ABSTRACT
With a geometrical scale ratio of 1:10, a tower column model is used to reproduce the upstream tower interference, as shown in Fig. 1. The section of the tower column model is 0.65 m × 0.85 m and its height is 3.3 m. The solid blockage of the tower column model is estimated to be 9.93%. The tower column model is made of timber plates with a thickness of 12 mm to ensure its body integrity and rigidity. The tower column model is placed on a base plate elevated 0.1 m over the tunnel floor and is fixed to the tunnel ceiling. It should be noted that the bridge towers in situ are not strictly stationary
1 INTRODUCTION
Violent vibrations of the vertical hangers have been observed in the longest suspension bridge of China. It was found vibrations of the vertical hangers are particularly violent in the vicinity of the bridge tower. Violent oscillations of the vertical hangers and their collisions raise concern over safety and durability in the bridge engineering community. Some possible excitation mechanisms have been proposed to explain the violent oscillations of the vertical hangers, especially for those in the vicinity of the bridge tower. Conventional vortex induced excitation as a possible mechanism responsible for the violent oscillations could be firstly excluded, for the simple reason that the onset velocity of the lock-in range is quite low, based on the Strouhal number, the diameter and the natural frequency of the vertical hangers. When the bridge is subject to crosswind, wake galloping responses of the two rear vertical hangers are likely to take place due to the aerodynamic interference of the front hangers. However, wake galloping cannot fully explain the violent oscillations, since the spacing between the front and rear vertical hangers is about 9 times the hanger diameters, at which the upstream interference is believed not that substantial. As the excitation mechanism of the vertical hangers and the role of the bridge tower have not been thoroughly clarified, in the present study, the interference effects of the bridge tower column on the vertical hangers are experimentally investigated.
