Aerodynamic Interference Effects on Vortex-Induced Vibration of a Streamlined Box Girder Parallel to Twin Bluff Box Girders

Aerodynamic interference effects (AIEs) between adjacent parallel decks have a pronounced influence on vortex-induced vibration (VIV). This study systematically investigates AIEs on VIV responses of a streamlined box girder parallel to twin bluff box girders. To clarify the characteristics of AIEs and evaluate the effectiveness of mitigation measures, wind tunnel tests and numerical simulations were conducted. The results show that the isolated streamlined box girder exhibits pronounced vertical VIV response at an angle of attack (AoA) of + 3 ° . When located upstream, the vibration amplitude at + 3 ° increases by about 83% compared with the isolated case, whereas it is completely suppressed when placed downstream. In the upstream condition, the strengthened dominant vortex intensifies the surface pressure fluctuations and enhances the contribution of the VIV driving region, thereby sustaining a stronger VIV response. In contrast, in the downstream condition, wake disturbance from the upstream bluff box girders suppresses the dominant vortex, disrupts the organized shedding process, and weakens the original VIV driving region, leading to the disappearance of stable VIV. Installing guide vanes provides limited mitigation of VIV, whereas optimizing the wind fairing is the most effective measure among those tested, since it suppresses the intrinsic VIV triggering flow structure of the streamlined box girder itself. These findings provide guidance for aerodynamic design and vibration control in similar parallel engineering applications.