远场地震动作用下大跨悬索桥抗震分析

Research on seismic behavior of long-span suspension bridge under far-field vibration exciting

远场地震动的特点是低频成分丰富、卓越周期长且持续时间长;而大跨悬索桥梁具有结构柔性大、自振频率低的特点,对地震波中的低频长周期成分敏感,受远场地震动影响大。通过对一跨长江大跨度悬索桥的模态分析,分析了大跨桥梁的频谱特性及振动特点;对比在远场及普通地震动作用下结构内力及位移响应,总结了远场地震动作用下结构动力响应规律;大跨径悬索桥的主梁位移由低阶振动控制,在远场地震动作用下,主梁纵向位移大,地震动影响明显;而桥塔由于其相对较大的刚度而对高阶振型敏感,远场地震动对桥塔位移的不利影响较小;由于桥塔内力由主梁传来,所以低阶振型影响占主导,同时远场地震动作用下塔底内力大于普通地震动的影响。

The characteristics of far-field seismic waves are abundant in low frequency component,bigger value of predominant period,and longer time during the vibration. The features of long-span suspension bridge are large flexible and low vibration frequency. So this kind of bridge structure is sensitive to the waves’ components with low frequency and bigger period. Thus the structures are easily affected by far-field vibration. This paper focuses on researching the difference response of a long-span suspension bridge across Changjiang River under the far-field seismic excitations and the ordinary ground motions. Based on the comparison of the two kinds seismic wages’ frequency spectrum characteristics,acceleration time-history curves,the features of remote-ground seismic waves are summarized. The spatial finite element model of the structure and its vibrating modes are established. The structure’s force and displacement response under the two kinds of waves are compared. The results show that the main girder’s vibration is controlled by the low order model,while the tower’s vibration is controlled by the high order model own to its higher stiffness. The far-field seismic wave has lots of low frequency components,so it can cause the girder much bigger longitudinal displacement. The internal force of tower is mainly controlled by the girder,so it is mainly affected by the low frequency components. The research can provide some useful references for similar projects.