Cost-effectiveness and road network resilience-based countermeasure strategy optimisation of bridges subjected to ground motion and tsunami

This paper presents an optimisation framework for bridge countermeasure strategies based on cost-effectiveness and road network resilience, targeting the impacts of both ground motion and tsunamis caused by the Nankai Trough earthquake, which has historically inflicted severe damage on Pacific coastal regions of Japan. Failure probabilities of bridge piers and bearings, including multiple failure modes such as tsunami-induced superstructure washout, are evaluated using hazard and fragility curves derived through Monte Carlo simulation. The analysis incorporates uncertainties related to fault movement and structural performance. The road network, including bridges, is modelled using graph theory to estimate the benefit-cost ratio (BCR) of countermeasures and road network resilience (R) based on post-disaster transportation functionality. Countermeasure options for each bridge include conventional seismic retrofitting and the post-disaster deployment of pre-stocked temporary bridge girders. A multi-objective optimisation problem is formulated and solved using the Non-dominated Sorting Genetic Algorithm II to identify strategies that simultaneously maximise BCR and R. Results indicate that tsunami countermeasures addressing superstructure washout offer effective and practical means to enhance the resilience of road networks with bridges in Pacific coastal regions.