Experimental investigation on wake-induced vibrations of the hangers of suspension bridges based on three-dimensional elastic test model

Large amplitude wind-induced vibrations of the hangers have been observed on several suspension bridges, and the underlying mechanism is not clearly clarified until now. In this study, the mechanism of wake-induced vibration of the hanger was studied by using wind tunnel tests based on three-dimensional (3-D) elastic test model. First, a new method was proposed to design 3-D elastic test model to accurately simulate a long cable in wind tunnel with a limited height. Second, taking the No.2 hanger of the Xihoumen Bridge as the background, a 3-D elastic hanger model was designed and manufactured by using the new method, and a series of wind tunnel tests were carried out within the spatial region of 3 <= P <= 10 and 0 degrees <= alpha <= 20 degrees to obtain the wake-induced responses of the hanger. The results show that obvious vibrations of the downstream cable are observed under all wind velocities tested (3 similar to 14 m/s), and the unstable region of the downstream cable tends to increase with the increase of wind velocity. Third, the effects of the structural damping on the wake-induced vibrations of the hangers were studied in detail. The results show that the wake-induced cable vibration of the hangers is not totally mitigated even if the structural damping ratio is as high as 1.37%. Finally, the effectiveness of two kinds of counter-measures (helical wires and spacers) on the wake-induced vibrations of the hangers of suspension bridges was experimentally studied. The results show that the helical wire can suppress the wake-induced vibration of the test case of P = 7, alpha = 5 degrees, but have no effect for the test case of P = 3.5, alpha = 20 degrees. It seems that the spacer is a reasonable countermeasure to mitigate the wake-induced vibrations of the hangers of suspension bridges.