Beam end displacement limits for high-speed railway bridges traffic safety evaluation during earthquake

Beam end displacements are prone to occur during the earthquake, which can endanger the running trains on the bridge. In order to investigate the evaluation method and the associated criteria for train safety based on beam end displacement under earthquake, a vehicle-track coupled vibration model was established. The track deformation curves corresponding to the beam end displacement were applied to the rail as the static track irregularities. The rail bottom excitation caused by earthquake was acted on the rail bottom in the form of sinusoidal wave by the large-mass method. The effects of beam end displacement, track vibration and speed on the safety of trains were analyzed. The calculated results show that the risk of train derailment was positively correlated with these factors, so the influence of the three should be considered when determining the limit values of beam end displacement during earthquake. The limit values of the three types of beam end displacements corresponding to the threshold values of derailment coefficient or the wheel unloading rate are obtained through the binary search method, considering different train speeds and various frequencies and amplitudes of the sinusoidal excitation. The 97.5% guarantee rate is applied to obtain the beam end displacement limit corresponding to different train speeds. The vehicle-track-bridge coupling vibration analysis is carried out under earthquake excitation by taking a 5-span high-speed railway simply supported bridge with a standard span of 32 m as an example. The limit of the beam end displacement determined by the dynamic method is obtained. It is compared with the result from static track displacement plus rail bottom excitation. The consistency of them shows the correctness of the beam end displacement limit. According to the proposed method and the beam end displacement limit, the bridge dynamic analysis under earthquake can be used instead of the vehicle-track-bridge coupling vibration analysis. This facilitates a rapid evaluation of the safety of high-speed trains during earthquakes. © 2023, Central South University Press. All rights reserved.