Seismic Resilience of Railway Bridges with Vertical–Lateral Resistance-Decoupled Girder Support and Semihinged Column–Footing Connections

Seismic isolation has become a mature and widely adopted strategy for mitigating earthquake-induced damage in high-intensity seismic regions. The incorporation of energy dissipation (ED) devices has further advanced this approach, leading to the development of vertical–lateral resistance-decoupled (VLRD) girder-support systems for high-speed railway bridges. This functional separation confines inelastic deformations to replaceable ED components, thereby preventing plastic hinge formation in primary structural members. However, in tall piers with large cross sections, insufficient control of pier-generated inertial forces during strong ground motions can amplify seismic demands and increase the risk of pile foundation damage. To address this issue, semihinged (SH) column–footing connections have been introduced to reduce force transmission to the foundation, but their integration with VLRD systems remains unexplored. The interaction between SH substructures and VLRD superstructures may induce complex force redistributions that affect overall safety and resilience. This study investigates the seismic resilience of high-speed railway bridges equipped with a novel combination of VLRD girder-support system and SH column–footing connection. Four connection configurations were analyzed: (1) transversely fixed girder-support with fixed-base piers (TF-F), (2) friction pendulum bearings with fixed-base piers (FPB-F), (3) FPBs combined with steel restrainer bars and fixed-base piers (SRB-F), and (4) FPB-SRB VLRD with SH piers (SRB-S). Detailed finite-element models incorporating validated hysteretic models of SRBs and SH connections were developed in OpenSees (version 3.7.0). Incremental dynamic analyses under spectrally diverse near-fault ground motions were conducted to quantify component- and system-level fragility. Results indicate that the proposed SRB-S system markedly reduces pier curvature and bending moment demands while effectively controlling girder-support relative displacements. These findings highlight the potential of integrating SH substructures with VLRD superstructures to enhance the seismic resilience of tall hollow piers in high-intensity seismic regions.