Seismic Parameter Analysis of the Vehicle–Track–Bridge-Coupled System Subjected to Across-Strike-Slip Fault Ground Motions

Across strike-slip fault ground motions, characterized by the fling-step effect and rupture directivity effect, pose a severe challenge to the seismic safety of railway bridges and the running safety of vehicles. In this study, ground motions are reconstructed using seismic parameters representing the forward directivity and fling-step effects. Specifically, pulse amplitude and period characterize the forward directivity effect, while permanent displacement represents the fling-step effect. Dynamic response evaluation of the vehicle–track–bridge coupled system under different seismic parameters is conducted, focusing on car-body acceleration, wheel–rail interaction forces, bearing deformation, and pier-top displacement. The results indicate that increasing pulse amplitude, period, and permanent displacement generally amplifies the dynamic response of the coupled system. Sensitivity analysis further reveals notable differences in how each response metric responds to the seismic parameters, with the system being most sensitive to pulse period. The findings provide a theoretical basis for the seismic design and running safety evaluation of railway systems subjected to across-strike-slip fault ground motions.