Dynamic Responses of Bridges under Effects of Asynchronous and Multiple Support Excitations

Abstract

Nonstationary earthquakes are very complex ground motions and they vibrate structural systems in asynchronous form. Spatial variation of an earthquake mainly originates from three sources; loss of coherence effects, wave passage and local soil conditions. In this study, a longspan bridge having multi-support excitations were analyzed for the effects of spatially varying ground motions in terms of wave passage and local site response effects. Two types of dynamic analyses were performed: a) same or different soil conditions for all supports b) same ground motions but different arrival times for wave propagation. For evaluations, the results obtained by considering asynchronous ground motions were compared with those of the synchronous ground motions. From the comparisons, significant differences were observed in case of spatially varying ground motions and this case show that the assumption of synchronous ground motions and identical local site conditions are inadequate to represent the earthquake load and soil model. Therefore, earthquake motions and actual local site properties should be characterized by their inherent properties to obtain more realistic responses.