A Numerical Study into the Reconstruction of Impact Forces on Railway Track-like Structures

This article presents the development of a process by which an impact experienced by a track-like structure can be reconstructed based on its vibration response. The process is essentially based on an inverse analysis technique, while a cepstral analysis technique is also used to improve waveform reconstructions. Firstly, a finite element (FE) model of a simple track structure was generated and calibrated to a real laboratory model to show that it was able to simulate impact events. The rail geometry was then replaced with a simple rectangular beam in order to allow simulation of a rolling wheel by means of a moving mean load. The simple beam geometry was necessary because the rail geometry carried an excessive computational cost when incorporating a moving mean load. This is a legitimate substitution because the inverse analysis technique is geometrically independent. It was found that the acceleration response of the track structure due to the dynamic impact was largely unaffected by the moving mean loading condition. It was also found that the inverse analysis technique shows potential for reconstructing input forces, but in some instances the reconstructed waveform has ambiguous peaks and excessive signal pollution around the force waveform. The cepstral analysis was then found to be useful in sufficiently ‘smoothing’ the transfer function spectrum such that an improved waveform reconstruction could be obtained. An error analysis showed that the regular transfer function as obtained by the inverse analysis technique when ‘smoothed’ by cepstral analysis gave a lower order of error. It was found that to provide sufficient coverage of a full crib of rail, three calibration points were required for the transfer function, with four accelerometers to pick up the track responses along the crib.