Research on Distribution Laws of Railway Rail Temperature and Longitudinal Force Under a Cross-Line Bridge

The shading effect of an overpass bridge changes the solar-radiation conditions of the rails beneath and outside the bridge, resulting in a non-uniform longitudinal rail-temperature distribution. In this study, fixed-point monitoring and manual longitudinal measurements were conducted on a ballasted continuously welded rail (CWR) section beneath a highway overpass bridge. The results show that the rail-temperature difference is mainly concentrated in the daytime heating period and varies considerably with weather conditions. Among 145 valid daily samples, 92.4% of the daily maximum rail-temperature differences between the open-track and under-bridge measurement points were within 0–10 °C, whereas 86.9% of the daily minimum differences were within −2–2 °C. Longitudinal measurements indicate that two rail-temperature transition zones with opposite gradients form near the bridge edges and interact beneath the bridge, producing an approximately V-shaped temperature distribution. Based on the measured temperature characteristics, a finite element model of ballasted CWR was established to investigate the effects of rail-temperature transition-zone length and rail-temperature difference on longitudinal rail response. The numerical analysis is used mainly for comparative evaluation of response trends rather than for direct prediction of in-service mechanical quantities.