Shape modification of bridge cables for aerodynamic vibration control

In this paper, the viability of modifying cable shape and surface for the purpose of controlling wind-induced vibrations is examined. To this end, an extensive wind-tunnel test campaign was carried out on various cable sections in the critical Reynolds number region under both smooth and turbulent flow conditions. Shape modifications of a plain cylinder included waviness, faceting and shrouding. The aerodynamic damping of each section is evaluated by applying 1- and 2-DOF quasi-steady aerodynamic models, which allow for the prediction of regions of aerodynamic instability. Whilst the plain, wavy and faceted cylinders are found to suffer from either dry inclined galloping, ”drag crisis” or Den Hartog galloping, the shrouded cylinder is found to be completely stable for all wind angles of attack, albeit with a slight increase in drag at traditional design wind velocities. The wavy cylinder is found to eliminate the risk of dry inclined galloping, with a reduction in lift fluctuations. Nevertheless, the particular cylinder is at risk of “drag crisis” instability. Finally, turbulent flow is shown to introduce a significant amount of aerodynamic damping by proving a more stable lift force over tested wind velocities.