Probabilistic multi-hazard fragility analysis of RC bridges under earthquake-tsunami sequential events

Abstract Coastal bridges may have been damaged by the prior earthquakes before the earthquake triggered near-field tsunami acting on the bridges. In this scenario, the bridges can be considered affected by the multi-hazard earthquake-tsunami sequential events. However, studies concerning fragility analysis of bridges under the sequential earthquake-tsunami events are limited. In this study, probabilistic fragility analysis is conducted for a reinforced concrete (RC) box-girder bridge under earthquake-tsunami sequential events. A two-phase analysis method is used for bridge damage analysis subjected to earthquake-tsunami sequential events. Joint multi-hazard fragility curves of the bridge under earthquake-tsunami sequential events are derived. The results show that the prior earthquake has more pronounced effects on stiffness than strength of the bridge columns. The effects of prior earthquake on post-shock bridge tsunami fragility are more pronounced at lower damage levels, whereas the prior earthquake has negligible effects on tsunami fragility at extensive and complete damage states. Compared with considering the individual earthquake hazard or tsunami hazard only, the bridge system becomes more vulnerable if multi-hazard of earthquake-tsunami is considered.