The John James Audubon Bridge is the only Mississippi River crossing between Natchez, Miss., and Baton Rouge, La. The 3,186-ft-long bridge has a main span of 1,583 ft.

Photo by Joe Dunn
The John James Audubon Bridge.

Featuring 11-ft-wide travel lanes, an 8-ft-wide outer shoulder and a 2-ft-wide inner shoulder, the bridge's deck is supported by 136 cable stays, each anchored to one of the bridge's two 520-ft towers. Each tower is anchored by 42 drilled shafts that extend 180 ft into the riverbed.

"Dealing with unpredictable water elevations of the Mississippi River was by far the most challenging aspect of the project from a construction perspective," says Frank Daams, project manager at Flatiron Constructors.

"Optimizing the cable and deck design to optimize the capacity of the erection equipment and the erection schedule was the most interesting aspect of the project," Daams adds.

The cofferdam design used for the bridge was constructed using a combination of precast concrete panels and sheet piles. A conventional sheet pile cofferdam was ruled out because of variable water levels during construction. The final structure had a 160-ft by 64-ft footprint, was three stories high and weighed 5,000 tons. Once assembled, hydraulic jacks were installed and the cofferdam was incrementally lowered 47 ft into the river.

"The use of a cofferdam attached to a concrete 'lost form' that could be erected above the water level and then lowered into the river was something we had not done before at this order of magnitude," Daams says.

The $409-million span, which was built by the Audubon Bridge Constructors joint venture, is Louisiana's first design-build project. The bridge's main span is now the longest cable-stayed span in the U.S.

The bridge is among the 55 transportation projects identified under the $5.2-billion Transportation Infrastructure Model for Economic Development (TIMED) program established by the Louisiana Legislature in 1989 and approved by voters.

John James Audubon BridgePointe Coupee Parish, La. Key Players

Owner: Louisiana Dept. of Transportation and Development, Baton Rouge, La.

General Contractor: Audubon Bridge Constructors, a JV of Flatiron Constructors, Granite Construction and Parsons Transportation, Benicia, Calif.; Louisiana TIMED Managers, Baton Rouge, La.

Lead Design: Audubon Bridge Constructors

Structural Engineer: Parsons Corp. and Buckland & Taylor, both Baton Rouge, La.

Civil Engineer: Parsons Corp., Evans-Graves Engineers, Burk-Kleinpeter and GO-TECH, all Baton Rouge, La.

MEP Engineer: Parsons Corp.

Submitted by Flatiron and Louisiana TIMED Managers