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.