Dynamic responses and cumulative damage of coastal bridges subjected to extreme sequential earthquake-tsunamis

Coastal bridges, as vital components of transportation networks, are vulnerable to damage from successive earthquake-tsunami (EQ-TS) events in rapidly developing coastal hazard-prone cities. Understanding how these bridges perform under the combined effects of earthquakes and tsunamis is crucial. Though studies have investigated coastal buildings facing these hazards, there is limited research on bridges experiencing extreme EQ-TS events, especially on the generation of load sequences, dynamic structural responses, and cumulative damage assessment. To overcome these limitations, this study aims to thoroughly examine the dynamic behavior of reinforced concrete coastal bridges subjected to successive EQ-TS hazards. To generate practical sequential EQ-TS loads, records of the 2011 Tohoku earthquake and resulting tsunami heights, which are calculated based on the earthquake magnitude and epicentral distance, are utilized for analyses. The tsunami wave load time series for each earthquake record is created using a high-fidelity computational fluid dynamics model. Nonlinear time-history analyses are then performed for the bridge model in OpenSees under the synthetic EQ-TS sequences, quantifying structural responses and cumulative damage. Moreover, the comparative results of structural performance under single and successive hazard scenarios are presented and discussed. Results indicate that successive EQ-TS hazards not only induce much larger structural responses as compared to a single EQ hazard, but also produce considerable residual displacements for both bearings and decks. The wave height is more appropriate than the peak ground acceleration as an individual intensity measure for predicting the cumulative damage of bridges under cascading EQ-TS hazards. Relying solely on peak responses for assessing the dynamic performance of piers under successive EQ-TS sequences may underestimate the actual damage.