Study On Flow Field Of Twin Box Girder During The Whole Process Of Wind Induced Vibration

Twin-box-girder(TBG) is a new form of long-span suspended bridge girder, which have splendid aerodynamic stability. Compared with the traditional box girder, the flutter critical velocity of TBG is much higher. At the same time, the TBG bridges are more sensitive of vortex-induced-vibration(VIV). According to the structural health monitoring system of a certain TBG suspended bridge, the vortex induced vibration at low wind velocity is relatively strong. For now, the inducing factor of VIV and flutter is still unclear. There’re no reasonable theory of the flow field’s evolution during the vibration.This research is concentrated on the overall process of wind induced vibration of TBG suspended bridges. A wind tunnel experiment is conducted and the vibration of a 1:200 TBG model is measured at different wind velocity. To identify the flow field around the model, PIV(Particle Image Velocimetry) system is involved. The exact work are as followed:1. The flow field around the static TBG model was measured to study its characteristics at different wind attack angles.2. The dynamic response and rounded flowing pattern of TBG model during VIV were measured and compared at different wind velocity to study the interaction between model and flow.3. The dynamic response and rounded flowing pattern of TBG model during flutter were measured and compared at different wind velocity to study the interaction between model and flow.The experiment result shows that TBG model has four separated VIV wind velocity ranges, two for having and two for twisting, while the vibration frequency of having and twisting are equal to the model’s natural frequency respectively. Havingtwisting coupled flutter occurs at high wind velocity. The flutter frequency is different from the natural frequency due to the aerodynamic damping. PIV shows the evolution of flow field around the model. The processing of vortex generating and shedding of vertex is observed. The information and characteristics of flow field is analyzed in order to explain the interaction between model’s vibration and wind.