Experimental study on distributed aerodynamic forces of parallel box girders with various slot width ratios and aerodynamic countermeasures during vortex-induced vibration

The widespread adoption of parallel box girders in bridge engineering is attributed to their superior traffic-bearing capacity and streamlined construction methodologies. Nevertheless, these structures are confronted with exacerbated vortex-induced vibration (VIV) challenges stemming from aerodynamic interference and intricate vortex shedding phenomena between the girders. In the present study, a series of extensive wind tunnel experiments are conducted to scrutinize the VIV behavior of parallel box girders with diverse slot width ratios, taking into account both sectional model oscillations and surface pressure. The mean pressure coefficient, fluctuating pressure coefficient, time-frequency attributes of the distributed aerodynamic force, and the contribution value of distributed aerodynamic force to vortex-driven force are meticulously analyzed and compared to ascertain the impact of slot width ratio on VIV. Drawing on the empirical findings, we put forth and assess aerodynamic countermeasures aimed at augmenting the VIV performance of parallel box girders. Furthermore, the control mechanism for VIV is studied with respect to alterations in the distributed aerodynamic force. Our investigation reveals significant aerodynamic interference between parallel box girders featuring distinct slot width ratios. The frequency multiplication effect and signature turbulence in the aerodynamic force amidst VIV is observed, although the oscillation characteristics persist primarily at a singular frequency. The VIV of parallel box girders is instigated by the marked fluctuating pressure on the upper surface in proximity to the slot side and the inclined web of the leeward girder, accounting for the heightened severity and intricacy of VIV in these configurations as opposed to single closed-box girders. The synergistic implementation of skirt plates and wind fairings or winglets efficaciously eradicates the root causes of VIV in the original girders and even transmutes the contribution value of the distributed aerodynamic force from positive to negative, thereby suppressing VIV.