such as the mean annual loss (in economic and/or life safety terms)and/or mean annual frequency (or probability) of certain limit states, such as globalinstability collapse or maximum interstory drift ratio (MIDR) greater than 5%.Further, looking to current advanced and future practice, it is assumed here that thebasis for these assessments will by non-linear “time history” structural analysis. Ascommissioned by the workshop convenors this paper will address two general areas,first, the “front end” input to such assessments and, second, the global subject ofprobabilistic analysis in performance-based seismic assessments (PBSA). The paperaddresses the workshop theme of performance-based seismic design (PBSD)indirectly in that it is assumed that such an detailed assessment is a step, perhaps onlya near-final confirmatory step, in PBSD.1 Dept. of Civil and Environmental Engineering, Stanford University, Stanford, CA, 94305-4020, USA39