Study On Running Performance Of Trains Moving On Mountain Railway Bridge Under Natural Disasters

The mountainous regions in Western China is great expansive,where is well known of the complex terrains and the harsh climate.Natural disasters such as ice damage,debris flow and seismic are frequent,and multi-hazard coupling effects such as debris flow disaster chain,ice flood and ice-lake outburst caused by seismic occur irregularly.With the rapid development of mountain railways,the proportion of railway bridges grow with each passing day.The probability of the trains moving on the bridges when natural disasters occur greatly increases,which seriously threatens the running performance of trains on the bridges.Therefore,to ensure the safe operation of mountain railways,it is important research topics to evaluate the ride comfort and running safety of trains on the bridges under the effects of the natural disasters or the multi-hazard,establish and improve the multi-hazard early warning system of mountain railways,and investigate the vibration control of trains when natural disasters occur.In this dissertation,a train-track-bridge dynamics model under the ice,debris flow and seismic loads is established from the perspectives of railway system dynamics,bridge disaster prevention and mitigation,and bridge vibration control.The dynamic behavior characteristics and the influence laws of the train-track-bridge system under natural disasters are revealed,and the running safety of trains on the bridges is evaluated.The control effect of tuned mass damper(TMD)installed on the bridges on the coupled vibration of train-track-bridge system is investigated,and the effect of TMD on the running safety of trains when extreme disasters occurs is analyzed,which provides a theoretical basis for disaster prevention and mitigation of mountain railway bridges and improves multi-hazard early warning system.This dissertation mainly carried out the following research work:1.The ice-bridge pier collision model considering the interaction of ice-water-pier is established using the fluid-structure coupling theory,and the impact loads of ice hitting pier are calculated.Then based on smooth particle hydrodynamics(SPH)theory,the whole process of debris flow impacting the bridge pier is simulated and the impact loads of debris flow are obtained.2.The train-track-bridge dynamics model under natural disasters is established,the vehicle adopts classical model with a total of 35 degrees of freedom,and the track structure and bridge structure are modelled using the finite element method,considering the fully wheel-rail dynamic interaction and bridge-rail interaction.In the dynamics model,the ice loads and debris flow loads are employed as the excitation input of the bridge pier,and the seismic loads is directly forced at the bottom of the bridge pier supporting points by acceleration.Based on the TMD vibration control theory,the optimal parameters and the best installation position of TMD are determined,then the train-track-bridge vibration control model under external loads is established.3.Aiming at the threat of ice damage,debris flow and seismic disasters to the running safety of trains in mountainous regions,the dynamic responses of bridge and vehicle in time domain and frequency domain with and without the ice,debris flow and seismic loads are systematically analyzed,and the variation laws of vehicle derailment factor and wheel unloading rate with load intensities under different running speeds are revealed,then the running safety threshold of trains moving on the bridges is investigated.4.The dynamic behavior characteristics of train-track-bridge system under multi-hazard coupling effects and its influence on the running safety of trains on the bridges are studied.The effect of coupled seismic-debris flow and seismic-ice on the dynamic response of train-track-bridge system is analyzed in detail,and the influence laws of coupled seismic-debris flow and seismic-ice on vehicle lateral acceleration,vehicle lateral stability index,derailment factor and wheel unloading rate under different running speeds are investigated.5.Based on the train-track-bridge vibration control model under the external loads,the vibration control effects of TMD on the dynamic response of bridge under ice,debris flow and seismic loads are investigated,and the influence laws of running speeds and TMD mass ratio on train running safety index are revealed,then the effects of TMD on train running safety under extreme ice,debris flow and seismic loads are analyzed.Finally,the strategy of using multiple tuned mass dampers(MTMD)to suppress the bridge structure vibration and the train vibration under the multi-hazard coupling effects is proposed.