Seismic Vulnerability of Curved RC Bridges Based on Displacement Ductility: Quantification and Curvature Effects

This study investigates the impact of varying bridge geometries on structural fragility, providing insight into the relationship between curvature and seismic vulnerability. A comparative analysis is conducted on four bridge configurations, one straight and three curved bridges with subtended angles of 25°, 45°, and 90°, subjected to a set of 38 earthquake ground motion records scaled to five intensity levels. Utilizing nonlinear time-history analyses (NLTHA), the research quantifies displacement ductility demands and assesses the evolution of damage states through fragility curves. Fragility curves were developed for four damage states: slight, moderate, extensive, and complete damage. Damage states were quantitatively defined based on structural column rotations, concrete and reinforcements strains, deck unseating due to excessive displacements and column shear capacities. The study further analyses damage indices at the onset of different damage states, demonstrating how displacement ductility ratios evolve with increasing seismic intensity and providing insights into the structural response of curved bridges. The findings indicate a significant correlation between bridges subtended angle and seismic demand, with increased deck curvature leading to higher displacement ductility requirements. Assuming a log-normal distribution for each damage state, the fragility curves were constructed by estimating the medians and log-standard deviations through likelihood maximization. Additionally, a regression-based model is developed, linking peak ground acceleration (PGA) thresholds to subtended angles, offering a practical tool for estimating fragility in curved bridge structures. These results contribute to a better understanding of the relationship between geometric configuration and seismic resilience, providing valuable guidance for both design and retrofitting strategies.