为研究近断层脉冲效应和土-结构相互作用(SSI效应)对大跨斜拉桥地震响应的影响规律,以苏通大桥斜拉桥为研究对象,采用系统化的集总参数模型表征地基土的动力特性,建立了考虑SSI效应的结构动力数值计算模型,计算分析了破裂前方效应脉冲、滑冲效应脉冲和无脉冲三组近断层地震动作用下结构的地震响应。计算结果表明:相对于塔底固结模型,SSI效应降低了斜拉桥自振频率,并改变了高阶振型的产生次序;近断层地震动作用下,SSI效应可增大主塔位移响应,对其内力有削弱作用,并可降低纵桥向激励时主梁的位移和内力响应,但横桥向激励时,脉冲效应地震动作用下SSI效应明显增大了主梁的响应;脉冲效应地震动引起斜拉桥地震响应明显高于无脉冲地震动,滑冲效应主要影响纵桥向激励时主塔响应以及纵桥向(或横桥向)激励下主梁响应,破裂前方效应对横桥向激励下主塔响应影响更加显著。研究成果可为大跨斜拉桥在近断层地震动作用下的抗震设计提供借鉴。
Abstract
The objective of this study is to determine the seismic responses of Sutong cable-stayed bridge taking into account near-fault pulse-type effect and soil-structure interaction effect(SSI). Systematic lumped-parameter models are used to describe the dynamic behavior of the foundation supported on soil. The dynamic finite element model of the bridge considering SSI effect is established. The seismic responses of the towers and deck subjected to three pulse-type ground motions, i.e. Forward-directivity effect pulse (FD), Fling-step effect pulse (FS) and non-pulse records, are investigated. The results revealed that SSI effects mainly affect the bridge responses through a systematic decrease of all modal frequencies and a substantial change in nature of dominant shapes especially for the higher modes of vibrations. When the bridge is subjected to pulse-type near-fault ground motions, SSI effect causes larger displacements of the towers, a significant decrease in the internal forces of the towers, and a certain degree of reduction in both the displacement and base moment of the girder under the longitudinal excitations. However, the response of the girder under horizontal excitations is obviously amplified by SSI effect. The seismic response of the cable-stayed bridge under the pulse-type ground motions is significantly higher than that under non-pulse ground motions. Fling-step ground motions amplify the response of the towers under the longitudinal excitations and the response of the girder under the longitudinal or horizontal excitations. Forward-directivity ground motions amplify the response of the towers under the horizontal excitations. The research results could be used to provide a reference for the seismic design of long-span cable-stayed bridge system located in near-fault zones.
关键词
近断层地震动 /
破裂前方效应 /
滑冲效应 /
系统化集总参数模型 /
土-结构相互作用 /
大跨斜拉桥
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Key words
near-fault ground motion /
forward-directivity effect /
fling-step effect /
systematic lumped-parameter model /
soil-structure interaction /
long-span cable-stayed bridge
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