Comparative Study on the Wake-Induced Vibration of PWS and WR Six-Cable Hangers of Suspension Bridges and Its Mitigation

With the continuous increase in the span of suspension bridges, six-cable hangers have been gradually adopted to meet the load requirements in the design of suspension bridges. However, the aerodynamic interference between the cables of the six-cable hanger is more complex, and the hangers are sensitively prone to severe wind-induced vibration. In this study, the features of wake-induced vibration of a parallel wire strand (PWS) and wire rope (WR) six-cable hanger and the effectiveness of different countermeasures were studied by using wind tunnel tests based on the three-dimensional (3D) elastic test model. First, two types of 3D elastic hanger models of the cables with smooth and rough surfaces, which respectively correspond to the PWS and WR six-cable hangers, were designed and manufactured. Then, a series of wind tunnel tests were carried out to obtain the wind induced vibration responses of the two types of hangers, and a comparison of features of the wind-induced vibration of the two types of hangers was carefully made. The results show that large-amplitude vibrations are both observed for the PWS and WR hangers. It appears that the large-amplitude vibration of the hangers is caused by the aerodynamic interference between the cables. Compared with the WR hanger, the PWS hanger shows better aerodynamic stability. Finally, the effectiveness of four types of countermeasures, including spacers, crossties, tuned mass dampers (TMDs), and increasing structural damping, were examined by means of wind tunnel tests. The results show that although the measures of increasing structural damping with separators can suppress the hanger vibration well, the structural damping required is very large, which is not a very economic countermeasure. In comparison, the countermeasure of the spacers combined with crossties is more economical, which can not only suppress the relative vibration of hanger cable at low wind velocity, but also suppress the overall vibration of hanger at high wind velocity.