Dynamic Response Of Wheel-Rail System To Rail Weld Irregularity

Due to the outstanding continuity and integrity, the continuously welded rail (CWR) has become the primary selection when a new railway line is designed. There is no doubt that the rail welding is one of the key technologies involved in the construction of the CWR, and the evenness of the rail welding joint draws more and more attention. It is of great realistic significance to perform the investigation into the influence of the weld irregularity, as it plays a crucial role in the dynamic performance of the vehicle-track system when wheels pass through the rail welding, even the service life of the rail welding.Following the review of the processing and results of the research done in the field of rail welding joint, the vehicle and track vertical dynamics model is set up basing on the vehicle-track coupling dynamics theory. The weld irregularity which is utilized as the input to the coupling model is taken from one of the subways in China. Firstly, the dynamic performance of the vehicle and track is studied with the excitation of the measured weld irregularity. Then, the difference between the responses caused by the measured weld irregularity and the harmonic irregularity is investigated via the coupling model established previously. The impact of some related parameters on the dynamic behavior is studied systematically, e.g. the velocity, the wavelength and depth of irregularity, the location of rail joint, the sleeper pitch, the mass of rail and the track structure. Specifically, the influence of the elasticity of fastener and rail pad is analyzed in detail.By simulation, the following conclusions can be drawn. Though the measured weld irregularity and the harmonic irregularity are not in agreement totally, the dynamic response is mainly controlled by the major part of the measured irregularity. While the parameters of the harmonic irregularity are selected appropriately, it could reproduce the effect of the measured irregularity basically.Some measures could be taken to improve the dynamic performance at the rail welding region, e.g. reducing the velocity, extending the wavelength, diminishing the depth of irregularity, or adopting such type of track which is more elastic. Either increasing or decreasing the sleeper pitch and rail mass should be determined according to the local situation, and the effect of such measure is not as evident as those mentioned above. When the rail weld is set in the middle of two sleepers, the load acting on the fastener and rail pad rises greatly in contrast with the situation when the rail weld appears above the sleeper. Therefore, it is highly recommended to prohibit the appearance of the later one. The descent of rail pad elasticity will worsen the dynamic response of the wheel-rail system caused by the weld irregularity and vice versa. Hence it is of great necessary to examine the quality of rail pads near the rail weld and substitute the senescent pads periodically. In order to improve the dynamic performance, it is advisable to replace3~4rail pads adjacent to the rail weld with low stiffness ones during the maintenance of the railway. If it permits, raising the quantity into5-6would be better. However, there is no more improvement when more rail pads are altered.