Investigation On Vibration Mitigation Of Stay Cable-Damped-Cross Tie System

As one of main types of large-span bridges at present, cable-stayed bridges hasbeen sidely adopted, and stay cables are one of the most key compone its ofcable-stayed bridges. Despite of its small mass, stay cables has obviousdisadvantages, such as small flexural rigidity, and low damping, this make staycables sensitive to external excitation. So stay cables are prone to exhibit manykinds of transverse oscillations of large amplitude under the function of wind loadand node displacement transmitted from decking or bridge tower. To mitigate thevibration of very long stay cables, in additiion to the aerodynamic means andinstallation of mechanical dampers, cross tie is also an effective countermeasures.Inoder to increase the damping of stay cable-cross tie system and to improve thevibration reduction effects, concentrated dampers is added to the cross tie systemand then the stay cable-damped cross tie is becoming a significant choice forvibration mitigation of stay cables of super long-span cable-stayed bridge.The stay cable-damped-cross-tie vibration mitigation method has no reliabletheoretical basis, and there remain imperfection for its parameter analysis andoptimal design. In this paper, by combination of theoretical analysis and numericalsimulation by ANSYS, the dynamic characteristics of the stay cable-damped-crosstie system and the influence rule for them and optimal design of dampers is studied.The main contents of this paper are as follows:(1)The damping and the inherent stiffness of dampers are simulatedrespectively by viscous damping and linear spring, they are connected in parallel.And based on the assumption of cross ties have infinitely stiffness, the physicalmodel of the stay cable-damped-cross tie system is set up. The equation of motionof each cable segment was formulated based on tight string theory[23], then by the setof boundary, compatibility and equilibrium conditions, the complex eigen-equationof the system is obtain, which is numerically solved for the dimensionless complexfrequency and the modal damping ratio.(2) In order to simply the calculation, the general model is simplified andassumed that the location of damper is near to the anchorage of cable, so anapproximately analytical solution of the complex eigen-equation is obtained, anduse it investigated the effects of the stiffness of dampers and the whole system onmodal damping ratio.(3) Numerical simulation by ANSYS is carried out for stay cables side inmiddle span of JinTang Bridge. By this method, the dynamic characteristics ofsingle cable and cross tie are researched, and the optimal design of the installation location of dampers is achieved on the bisis of modal damping ratio. At last, thevibration reduction effectiveness of this method is verified via wind-inducedvibration of stay cable-damped-cross tie system.