Research On Seismic Performance And Design Method For High-speed Railway Bridges Based On Track-bridge Integrated Model

Most of high-speed railway bridges in China have been built in regions of high-intensity seismic,and ballastless track systems are widely used as the track structures.Due to the large longitudinal stiffness of ballastless track system,the seismic coupling between adjacent bridges is obvious.In the seismic response analysis of bridges,the constraint effect of ballastless track system is not considered in the existing seismic models.Therefore,the main research work for ballastless track beam bridges in this paper can be described as follows:(1)In view of the different kinds of ballastless tracks used in high-speed railway bridges,a simplified seismic calculation model for slab ballastless track bridges is proposed,and then verified by comparing with the refined seismic calculation model.At the same time,an integrated track-bridge seismic calculation model of double-block ballastless track bridge is also proposed,and then verified by comparing with the refined seismic calculation model.(2)Based on the 32 m simply supported girder bridge with ballastless track of high-speed railway,the seismic response under the action of different seismic intensity of the seismic wave were studied with a 1:20 single-span simply supported beam bridge model by shaking table test and finite element analysis with and without track constraints respectively.The results show that the track system can effectively improve the overall seismic performance of the bridge,which enhances the coupling between the bridge spans,which has a significant impact on the seismic response of the bridge.In the seismic design and analysis of the high-speed railway simply supported girder bridge,the track constraint effect should be fully considered.(3)From the point of performance-based seismic design,the theoretical framework of seismic design for ballastless track bridges of high-speed railway in China is proposed.Based on the integrated track-bridge seismic calculation model of ballastless track bridge,the seismic analysis method under low-level and high-level earthquakes and the seismic checking method for each component of bridge are put forward respectively.Based on the analysis of IDA,it is concluded that when the horizontal resistance of the support takes 20% of its vertical bearing capacity,the support becomes the weak part of the structure.when the horizontal resistance of the support takes 30% of its vertical bearing capacity,the pier becomes the weak part of the structure.The seismic weak parts of bridge under large earthquakes should be properly arranged and designed in the course of seismic design of high-speed railway bridges.(4)The girder bridge with double-block ballastless track on a high-speed railway is studied by IDA.The dynamic characteristics of bridge and seismic vulnerability of gravity piers with and without track system are studied respectively.At the same time,the influence of reinforcement ratio on the vulnerability of gravity piers under track constraints is alsostudied.The results show that the existence of the track system improves the overall stiffness of the bridge.With the increase of reinforcement ratio of piers,there is a good transition between the damage states of piers,showing partial ductility and complete ductility failure characteristics in turn.The fixed pier of continuous girder bridge under medium damage state controls the vulnerability of the whole pier system.Once the pier enters the state of complete damage,the fixed pier no longer controls the vulnerability of the whole pier system,and needs to integrate the vulnerability of fixed piers,joint piers and movable piers at the same time.(5)The influence of the bearings of the high-speed railway bridge on its substructure under different damage states with and without track system are studied respectively.The results show that the longitudinal restraint effect of the orbit has different influence rules and influence degrees on different bridge types,and the damage state of different supports has obvious influence on the seismic response of the lower bridge structure.For the seismic calculation of bridges,the working modes should be considered reasonably in order to obtain the unfavorable stress state of the bridge pier.