Comparative Seismic Fragility Assessment of an Existing Isolated Continuous Bridge Retrofitted with Different Energy Dissipation Devices

Seismic isolation is a commonly adopted approach for designing bridges against earthquakes. However, the period elongation in an isolated bridge will generally lead to a large superstructure displacement, which may result in pounding, bearing unseating, or even span collapse. This study focuses on the implementation of energy dissipation devices for retrofitting an existing bridge isolated by lead rubber bearings (LRBs). Four different retrofit measures, namely yielding steel cables (YSCs), viscous dampers (VDs), friction dampers (FDs), and superelastic shape memory alloy cables (SMAs) were considered in this study. Fragility analyses were performed to evaluate the relative effectiveness of these devices in minimizing the seismic vulnerability of the bridge. The results indicate that all the devices show comparable performance in reducing the probability of damage of the isolation bearings without imposing much additional vulnerability on the bridge piers. The SMAs are the most effective in mitigating the seismic vulnerability of the bridge system at all the damage states, followed by FDs, VDs, and YSCs. Due to the superior self-centering capacity, the SMAs retrofitted bridge exhibits better recentering performance with a reduced residual displacement of superstructure compared with the bridges with other retrofit measures. (c) 2019 American Society of Civil Engineers.