VFIFE Based Investigation On Vibration And Control Of Stay Cables

Stay cables are prone to vibration due to the features of small mass, high flexibility and low inherent damping. The transverse vibration will not only cause the fatigue of the anchorage and the failure of the protect system, but also threaten the safety of the bridge. Transversely attached damper near the cable/deck anchorage could mitigate the large vibration of the cable. Existing damper design method is commonly based on the modal damping ratio of the cable-damper system. And the modal damping ratio is greatly influenced by the parameters of the damper. In this paper, the parametric vibration of the stay cable and the influences of the damper parameters on the modal damping ratio are investigated, the detailed work is as follows:(1) The vibration equation of the stay cable under the vertical displacement excitation of the cable/deck anchorage is derived, consequently the mechanism of the large vibration under this kind of excitation is illustrated. The model of the stay cable under the displacement excitation is established using the Vector Form Intrinsic Finite Element(VFIFE) method. The frequency range which could induce large vibration and the vibration category are determined. Then the parametric vibration of a vertical cable is studied. The influences of the initial disturbance, the excitation amplitude and the inherent damping is investigated in detail. It is found that enforced vibration and parametric vibration could be induced under the vertical supporter displacement excitation. The increasing of the excitation amplitude could amplify the frequency range and the maximum vibration amplitude. The initial disturbance has little influence on the frequency range and the vibration amplitude. The parametric vibration of the vertical cable has critical damping.(2) The cable-damper system is modelled using the VFIFE method, and the modal vibration of the cable is simulated. According to the decay time history of the cable, the modal damping ratio is recognized using the Hilbert transformation. Then the influences of the parameters of the damper and the sag of the cable on the modal damping ratio of the system are studied. It is found that the system has the maximum damping ratio and optimal damping coefficient. The increasing of the inherent stiffness and the decreasing of the support stiffness of the damper could decrease the damping ratio of the system. The increase of the damper mass enhances the damping ratio. And the sag of the cable has large influence on the first mode, but little influence on the second and third modes.(3) The experimental model of the cable-damper system is set up. The changes of damping coefficient, inherent stiffness, support stiffness and motion mass of the damper are modeled. Then the influences of damper parameters on the modal damping ratio are studied by experiments. It is indicated that for the first three orders, the experimental results approximately agree with the theoretical results.The innovation of this paper is to investigate the vibration control of stay cables using VFIFE method. This method could consider the geometric nonlinearity and the discontinuous behavior of the structure. And the analysis program is simple and systematic. This paper could provide basis for the investigation of the semi-active and active control of the stay cables and reference for the vibration control of structures considering the failure process.