Research On Dynamic Response Characteristics And Structural Optimization Design Of Rail Expansion Joint On Suspension Bridges In High-speed Railways

With the development of construction materials and improvement of bridge designing technology,long-span suspension bridges have been gradually applied to high-speed railway infrastructure.Continuous welded rail(CWR)is widely used in high-speed railway.CWR on suspension bridge is facing the problem of adaptability to the environment and coordination with the infrastructure.There are relatively few existing researches on the analysis of mechanical characteristics of CWR on suspension bridges,dynamic response and optimization design of(rail expansion joint)REJ.As the infrastructure of high-speed railway,the design rationality of CWR on suspension bridge directly affects the safety and comfort index of running and the maintenance cost of track.Therefore,it is very important to study the longitudinal mechanical characteristics of CWR and dynamic response of REJ on suspension bridge,as well as to optimize the layout of REJ on suspension bridge.The research results can provide a theoretical reference for the design,operation and maintenance of CWR on high-speed railway bridge.Based on the ballasted CWR on suspension bridge,the finite element models include train-track-bridge spatial coupling dynamics model and suspension bridge-CWR spatial coupling statics model which can consider geometrical nonlinear factors such as stress stiffening and large deformation effect are established.The rail longitudinal force analysis on suspension bridge,the dynamic response of the REJ under the action of seismic load,the matching design of sleeper-supporting apparatus are analyzed in this paper.The laying position of the REJ and the sleeper-supporting apparatus at the beam end are optimized.The research conclusions are as follows:(1)The additional expansion force of CWR on suspension bridge mainly depends on the environmental temperature difference and longitudinal resistance.The influence of temperature difference of main tower and suspender on the rail longitudinal force on suspension bridge is negligible.When the train load is closer to the bridge tower,the rail longitudinal force and deflection are greater.When the train load is closer to the midspan of suspension bridge,the changing of suspender and main cable axial force are greater.Increasing the fastener resistance can increase the rail braking force,reduce the beam-rail relative displacement and decrease the axial force of main cable and suspender will decrease but not significantly.Increasing the longitudinal stiffness of damping device can reduce the rail braking force and the beam-rail relativedisplacement.When the stiffness of the damping device reaches 5 times of the original stiffness,the effect of reducing the rail longitudinal force is not obvious.REJ can reduce the longitudinal force of the CWR on the bridge,coordinate the deformation of the rail and the bridge,and its layout is more flexible.(2)REJ can reduce the rail deformation and release rail longitudinal force under the seismic load.When the REJ is further away from the beam end,the expansion amount of REJ and beam-rail relative displacement at the beam end will decrease,the rail longitudinal force at beam ends and fixed pier longitudinal force of the sidespan continuous beam bridge can increase.With the increasing of seismic acceleration,the expansion amount of REJ and the fixed pier longitudinal force of side span continuous beam gradually increase.Increasing the longitudinal stiffness of damping device between the main tower and beam is conducive to reducing the expansion amount of REJ and beam-rail relative displacement under the action of seismic load,while the longitudinal force of fixed pier of side span continuous beam is little affected by the stiffness of damping device.(3)After REJ is equipped on the bridge,when trains pass through the REJ,the vibration of track and bridge,wheel-rail force and wheel unloading rate on REJ zone increase significantly.Considering the coupling of unsupported sleeper and vehicle dynamic load,when the installing position of REJ is closer to beam end,the vertical deformations of rail,bridge and other structures are smaller,but vibration of bridge and track,wheel-rail force,derailment coefficient and wheel unloading rate are significantly increased.(4)When REJ is closer to the beam end,the dynamic responses of REJ and bridge under seismic load and train dynamic load are greater,the beam-rail relative displacements under static temperature and braking loads are also greater.The above mechanical deformations of structure are not conducive to the stability of the ballast bed and track geometry,the deformation and longitudinal force of fixed pier of side-span continuous beam are also unfavorable.It is suggested that REJ could be equipped at the position of 30 m from the beam end instead of laying on the beam end.At the same time,a certain length of small resistance fasteners should be paved on the side of stock rail to ensure the stability of ballast bed on beam end.(5)Due to the long span of steel truss bridge,the expansion amount of beam joint is large.When the train passes through beam joint,wheel-rail force fluctuations are intense,and wheel unloading rate is severe.Sleeper-supporting apparatus can effectively improve the stiffness uniformity of beam joints and increase the running stability of train.In order to solve the problems such as large deformation and skew of the movable steel sleeper,uneven spacing of the sleeper etc.,it is suggested that a steel longitudinal beam can be equipped on the center of sleeper-supporting apparatus to achieve the purpose of multi-point traction and increasing the vertical stiffness of sleeper-supporting apparatus.