Effects of wind-induced static angle of attack on flutter performance of long-span bridges using 2D bimodal and 3D multimodal analysis

Flutter performance of long span bridges is directly affected by winds featured with large angles of attack (AoAs) in typhon climates and mountainous areas. Flutter critical wind speed and flutter derivatives (FDs) of a streamlined closed-box girder under various initial AoAs are obtained by free and forced vibration wind tunnel tests of a section model, based on which the two-dimensional(2D) and three-dimensional (3D) flutter performance and evolution mechanisms are further investigated. The results indicate that FDs identified at small vibration amplitudes through different forced vibration control methods, i.e., fixing wind speed or vibration frequency, in wind axis or body axis are almost identical. The flutter performance of the closed-box girder is susceptible to the AoA. The flutter critical wind speed changes significantly with the initial AoA due to the nonlinear variation of some typical FDs. The sign of A2* shifts from negative to positive and the reduced wind speed associated with the sign change becomes lower as the initial AoA increases, which worsens the flutter performance. The flutter critical wind speed would significantly decrease because of the consideration of the static additional AoA in the range of positive initial AoA. In addition, the participation of multi modes and different longitudinal distribution of static additional AoA are taken into consideration in 3D numerical analysis, which have little influence on the flutter critical wind speed of long span bridges between the 2D and 3D numerical analysis.