Study On Vibration Energy Transfer Mechanism And Crack Propagation Of Box Girder Roof Under High-Speed Driving Excitation

With the rapid development of my country’s high-speed railway system,the train running speed is increasing,and the wheel-rail dynamic effect is also increasing.The vehicle-induced vibration energy and its vibration propagation to the under-line infrastructure can not be ignored.The long-term operation of high-speed railway bridges with different degrees of damage is bound to cause the redistribution of vibration energy in the interlayer structure and affect the dynamic characteristics of the coupled vibration system.The propagation law of vibration energy between structures is not clear,so it is difficult to deeply understand the evolution law of service performance of high-speed railway bridge system.Therefore,taking the simply supported box girder structure of CRTSⅡ slab ballastless track on the Beijing-Shanghai line as the research object,and reveals the transmission law of vibration energy from top to bottom in the coupled system.The distribution characteristics and propagation law of the structural sound intensity of the bridge-roof are explored.The sensitive factors affecting the crack propagation in the roof are clarified.The main conclusions of this paper are as follows:(1)Based on the vehicle-rail-bridge coupling vibration theory and the joint simulation of ABAQUS and SIMPACK,a vehicle-rail-bridge coupling vibration analysis model considering wheel-rail contact and random irregularity of track are established.The dynamic responses of train,track,and bridge structures are obtained.The dynamic response of each structure is explored when the train speed increases from 250km/h to 400km/h.The results show that the acceleration and displacement of the rail and the displacement of the bridge increase with the increase of the speed,but they do not exceed the code limit.Each safety index of the train also increases with the increase of vehicle speed and does not exceed the limit.After a comprehensive comparison of various indexes,the dynamic performance of the crh380b train is the best.(2)Based on the power flow theory,the vibration energy analysis model is established by using the collaborative modeling method of ABAQUS,FORTRAN subroutine,and Python.The influence of track structure parameters on the vibration transmission law of the bridge is analyzed.The results show that the power flow decreases layer by layer between the system structures.The attenuation effect of the fastener system on vibration energy is the strongest,followed by the mortar layer,and the attenuation effect of the sliding layer on energy is the weakest.In the parameter analysis of track structure,the stiffness and damping of the fastener system have a great influence on the vibration energy of rail and track plate;The stiffness of the mortar layer has a great influence on the vibration energy of the track,base plate,and bridge structure.In the parameter analysis of the bridge structure,the greater the thickness of the bridge section,the smaller the vibration energy of each layer structure in the frequency of 1～200Hz and the greater the vibration energy in the frequency of 500～800Hz.Bridge-roof damage will increase the vibration energy of the bridge track interlayer structure,and reduce the interlayer energy transfer rate,and the closer it is to the foundation structure,the greater the impact.(3)Based on the structural sound intensity theory,the structural sound intensity distribution of bridge-roof under transient and steady-state conditions is analyzed.The results show that in the transient analysis,the structural sound intensity converges to the compression side and simply supported end.When there are cracks,the structural sound intensity gathers at the non-stressed end and increases.Due to the propagation of structural sound intensity being blocked,the energy decreases on the stress side.The influence degree of structural sound intensity field is positively correlated with the length,number,and deterioration degree of cracks.In the steady-state analysis,the distribution of structural sound intensity changes with the change of frequency.The change of crack parameters has a great influence on the structural sound intensity at 4Hz,28 Hz,and other frequencies,and has little influence on the structural sound intensity near 22 Hz.(4)Based on the extended finite element method,the effects of the temperature gradient,crack characteristics,driving speed,axle load,and other factors on concrete crack propagation are studied.The results show that under the action of temperature gradient and trainload,the lower edge of the bridge-roof has large tensile stress only in the transverse direction,and the maximum tensile stress reaches 2.37 mpa.The crack propagation displacement amplitude of the bridge-roof is less affected by the crack length and vehicle speed,but more affected by crack height,bond-slip,axle load,and temperature.In the analysis of the influence of crack propagation on energy,the energy integral difference is defined,which intuitively presents the influence law of crack on energy when the train crosses the bridge.