Research On Multi-dimensional Response And Isolation Design Of Long-span High Speed Railway Bridge Subjected To The Near-fault Ground Motions

With the increase of the percentage of high-speed railway bridge accounting for the total length of line,the probability of trains passing over trains have been increasing when earthquake happening.At the same time,with the increasing of train travelling speed,the dynamic response of bridge structures will be even more significant.The lead rubber bearing has good seismic isolation efficiency for the seismic isolation design of the bridge,the existing research has been focusing on seismic response of the bridge under the far field ground motions,little studies have been carried out on the seismic performance of the bridge under the near fault ground motion with long period pulse.Taking Dongchagou bridge in Baoji to Lanzhou passenger dedicated line(72+120+72)m as a case study,the influence of different parameters on isolation efficiency of large-span high-speed railway bridge have been analyzed.The research conclusions are as follows:(1)Based on the finite element analysis ANSYS software,using APDL programming language,the global finite element calculation model of large-span high-speed railway bridge is set up.Firstly,lead rubber bearing model used in this paper is presented,the modal analysis has been carried out considering the influence of track irregularity.According to the proper vibration isolation period,the design process of dynamic parameters of seismic isolation bearings has been presented.(2)In terms of the global seismic isolated large-span high-speed railway bridge model.The nonlinear time history analysis method is used the seismic response of the seismic isolated bridge.The effect of the ratio of peak ground acceleration and peak ground velocity(Ap/Vp),the characteristics of different Q/W(the ratio of the characteristic strength to the bearing load.)and the different damping ratio on isolation efficiency of isolated large-span high-speed railway bridge have been analyzed.The isolation efficiency of the isolated large-span high-speed railway bridge have been analyzed.The results indicat that when the optimization parameter of Q/W is in the range of 1.2%～1.5%and the damping ratio is in the range of 0.15～0.25 the siesmic isolation efficiency of bridgeis better.(3)Considering the influence of vertical ground motion on the seismic response of the bridge,the vertical and horizontal peak acceleration ratio and the ratio of the vertical ground motion peak acceleration and peak velocity of Av/Vv have been analyzed.Research results show that the vertical ground motion can cause axial force change,which influence the siesmic isolation efficiency of bridge by the interaction of axial force and shear-bending moment.