Decoupling between rail pad stiffness and assembly-level stiffness in vibration-damping fasteners: Experimental evidence and mechanism-based numerical interpretation

Rail fastening systems play a critical role in controlling track stiffness, vibration transmission, and long-term railway performance. Conventional design philosophy assumes that stiffer rail pads produce higher system-level stiffness. This study challenges that assumption through a combined experimental and numerical investigation of vibration-damping and conventional rail fasteners. Static and dynamic stiffness tests were conducted according to EN 13146 standards, and a three-dimensional finite element model was developed to analyze load transfer mechanisms within the fastening assembly. Experimental results show that although the vibration-damping rail pad exhibits 113% higher static stiffness than the conventional pad (62.84 kN/mm vs 29.52 kN/mm), the complete fastening assembly demonstrates lower global static stiffness (22.12 kN/mm vs 33.14 kN/mm). Numerical simulations attribute this behavior to controlled deformation at the clip–insulator–pad interfaces, which introduces distributed compliance and enhances energy dissipation. Dynamic testing further shows an 11.4% increase in system dynamic stiffness, a 27% reduction in resonance amplification, and a 2.32 dB reduction in ground-borne vibration (VLz) for the vibration-damping fastener. These findings demonstrate that rail pad stiffness alone cannot characterize fastening system performance; instead, assembly-level design governs the balance between stiffness, damping, and vibration mitigation. The results provide new mechanistic insight into fastening system behavior and offer guidance for the design and selection of rail fasteners in vibration-sensitive railway environments.