大跨斜拉桥的近断层地震响应及减震控制

近断层地震长周期成分丰富,存在速度大脉冲效应;而大跨度斜拉桥一般采用半漂浮体系或漂浮体系,所以固有频率较低。为了研究大跨度斜拉桥在近断层地震作用下的反应规律及减震措施,利用ANSYS软件分析了某半漂浮体系的大跨斜拉桥在近断层地震作用下的时程响应,并对其减震控制方法进行了探讨。研究表明,大跨度斜拉桥的近断层地震响应随着PGV/PGA值的增大而增大,且增大幅度较大,近场脉冲效应较为显著;对于近断层地震作用,不建议采用塔梁弹性连接装置作为主梁纵漂的减震措施,而采用参数适宜的铅挤压阻尼器和粘滞阻尼器则均能获得很好的减震效果;由于大跨度斜拉桥的近断层地震反应较大,应提高其支座的设计允许位移。

Seismic Response Analysis and Control of Long-span Cable-stayed Bridges under Near-fault Earthquakes

Near-fault earthquake has abundant long period components and large velocity pulses,while long-span cable-stayed bridges adopt a floating or semi-floating system generally and have a lower natural frequency.So based on a long-span cable-stayed bridge with semi-floating system,the 3-D spatial finite element model was built by softwave ANSYS to study the seismic response time history of the bridge under near-fault ground motions and discuss the seismic control technology.The analysis shows that the seismic response of near-fault long-span cable-stayed bridges increases obviously as the ratio of PGV to PGA increases, and the large velocity pulses is quite remarkable;the elastic link is not suitable for controlling the displacement of the deck,while the lead extrusion dampers and viscous dampers can play an important role of seismic control if the optimal design of damper parameters can be carried out.However,because of the significant seismic response of neat-fault long-span bridges,it is quite necessary to increase the allowable displacement of bearings.