Effect of sway movement and motion axis on flutter and vortex induced vibration in a 3 DOF wind tunnel sectional test

Bridge stability is typically investigated based on 2 DOF wind tunnel measurements and very few wind tunnel facilities are available to simulate 3 DOF flutter of sectional model. In the absence of experimental capacity for extracting the flutter derivatives related to the sway, the quasi-steady approach is generally used for their evaluations. Also, the change of angle of attack is generally achieved by rotating the model relatively to the balance, forcing then the model to move according to the wind׳s axis as opposed to the section׳s principal axis. The impact of this experimental limitation needs to be studied. This paper presents a new 3 DOF dynamic force balance and its use to investigate the stability of a typical bridge deck section. The effect of the axis of motion is also studied. An interaction between sway and twist was observed during flutter and, for some angles of attack, the results show that the speed at which the flutter is reached might be influenced by the sway and the direction of motion as compared to principal axis of the section. Further research is needed to properly asses these effects.