半开口和分离边箱开口断面主梁竖向涡振性能对比

为深入研究不同截面形式开口断面主梁的涡振性能及其发生机理，针对半开口和分离边箱开口断面2种主梁，进行了1∶50节段模型风洞试验，考虑等效质量、风攻角和阻尼比等因素的影响，计算了2种主梁断面的斯托罗哈数；基于线性和非线性理论，估算了实桥竖向涡振振幅；建立了二维数值模拟分析模型，验证了数值模拟方法的准确性，并对比了2种主梁断面周围的瞬时涡量和平均流线结构。分析结果表明:2种主梁在风攻角为3°和5°时均发生竖向涡振，且出现2个涡振区，第2个涡振区主梁竖向涡振最大振幅明显大，5°风攻角时2种主梁竖向涡振振幅比3°风攻角时大75%；风攻角为5°，阻尼比为0.8%时，分离边箱开口断面主梁竖向涡振最大振幅比开口断面大28%；随着Scruton数的增大，主梁竖向涡振的最大振幅接近线性减小，相同Scruton数工况下，5°风攻角时分离边箱开口断面主梁竖向涡振振幅最大，3°风攻角时半开口断面主梁振幅最小，说明正风攻角越大，主梁断面越钝，其涡振性能越差；5°风攻角时分离开口断面更钝，引起气流更大的分离，来流风在2种主梁断面的桥面上方和主梁开口处均形成漩涡，由于斜腹板和风嘴作用，主梁开口处尺寸较大的漩涡被打碎为几个尺寸接近的较小漩涡，优化了主梁的涡振性能。 

Comparison of vertical vortex-induced vibration characteristics between semi-open girder and separated edge-boxes open girder

Wind tunnel tests on sectional models with a scale ratio of 1∶50 were performed to comprehensively investigate the vortex-induced vibration characteristics and associated mechanisms of open girders with different cross sections. The vortex-induced vibration characteristics of semi-open girder and separated edge-boxes open girder were analyzed and compared. The influence factors, including the equivalent mass, wind attack angle, and damping ratio, were considered. In addition, the Strouhal numbers of the two girder cross sections were computed. Based on the linear and nonlinear theories, the vertical vortex-induced vibration amplitudes of real bridge girders were calculated. A two-dimensional numerical simulation model was established, and the accuracy of the numerical simulation method was verified. Then, the instantaneous vorticity contours and mean streamline structures around the two girder cross sections were compared. Analysis results show that at the wind attack angles of 3° and 5°, the vortex-induced vibration is observed for both girders, and there are two vortex-induced vibration regions. The maximum amplitude in the second vertical vortex-induced vibration region is significantly larger than that in the first one. The vertical vortex-induced vibration amplitude at an wind attack angle of 5° is 75% larger than that at an wind attack angle of 3°. When the wind attack angle is 5° and damping ratio is 0.8%, the maximum vertical vortex-induced vibration amplitude of separated edge-boxes open girder is 28% larger than that of the semi-open girder. The maximum vertical vortex-induced vibration amplitude decreases almost linearly as the Scruton number increases. For the same Scruton number, the vertical vortex-induced vibration amplitude of separated edge-boxes open girder peaks at a wind attack angle of 5°, whereas the vertical vortex-induced vibration amplitude of semi-open girder is at its minimum at a wind attack angle of 3°, indicating that the larger the positive wind attack angle, the blunter the cross section of the girder, and the worse the vortex-induced vibration characteristics. When the wind attack angle equals 5°, the separated edge-boxes open girder is blunter, causing increased air fluid separation. There are vortexes above the girder deck and at the openings of the girder formed by the incoming wind, the inclined web and wind fairing may break the large vortexes at the openings into several smaller vortexes with similar sizes, thus optimizing the vortex-induced vibration of girders. 3 tabs, 9 figs, 31 refs.