Study On The Vehicle-Track-Bridge Dynamic Response And Track Irregularity At Long Span Bridge Beam End

With the continuous development of Chinese high-speed railway,high-speed railway bridges with a span of more than 1000 meters have been widely used.The bridge expansion joint(BEJs)is a special device installed at the beam end of the long-span railway bridge.Since the track structure at beam end is complicated,track state maintenance has become a key issue in the operation and maintenance of long-span railway bridges.At present,the research on track deformation characteristics at beam end is not deep enough,and its influence on vehicle driving performance is not clear.Furthermore,there is no acceptable standard to evaluate the working state of the BEJs.In this paper,the track irregularity at beam end of long-span railway bridges is taken as the research object.The mapping law between track and bridge deformation at beam end under complex load cases is studied.The vehicle-track-bridge coupling dynamic model for complex track structures is developed.The influence of the track geometry at beam end of bridge on the dynamic response of train-track system is analyzed.The dynamic irregularity characteristics of the track at beam end of bridge are studied.The acceptance criteria of profile irregularity at the BEJs area are proposed.The main work includes:(1)A detailed spatial coupling model of bridge-ballasted track-BEJs at beam end of long span suspension bridge is established.This model can simulate the adjustment effect of the BEJs on track structure,and more accurately analyze the influence of different loads on track deformation.Based on this model,the influence of the displacement of bridge at beam end on track geometry under complex load is analyzed,and the rail-bridge deformation mapping relationship at beam end is established,which is helpful for further exploring the influence of additional deformation of track on the dynamic performance of train-track structure.The concrete rail-bridge deformation mapping relationship is as follows: the rail deformation is consistent with the bridge deformation on the bridge,and the rail deformation transits smoothly in the middle of the beam joint;At the beam end,the rail is locally convex when the beam end is tilted up and the rail is locally concave when the beam end sinks,both vertically and horizontally;In the area of BEJs,the vertical and horizontal deformations of rail are coupled;The range of vertical deformation difference between rail and bridge is about 6 m,which is within the length of supporting beam;The range of lateral deformation difference between rail and bridge is about 10 m.(2)Applying vehicle-track-bridge coupling vibration theory to the beam end area,a vehicle-track-bridge coupling dynamic model based on the track-bridge separation model and the detailed modeling of the BEJs was established,and corresponding programs were developed,which includes pre-processing and post-processing modules.The motion equations of track structure and bridge structure are established by finite element method,which can simulate the change of track structure at beam end area.With the finite element model of track and bridge separated from each other,the interaction force between track and bridge is transformed into the equivalent load of forced motion,which makes the bridge model no longer limited by the sleeper spacing.This method scales down the bridge model and saves computational resources.There are two wheel-rail force calculation modules: wheel-rail close-fitting model and wheel-rail separation model,which can meet the needs of high-precision and fast calculation separately;The program adopts modular design,which facilitates the modification and expansion of software functions.(3)Based on the detailed finite element model of the track-bridge structure and the compiled dynamic analysis program,the dynamic response of the train-track system at beam end is analyzed by taking the track deformation on the bridge under multiple working conditions as additional irregularity.And the influence of the disease state of the BEJs on the dynamic response of the system is studied.The change of track structure in the beam end area will have a significant impact on the dynamic response of vehicles,which is consistent with the laws obtained from the test.The wheel-rail interaction and the dynamic performance of the BEJs are greatly influenced by the sleeper spacing,and the most unfavorable situation is that the movable sleeper spacing is the largest.The abnormal working state of the BEJs mainly affects the vertical dynamic response of the train and track,and the results may exceed the limit in serious cases.(4)The dynamic track irregularity of long-span railway bridges is analyzed,and the time domain characteristics of track irregularity at beam end are explored.The wavelet transform theory is applied to the analysis of track irregularity at the beam end,and the wavelength characteristics of track dynamic irregularity at the beam end are cleared.Rail gauge abrupt peak will be produced at the point of the rail expansion joint,which can be used as the basis for accurate positioning of the mileage at the beam end.There are local peaks of profile irregularities at the beam joint,and there are local peaks of gauge and alignment irregularity at the tip of the switch rail.The BEJs mainly affects the profile irregularity,and the corresponding wavelength range is within 5 m,which is within the length of the supporting beam.The corresponding wavelength of gauge and alignment irregularity produced by the rail expansion joint is 0.5～8.07 m,which is within the length of the rail expansion joint.(5)Suggestions on the acceptance criteria of profile irregularity in the area of BEJss are put forward.The mileage of dynamic and static irregularity data is calibrated through the correlation of gauge irregularity,and the difference value of dynamic and static profile irregularity measured by 5 m chord is used as the acceptance index,with the limit is 2mm.The rationality of the criteria is verified by comparing with the results of sleeper suspension disease in the subgrade section,and by using this index to evaluate the sleeper suspension disease of the BEJs.This work can fill the blank of the acceptance criteria of profile irregularity applicable to the beam end area,and provide a basis for the opening of lines on long-span bridges.