Research On Interaction Between Track And Multi-span Simply Supported Beam Railway Bridge Under Ground Motions

At present,Chinese mature and advanced high-speed railway technology system has been formed.In the process of high-speed railway construction at home and abroad,high-speed railway bridges are widely distributed in various operating lines due to their geographical requirements.In the seismic research process of traditional railway bridges,the orbital system is only considered as the form of mass,and the restraining effect of the orbit on the bridge is neglected.Furthermore,in order to meet the high-speed and stable operation requirements of the train,for the conventional railway bridges,the railway track of the bridge deck is basically in a continuous state,and the influence of the restraining effect of the track on the bridge on the dynamic response of the bridge under action of earthquake is particularly important.In this paper,it mainly studies the dynamic response law of bridges under multi-span simply supported beam railway bridge considering the effect of orbital constraints and without considering the orbital constraints.The main research work and conclusions are as follows:1?The method of establishing the traditional beam-rail integration model is compared and researched,and the refined finite element model of the upper structure including the main beam,the base plate,the CA mortar,the track plate,the track and the track fasteners is proposed.2?In order to study the influence of orbital restraint on the seismic response of multi-span simply supported beam railway bridge,a six-span simply supported beam railway bridge is used as a example,and different abutment stiffness is selected as the main parameter variable.Three types models were selected,four large working conditions,and seven seismic response spectra and seismic waves with high spectral fit were calculated for each working condition.The nonlinear time-history analysis of the structure was carried out.The main conclusions are as follows:(1)Under the action of different ground motions,regardless of the orbital constraints or not,whether the abutment stiffness changes or not,the law of the internal force of the pier bottom,the displacement of the pier top,and the displacement diagram of the main beam displacement are all“large in the middle,two ends small of"convex parabolic line type";when the orbit constraint is not considered,the symmetry of the envelope diagram is stronger than the corresponding envelope diagram when considering the orbit constraint.In particular,the dynamic response of some piers may be underestimated without considering the orbital constraints;(2)After considering the orbital restraint effect,the amplitude range of the pier bottom,the amplitude range of the pier top displacement,and the amplitude range of the main beam displacement are significantly reduced,and the positive and negative values are also reduced,and the amplitude is reduced.The degree of small increase with the increase of the longitudinal stiffness of the abutment,and the maximum reduction of each parameter is up to 35.92%;(3)Due to the existence of orbital constraints,the bridge is more integrated and the internal force distribution is more uniform.At the same time,CA mortar can ensure that under the action of earthquakes,the upper rail system allows a certain slip to play a role in seismic energy dissipation,which reduces the internal force and displacement to a certain extent.Furthermore,the orbital constraints can form a new force transmission system between the various members of the bridge,resulting in the redistribution of internal forces.When the longitudinal stiffness of the abutment is large,the internal force redistribution phenomenon is not significant;when the abutment stiffness takes the minimum value of 3×10~8N/m,this internal force redistribution becomes more pronounced,and the position of the control pier is changed.3?In order to study the influence of the interaction between the multi-span and simply supported beam railway bridge track and bridge on the seismic response of the structure under multi-point excitation,the important parameters affecting the traveling wave effect are:the seismic wave type,the apparent wave velocity and the structural stiffness of the bridge.Discuss and analyze the nonlinear time history of multi-point ground motion input for high-speed railway bridges considering orbital constraints and without considering orbital constraints.The main conclusions are:(1)Considering the traveling wave effect of seismic waves:Considering the restraining effect of the orbit,it is not always possible to reduce the shear force and bending moment of the pier.There is a certain degree of similarity between the bottom ground shear force and the bending moment dynamic response under the same ground motion and different apparent wave velocity.With the increase of the apparent wave velocity,the structural dynamic response is closer to the dynamic response under uniform excitation,and the structure is more sensitive to the small apparent wave velocity.This is because the smaller the apparent wave velocity,the more obvious the time lag phenomenon of ground motion,and the difference in dynamic characteristics between adjacent structures is amplified.(2)Under different ground motions,the collision response of the main beam has a certain difference,which mainly depends on the structural dynamic characteristics between adjacent structures and the spectral characteristics of ground motion.The existence of orbital restraint does not necessarily reduce the number of collisions between the ends of the main beam,but it can reduce the collision stress of the main beam end to a certain extent;the smaller the apparent wave velocity,the more obvious the hysteresis of the ground motion,the number of collisions between the ends of the main beam is bigger;(3)Considering the sudden change of pier stiffness:the dynamic response of the bottom section of the pier is reduced to a certain extent,but the dynamic response of adjacent piers and piers is increased to some extent;Considering the orbital restraint can reduce the main beam collision response.However,considering the restraining effect under partial ground motion,the collision stress of some beam-girder beams increases,so the negligence of the orbital constraints may underestimate the collision response of some beam-girder ends.