静风稳定性是千米级超大跨斜拉桥抗风性能的主要考验之一。以某主跨2×1 500 m三塔两跨斜拉桥结构体系为研究对象，采用全桥气弹模型风洞试验与数值计算相结合的方法，对失稳过程结构位移响应和与之同步的拉索索力进行跟踪，从失稳过程结构刚度演变特性方面深入揭示了该结构体系静风失稳机理。风洞试验发现，结构在+3°和0°初始风攻角下出现了明显的静风失稳前兆，静风失稳先于颤振失稳发生。基于增量与内外两重迭代相结合的非线性静风稳定分析方法，研究了结构失稳过程结构位移响应演变特性，并与风洞试验结果进行了对比，表明二者具有较好的吻合性。-3°初始攻角下的静风失稳临界风速远高于+3°和0°初始攻角。为了揭示上述现象发生的内在机理，提取与结构位移同步的拉索索力，阐述了失稳过程结构刚度与结构响应之间的同步演变关系，研究表明：结构静风稳定性取决于失稳过程结构刚度演变特性，而后者与结构响应密切相关。-3°初始攻角下主梁整体向下的竖向位移强化了拉索、主梁和桥塔形成的稳定三角关系，这是该初始攻角下静风稳定性远优于+3°和0°初始攻角的最根本原因。-3°初始攻角时，结构失稳形态表现为明显的主梁一阶正对称扭转与主梁一阶反对称扭转耦合振型失稳，与单主跨斜拉桥明显不同。研究首次在风洞试验中再现了双主跨大跨度斜拉桥静风失稳现象，并揭示了大跨度斜拉桥静风失稳内在机理，对今后我国超大跨径斜拉桥的抗风设计具有借鉴意义。
Abstract
Aerostatic instability is one of main assessments for wind-resistant performance of a ultra-long span cable-stayed bridge.Here, taking a cable-stayed bridge with double main spans of 1 500 m as the study object, the whole bridge’s aero-elastic model wind tunnel test combined with numerical computation method was used to track displacement responses and the bridge’s synchronous cable forces in its instability process, and deeply reveal the structure’s static wind instability mechanism with evolutionary characteristics of structural stiffness in its instability process.Wind tunnel test results showed that there are obvious omens of aerostatic instability at the initial wind attack angle of + 3 ° and 0 °, aerostatic instability happens before flutter instability.Based on the nonlinear FEM, evolutionary characteristics of the bridge’s displacement responses in instability process were studied and then compared with the wind tunnel test results, it was shown that they agree better with each other; the critical wind speed of aerostatic instability at the initial attack angle of -3 ° is much higher than those at the initial attack angles of + 3 ° and 0 °, respectively.In order to reveal the inherent mechanism of the above mentioned critical wind speed phenomenon, cable forces synchronous with displacement responses were extracted to analyze evolutionary characteristics of structural stiffness in instability process.The results showed that the structural aerostatic stability depends upon evolutionary characteristics of structural stiffness, and the latter is related to structural responses; the vertical downward displacement of the main girder at the initial wind attack angle of -3 ° enhances the stable triangular relationship among cable, main girder and bridge tower, this is the essential reason to cause the aerostatic stability at the initial wind attack angle of -3 ° being far superior to those at the initial attack angles of + 3 ° and 0°; the structure instability pattern at initial attack angle of -3° is characterized by obvious main girder’s first order symmetric torsional-first order asymmetric torsional coupled modal shape, this pattern is significantly different from that of a single-main span cable-stayed bridge; the study results for the first time reproduce the aerostatic instability phenomenon of a long-span cable-stayed bridge with double main spans in wind tunnel tests, reveal the inherent mechanism of aerostatic instability of long-span cable-stayed bridges, and provide a reference for further wind-resistant design of our country’s super-long span cable-stayed bridges.
关键词
静风稳定 /
双主跨斜拉桥 /
数值模拟 /
演变特性 /
颤振稳定
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Key words
aerostatic instability /
cable-stayed bridge /
numerical simulation /
evolutionary characteristics /
flutter
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