Research On The Vertical Vibration Mechanism Of The High-speed Railway On Continously Installed General Free Beam Bridges Under The Soft Soil Foundation

With the rapid development of high-speed railway construction in China,the original vehicle-bridge coupled vibration theory system has been difficult to meet the precision requirements of high-speed train research at this stage.The continuous acceleration of train speeds has also aggravated the coupled vibration of vehicles and bridges while the trains are on soft ground.In the upper run,the compression of the underlying load will increase the severity of the coupled vibration of the vehicle and bridge,which will greatly reduce the safety of the train.In order to ensure the safety of high-speed trains operating on bridges in soft ground,it is urgently needed to analyze the coupled vibration of the axle system under consideration of the influence of soft ground.In this paper,the coupled vehicle-bridge vibration model considering the soil-structure interaction under the commonly used span-simple beam bridge with continuous span is established through the finite element software LUSAS,and the dynamic characteristics and various influencing parameters of the vehicle-bridge coupled model are analyzed in detail.The research content and conclusions are as follows:(1)Based on the analysis of the influence of the main factors causing the coupling vibration of the axle system,a simplified model of the coupled vibration of the axle system considering the SSI effect is proposed.Among the factors causing the coupling vibration of the axle system,there are mainly the vehicle model,the bridge model and the foundation model.The vehicle model adopts the two-train suspension four-axle locomotive model.The bridge structure is established with the beam element and simulated by the equivalent soil spring under the m method.The pile-soil interaction and the step-by-step integration method are used to solve differential equations with time-varying coefficients,which greatly improves the computational efficiency of the model.(2)Three simplified finite element models for vehicle-bridge,vehicle-bridge-pier,vehiclebridge-pier-soil-soil(SSI)were established respectively,and the dynamic response characteristics of the bridge were performed in both time and frequency domain.Calculated analysis.By comparison,after considering the effect of pile-soil,the natural vibration frequency of the structure is significantly lower than that of the bottom of the bridge,and the overall rigidity of the structural system is reduced.The vertical vibration frequency of the main beam is reduced from 5.62 Hz to At 4.87 Hz,the dynamic characteristics of the structural system are greatly changed.Therefore,when the vehicle-bridge coupling analysis is performed,the effect of the pile-soil interaction must be considered.(3)When considering the SSI effect and not considering the SSI effect,when the train crosses the bridge at different speeds,the vibration response law of the bridge mid-span dynamic response.Under the vehicle-bridge-pier system and the vehicle-bridge-pier-pile-earth system model,the bridge structure displacement response and the vehicle speed are not simply monotonically increasing or decreasing.The two models are close to the vehicle speed.At 500km/h,the bridge mid-span displacement reaches a maximum.It can be seen that when analyzing the train resonance speed and the analysis of train operation indicators,the SSI effect will have a non-negligible impact on the numerical analysis.When the train speed reaches the resonance speed,all the safety indicators of the train undergo great changes.(4)Based on the SSI effect,the effects of parameters such as vehicle model,axle load,bridge bending stiffness,bridge span,pile-soil depth,and track irregularity on the vertical dynamic response of the bridge in a vehicle-bridge coupled system are studied.The following conclusions can be obtained: :1 The four-axle secondary suspension vehicle can better reflect the real condition of the vehicle than the two-axle one-train vehicle and the single-wheel model;2 The bridge mid-span dynamic response monotonously increases with the axle load of the train;3 The increase of the vertical stiffness of the bridge does not significantly reduce The dynamic response of the axle;4 As the depth of the pile increases,the vertical displacement of the bridge mid-span does not change much,and the vertical acceleration in the middle of the bridge has a certain effect,but the change tends to be gentle after the length of the pile exceeds a certain value,which indicates the depth of the pile.There is a certain influence on the vertical dynamic response of the bridge,but the impact is not significant;5 rail surface irregularity does not change the basic vibration law of the vehicle-bridge coupling.