Dynamic Responses Of Coupled Train-track-bridge System Subjected To Debris Flow Impacts And Running Safety Analysis Of High-speed Train

With the rapid development of high-speed railway,an increasing number of bridges are being constructed,many of them located in mountainous areas with common debris flows.Debris flow with moderate intensity is the most common and likely to pose a great threat to the safety of trains passing on a bridge.Under this background,this thesis carried out a series of studies of the dynamic responses of coupled train–track–bridge system subjected to debris flow impacts and analysis the operation safety of high-speed train.Firstly,the research status of impact load amplitude and load time history of debris flow in existing literature is summarized.Then,the Walnut Ravine Bridge on Chengdu-Lanzhou Railway is selected as the case study,and the numerical simulation of the boulders impact is carried out.Based on that,a model of debris flow impact load is first proposed based on the latest research findings,in which the time history of the debris flow impact load is assumed.The coupled train–track–bridge system subjected to debris flow impact is established on account of the Train-Track-Bridge coupling theory,and the debris flow load is regarded as external load excitation.Based on that,the corresponding simulation analysis program is developed.Then,aiming at the example,the dynamic performance and traffic train running safety have been analyzed by the simulation program.Further,the parameters of the selected examples have been analyzed,including the moment of impact load,slurry impact force,boulder impact force,vehicle speed,foundation stiffness and track irregularity spectrum.The main conclusions are as follows:(1)The proposed model of debris flow impact load consists of two parts: dynamic slurry pressure and boulders impact.The time-history curve of dynamic slurry pressure is a gentle rectangle,and the time-history curve of boulders impact is a short pulse triangle peak.(2)The dynamic responses of the bridge and track are greatly affected by debris flow impact load.The lateral displacement and acceleration of the bridge caused by debris flow impact load are much larger than those by train loading.The dominant frequency components of bridge responses are close to the lateral bending frequencies of the whole bridge.(3)The train running safety indices are significantly affected by the debris flow impact load.Compared to the slurry pressure,the boulders impact has more adverse effects on the running safety of the train.(4)The debris flow impact intensity and train speed jointly influence the running safety indices.When the speed of train exceeds 280 km/h,the increase of running safety indices is much more pronounced with increasing debris flow impact intensity.(5)The foundation stiffness and track irregularity spectrum jointly influence the running safety indices.Generally,the influence of foundation stiffness is not significant without debris flow impact,while the influence of track irregularity is significant under the same circumstance.