Wind-tunnel investigations of an inclined stay cable with a helical fillet

An experimental study of the effect of adding a helical fillet to the surface of a stay cable in relation to its response to wind-induced excitation was carried out on a 1:1 scale free-to-respond sectional model at the National Research Council Canada. The experiments revealed that a stay cable with a helical fillet inclined at 60° to the flow can experience wind induced vibrations with large amplitudes in smooth or turbulent flow for a low level of structural damping. The oscillations observed appeared to be self-limited in amplitude and could be mitigated with an increase of structural damping. The experiments revealed also that the aerodynamic forces at the source of the vibrations were highly sensitive to a rotation of the cable model about its axis. Measurements of the external diameter of the smooth cable model have shown a maximum eccentricity equivalent to 1% of the mean diameter which appeared to be sufficient to influence the aerodynamics of the cable model, even with the helical fillet in place.