Seismic Analysis and Design Evaluation of Continuous Plate-girder Bridges: A Case Study

The currently-used AASHTO seismic design code for continuous plate-girder bridges built in areas of low to moderate seismicity is evaluated. The seismic behavior of a typical plate-girder bridge, designed according to the code, is studied in detail using a linear time-history analysis, and the peak response values of important parameters are computed. The effects of vertical ground excitation, seismic wave propagation, and change in support conditions on the bridge seismic response are investigated. The results are compared with those obtained using the current AASHTO seismic design code. The study concludes that the effect of vertical ground excitation on the plate-girder bending moments could be significant. It was found that the effect of seismic wave propagation on bending moments and shear forces in the bridge piers should be considered in the analysis of continuous plate girder bridges with several immovable supports when built in zones of low wave propagation speeds (e.g. 244 to 488 m/s). The study further concludes that AASHTO single mode spectral analysis slightly underestimates the forces in the bridge piers.