Cable parametric oscillation and its control for cable-stayed bridges

The stay cables in cable-stayed bridges are prone to exhibiting oscillation of large amplitude due to their large flexibility, small mass, and small damping. Continued oscillation of the cables may seriously influence the safety and durability of cable-stayed bridges. Apart from the rain-wind-induced cable vibration, large-amplitude oscillation of cables caused by parametric excitation due to support motion was recently observed in cable-stayed bridges. This kind of cable oscillation is produced by the deck and/or tower motion induced either by moving traffic or by buffeting response of gust wind. The oscillation mechanism and control methods of stay cables excited by the deck and/or tower motion are less studied than the rain-wind-induced vibration. In this paper, a nonlinear dynamic model for the simulation and analysis of a kind of parametrically excited vibration of stay cables caused by support motion in cable-stayed bridges has been proposed. The proposed model takes into account the cable inclination and sag effect. Based on this model, the oscillation mechanism and dynamic response characteristics of this kind of vibration are analyzed through numerical calculation. It is found that under certain conditions, the parametrically excited oscillation of stay cables in cable-stayed bridges may occur due to deck vibration when the natural frequency of a cable approaches to about half of the first modal frequency of the bridge deck system. A new vibration control system installed on the cable anchorage is proposed as a possible means to suppress the cable parametric oscillation. The numerical simulation results show that the cable oscillation due to motion of the deck and/or tower can be considerably reduced by use of this control device.