Effect of Regional Distribution and Degradation of Ballast Resistance on Longitudinal Force of Rail

In order to explore the effect of ballast resistance evolution on the mechanical behavior of the continuously welded rail (CWR) on bridge, tests were conducted for the longitudinal and lateral ballast resistances on bridge and roadbed sections. Taking an example of an extra-large double-line continuous beam bridge commonly used in railway, the track resistance distribution characteristics on bridge were obtained, and the local ballast resistance degradation was discovered in the ballast service. On this basis, the longitudinal mechanics behavior model of CWR on bridge was established, which takes into account the non-uniform distribution and degradation of ballast resistance. The results show that the distribution of ballast longitudinal resistance on bridge shows significant regional distribution characteristics, the maximum longitudinal resistance was 31.8 kN per sleeper at the central span of bridge, and the longitudinal resistance near the beam joint was relatively small, 21.7 kN per sleeper, demonstrating obvious ballast resistance degradation. The lateral resistance distribution on bridge also has moderate regional distribution characteristics, the lateral resistance at the central span of bridge was 31.7 kN per sleeper and the lateral resistance near the beam joint was 25.5 kN per sleeper, while the degradation does not obvious. As thermal load leads to beam expansions and the dynamic loads of trains cause bridge vibration displacement and rotation angles at the beam support, the crushed-stone ballast dynamically changes between tension and compression, and the ballast resistance shows obvious degradation characteristics. When there is ballast resistance degradation, the rail longitudinal force, rail displacement and relative displacement between bridge and track under thermal loading has a certain attenuation. Thus, the maximum rail longitudinal additional force with the temperature span of 140 m was reduced by about 11.7%, and the attenuation rate increases linearly with the increase of temperature span. The beam-rail interaction is relatively large if it is calculated according to specifications.