An analytical method for accumulated longitudinal deformation and stress of in-service continuously welded ballastless turnouts under cyclic loading considering hysteresis and degradation effects of track resistance

Abstract

In regions with significant diurnal temperature variations, continuous welded turnouts (CWTs) are susceptible to excessive longitudinal rail displacement under cyclic thermal loading and progressive resistance degradation, ultimately leading to abnormal turnout conversion and service failure. To analyze the longitudinal mechanical behavior and assess the safety of CWTs in service, this paper develops a data-driven finite element analysis model for ballastless turnouts and presents a novel algorithm for service-state reconstruction and resistance constitutive curve updating. The model fully accounts for the hysteretic behavior and loading history of the fastening resistance, with cyclic thermal loading and various resistance degradation processes selected as typical working conditions to be simulated. The analysis is conducted from multiple perspectives, including the hysteretic loop morphologies of fasteners under different constraints, the longitudinal distribution of resistance curve offsets along the CWTs, rail residual displacement/stress, and longitudinal forces in load-transferring components. Results showed that the data-driven finite element model achieved a displacement error of less than 0.0002 mm in reconstructing the in-service status. The greater the asymmetry of the cyclic temperature loading, the more pronounced the effects of hysteresis loop offset and residual displacement accumulation become. After 25 extreme temperature cycles (− 45~10 °C), the maximum longitudinal residual rail deformation reached 4.32 mm, already 43.2% of the stress-release maintenance limit (10 mm). Neglecting continuous resistance degradation led to an underestimation of longitudinal cumulative plastic displacement, necessitating the inclusion of its long-term evolution in-service status predictions. This study provides a theoretical basis for longitudinal displacement control and long‑term condition assessment of CWTs.