PENOBSCOT NARROWS BRIDGE
Location: Verona Island - Prospect, ME
Client: FIGG Bridge Group/MDOT
Summary: For the 2nd time since the opening of the Penobscot Narrows Bridge in 2006, Sebago’s survey team conducted the 2018 routine periodic survey of the bridge’s geometric existing condition. Site work consisted of re-establishing the site survey control network used for the 2013 survey. Leica’s long range P50 laser scanner was used to capture the existing condition of the bridge superstructure, upper and lower pylons, and 80 individual cable stay HDPE protective coverings. Supplemental elevation data of the superstructure (bridge deck) was collected, using 56 separate existing monuments along the exterior edges of the road deck. Minimizing movement and variables such as thermal expansion were addressed to comply with a required tolerance of less than 0.015’ error within the entire deck profile. This data was collected during a 5-hour night traffic closure (10 PM to 3AM), minimizing impact to both local traffic and area commerce. Modeling of the 80 individual HDPE cable stays was completed using the registered point cloud data while maintaining a maximum sweep deviation of 0.02’.
Unobtrusive data collection from breakdown lanes and edge of right-of-way, road closures were not required to collect laser scan data, collected data during off peak hours. These factors minimized the traffic exposure risk for crew onsite.
Statistics & Supplemental info:
LF of cable stay modeled – 25,506 LF Combined
Pylon cut sections-27 each (Prospect Tower and Verona Tower)
Tower height above road deck- 285’
A majority of the superstructure as well as upper and lower pylons are nearly inaccessible to be collected via conventional survey methods.