Combined effects of skew and curvature on the seismic performance of RC multi-frame box-girder bridges

Abstract

Abstract

Recent seismic events have highlighted the vulnerability of skewed highway bridges, particularly when combined with deck curvature. The interaction of skew angle and horizontal curvature induces complex torsional and asymmetric responses, complicating seismic performance assessment of multiple-frame bridges. This study develops component- and system-level fragility curves for skew-curved RC box-girder bridges using nonlinear time-history analyses in OpenSees. System-level damage states are defined based on FEMA HAZUS-MH guidelines, enabling a consistent probabilistic evaluation framework. The results indicate that both increasing skew angle and decreasing deck radius significantly elevate seismic fragility, with the most pronounced effects observed in deck unseating and columns. Bridges with small deck radii exhibit markedly reduced median fragility thresholds, while skew further amplifies vulnerability through asymmetric force redistribution. At low damage levels, joint seals are the most vulnerable components, whereas deck unseating and columns govern system performance at higher damage states. Overall, the findings demonstrate that deck curvature is the dominant geometric driver of fragility, with skew acting as a critical amplifier, underscoring the need to explicitly account for both parameters in the seismic design, evaluation, and retrofit of skew-curved bridge systems.