The Pacific Earthquake Engineering Research Center is developing a probabilistic performance- based earthquake engineering framework, one component of which is a seismic demand model. Probabilistic seismic demand analysis was used to compute values of bridge-specific engineering demand parameters (EDP), such as curvature ductility, given ground motion intensity measures (IM), such as peak ground acceleration. A representative relation between chosen IM-EDP pairs forms the basis of the probabilistic seismic demand models (PSDM) presented.
The objective of this report was the development of an optimal PSDM for typical highway overpass bridges. An optimal model is defined as one that is practical, sufficient, effective, and efficient. For single-bent bridges with roller abutments, the optimal model comprises a spectral IM, such as
Sa(T 1) and one of several EDPs. Different EDPs are considered for local (material stress), intermediate (column moment), and global (drift ratio) response quantities. Given the optimal PSDMs, bridge design parameter (such as column diameter) sensitivity studies were performed. Relations for each design parameter can be developed, giving bridge designers a quantitative tool for evaluating the effect of design choices on structural performance. The same PSDMs were then re-computed using incremental dynamic analysis (IDA) to assess the equivalency of response produced using the two analysis methods. Selection of an optimal PSDM was then extended to the case of multiple-bent bridges and bridges with different abutment models.
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