Fatigue performance of HFRP-reinforced track composite slabs: Experiments and numerical simulation

To address the risks of corrosion susceptibility and reduced electrical insulation in ballastless track structures during service life, replacing conventional steel bars with fiber-reinforced polymer (FRP) bars has emerged as a promising strategy. However, current research still lacks a comprehensive understanding of the fatigue evolution mechanisms across the structural layers of FRP-reinforced ballastless tracks when subjected to high-frequency train loads. This study conceptualizes the track slab and self-compacting concrete (SCC) filling layer as a track composite slab structure with equivalent service life. A three-point bending fatigue test was employed to investigate the effects of steel bars, basalt FRP (BFRP) bars, and hybrid FRP (HFRP) bars on fatigue failure modes, stiffness degradation patterns, and strain-slip responses of the track composite slab. Additionally, a constitutive model for concrete fatigue damage was developed and implemented via a user defined material (UMAT) subroutine within a finite element framework to elucidate track composite slab fatigue evolution mechanisms. Results demonstrate that HFRP-reinforced track composite slabs exhibit mid-span delamination failure after 1.32 million load cycles. Compared to BFRP-reinforced systems, HFRP-reinforced systems enhance fatigue life by 13.79 % and reduce stiffness degradation rates by 22.10 %. Numerical simulations reveal that fatigue damage in HFRP-reinforced track composite slabs initiates at slab edges, propagates gradiently through the thickness direction, and ultimately triggers interfacial cracking. Optimization of the track slab reinforcement ratio to 0.55 % achieves near-critical equilibrium in interlayer strain coordination, enhancing material efficiency while maintaining structural fatigue resistance.