Modeling the Transverse Response of Short Bridges Subjected to Earthquakes

The transverse response of short bridges is often critical to their seismic performance. When transverse displacements are large, damage to substructure columns may occur, often in the form of plastic hinges, shear failures, or lap splice failures. A significant component of the transverse response is due to the dynamic response of the embankment. Current design provisions (ATC-32 1996, Caltrans 1999) neglect this contribution entirely, and other researchers have only investigated linear models of embankment contribution (Wilson and Tan 1990; Werner et al. 1993; Goel 1997). This report focuses on the modeling of short bridges to improve estimates of column displacement demands. In particular, improved approach-embankment models are developed based on seismic response data recorded at two short bridges in California. The models are nonlinear and can be used in conjunction with software programs such as DRAIN-2DX and DRAIN-3DX. One model explicitly considers the piles and embankment soils, while a second, simpler, model considers only the embankment soils. Both models are calibrated to the recorded California bridge data. The more complex model is used to generate response data for representative Illinois bridges, and this data is used to calibrate the simpler model for Illinois bridges. Furthermore, when transverse demands are excessive, one mitigation technique is the use of conventional elastomeric bearings to seismically isolate the superstructure. Nonlinear models for Illinois Type I, II and III elastomeric bearings are developed. The effectiveness of the bearings for reducing column displacement demands is addressed by analytical studies. These studies consider potential effects of cold temperatures on bearing stiffness.National Science Foundation EEC-970178