Study On Dynamic Characteristics Of Ballastless Track In The Transition Section Of Road And Bridge In Cold Region Under Seismic Response

In the construction and operation of high-speed railways in China,in order to reduce the impact of construction projects on land occupation and the environment,most of them choose to use bridges instead of roads.In severe cold regions,uneven deformation is easily generated near the transition between subgrade and bridge,resulting in uneven rail surface,which further affects the safety and stability of driving.At the same time,earthquake is a common natural disaster.In the earthquake area,track structures may undergo various forms of damage due to the impact of seismic loads.Existing studies have not considered the effects of frost heave in the subgrade area,uneven deformation in the transition section of the road bridge,and the combined action of earthquakes on the track structure and trains.However,with the improvement of railway construction standards,the proportion of bridges is gradually increasing,and earthquake disasters occur frequently.Due to the prominent practical problems,research cannot be limited to a single field,but must be comprehensively considered.Therefore,it is necessary to carry out research on the dynamic characteristics of ballastless tracks in the transition sections between roads and bridges in severe cold regions under earthquake action,which can provide theoretical guidance for the optimal design and maintenance of high-speed railways in China.Focusing on the strategy of strengthening transportation,this paper takes CRTS-III slab ballastless track of high-speed railway in severe cold regions as the research object,and establishes a dynamic coupling model of vehicle-ballastless track-road bridge transition section based on finite element theory simulation and seismic engineering numerical analysis.The influence of ballastless track structure and vehicle dynamics characteristics with or without seismic action is studied when considering the complex deformation of the lower foundation of the road-bridge transition section(cosine frost heave,half-cosine settlement,angle deformation).Based on the vehicle dynamics evaluation index,the foundation deformation control standard is further proposed.Finally,under the premise of considering the frost heaving of subgrade and track irregularity,the early warning threshold of train in the transition section of road and bridge in cold regions under earthquake response is studied.The main research results and conclusions are as follows:(1)Based on the established vehicle ballastless track bridge transition coupling model,the dynamic response of the track structure with or without earthquake considering subgrade frost heave and uneven road bridge transition conditions was studied.Research shows that for subgrade frost heave,earthquakes can increase the initial track structure irregularities,leading to increased track structure response,and have a significant impact on the beginning of single wave frost heave in the subgrade and the maximum point of continuous and uniform multi wave frost heave separation joints.When the amplitude of single wave subgrade frost heave is large and the wavelength is small,and the number of continuous and uniform multi wave frost heave waves is large,the impact of earthquake on the track structure will be greater,which will exacerbate the damage of the track structure.At the same time,for the uneven deformation of the transition section,the earthquake has a significant impact on the starting point of the transition section,which will exacerbate the development of separation joints between the track structure layers at this point.When the half cosine settlement wavelength is small and the bending angle is large,the vertical vibration of the track structure changes greatly due to earthquakes,which will affect the comfort of train operation.(2)Based on the established dynamic model,from the perspective of train operation safety and stability,the dynamic response of the vehicle body with or without earthquakes under the conditions of considering subgrade frost heave and non-uniformity of the road bridge transition section is studied,and the limit values of subgrade frost heave and non-uniform settlement of the transition section are obtained.Research shows that for subgrade frost heave,earthquakes can increase the dynamic response of vehicle bodies,and the impact on vehicle body dynamics is positively correlated with the amplitude of subgrade frost heave and the number of continuous and uniform multi wave frost heave waves,while negatively correlated with the wavelength of subgrade frost heave.At the same time,for the non-uniform deformation of the transition section,the earthquake has a significant impact on the vertical acceleration of the vehicle body under the condition of half cosine settlement,and the impact on the vehicle body dynamics is negatively correlated with the settlement wavelength;Earthquake has a significant impact on the vertical acceleration and wheel load reduction rate of the vehicle body under the condition of uneven angular deformation,and its impact on vehicle body dynamics is positively correlated with the magnitude of the angular deformation.(3)Based on the safety and comfort index of train operation,the dynamic response of train passing through the frost heaving area of subgrade in the transition section of road and bridge under three conditions of seismic wave with different spectral characteristics,different ground motion intensity and different driving speed is studied.Finally,the El-Centro seismic wave is taken as an example to excite the system,put forward the recommended value of the limit value of high-speed train operation,and obtain the safety limit diagram of the ground motion intensity and train operation speed.On this basis,the alarm threshold when the train encounters an earthquake is obtained.