Determining effective earthquake countermeasures for bridges considering seismic and tsunami hazards based on expected post-disaster recovery time

Current technologies cannot completely prevent bridge damage from giant tsunamis, such as superstructure washouts. Practical earthquake countermeasures include both conventional seismic retrofitting to improve structural performance and the use of prepared temporary bridge components for rapid recovery post-tsunami. However, few studies have quantitatively assessed the effectiveness of these countermeasures in terms of expected recovery time considering multiple hazards. This paper presents a methodology to determine the most effective countermeasure—seismic retrofitting or temporary bridge components—for bridges impacted by the anticipated Nankai Trough earthquake (NTE)-induced ground motion and tsunami, which have historically caused severe damage across Japan’s coastal areas. Probabilistic hazard analyses are used to estimate seismic and tsunami hazard curves for individual bridge locations, while seismic and tsunami fragility curves for piers and bearings are developed numerically. The effect of seismic damage prior to tsunami actions is incorporated into the tsunami vulnerability assessments. The expected recovery time for bridges from NTE is estimated using risk concepts, with resilience defined as the reduction in recovery time. An illustrative example for bridges in Wakayama City, Japan, is provided, discussing the appropriate countermeasures and their priorities based on cost-effectiveness and the importance of each bridge.