Aerodynamic damping of inclined bridge stay cables in unsteady wind
Proceedings of the 8th International Conference on Structural Dynamics, EURODYN 2011
Aerodynamic damping, Bridge stay cables, Unsteady wind, Vibration
Large amplitude wind-induced vibrations of stay cables on cable-stayed bridges have been observed in field and wind-tunnel studies. The catastrophic consequence of these violent oscillations causes serious concerns in the bridge industry. The occurrence of dry inclined cable galloping under unsteady wind condition has been studied analytically using a proposed expression for the aerodynamic damping of an inclined and/or yawed rigid circular cylinder in unsteady wind. The earlier works on dry inclined galloping of stay cables were mostly based on smooth flow conditions and the unsteady nature of natural wind was ignored, which could considerably distort the actual interactions between cable and wind, and lead to a more conservative or more optimistic solution for designing vibration controlling means. In view of this, the current paper thus aims at proposing a quasi-steady analytical model to study the effects of unsteady wind on the dynamic behavior of an inclined cable, and provide qualitative insight to refinement of the onset conditions of dry inclined cable galloping by considering unsteady wind in the formulation. The aerodynamic damping of the cable, which is a function of Reynolds number, aerodynamic force coefficients, cable orientation, cable motion and wind characteristics is derived based on a single degree of freedom oscillation of a circular cylinder. The significance of unsteady wind in the initiation of galloping type of motion on dry inclined cables was studied by comparing with the results in smooth flow conditions. As a first attempt to study the impact of unsteady wind on the onset conditions of violent cable vibration, in the present study, the unsteady components in the wind are assumed as harmonic terms derived from wind spectra. The results suggested that the more realistic assumption of unsteady wind could greatly affect the necessary onset condition for the galloping response of stay cables within the critical Reynolds number regime of which the negative slopes of lift and drag force coefficients with respect to Reynolds number were significantly present.
Raeesi, Arash; Cheng, Shaohong; and Ting, David S.K.. (2011). Aerodynamic damping of inclined bridge stay cables in unsteady wind. Proceedings of the 8th International Conference on Structural Dynamics, EURODYN 2011, 1615-1622.