Track–Bridge Interaction and Low-Resistance Fastener Layout for a 4 × 40 m Continuous Rigid-Frame Bridge on the Nan-zhu-Zhong Intercity Railway

Understanding the non-linear dynamic interaction between tracks and bridge structures is essential for maintaining the safety of continuous rigid-frame bridges. To accurately capture these beam–rail interactions, this study develops a detailed 3D finite element model based on the principle of stationary total potential energy. This framework fully integrates the track, main girders, and piers into a single system. Based on a 4 × 40 m continuous rigid-frame viaduct in an urban transit network, the numerical model accounts for the bilinear mechanical behavior of the rail fasteners. The study compares the transmission of longitudinal forces along the continuously welded rail (CWR) under two fastening layouts. The baseline case uses uniform constant-resistance fasteners across the entire bridge, while the optimized scheme places small-resistance fasteners at the final 20% of each structural segment. Analysis shows that placing low-resistance fasteners in the high-displacement areas near the girder ends creates an effective longitudinal “release zone.” This design effectively interrupts the buildup of longitudinal forces, resulting in a much smoother force distribution along the rails. Quantitative results indicate that this optimized fastener layout has only a minor effect on structural deflection and braking-induced rail stresses, keeping deviations below 11%. At the same time, it significantly reduces the peak expansion stress and broken-rail stress by 43.4% and 22.2%, respectively. By shifting the stress regulation philosophy from “rigid resistance” to dynamic “force channeling,” these findings demonstrate that local low-resistance fastener deployment improves the overall mechanical compatibility of the track–bridge infrastructure. Ultimately, this work offers a solid theoretical basis for the design and maintenance of CWR systems on long-span rigid-frame bridges.