The Prototype Testing of Kessock Bridge: Response to Vortex Shedding

Abstract Measurements of the dynamic response of Kessock Bridge made between October 1991 and May 1992 indicated that on three occasions the bridge experienced abnormally large response. Data from these three events are presented and discussed. These show that the peak dynamic displacement occurred due to resonance of the first vibration mode with vortex shedding, and was in excess of 110 mm. The duration of the large amplitude displacements was determined by the turbulence of the incident wind and reached 3 min during the more steady Easterly winds. A large torsional response was also noted during one of these events, which indicates a previously unobserved and potentially serious behaviour. Finally, inspection of the tuned mass dampers installed on the bridge to reduce the level of vibration in the first mode showed that they were not functioning correctly after the last event.