The A. Piatt Andrew Bridge is a steel arch bridge completed in 1950 and serves as the primary gateway from Gloucester and Rockport, Massachusetts via Route 128 to the mainland. The bridge sits 90 feet above the Annisquam River as it flows between Cape Ann Island and the mainland. It is 856’ in length with an arch span of 436’. A recent inspection of the bridge by the State of Massachusetts Department of Transportation (MassDOT) revealed that 12 of the 19 steel bracing elements of the bridge needed to be replaced.
CIANBRO, the General Contractor, was awarded the contract to repair the bridge and turned to Sebago Technics to help with documenting this bridge’s current geometry. The expedited fabrication timeline of the new bracing and the constraint of the existing steel arches being left in place required a measurement technique that would save Cianbro and the MassDOT mobilization and equipment costs over conventional measurement methods.
Sebago turned to the use of High Definition Scanning (HDS) technology to capture the structural elements of the bridge. A total of twelve (12) different scan stations were needed to capture the structural components of the bridge within a point cloud has a density of 1mm x 1mm. Sebago used this point cloud to obtain dimensions to 1/16th of an inch of the center of arch to the center of the arch, the height of the arch at each bracing location and downspout standoffs.