Nonlinear Response of Bridges under Multisupport Excitation

The authors present 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 for nonsynchronous and synchronous motion, and subsequently, have been analyzed in the nonlinear range under nonsynchronous input motion. The purpose of this investigation was 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. Findings revealed that displacement ductility demands in bridges designed by the q-factor method for a multisupport excitation were in good agreement with the chosen value of q. The bridges designed for synchronous input and then examined for nonsynchronous motion displayed an excess of strength in the central piers, whereas the opposite happened for those near the abutments, which may have displacement ductility demands larger than those requested under synchronous motion.