桩基冲刷对近海大跨斜拉桥地震响应的影响分析

为研究桩基冲刷对近海大跨斜拉桥地震响应的影响，本文以实际工程为背景，建立全桥三维模型，根据现有经典理论计算背景工程的最大冲刷深度，将土对桩基的作用等效为土弹簧，采用“m”法计算冲刷线以下的桩-土相互作用刚度，从而得到不同冲刷深度下的全桥分析模型。通过对结构进行动力特性分析及地震响应时程分析，对比研究了不同桩基冲刷深度对大跨斜拉桥抗震性能的影响。研究表明:冲刷使得桥梁结构整体变柔，自振周期变长；冲刷深度越大，桩基在地震作用下的位移响应也越大；冲刷深度对桩基剪力的影响与桩长有关，桩基越长，剪力变化趋势越复杂；IDA分析显示，冲刷对桥梁的不利影响随地震动强度的增大而增大；结果表明桩基的局部冲刷会进一步加剧桥梁在地震作用下的危险性，冲刷问题在抗震设计中应予重视。

Effect of Pile Scouring on the Seismic Response of Large-span Offshore Cable-stayed Bridges

In order to study the influence of pile scour on the seismic response of offshore long-span cable-stayed Bridges, the three-dimensional models of the whole bridge are derived under different scouring depths by calculating the maximum scouring depth of the background engineering according to the existing classical theory and the stiffness of pile-soil interaction below the scouring line by "m" method, and effect of soil on pile foundation is equivalent to soil spring.Through dynamic analysis and seismic response time history analysis of the structure, the influence of different scouring depth of pile foundation on the seismic performance of long-span cable-stayed bridge was studied comparatively.The results show that the scouring makes the whole bridge structure more flexible and the natural vibration period longer; the greater the scouring depth, the greater the displacement response of pile foundation under earthquake; the influence of scouring depth on the shear force of pile foundation is related to the length of pile; the longer the pile foundation, the more complex the change trend of shear force; the adverse impact of scouring on the bridge increases with the increase of vibration intensity; the local scour of pile foundation will further aggravate the risk of bridge under earthquake action, and the scour problem should be paid attention to in seismic design.