Effects of impact on the seismic response of MSSS bridges

This paper presents results of a study on the effect of impact on seismic response of Multi-Span Simply-Supported (MSSS) bridges. The investigation includes detailed dynamic analysis of three actual bridges as representatives of 2, 3, and 4 span bridges, which are common in the Eastern United States. Furthermore, using a Stiffening Single-Degree-Of-Freedom (S-SDOF) model a series of parametric study are performed. The objectives are to better quantify the effect of impact on the seismic performance of MSSS bridges and to provide the knowledge base for development of design guidelines within a performance-based framework. Several damage criteria, namely displacement, dissipated hysteretic energy, and low-cycle fatigue damage index are considered. It is shown that on the average displacement demands are lower for S-SDOF systems, consistent with pushover analysis based on current seismic codes. However, considering other damage criteria, it is quite possible for an S-SDOF system to sustain more damage than an elastic-plastic system. Design implications and the needs for future research are also discussed.