Influence of the side ratio and main longitudinal beam shape on vortex-induced vibration and aerodynamic force characteristics of Π-shaped composite girders

Abstract

Π-shaped composite girders in long-span bridges are prone to vortex-induced vibrations (VIVs). Therefore, it is important to study their VIV characteristics and corresponding countermeasures. In the present study, the effects of the side ratio (B/H = 7.00–14.00, where B and H represent the width and height of the girder, respectively), the bottom plate width of the main longitudinal beam (b = 0.30H–1.50H), and the inclination angle (β = -20°–30°) on VIVs, aerodynamic characteristics, and flow patterns were comprehensively compared. Additionally, the mechanisms underlying VIV suppression were preliminarily explored. The results indicate that the side ratio and the shape of the main longitudinal beam of the Π-shaped composite girder significantly affect the VIVs. However, the influence patterns differ and are highly related to the wind attack angle and vibration mode (vertical and torsional). The distribution patterns and values of the mean and fluctuating pressure coefficients on the upper and lower surfaces of the Π-shaped composite girder are different. These are notably influenced by the side ratio and β but are almost unaffected by b. VIVs are typically suppressed when the surface pressure frequency distribution becomes scattered and the pressure amplitude spectrum shows no distinct dominant frequency. Additionally, A reduction in the size of surface vortices is beneficial for controlling vertical VIVs. However, when the vortices are concentrated at the front of the model, they will induce torsional VIV. Within the studied parameter range, the optimal parameter combination for suppressing VIVs is B/H = 10.00, b ≥ 1.00H, and β = 10°. In general, practical engineering applications should consider specific conditions, such as the characteristics of the incoming flow.