Influence of long-span bridge deformation on driving quality of high-speed trains

Bridge time-varying deformation is the time-spatial dynamic deformation of a bridge excited by train motion, which serves as the direct alignment affecting a train's dynamic response and usually moves ahead of the train. In this study, we investigated the influence of the bridge time-varying deformation on the vertical acceleration of a train with 16 cars on a long-span suspension bridge through the train-track-bridge coupled vibration analysis and chord measurements of dynamic spatial alignment. The analysis and measurements reveal the mechanism of the influence of different bridge positions on the car-body acceleration of different cars. Furthermore, we developed a simple method to identify the most unfavourable intersection position of multi-line driving based on the observed mechanism. In single-line operation, the maximum curvature of the main girder caused by bridge deformation with wavelengths above 200 m appears at the bridge tower and mid-span, while the maximum chord-measurement alignment with wavelengths below 200 m appears at the bridge tower, showing that the deformation at the tower area is more significant and that first car or sixteenth car will experience the maximum acceleration. For the multi-line operation, the curvature and chord measurements can be calculated by the superimposition of alignment with the wavelengths above and below 200 m, consecutively; hence, the most unfavourable intersection can be predicted according to the location and intersection of the maximum value. The intersection of two trains can increase the train's centrifugal and vibration accelerations, causing the maximum acceleration to occur at the tower, where two trains meet at the most unfavourable one-fourth span of the bridge, which is verified by the train-track-bridge system.