Louisiana Department of Transportation and Development – Ouachita River Bridge Project

Ouachita River bridgeThe new Ouachita River Bridge in Harrisonburg, La., will greatly improve traffic flow in the region.

By Jim Harris

The Louisiana Department of Transportation and Development (LaDOTD) early next year will complete the replacement of a more than 80-year-old bridge.

Contractor Gilchrist Construction in May 2014 began work on the new bridge, located on state route LA-8 in Harrisonburg, La. The $37 million bridge, which spans the Ouachita River, replaces a structure built in 1932, LaDOTD Project Engineer Charlie Franklin says. The contract for the project was awarded in late 2013.

“[The current bridge] is a riveted steel truss swing span structure that is functionally obsolete because of the load-carrying capacity of its structural members and its vertical and horizontal clearance,” Franklin says. The bridge is 1,100 feet long and has a 320-foot swing span, divided by a central pier over the river.

The existing bridge’s low clearance of 40 feet when the river is at pool stage often requires it to be opened 15 to 20 times a month to accommodate marine traffic, which interrupts motor vehicle movement. The bridge also requires continual maintenance as a result of wear and tear from both marine and motor vehicle traffic accumulated over its long existence, he adds. 

The original bridge was built to replace a ferry that crossed the Ouachita River. The Harrisonburg region has a long history that includes being the location of Fort Beauregard, the site of a Civil War battle in 1863.

Load Bearers

The new 3,275-foot-long bridge is a pre-stressed concrete and steel girder structure with a main span of 380 feet. The structure’s clearance over the river at pool stage is 79 feet. The new bridge will have no load restrictions, an improvement over the existing structure’s load maximum of 15 to 25 tons, Project Engineer Charlie Franklin says.Ouachita River bridge box

The new bridge will have two 12-foot-wide lanes with two 10-feet wide shoulders; the current bridge’s lane configuration is two 10-foot-wide lanes, Franklin says.

The bridge’s structure was the subject of a research project conducted by the Louisiana Transportation Research Center. The project concentrated on the bridge’s use of continuous deck links, also known as deck slabs, instead of continuity diaphragms. The center placed strain gauges in the deck slabs and girders to study the effect of traffic and temperature loads under various continuous link details.

“The primary benefits of this new detail are to simplify the continuity detail and make it easier for future replacement of damaged girders and minimize and control cracking of the concrete deck,” the center says. “We also wanted to eliminate the need for continuity diaphragms, significantly reduce the need for deck continuity reinforcing steel, improve the overall performance of pre-stressed concrete girder bridges and prolong the concrete deck life.”

Working Together

Flooding in the Ouachita River is the main challenge faced by LaDOTD and its contractors during the project. Cofferdams were built in the river before work began on the two main spans of the new bridge; those cofferdams have flooded three times within the past few years. “The river has been extremely high during this time,” Franklin adds, noting that water levels have reached 20 feet above pool stage.

LaDOTD has worked closely with Gilchrist Construction and its subcontractors to overcome construction challenges. “We have a very good working relationship with the project superintendent and foremen at Gilchrist,” Franklin says. “We meet once a quarter with all the players on the project, from central headquarters to the foremen working on the job, to hash out any problems that arise.”

Based in Alexandria, La., Gilchrist Construction is a civil infrastructure contractor whose services include piling, bridge structures, asphalt construction, concrete production and paving. In addition to roads and bridges, the company also performs site preparation, heavy foundation and industrial work. 

“We are proud to be the contractor and partner on many great infrastructure and industrial projects throughout Louisiana, both current and completed,” the company says. “We strive to live our vision to be the leader in safety, quality, innovation and efficiency. We are proud of our teams, proud of our state and proud to be one of Louisiana's top highway contractors.”

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