Evaluation of Spring Stiffness of Resilience Pads for Sleeper Floating Track Through Modal Testing

The resilience pads of sleeper floating tracks (STEDEF) are key components that absorb shock loads and vibrations induced by train traffic. Currently, under the Korean domestic guidelines for track facility performance evaluation, one sample per 500 m is collected from the field, and the static spring stiffness is assessed through laboratory testing. However, this approach requires nighttime track possession, incurs significant manpower and cost, and provides limited reliability because the condition of an entire section is inferred from a small number of samples. Therefore, this study proposes an impact-hammer–FRF-based method for evaluating the spring stiffness of resilience pads without pad extraction. Field impact-hammer tests were conducted to identify the dominant first-mode natural frequency of the track-support system. Configuration-specific finite element models were then used to derive frequency–stiffness relationships for the investigated STEDEF configurations. The novelty of the proposed method lies in converting the local first-mode frequency measured in situ into a static-equivalent stiffness index that can be directly compared with the maintenance reference value used in the Korean inspection framework. The finite element model reproduced the mean natural frequencies of the reference configurations with differences of 0.08–3.61%. Based on the configuration-specific relationships, estimation equations were developed to support in situ screening of resilience-pad stiffness at the measured locations.