The design of this prestressed concrete superstructure in Brewerton, NY, features unique post-tensioning patterns. The 70-foot anchoring wingspans cantilever over the piers and carry the drop-in girders to make a 320-foot channel span.
Portions of the lower flange of the fascia beam and the post-tensioning wires had been compromised due to internal and external concrete deterioration from scupper downspouts. NYSDOT first completed an emergency repair contract where external post-tensioning was added to strengthen the main span, then selected our firm to perform an in-depth structural evaluation of the existing structure to understand the condition of the existing post-tensioning, load-carry capacity, and remaining useful life of the structure more clearly. As a result of the investigation, a rehabilitation contract was executed.
The two-year inspection included computer modeling for structural analysis to duplicate how the bridges were built to understand how the method of construction locked in tendon and concrete stress. We achieved this through 3D modeling and analysis using SAP2000 and CSiBridge software.
The hands-on visual and technical inspection and analysis of the entire structure included multiple methods of high-tech testing to assess the interior conditions of the concrete. Half-Cell Potential and Ultrasonic Shear-Wave Tomography (UST) technologies were used to create a preliminary model to evaluate the problem areas fully, in preparation for designing rehabilitation recommendations.
The resulting decision to design for rehabilitation instead of replacement was highly beneficial to New York state. Replacement would have required a wider structure at significant cost, and detours would have impacted both commuter and commercial concerns, including Fort Drum’s heavy vehicle passage.
Due to the bridges’ unique design and the complexity of the modeling analysis, NYSDOT asked our firm to write an owner’s manual to document for future administrations how the I-81 bridges were built, how the repair work was completed, and bridge maintenance best practices.
2019 Silver Award
American Council of Engineering Companies (ACEC) of New York