Wind-induced response and excitation characteristics of an inclined cable model in the critical Reynolds number range

Abstract

This paper focuses on wind-induced vibrations of dry inclined bridge cables in the critical Reynolds number range. The cable response and the associated wind load characteristics are studied experimentally, in the third phase of a major wind tunnel investigation on cable aerodynamics at the National Research Council Canada. The displacement (and acceleration) response of a 6.7m long section cable model, 160mm in diameter, was monitored simultaneously with 162 surface pressure taps, for inclinations of 60°, 77° and 90°. The data corroborate the susceptibility of dry cables to respond, primarily in the across-flow direction, to load variations associated with transitions between flow regimes throughout the drag crisis region. The most vigorous vibrations (stopped at approximately 60% diameter response amplitude) were observed at 60°, with damping ratios below 0.2%. Significant “lock-in” between the lift force and the violent sway cable response was identified in terms of the transfer function between the two during the large vibration events. The large responses were confined to a narrow Reynolds number range, often at flow conditions giving the minimum normal (drag) coefficient and a significant derivative of the lift coefficient with respect to Reynolds number. Throughout the drag crisis region, significant variation in flow characteristics along the cable aligned at 60° has been observed, in terms of both mean pressure distributions and pressure fluctuations.