Mediterranean coastal bridges’ vulnerability to combined earthquake-tsunami actions: fragility assessment

During natural disasters, such as earthquakes followed by tsunami events, bridges represent critical infrastructures whose failure can severely hinder emergency response and recovery efforts. Coastal regions are among the most susceptible to facing these unfortunate occurrences and it is also well established that even Mediterranean areas have experienced significant events of combined earthquake-tsunami actions. The 1908 Messina tsunami, triggered by a powerful earthquake, devastated southern Italy, causing many facilities and leaving a lasting memory to the Mediterranean regions’ inhabitants. The focus of this research is to provide insights useful for more resilient infrastructure design standards for multi-hazard scenarios and effective mitigation measures. A probabilistic multi-hazard fragility assessment framework is presented to evaluate the structural vulnerability of bridges subjected to sequential earthquake and tsunami loads, since a significant increase in vulnerability occurs when seismic damage precedes tsunami loading, underscoring the need for integrated design and assessment strategies. The proposed methodology employs Monte Carlo simulations to account for uncertainties in tsunami forces and structural configurations, providing a statistically robust tool for vulnerability assessment. Representative bridge typologies from Mediterranean coastal zones are analyzed through a two-step process: nonlinear time-history analyses simulate seismic action, then force-controlled pushover analyses model tsunami impact. The simulation results have been examined to identify the most appropriate analytical lognormal-distributions capable of accurately representing structural fragility. A comprehensive comparison between the numerical results and the derived fragility functions has been conducted, confirming the robustness and precision of the proposed methodology.