Wind-Induced Motions of Deer Isle Bridge

The Deer Isle-Sedgwick Suspension Bridge across Eggemoggin Reach in Maine connects the Little Deer Isle to Sedgwick on the mainland. This paper summarizes the observations made in examination of the field response of the structure (at several wind velocities) combined with the results of some wind-tunnel experiments conducted to corroborate the current methodology for wind response prediction of long-span bridges. Field data demonstrate two types of wind-induced vibrations of the Bridge. Vortex-lock-in-type motion at a wind velocity of 9.11 m/s causes significant levels of response that exceed those observed even at 16 m/s due to buffeting. The deck accelerations of the Deer Isle Bridge at 9.11 m/s is marginal. This demonstrates that the vortex-induced motions at low wind velocities can be as important as the buffeting response at higher velocities from a serviceabililty point of view. These and other observations are discussed.