Seismic Vulnerability of Typical Multiple-Span California Highway Bridges

Multiple-span reinforced concrete highway overpass bridges constitute a large number of the total inventory of bridges in California, particularly bridges of new design. Performance of these bridges is therefore integral to the evaluation of transportation network performance under high intensity earthquake scenarios. Additionally, probabilistic quantification of bridge response and vulnerability will provide insight into the evaluation of current designs at different levels of seismic hazard. Performance of bridges at the demand, damage, and loss levels can be evaluated using the Pacific Earthquake Engineering Research (PEER) Center’s performance-based earthquake engineering framework. This paper illustrates probabilistic seismic bridge vulnerability evaluation using two typical single column-per-bent, five-span, post-tensioned box girder, reinforced concrete highway bridge types. The first bridge type has a straight deck and 22-foot columns of equal height above grade. The second bridge type has 50-foot high columns. Each bridge type has a variety of column configurations designed for different seismic demands typical for a variety of bridge sites in California. A complex model of the structures is created in OpenSees that accounts for nonlinear behavior of the columns, deck, abutments, and expansion joints at the abutments. This model is developed in a modular fashion to allow incorporation of improved soil models, models for emerging structural components, technologies, and use of new analysis methods. Seismic demand models are then developed using nonlinear time history analysis, including far- and near-field excitation. Damage in the columns is determined from a database of experimental tests and, finally, approximate repair cost ratios are estimated from the ascertained discrete damage states. Four bridge models are implemented for both types of bridges considered. The vulnerability of the base bridge types is presented in this paper as a benchmark with which to compare the use of enhanced performance structural elements and demands due to liquefaction and lateral spreading, when coupled with geotechnical models of the bridge-soil system.