Research On Dynamic Performance Of Bridge-track System With Simple Supported Beams On High-speed Railway Under Pulsed Near Fault Ground Motion

In recent years,with the rapid development of China’s high-speed railway construction and gradually advancing towards the Western multi-fault area,the construction of high-speed railway bridges is facing the impact of near-fault earthquakes.Structural damage is particularly severe due to the velocity pulse effect of near-fault ground motion.At present,the relevant railway seismic design codes in China do not fully consider the impact of near-fault seismic motion on high-speed railway bridges.As more and more high-speed railway bridges are built in the near-fault area,it is of great practical significance to study the impact of near-fault pulsed ground motion on the high-speed railway bridge-rail system.Therefore,the following research work has been carried out:1.In order to study the influence of near-fault ground motion on bridge-rail system of simple-supported beam on high-speed railway,a beam-rail integrated finite element model considering rail structure and boundary conditions of subgrade was established based on ANSYS finite element platform.The characteristics of near-fault ground motion with pulse effect are revealed in terms of time and frequency domain by spectrum analysis of near-fault ground motion.The influence of near-fault seismic motion on high-speed railway bridge-track system is analyzed by using selected near-fault seismic motion and common far-fault seismic motion.The main conclusions are as follows:(1)Under the action of earthquake,the bending moment of pier bottom,shear force of pier bottom and displacement of pier top along the bridge direction all show the rule of increasing first and then decreasing;compared with the far-field seismic motion,whether along the bridge or transverse direction,near-fault seismic motion results in greater plastic deformation,which requires higher ductility of pier and increases the relative displacement between beam and beam,making it easier to collide.(2)The rail stress is always maximum near the abutment and decreases gradually when the rail is far away from the abutment.When the rail on the subgrade is long enough,the rail stress decreases to 0.Under the action of near-fault earthquake,the maximum stress and displacement of rail are significantly increased,the maximum stress of rail is 56.9% higher than that of far fault ground motion,and the maximum displacement of rail is 97.2% higher than that of far fault ground motion.Near-fault ground motion significantly increases the relative displacement of rail and the transverse relative displacement of rail at beam joint.2.In order to study the influence of fastener resistance on the seismic response of high-speed railway simple-supported beam bridge rail system,five different fastener longitudinal and transverse resistance models are defined,impulse near-fault seismic excitation is input,non-linear time history analysis is carried out on high-speed railway bridges,and the influence of different fastener resistance on longitudinal and transverse seismic response of beam-rail system is discussed.The main conclusions are as follows:(1)The deformation of pier decreases with the increase of longitudinal resistance of fasteners.When the longitudinal resistance of fasteners increases from 5k N/group to25 k N/group,the longitudinal displacement of pier crest of each pier decreases by 17.5%on average and the relative displacement of adjacent beams decreases by about 45%.The increase of longitudinal resistance of fasteners can significantly reduce the relative displacement of adjacent beams and reduce the risk of collision.(2)When the longitudinal resistance of the fastener is 25 kn / group,the maximum stress of the rail in the whole bridge range is 162.9% higher than that of 5kn / group,and the maximum stress of the rail increases significantly.The increase of the fastener resistance is beneficial to the seismic resistance of the pier and unfavorable to the track,and too high fastener resistance may lead to the overrun damage of the rail.The increase of the transverse resistance of fasteners has little influence on the transverse internal force,displacement of piers and the displacement of main beams,but it may increase the relative lateral displacement of rails at beam joints.3.In order to analyze the influence of pier height on seismic response of high-speed railway simple-supported beam bridge,dynamic responses of beam-rail systems with five different pier heights are calculated by adjusting pier height and input impulse near-fault seismic motion.The main conclusions are as follows:(1)Pier height has a significant influence on seismic response of high-speed railway bridges.With the increase of pier height,longitudinal and transverse displacements of pier and girder and relative displacements of end of girder significantly increase.(2)With the increase of pier height from 10 m to 18 m,the maximum stress of rail increases by 40.2%,the transverse relative displacement of rail at each beam joint increases by more than 60%,and the stress and transverse deformation of rail increases obviously with the increase of pier height.4.Considering that the track and bridge of the high-speed railway simple-supported beam bridge are connected as a whole and are no longer small-span structures in traditional sense,the spatial effect of ground motion may affect the seismic response of the structure.Apparent wave velocity is selected as the main variable and the traveling wave effect on the rail system of high-speed railway simple-supported beam bridge under near-fault ground motion is studied by comparing with uniform excitation.The main conclusions about the influence of system dynamic response are as follows:(1)The traveling wave effect reduces the longitudinal bending moment of pier bottom and the longitudinal displacement of pier top,but the increase of longitudinal shear force at pier bottom partially decreases under the condition of uniform excitation.When the apparent velocity increases from 600 m/s to uniform excitation,the longitudinal displacement of pier crest increases by 51.7% on average.(2)Considering the traveling wave effect,the rail stress in the middle part of the whole bridge increases greatly,and the stress distribution of the whole bridge becomes more uniform.With the increase of apparent velocity,the rail stress distribution gradually approaches the uniform excitation.