Response of conventional and isolated bridges under non-synchronous seismic motion

Abstract

The results of an extensive numerical study on the nonlinear response of bridges subjected to non-synchronous seismic excitation are presented. Spatial variability of seismic motion represents one of the aspects that all of the modern seismic Codes encourage to consider in the design of bridges. This work wants to be a contribution to the interpretation of such effects on typical structures such as long-span bridges. The analysed bridge is a six-span straight bridge, continuous between abutments with single column bents of equal heights and with a twin box girder superstructure and subjected at the supports to seismic inputs with assigned coherence, generated by the spectral representation method. Bridges of varying stiffness and ductility have been designed, as in current engineering practice, for synchronous motion with and without isolating devices, and have been subsequently analysed in the non linear range. The results obtained are useful to assess the relevance of non-synchronous input motion on the ductility demand in the piers of conventional bridge structures and on the isolator displacements of isolated bridges.