When the 1939 Deer Isle/Sedgwick Bridge needed repairs, the Maine Department of Transportation and the Structural Engineer needed more information about the cables. Sebago Technics was employed to verify vertical suspension cable lengths on the 2,048 foot long suspension bridge.
This was not an easy feat as the bridge deck and cables move with traffic, wind, and even temperature changes. We utilized our past experience on many other bridge surveys which incorporated several techniques used depending on the conditions. Several techniques were analyzed to maximize accuracy and efficiency while measuring the cables, and minimize the impact on the coastal communities.
A control network was established utilizing dual frequency GPS observations together with total station observations and least squares analysis. Survey grade prisms were placed on the top pin of all 142 vertical cables. Several short road closures were scheduled to minimize movement of the bridge, allowing us to occupy the bridge with four total stations and minimizing the effect on the local traffic. During each road closure, four of our survey crews performed locations of the top and bottom pin of all cables, and located the bridge deck at each cable. This process was repeated during a few observation sessions at different temperature conditions to analyze the changes on the bridge cables and to verify the accuracy of our observations.
The information gathered was analyzed and profiles were prepared of each side of the bridge for each different observation session. Spreadsheets were also prepared showing all of our observation data.
Project DetailsDeer Isle Bridge
- Location: Deer Isle/Sedgwick, Maine