Civil Engineering Association

Performance Based Earthquake Engineer ing: Application to an Actual Bridge-Foundation-Ground System

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. This paper presents
the application of the PBEE methodology developed at the Pacific Earthquake Engineering Research
(PEER) Center to the Humboldt Bay Middle Channel (HBMC) Bridge modeled and analyzed as a nonlinear
soil-foundation-structure interaction (SFSI) system. The HBMCB, with precast and prestressed concrete Igirders
and cast-in-place concrete slabs, is fairly representative of older AASHTO-Caltrans girder bridges. It
is supported on pile groups in soils potentially vulnerable to liquefaction during an earthquake, which could
induce lateral spreading and permanent soil deformations.
This paper presents the nonlinear finite element model of the bridge-foundation-ground (BFG) system used in
this study and then focuses on the several analytical steps of the PEER PBEE methodology as applied to this
bridge. This methodology integrates in a probabilistic framework seismic hazard analysis, seismic demand
analysis, capacity analysis, reliability/damage analysis, and loss analysis. Several potential failure mechanisms
of the HBMC Bridge are considered: flexural failure of bridge piers, failure of shear key(s), and unseating.
For each failure mechanism, several limit/damage-states measuring the stage of formation of the mechanism
are defined. The seismic reliability against these limit-states is evaluated in terms of mean annual
rate/frequency of exceedance or, alternatively, return period. As outcome of seismic loss analysis, the seismic
loss hazard curve expresses the mean annual frequency of exceeding any total annual seismic repair/
replacement cost. The paper presents selective results illustrating the various steps of the PEER PBEE
methodology as applied to the HBMC Bridge