Identification of aeroelastic forces on twin bridge cables from full-scale measurements in skew winds

Despite much research in recent years, large amplitude vibrations of inclined bridge cables continue to be of concern. Various mechanisms for the excitation have been suggested, including rain-wind excitation, dry inclined cable galloping, high reduced-velocity vortex shedding and excitation from the deck and/or towers.
Since 2010, the Technical University of Denmark has been monitoring the vibrations of the twin inclined cables of the Øresund Bridge. From the acquired data, Georgakis and Acampora [1] showed that the cable aerodynamic damping can be determined for wind orthogonal to the twin cables, in dry and wet conditions. In parallel, Acampora et al. [2] showed for the same cables that both coupled and uncoupled aeroelastic forces can be determined from the monitoring data, again when the wind is orthogonal to the cable and in dry conditions. In an expansion of the previous work, the aim of this paper is to identify the aeroelastic forces for in-plane and out-of-plane vibrations of bridge cables in dry conditions as in [2], but now for skewed winds. To achieve this, an output-only system identification employing the Eigenvalue Realisation Algorithm (ERA) [3] has been applied to selected vibration events. From this, the effective stiffness and damping matrices (including aeroelastic effects) have been identified from the cable vibrations.