非对称悬索桥在静风荷载下失稳过程研究

Analysis of instability process of asymmetric suspension bridge under aerostatic wind load

悬索桥作为柔性结构在强风作用下会产生较大的变形甚至失稳,存在较大安全隐患。以实桥作为背景工程,考虑到桥梁结构及作用在其上风荷载的非线性,采取增量内外双重迭代法得到其临界速度约为120 m/s;利用有限元软件ANSYS得到桥梁在对称性、矢跨比因素影响下的自振特性的变化规律。结果表明:结构对称性对其自振频率没有太大影响,仅在高阶时非对称结构频率有所增加;整体刚度随着矢跨比的减小而增大,自振频率也随之增大;在施加风荷载后进行静风稳定性分析失稳过程以及风速变化下的桥梁各构件的变形及内力变化,发现三分力系数随风速增加正负发生变化,使得桥梁竖向变形方向由向下转变为向上;除作用在主梁和主缆上的风荷载,其他桥梁结构所受风荷载可忽略不计。失稳时主梁近风侧主缆和吊杆应力大幅度减小,减小比例约为30%,失稳过程可看作缆索和吊杆松弛而受力减小退出原有功能的过程。

As flexible structures,suspension bridges will produce large deformation and even instability under the action of strong wind,which will lead to a large safety hazard.Taking a real bridge as the engineering background,considering the nonlinearities of the bridge structure and the wind load acting on the bridge structure,the critical wind speed of the bridge is about 120 m/s by using the incremental internal and external double iteration method.The variation rules of the natural vibration characteristics of the bridge under the influence of symmetry and rise span ratio are obtained by using the finite element software ANSYS.The results show that the structural symmetry has little effect on the natural vibration frequency,and the frequency of asymmetric structure increases only in the high order.For the rise span ratio,the overall stiffness of the bridge increases with the decrease of the rise span ratio,and the natural vibration frequency also increases.After the application of wind load,the static wind stability analysis is carried out to analyze the instability process and the deformation and internal force changes of the bridge components under the change of wind speed.It is found that the three-component force coefficient changes with the increase of wind speed,which makes the vertical deformation direction of the bridge change from downward to upward.Except for the wind load acting on the main beam and main cable,the wind load on other bridge structures can be ignored.During the instability,the stress of the main cable and suspender on the windward side of the main girder is greatly reduced,and the reduction ratio is about 30%.The instability process can be seen as the process of the stress reduction and withdrawal from the original function due to the relaxation of the cable and suspender.