Optimal design of viscous dampers for multi-mode vibration control of bridge cables

Viscous dampers have been widely used for mitigating rain-wind-induced vibration of bridge stay cables. Designing a damper with optimal damping in a specific mode may leave the cable susceptible to vibration in other modes, and it is almost impossible to specify a priori the dominant mode in which optimal performance should be achieved. In the present paper, a new method for optimal design of viscous dampers to achieve multi-mode cable vibration control is developed. With reference to a cable-damper model taking into account cable sag, inclination and bending stiffness, a method to determine the optimal damper size for cable vibration control in assigned multiple modes is proposed based on optimal LQG control theory. The system damping ratios obtained from the proposed strategy are thus found to satisfy the Irwin's criterion for all the assigned modes. Case studies of prototype cables on a real cable-stayed bridge which experienced rain-wind-induced oscillation show the efficiency of the proposed method.