WAKE FLOW INDUCED VIBRATIONS OF VERTICAL HANGERS BEHIND THE TOWER OF A LONG-SPAN SUSPENSION BRIDGE

Violent vibrations have been reported in the vertical hangers of a long-span suspension bridge, especially for those located in the vicinity of the towers. An experimental investigation is performed to characterize the wake flow induced vibrations of vertical hangers behind the tower of a suspension bridge. Arranged at different stations behind the tower column model, the vertical cables experience violent vibrations. Frequency detuning phenomenon referred to as soft lock-in is observed, as the vibration frequencies of the vertical cables are larger than their natural frequency. The vibration frequencies of the vertical cables are locked onto the upstream vortex shedding within a certain velocity range, during which extraneously lock-in cable vibrations take place. Based on the velocity of incoming airflow, the vertical cables subject to tower wake flow experience three kinds of dynamic responses: lower-branch buffeting, extraneously induced lock-in vibration and upper-branch buffeting.