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.
Key words
aerostatic instability /
cable-stayed bridge /
numerical simulation /
evolutionary characteristics /
flutter
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