中央扣对大跨悬索桥颤振稳定性的影响

Influence of Central Buckle on Flutter Stability of Long-span Suspension Bridge

为研究中央扣对大跨度悬索桥颤振稳定性的影响,以矮寨大桥为工程背景,基于大桥精细化空间桁架梁有限元模型,根据主梁整体刚度等效原则,采用悬臂梁位移法建立了大桥等效单主梁有限元模型;考虑了跨中短吊杆(无中央扣)、一对柔性中央扣、三对柔性中央扣和刚性中央扣4种不同结构形式,计算分析了中央扣对大跨度悬索桥自振特性的影响;基于试验获得的颤振导数,采用脉冲响应函数结合Roger有理函数并利用非线性最小二乘拟合方法拟合其系数从而得到主梁断面自激力的时域表达式,随后利用ANSYS二次开发,实现了大桥颤振稳定性时域分析,研究了中央扣对颤振临界风速、颤振频率及全桥三维颤振姿态的影响规律.结果表明:不论柔性还是刚性中央扣都能够显著提高主梁纵飘振型的振动频率,其对反对称侧弯和反对称扭转频率的影响比正对称大;刚性中央扣能够大幅提高反对称扭转振型的频率.由于矮寨大桥是以一阶正对称竖弯、二阶正对称竖弯和一阶正对称扭转相互耦合的振型发生弯扭耦合颤振,因此,中央扣对颤振临界风速的影响极小,但对颤振频率与主梁三维颤振姿态有一定影响,并一定程度上有利于颤振稳定性.此外还发现当结构阻尼很低时,由于颤振频率落于固有频率分布十分密集的区域,主梁颤振状态有复杂拍振现象(间歇性颤振现象)的出现.

To investigate the effects of central buckles on the flutter stability of long-span suspension bridges,the Aizhai Bridge in China was selected as the engineering background.Based on a refined spatial-truss-girder model and according to the principle of stiffness equivalence of the main girder in all directions,an equivalent-single-girder finite element model was firstly established by using the displacement method of a cantilever beam.Subsequently,four different connection options between the main cable and the girder near the mid-span position,namely,a short suspender,one pair of flexible central buckles,three pairs of flexible central buckles and one pair of rigid central buckles,were considered and their effects on the dynamic characteristics of long span suspension bridges were studied.Then,based on the flutter derivatives obtained from wind tunnel tests,the time domain formulations of self-excited forces in the girder section,expressed in terms of convolution integrals of impulse response functions,were ob-tained using a nonlinear least square fitting method.Based on APDL(ANSYS Parametric Design Language)offered by ANSYS,a time-domain flutter analysis was realized.Finally,the influences of the central buckles on the critical flutter velocity,flutter frequency,and three-dimensional flutter states of the bridge were investigated.The results show that the central buckles can significantly increase the frequency of the longitudinal floating mode of the bridge and have greater influence on the frequencies of asymmetric lateral bending mode and asymmetric torsion mode than that of symmetric ones.The rigid central buckle can largely increase the frequency of asymmetric torsion mode.The central buckles have negligible impact on the critical flutter velocity because the flutter mode shape of the Aizhai Bridge is coupled with the symmetric vertical bending mode shape and the symmetric torsion mode shape.However,it has a certain impact on the flutter frequency and the three-dimensional flutter states of the bridge,which benefits the flutter stability.In addition,it is found that the phenomenon of complex beat vibration(called intermittent flutter phenomenon)appeared when the structural damping was very low,because the flutter frequency falls in an area where the natural frequency distribution is very dense.