Effective wind fairing combination aerodynamic measures against vortex-induced vibrations of Π-shaped composite bridge decks

Long-span bridges with the Π-shaped composite girder are prone to significant vortex-induced vibrations (VIVs) because of the odious flow around the blunt deck. In this paper, the VIV performance of a Π-shaped composite girder and the suppression efficiency of different shaped fairings were systematically studied through experimental and numerical approaches. Severe VIVs of the original Π-shaped girder were observed in wind tunnel tests, and the installation of a lower central vertical stabilizer (LCVS) can reduce the VIV but cannot eliminate it thoroughly. Then, the flow mechanism triggering VIVs of the girder with the LCVS was investigated through computational fluid dynamics with the dynamic mesh technology. After that, eight wind fairings were designed. The flow fields of the fixed girder installed with different fairings were investigated through numerical methods. The results indicate that the leading-edge vortex on the upper surface and the rear-body vortex generated at the lower inclined web of the leeward fairing are the main causes of the VIV. A smaller degree of the upper inclined web can reduce the leading-edge vortex on the upper surface, and the installation of a horizontal stabilizer at the fairing nose can also achieve the same effect. The shedding characteristics of the rear-body vortex are mainly influenced by the length of the fairing. Then, an effective fairing-based aerodynamic measure with optimal shape was proposed. Finally, the suppression efficiency of the proposed countermeasure is verified experimentally.