Analysis On Collapse Failure Process For A Cable-stayed Bridge Subjected To The Near-fault Earthquakes

Cable-stayed bridge is one of the most widely used bridges in China.In current seismic analysis of cable-stayed bridges,far-field ground motions rather than near-fault ground are often used in earthquake response analysis.However,recent studies have shown that near-fault ground motions with large velocity pulses and long-period components often cause large seismic responses of cable-stayed bridges,and even collapse under strong earthquake.Therefore,based on the study of various motion characteristics of near-fault ground motions,a large-span double-tower cable-stayed bridge is taken as the object of study.Based on the shaking table test and numerical simulation,the seismic response of the long-span cable-stayed bridge is analyzed,and the collapse failure process of cable-stayed bridge under strong near-fault earthquake is further analyzed.The main contents of this paper are as follows:1.The ground motion characteristics of near-fault ground motion are discussed.The near-fault ground motion records of 18 typical near-fault earthquakes in Taiwan were collected.The response spectra and the Fourier transform of the near-fault ground motions were used to study the ground motion characteristics of the near-fault earthquakes.The displacement responses of bilinear SDOFs were analyzed.The results show that the effect of velocity pulse is easy to cause large earthquake response of long period structure.From the displacement response of single degree of freedom under the near-fault earthquake,the ground motion of the high wall is larger than that of the foot wall plate;the normal component is larger than Parallel component.2.Based on the shaking table test and numerical analysis,the influence of near-fault ground motion on the seismic response of long-span cable-stayed bridge is discussed.The experimental results show that the damping system has better seimic effect than the far-field earthquake,and the seimic efficiency of the elastic system decreases when the cable-stayed bridge is under the near-fault ground motion.The numerical results show that the influence of near-fault ground motion on the seismic response of long-span cable-stayed bridge is not identical with that of bilinear SDOFs.The effect of velocity pulse on the displacement response of cable-stayed bridge is very prominent;The absolute value of the seismic responses of the three structural systems is significantly enhanced,and the elastic response of the tower girder can reduce the displacement response of the structure,but the internal force of the tower bottom will increase.The damping system can reduce the internal force and displacement of the structure to 20%?30%,and has good seimic efficiency.3.The elastic-plastic model of the structure was established by using SAP2000.The influence of different characteristics of near-fault ground motion on the collapse of cable-stayed bridge was analyzed.The results show that:(1)Compared with the El Centro wave,the PGA of the destroyed cable-stayed bridge components under the action of the TCU054NS wave is smaller for the first time,and the components are more likely to be destroyed.The residual deformation is existed after the component is destroyed.(2)Under the action of far-field earthquake,the plastic yield failure of piers and towers is from bottom to top,and the piers are destroyed before the tower.The critical PGA of the collapse is bigger and the risk of damage is smaller.Under the action of near-fault seismic waves,the tower is damaged before the piers.The critical PGA is small and the risk of damage is larger.With the increase of PGA,the damage initiation time of the component will be advanced;and the damage order of the components will change under the different PGA of the same seimic wave.(3)Under the action of near-fault ground motion,the critical acceleration of cable-stayed bridge collapse is smaller,the minimum is 0.6g,the damage time is relatively concentrated,the time interval from the first component to structural collapse is the shortest 6s;The collapse mode of the cable-stayed bridge of the floating system is mainly the failure of the bearing,the damage of the bottom of the main tower and the bottom of the tower.