Optimal design of two viscous dampers for multi-mode control of a cable covering broad frequency range

Abstract

For the conventional design of viscous dampers attached to cables, only the first few modes are of interest. However, a recent cable vibration event occurred on the Sutong Bridge highlights that the higher mode vibrations of cables also need to be controlled. To this end, a novel optimal design of two viscous dampers near to a cable anchorage is explored which can broaden the control frequency range covering both the lower and higher modes. In the proposed design scheme, the one damper nearest to the cable anchorage is targeted for lower-mode control and the other damper is targeted for higher-mode control. The mode shape characteristics of a cable with two viscous dampers, which is prerequisite for optimal damper design, are investigated. Based on that, the optimal design of the two dampers in a cable is simply reduced to two individual designs of one single viscous damper, which can lower the design complexity. The control performance of the proposed design both for lower and higher vibration modes is numerically validated by a cable on the Sutong Bridge and compared with the conventional design considering only lower vibration modes. Finally, the effects of parametric variations of the two dampers in the proposed design are discussed. It is shown that the proposed design using two dampers can both increase damping ratios of cables for lower and higher vibration modes, and the acceleration response of the cable is effectively reduced to around 60% of that using the conventional design.