13 th World Conference on Earthquake Engineering Vancouver, B.C., Canada August 1-6, 2004 Paper No. 2978 SEISMIC RELIABILITY ASSESSMENT OF A BRIDGE GROUND SYSTEM Yuyi ZHANG 1 , Gabriel ACERO 1 , Joel CONTE 1 , Zhaohui YANG 1 and Ahmed ELGAMAL 1 SUMMARY Performance-based earthquake engineering (PBEE) is emerging as the next-generation design and evaluation framework under which new and existing structures will be analyzed for seismic adequacy. Various analytical approaches to PBEE are in development [1]. The PBEE methodology developed by the Pacific Earthquake Engineering Research (PEER) Center, headquartered at the University of California, Berkeley, is being exercised and illustrated on real, existing facilities (buildings, bridges, network of highway bridges, campus of buildings) called testbeds. This paper presents the application of the PEER PBEE methodology to one of the six PEER testbeds, namely the Humboldt Bay Middle Channel (HBMC) Bridge, one of three bridges that cross Humboldt Bay, near Eureka in northern California. It is a 330 meter long, nine-span composite structure with precast and prestressed concrete I-girders with cast-in-place concrete slabs, fairly representative of older AASHTO-Caltrans girder bridges with moderate traffic loads. It is supported on eight pile groups in soils potentially vulnerable to liquefaction during an earthquake, which could induce lateral spreading and permanent soil deformations. This bridge testbed is analyzed as a nonlinear structure-foundation-soil system. This paper focuses on the several analytical steps of the PEER PBEE methodology to assess the seismic reliability of the HBMC Bridge. This methodology integrates probabilistic seismic hazard analysis for the bridge site, advanced computational modeling of the bridge-foundation-soil system, probabilistic seismic demand analysis, probabilistic capacity (or fragility) analysis, and reliability analysis. The earthquake response of the bridge ground system is simulated using a two-dimensional, advanced nonlinear finite element model of the structure-foundation-soil system developed in OpenSees, the new PEER software framework for advanced finite element modeling and seismic response simulation of structural and geotechnical systems. Several potential failure mechanisms are considered such as flexural failure of bridge piers, failure of shear key(s), and unseating. For each failure mechanism, several limit-states or damage-states measuring the stage of formation of the failure mechanism are considered. The seismic reliability against these system-level limit-states is expressed in terms of mean annual frequency (Poisson rate) of exceeding these limit-states or, alternatively, the return period of these limit-states. The paper presents selective results illustrating the various steps of the PEER PBEE methodology as well as their integration. 1 Department of Structural Engineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0085 USA, E-mails: jpconte@ucsd.edu , elgamal@ucsd.edu