Effects of nonstationary spatially varying ground motions on dynamic reliability of isolated curved bridges

Isolated curved girder bridges (ICGBs) are highly sensitive to the spatial variability of earthquake ground motions (SVEGM) and their nonstationary features due to geometric asymmetry and bending-torsion coupling. This study systematically investigates the effects of nonstationary SVEGM on the dynamic reliability of ICGBs. A multidimensional, multisupport nonstationary evolutionary power spectral model incorporating wave-passage, partial coherence, and local site effects is constructed. Using an improved absolute displacement method combined with the pseudo-excitation method (PEM), a nonlinear finite element model is developed for dynamic time-history analyses. The time-frequency-domain formulation of first-passage dynamic reliability is then extended to nonstationary excitations using Poisson and Markov upcrossing assumptions. System reliability is evaluated across various SVEGM patterns. Results demonstrate that SVEGM significantly impacts the frequency-domain characteristics of structural responses and dynamic reliability. Specifically, lower apparent wave velocities, nonuniform site conditions, and fully coherent excitations substantially reduce system reliability, with the coherence effect acting as the dominant governing factor. Furthermore, neglecting ground motion nonstationarity underestimates structural seismic performance and fundamentally alters the evolution of system dynamic reliability. Finally, geometric factors, including pier height and curvature radius, noticeably affect reliability. These findings provide a theoretical framework for the seismic design and performance assessment of ICGBs.