地震下三塔悬索桥主缆-鞍座摩擦滑移行为及其影响

Study of frictional slip of cable-saddle interface in three-pylon suspension bridge under the earthquake

三塔悬索桥中塔两侧主缆并未直接与锚锭连接,中塔处主缆的纵向约束较弱,地震下主缆-鞍座易发生显著的摩擦滑移。为了揭示三塔悬索桥中主缆-鞍座摩擦滑移及其对结构地震响应的影响规律,本文依托浔江大桥实际工程,建立了三塔悬索桥的非线性有限元模型,利用摩擦单元重现了主缆-鞍座界面的摩擦滑移行为,揭示了地震下主缆在边塔和中塔处的不同滑移变位,分析了摩擦系数对于界面滑移、主塔内力等响应量的影响规律。分析结果表明:摩擦系数大于0.1,在设计地震下主缆-索鞍界面无摩擦滑移,而在罕遇地震和极罕遇地震下,有一定的摩擦滑移,最大摩擦滑移量随着摩擦系数增大而减小;主缆-索鞍界面在地震作用下会发生明显滞回现象,最大可提供约2.0%的等效阻尼比;边塔顶剪力对塔底弯矩的贡献率达到了50%~70%,而中塔由于设置阻尼器,剪力贡献率仅为20%~40%;适当减小摩擦系数有利于降低塔的响应,但摩擦系数降低至0.001时,主缆将失去对塔变形的约束能力,将显著改变塔的变形模式与动力效应。

In the three-pylon suspension tower,the main cable on both sides of the central tower is not connector to the anchor,leading to the relatively weak constraint to the main cable in longitudinal direction.The frictional slip at the cable-saddle interface is more prone to occur under the earthquakes.To explore the frictional slip at the cable-saddle interface and its influence on the seismic response of the three-pylon suspension bridge,this paper established a nonlinear finite element model of one typical three-pylon suspension,named Xunjiang Bridge.Frictional elements were used to reproduce the frictional slip at the cable-saddle interface,which well revealed different interfacial slip between the side and central pylons.The influence of the frictional coefficient on the local slipping behavior and global structure response was discussed.When the frictional coefficient was greater than 0.1,there was no frictional slip under design-based earthquakes,while under maximum considered and very rare earthquakes,the frictional slip occurred,and the peak slip decreased with increment of the frictional coefficient.The cable-saddle interface exhibited obvious hysteresis behavior,which provided a maximum equivalent damping ratio of about 2.0%under very rare earthquake.The contribution from the frictional force at the pylon top to the sectional moment at pylon bottom accounted nearly 50%-70%of its peak value for the side pylon.While for the central pylon,the contribution ratio was only 20%-40%due to its heavy self-weight and damping force at the deck height.It can be concluded that properly reducing the frictional coefficient was beneficial to the internal force of the pylons under earthquakes,but when the friction coefficient was reduced to 0.001,the main cable will lose its longitudinal constraint to the central pylon,and significantly altered the deformation mode and dynamic effects of the pylons.