Seismic Fragility of Retrofitted Multispan Continuous Steel Bridges in New York

Abstract

Various retrofit measures, such as elastomeric bearings, lead-rubber bearings, viscous dampers, and jacketing with carbon fibers, are commonly used to improve the seismic performance of multispan continuous steel highway bridges. In this paper, we have investigated the effectiveness of these retrofit measures through comparisons of seismic fragility of as-built and retrofitted multispan continuous steel bridges. Both elastomeric and lead-rubber bearings reduce the fragility of bridge piers significantly through isolation effects. Wrapping of piers with fiber-reinforced polymer (FRP) increases the effective ductility of piers through confinement and shifts the failure mode of a FRP wrapped pier to rupture of the FRP at much higher peak ground acceleration. The use of viscous dampers in combination with elastomeric bearings is effective in reducing fragilities because of both pier ductilities and bearing displacements. Hence, all four seismic retrofit strategies are effective in improving the safety of bridge components during earthquakes.