Direct determination of dynamic properties of railway tracks for flexural vibrations

The vertical vibration of rails constrained and supported by fastening systems occurs due to moving dynamic loads induced from rotating train wheels. The dynamic stiffness and damping capability of the railway track on the viscoelastic medium are essential to evaluate their performance on minimizing rail vibration and environmental noise generation. In this study, a new experimental method to measure the viscoelastic properties of the railway track for flexural vibration was proposed using the wave propagation approach. The proposed method was used to analyze the generation and transfer of vertical rail vibration at frequencies of rolling noise generation and to test actual track models. A slab track model and embedded railway tracks were used in the experiments. The rail was excited by a shaker or an impact hammer, and the resulting acceleration responses were measured at two locations. The flexural wave propagation was found to occur only at frequencies higher than the mass-spring resonance frequency of the rails. After obtaining the wavenumber from the transfer function between the measured responses, the frequency-dependent stiffness and loss factor of the track structures were calculated. The viscoelastic properties of different railway tracks of finite length were measured accurately in the laboratory setups. Then, for validation of the proposed method, the field test was performed using the infinitely long embedded tracks used for a tramway. The measured dynamic stiffness from the finite embedded tracks in the laboratory was very similar to the field test results. The proposed method enables direct determination of the dynamic properties and comparison of flexural wave propagation characteristics of different railway tracks.