Seismic Fragility Assessment of an Existing Multi-span Isolated Bridge in Eastern Canada

Seismic fragility analysis is deemed to be a functional tool for evaluating the performance of bridges subjected to natural hazards such as earthquakes. Although there have been many studies on developing fragility curves for generic bridges, few have focused on the existing bridges (particularly long-span bridges). Moreover, the majority of studies have been conducted using as-built bridge parameters, whereas the seismic performance assessment of retrofitted bridges has not been investigated to the same extent. This study aims to develop fragility curves for the original as-built configuration of an existing bridge and its constitutive components and then compare them with those developed for the current retrofitted bridge. The employed retrofit technique in this study is seismic isolation of the superstructure utilizing a novel type of isolation system known as Unbonded Fiber Reinforced Elastomeric Isolators (U-FREI). A comprehensive three-dimensional model of an existing bridge is generated in OpenSees. Incremental Dynamic Analysis (IDA) is performed to monitor the seismic performance of the bridge components under a range of earthquake intensities. Derived fragility curves show that isolating the superstructure using U-FREI can effectively reduce the seismic demand by allowing the deck to have larger displacements and avoiding the formation of plastic hinges in the columns.