Keywords: unsupported sleepers, void depth, void length, rail joints, fishplates, axle box acceleration, fatigue life, numerical simulation.

The unsupported sleeper detection method enables estimation of both the void depth and void length between the underside of an unsupported sleeper and the supporting surface from dynamic track waveforms measured by a track geometry car. As a result, the vertical displacement of the rails during vehicle passage can be readily identified, and this information is increasingly utilized for evaluations such as the fatigue strength of track components. However, at rail joints, decreased accuracy in calculating the void depth is frequently observed, and there are few practical examples of this method’s application. Since damage events at rail joints are not fail-safe and managing them is challenging, this study aims to establish a rational approach for preventing fishplate damage. Specifically, we examine the estimation of bending stress generated in fishplates located within unsupported sleeper sections during train passages. In addition, the validity of the present findings is discussed based on a comparison with the actual distribution of unsupported sleepers at rail joints and the number of fishplate failures observed on operational lines.

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