Nonlinear response of bridges under multisupport excitation

This work presents the results of an extensive numerical study on the nonlinear response of bridges subjected to multisupport seismic excitation. Bridges of varying stiffness and ductility have been designed both for nonsynchronous motion and, as in current engineering practice, for synchronous motion, and have been subsequently analyzed in the nonlinear range under nonsynchronous input motion. The purpose of the study has been to assess the effects on the peak inelastic response of bridge structures and the extent of validity of the force reduction factor (q-factor) approach for the design. The results show that displacement ductility demands in bridges designed by the q-factor method for a multisupport excitation are in good accordance with the selected value of q. The bridges designed for synchronous input and then checked for nonsynchronous motion exhibit an excess of strength in the central piers, whereas the opposite occurs for those close to the abutments, which may have displacement ductility demands larger than those requested under synchronous motion.