考虑桥塔气动干扰和斜风作用的斜拉桥典型施工阶段抖振响应研究

Balanced cantilever method is widely employed for the construction of cable-stayed bridge. It is known as to be an extremely flexible structural system susceptible to wind action, for example buffeting response, because of its lack of overall structural stiffness. The dynamic wind loads pertaining to buffeting is the dominant loading for structural design. However, What should be emphasized is that the most adverse buffeting usually occurs under the wind not nomal to the bridge axis, which also varies largely with different bridge deck section and pylon types. Especially, the present theory on buffeting analysis of cable-stayed bridge under skew wind during its construction, particularly for dural max cantilever stage, may yield relatively large errors. Consequently it can result in a conservative design for wind resistent means and unnecessary resource input. The objective of this study is to investigate refinedly the wind load and wind-induced vibration of cable-stayed bridge under skew wind during its most adverse construction stage.The cable-stayed bridge under maximum dural cantilever stage with three kinds of deck sections and four type of pylons, are chosen as the objects of this study. The static load coefficients, aerodynamic admittance, flutter derivatives and buffeting responses of the deck strips, include skew strips and normal strips, will be measured by wind tunnel test technique. By comprehensive comparison and analysis of conventional buffeting approaches, the simplied buffeting analysis method on cable-stayed bridge under skew wind during dural max cantilever stage will be established by taking the wind direction and aerodynamic interference of pylon into consideration. Furthermore, the equivalent wind load will be proposed for the convenience of designer's usage.

大跨度斜拉桥常采用悬臂施工方法。在施工期间，结构刚度低，对风的作用较敏感，抖振是易发的一种风致振动现象,也是结构设计的控制动态风荷载。通常最大抖振响应不在正交风下出现，不同的主梁断面形式和桥塔类型，最不利风向角不尽相同，无明确规律可循。现有的斜风抖振分析方法在应用于斜拉桥施工阶段特别是最大双悬臂施工阶段时，还存在较大的误差，从而可能导致附加抗风措施设计的过于保守。 本课题着眼于斜风作用下斜拉桥最不利施工状态的风荷载和风致振动特性的精细化研究。拟选取3种主梁断面、4种桥塔形式所组合的斜拉桥双悬臂施工态作为研究对象，通过大量风洞试验研究斜风作用下桥塔干扰效应对于主梁(包括正、斜片条)静力系数、气动导纳、颤振导数以及抖振影响的规律。通过现有斜风抖振分析方法的对比分析，建立一种包含斜风作用和桥塔气动干扰效应的抖振简化分析方法，进而得到能够直接应用于桥梁结构设计的等效风荷载。

大跨度斜拉桥常采用悬臂施工方法。在施工期间，结构刚度低，对风的作用较敏感，抖振是易发的一种风致振动现象，也是结构设计的控制动态风荷载。通常最大抖振响应不在正交风下出现，不同的主梁断面形式和桥塔类型，最不利风向角不尽相同。此外，大气边界层内的紊流风具有显著的三维效应，这对于斜拉桥双悬臂状态的抖振不容忽视。因而对考虑桥塔气动干扰和斜风作用的斜拉桥典型施工阶段抖振响应的研究具有一定价值。.本课题首先根据Ribner三维抖振分析理论，研究了三维紊流场中的桥梁主梁所受到的非定常气动力，建立了可考虑紊流三维效应并适用于大跨度桥梁施工态抖振分析的广义二波数谱模型；然后提出了桥梁断面二波数气动导纳的识别方法，并通过风洞试验对流线型箱梁和桁架梁的二波数气动导纳进行了识别；应用提出了广义二波数抖振力谱模型，对大跨度斜拉桥双悬臂施工态进行了数值计算分析，研究了不同平均来流风速、不同紊流积分尺度以及不同结构的阻尼比条件下紊流三维效应对大跨度斜拉桥双悬臂施工态抖振位移的影响；最后以舟岱通道桥和南京长江第五大桥主桥为研究背景，通过全桥气动弹风洞试验，考察了不同来流风速和不同风偏角（包括0°、5°、10°、15°、30°、45°、60°和90°）斜风作用下的最大双悬臂施工阶段主梁的横向抖振位移和竖向抖振位移均方根值，并研究了桥塔干扰效应的影响，分别比较和讨论了有塔和无塔条件下主梁在不同风偏角下主梁抖振位移均方根值的差异性。