Seismic behavior and capacity/demand analyses of three multi-span simply supported bridges

This paper presents the results of an analytical study on the seismic response of three Multi-Span-Simply-Supported (MSSS) bridges in New Jersey. The main goal is to determine the capacity/demand ratio for various components in order to evaluate the seismic vulnerability and to develop retrofit strategies. Another important objective is to investigate the effect of those response characteristics that are unique to this class of bridges on their seismic performance. Furthermore, the effect of modeling approach and appropriateness of pushover analysis using existing demand curve are also addressed considering the stiffening-interaction between the bridge and the abutments. The investigation includes detailed nonlinear time history analyses of three actual bridges as representatives of typical 2, 3, and 4 span bridges, which are common in New Jersey and the Eastern United States in general. Both 2-D and 3-D models were employed in order to evaluate the effect of modeling. Several parameters prove to have an important effect on the seismic response of MSSS bridges, such as soil–structure interaction, impact between adjacent spans, steel bearings, and plasticity at pier columns. Therefore, the seismic response of MSSS bridges is evaluated in light of a comprehensive parametric study based on these factors and quantified through capacity/demand  (C/D)(C/D) ratios for critical elements. Furthermore, the research needs related to the seismic evaluation, retrofit, and design of MSSS bridges are also discussed.