Influence of non-uniform grid plates on the vortex-induced vibration performance of twin-box girder section

Abstract

The wind resistance design of long-span bridges necessitates addressing the issue of vortex-induced vibration (VIV) and implementing appropriate counter measures to mitigate it. The present study focused on the examination and comprehensive analysis of a self-anchored suspension bridge. Wind tunnel tests were conducted on sectional models to analyze the effect of wind attack angles on the VIV performance of the girder. Moreover, the investigation examined the impact of opening slot ratio and the configuration of grid plates on the trigger mechanism and performance of VIV. From the results, it is observed that the main girder displays vertical VIV when the damping ratio reaches 0.25%. At wind attack angle of − 3°, 0°, and + 3°, the dimensionless maximum amplitude of the vertical VIV normalized by the height of the girder section, represented as ymax/D, is measured to be 0.032, 0.033, and 0.023 correspondingly. When the opening slot ratio of the grid plates reaches 50%, and the grid plates are non-uniformly arranged on the opening slot, that is the sides of the opening slot position, the vertical VIV becomes non-existent. Furthermore, it is observed that when the grid plates are arranged uniformly with the same opening slot ratio, the suppression effect on VIV is relatively worse and the dimensionless maximum amplitude of the vertical VIV is reduced to 0.013 from 0.032. The flow structure mechanism is that the upside airflow is separated at the windward edge of the girder section, leading to the formation of a large upper vortex. The upper vortices interact with the airflow passing through the upper and lower portions of the central slot, colliding with the top and bottom surfaces of the downstream section. Eventually, the vortices are shifted towards the tail side of the girder section and eventually shed, causing VIV. After implementing grid plates, vortices with a certain size still form at the gap. The grid plate effectively separates the vortices from the upper and lower sections of the girder, reducing their impact on the downstream section and optimizing the VIV performance of the main girder. These research findings could serve as a guide for designing the two-box girder section.