A custom-made man lift was used to inspect the cables without damaging their protective covering.
Design work is now under way to replace all 72 stay cables on the 25-year-old Hale Boggs Memorial Bridge, a landmark crossing that carries Interstate 310 across the Mississippi River between Luling and Destrehan, La. The estimated $20-million to $30-million project, a first for a North American bridge, would repair longstanding corrosion problems associated with cracked sheathing.
The weathering steel frame, $135-million bridge carries 45,000 vehicles daily over its 1,222-ft-long main span and 495-ft and 508-ft back spans. Also also known as the Luling Bridge, it was designed by Modjeski and Masters Inc., Harrisburg, Pa., and Frankland & Lienhard and constructed by a team led by Williams Brothers Construction Co. Inc., Houston. It was the first high-level, long-span cable-stay bridge built in the U.S. and has twin 350-ft tall, modified A-frame pylons.
Stay cables are arranged in groups of two or four, with a total of 24 groups or 72 individual cables. The stays’ protective 1⁄4-in.- to 1-in.- thick, high-density polyethylene sheathing has deteriorated and there is also rust and water leakage in anchorages. “We determined that the most economical solution was to replace all of the cables, since that would prevent the need for future repairs and extend the useable life of the bridge by about 75 years,” says Sherry Dupre, Louisiana Dept. of Transportation and Development (DOTD) spokesperson. “We are about 10% into the final design phase and will begin to accept competitive bids at the end of December 2008 or the beginning of January 2009.”
DOTD notes that the bridge is safe. Currently, with the exception of super loads over 230,000 lb, there are no weight or speed restrictions. A cable-monitoring system will be installed before and after the replacement process.
In 2002 DOTD hired CTLGroup, Skokie, Ill., to evaluate the stays visually and non-destructively with infrared cameras and acoustic sounding. Subsequently, CTL, working with three other firms, was selected to design the replacements
The cables, which range in size from 103 to 307 1⁄4-in.-dia parallel wires, use button head anchorages. The stays were prefabricated and the sheathing cracked before and during installation. The cement grouting process also likely induced further cracking, exposing the wires to corrosion. “The sheathing was damaged before and during installation and repair attempts were made on successive oc-casions but were not effective in preventing moisture intrusion,” says Adrian Ciolko, CTL principal in charge.
CTL is evaluating alternatives. “We are choosing between a parallel wire cable or a strand-based cable design that fits the geometry of the bridge cable anchorages,” says Ciolko. “Another part of the design process is developing construction staging guidelines and temporary stay-cable system to support the superstructure while the existing cables are removed.”
To date, stay cables have been replaced on bridges in Argentina and Malaysia, he says.