Study On Longitudinal Dynamic Interaction Mechanism Between Heavy Haul Trains And Bridges And Load Parameters

With the continuous development of domestic heavy haul railways,long-heavy marshaling trains,wireless synchronous operation technology,and higher axle loads are adopted to increase the heavy haul railway capacity further.As the train axle load increases,the load that is acted on the line and bridge increases correspondingly.Most of the previous studies focused on the vertical force and deformation characteristics of the track and bridge caused by the increase in the train’s axle load.Little research has been carried out on the load increasing problem for the track and bridge structures induced by synchronous control technology and axle load elevation.For the existing bridge design methods in China,the longitudinal load value is usually selected at 10% of the vertical live load.However,in actual operation,some bridges have been damaged due to insufficient longitudinal bearing capacity.The current design method no longer has a sufficient safety reservation.With the load on the bridge increasing and the capacity calculated by the existing design theory decreasing,the longitudinal force capacity would be insufficient,which will cause transportation safety failure.Besides,there are relatively few solutions or design cases on improving the bridge’s longitudinal force behavior.In response to the above problems,the longitudinal interaction between the long-heavy marshaling train and the bridge is considered the research object.Through the comprehensive application of multiple methods such as theoretical analysis,numerical simulation,and field testing,the train and the bridge’s longitudinal dynamic mechanism is systematically studied.The critical parameters of the longitudinal design load of the bridge are determined.The optimization measures for the longitudinal force transmission of the heavy haul railway bridge structure are proposed and verified on site.Taking the 32 m simply-supported beam bridge in heavy haul railway in China as the typical structure,the research content is as follows:(1)Transmission mechanism of the longitudinal impulse of long-heavy marshaling train under braking conditions A refined theoretical analysis model for the longitudinal dynamics of long-heavy marshaling trains is established.The model can fully consider the influence of train marshaling mode,control mode,brake cylinder boost,and brake propagation time on long-heavy marshaling trains’ longitudinal impulse characteristics.With this model,the influence of train operating conditions,coupler types,and train marshaling on trains’ longitudinal impulses are systematically analyzed.Through theoretical analysis,it is reasonable to set 0.164 as the braking force ratio.(2)Longitudinal mechanical transfer characteristics of heavy haul railway track-bridge system Considered the nonlinear effect in the track-bridge system,a track-bridge three dimensional coupling static model for heavy haul railway is established,and the ZH load pattern is analyzed in the form of traversal from the front of the car to the rear of the bridge.The longitudinal force distribution characteristics of the bridge,the influence law of including the number of bridge spans,the longitudinal resistance of the line,the stiffness of the pier and the train’s axle load on the interaction between track and bridge is studied.It is found that the pier longitudinal force is increased as the vertical vehicle axle load increases.When the ZH load diagram is used for analysis,under the 30 t axle load condition,the bridge pier’s longitudinal load is 12% of the bridge span’s vertical load,which exceeds the 10% limit given in the current code.(3)Longitudinal dynamic effects and influencing factors of heavy haul train-track-bridge Based on the vehicle-track coupling dynamics,structural dynamics and the rigid-flexible coupling theory,the spatial motion formula of the long-heavy marshaling trains are coupled with that of the track-bridge-pier system through the wheel-rail interaction as a link,and the long-heavy marshaling trains-track-bridge spatial coupling refined model is established.A field test was carried out to verify the reliability of the model.With the dynamic analysis model,the track and bridge’s longitudinal dynamic force transmission mechanism under train braking is revealed.The influencing law of the factors such as marshaling mode,braking pattern,and synchronous control braking and axle load on the bridge’s longitudinal force is analyzed.(4)Research on load parameters and optimization measures for bridge longitudinal force transmission and field verification For the design of new lines in the heavy haul railway,the effective braking force ratio’s recommended value is proposed.The rationality of this value is verified by combining with the on-site train braking test.For the existing lines in heavy haul railway,the effectiveness of the speed locker solution for improving the longitudinal force of the pier and the reasonable value for speed lock’s damping rate is studied based on the refined dynamic model of marshaling train-track-bridge spatial coupling model and the improvement effect of the longitudinal pier force after the speed locker installed was studied and verified against field test results.The researches above can provide evidence and proof for new line bridge design and existing line bridge longitudinal interaction improvement in the heavy haul railway.