Louisiana’s Department of Transportation and Development, concerned about rusting and water leakage in the anchorages and splitting of cable cover pipes, contracted with CTLGroup to perform a structural evaluation of the Hale Boggs Bridge staycable array. This twin-pylon cable-stayed bridge has a main span of 1,222-ft. Each of the 72 stay cables is composed of 103 to 307 ¼-in diameter parallel steel wires, sheathed in a polyethylene cover pipe, and filled with cement grout. The cable sheathing serves as the primary corrosion barrier for this older stay cable system, erected in the early 1980s.
CTLGroup considered several nondestructive evaluation methods, including impulse response, impulse radar, and radiography, and tested them on mock-up samples before selecting thermography to supplement visual inspection. Thermography offered the best combination of effectiveness, cost-efficiency, and adaptability for field conditions. The firm then custom designed an inspection hoist that could ride the stay cables without damaging them.
CTLGroup checked the entire length of the cable cover pipes for signs of damage and deterioration. Where evidence indicates a breach in the cable sheathing, the team is selectively employing infrared thermography to detect possible moisture intrusion.
Over the course of about 12 weeks, the inspectors covered 28,800-ft (5.5 miles) of cable to complete the survey and develop a clear picture of the stay cables’ condition. CTLGroup was joined on the project team for this phase of the work by Bridge Engineering Solutions of Niagara Falls, NY, Dean Peryea LLC (rigging, access and traffic control), and Lisbon Hoist.
