Dynamic response and damage evolution of coastal bridges under sequential earthquake-tsunami hazards

Coastal bridges subjected to sequential earthquake-tsunami hazards may exhibit damage mechanisms that differ fundamentally from those under single-hazard loading. Neglecting the evolving post-earthquake structural condition may therefore lead to inaccurate assessments of vulnerability and failure risk. In this study, a three-span simply supported bridge is analyzed using a nonlinear OpenSees model coupled with computational fluid dynamics (CFD)-based tsunami forces. Earthquake-tsunami load pairs are generated through a Copula-based joint probability model to ensure hazard consistency. A damage contribution coefficient, log R 0 , is further proposed to quantify the relative contributions of the earthquake and tsunami stages to overall structural damage. The results show that superstructure rotation is mainly governed by tsunami loading, whereas bearing and pier responses are strongly affected by earthquake-induced damage to restraining components. Partial degradation of restraints reduces the transfer of tsunami-induced forces to the piers, whereas complete failure leads to rapid damage escalation. Compared with conventional laminated rubber bearings (LRB), tension-compression bearings (TCB) effectively limit superstructure rotation and bearing displacement but increase pier demand due to more direct force transmission. These findings highlight the critical role of restraining components in damage redistribution and underscore the need for system-level coordination in the seismic-tsunami design of coastal bridges.