Experimental Research On Piers Of High-speed Railway Bridges Subjected To Seismic-induced Horizontal Impact Load

Due to strong earthquakes,the relative displacement between adjacent structures of the bridge structure might exceed the reserved gap.It will lead to poundings of adjacent beams,main beams and transition piers,shear keys and bearing and other components,significantly altering the responses of the bridge pier.In this thesis,the high-speed railway bridge piers were selected as the example.Scaled models of the bridge piers with different heights were designed and manufactured.A series of horizontal pounding tests were conducted to investigate the influence of seismic-induced poundings on the mechanical behavior of the pier.The main results of this thesis are as follows:(1)Based on ANSYS finite element software,finite element models of 3-span 32 m simply-supported girder bridge with different pier heights were established.Three ground motions with different spectral characteristics were selected for nonlinear time history analysis,and the seismic response of the bridge was obtained.The results show that the collision between shear keys and bearing bases occurs several times in succession;The relative collision velocity between the pier and beam was obtained and provided theoretical basis for the experimental design.(2)The bridge piers with heights of 10 m,20m and 30 m for high-speed rail were considered and scaled.The horizontal impact tests were conducted on the scaled piers,and the parameters including impact mass,velocity,materials,and direction were tested.The result indicates that the pounding force,relative displacement between the contact members,piertop displacement,and restitution coefficient are correlated to impact velocity and material.An increasing mass will not increase the pounding force peak value of the ascending stage,but can increase that of the rebound stage.Compared with the longitudinal pounding,the lateral pounding will lead to a larger pounding force and restitution coefficient,a smaller pier-top displacement,and a shorter pounding duration.(3)Based on LS-DYNA,the high-speed rail piers subjected to horizontal impact loads at the pier top were simulated.The accuracy of the finite element model was verified by the experimental result,and behavior of the piers due to the impact loads are discussed.The results show that there will be a hysteresis effect and multi-peak oscillations in the downward transmission of shear force and bending moment.Because of the inertial effect,negative bending moment will be produced in the pier,which is significantly different from static loads.(4)By analyzing the results obtained from the quasi-static tests and impact tests on the high-speed rail piers,it is found that the contact stiffness of Hertz-damp impact model is mainly affected by the impact velocity,restitution coefficient,and structural stiffness.Based on the the collinear impact model of two rods and the equivalent rigid-body impact model,a method for determining the stiffness of Hertz-damp model was proposed and verified.This thesis contains 115 figures,32tables,and 115references...