THE PROTOTYPE TESTING OF KESSOCK BRIDGE - RESPONSE TO VORTEX SHEDDING

Measurements of the dynamic response of Kessock Bridge made between Oc tober 1991 and May 1992 indicated that on three occasions the bridge e xperienced abnormally large response. Data from these three events are presented and discussed. These show that the peak dynamic displacemen t occurred due to resonance of the first vibration mode with vortex sh edding, and was in excess of 110 mm. The duration of the large amplitu de displacements was determined by the turbulence of the incident wind and reached 3 min during the more steady Easterly winds. A large tors ional response was also noted during one of these events, which indica tes a previously unobserved and potentially serious behaviour. Finally , inspection of the tuned mass dampers installed on the bridge to redu ce the level of vibration in the first mode showed that they were not functioning correctly after the last event.