Ballasted High-Speed Railway Track Ageing: A Global–Local Numerical Framework for Dynamic Response and Sleeper Fatigue Assessment

This study presents a global--local finite element framework for assessing the influence of degradation on the dynamic response and concrete fatigue of ballasted high-speed railway tracks. A three-dimensional global track model is first calibrated and validated against field measurements of acceleration and displacement obtained from a high-speed railway line. The validated model is then used to investigate representative degradation conditions, including transition zones, hanging and partially supported sleepers, wet-bed conditions, abrasion, cracking, and reinforcement corrosion. Dynamic histories obtained from representative track locations are transferred to a refined three-dimensional model of a reinforced-concrete bi-block sleeper. Concrete stress histories are extracted independently at the integration-point level and processed using rainflow cycle counting, stress-state-dependent S--N relationships, and Palmgren--Miner cumulative damage. The largest fib-based valid-cycle fatigue contributions are obtained for the unsupported block of the partially supported sleeper and for the abrupt transition. The results demonstrate that global dynamic severity cannot be used directly as a measure of local concrete fatigue severity and that asymmetric support conditions can be particularly critical. The proposed framework provides a physics-based basis for linking track-scale degradation to component-scale fatigue and for supporting condition-based maintenance of high-speed ballasted railway infrastructure.