Rooted in structural dynamics theory, two approximate procedures for estimating peak responses of linearly elastic “ordinary” bridges crossing fault-rupture zones are presented: response spectrum analysis (RSA) procedure and a linear static analysis procedure. These procedures estimate the peak response by superposing peak values of quasi-static and dynamic responses. The peak quasi-static response in both procedures is computed by static analysis of the bridge with peak values of all support displacements applied simultaneously. In RSA, the peak dynamic response is estimated by dynamic analysis including all significant modes, which is simplified in the latter procedure to static analysis of the bridge for appropriately selected forces; usually only one mode—the most dominant mode—is sufficient in the RSA procedure. Appearing in these procedures is the “effective” influence vector that differs from the influence vector for spatially uniform excitation, and the response spectrum used in the RSA procedure differs from the standard California Department of Transportation (CALTRANS) spectrum. Both of these simplified procedures provide estimates of peak response that are close enough to results of the “exact” response history analysis to be useful for practical application.
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