The foundation conditions of piers for multi-span long-distance heavy-haul railway bridges inevitably vary at different locations, which may lead to non-uniform ground motions at each pier position, potentially causing adverse effects on the bridge's seismic response. To investigate the seismic response of bridges and the running safety of heavy-haul trains as they cross the bridge during an earthquake, a three-dimensional heavy-haul railway train-track-bridge (HRTTB) coupled system model was developed using ANSYS/LS-DYNA. This model incorporates the nonlinear behavior of critical components such as bearings, lateral restrainers, piers, and wheel-rail contact interactions, and it has been validated against field-measured data to ensure reliable dynamics parameters for seismic analysis. A multi-span simply supported girder bridge from a heavy-haul railway (HHR) was employed as a case study, in which a spatially correlated non-stationary ground motion field was generated based on spectral representation harmonic theory. Comparative analyses of the seismic responses under spatially varying ground motions (SVGM) and uniform seismic excitation conditions were performed for the coupled system. The results indicate that the presence of heavy-haul trains prolongs the natural period of the HRTTB system, thereby appreciably altering its seismic response. At lower apparent wave velocities, more piers exhibit a low-response state, and some pier bases enter the elastic-plastic stage under local site effects. Compared with the piers, the bearings show higher sensitivity to seismic inputs; fixed bearings experience damage when subjected to traveling wave effects and local site effects, which is subsequently followed by the failure of lateral restrainers. Train running safety is markedly reduced when crossing local soft soil site conditions. The conclusions drawn from this study can be applied in the seismic design and running safety assessment of HHR bridge systems under SVGM.

Currently, while various earthquake mitigation strategies for railway bridges have reached a mature stage, the focus on ensuring train safety during seismic events remains limited. Based on considering different earthquake intensities and sites, this study introduces a three-dimensional train-track-bridge coupling model by taking China Railway Track System (CRTS) II plate ballastless track, a simply supported girder bridge and a train set as examples. It refines traditional train running safety indexes and evaluates the influence of spherical steel bearings (SSBs) on the running safety of trains amid seismic activities. The results show that in areas with hard soil layers, the number of SSB damages varies with the earthquake intensities, and whether the SSB is damaged marginally affects trains running safety during earthquakes. However, in regions with soft soil layers, the longer ground motion periods adversely affect SSBs, leading to significantly larger displacements in damaged SSBs compared to undamaged ones, thereby posing a greater risk to train running safety, especially as the earthquake intensity increases. Thus, for enhanced running safety, particularly in areas with suboptimal soil conditions, larger displacement design values (i.e., increased bearing stiffness) should be adopted, and efforts should be made to limit the sliding of SSBs post-damage.