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When completed in April 2008, the new U.S. Hwy. 82 Mississippi River bridge near Greenville, Miss., will have cost about $245 million. It will be the longest cable-stayed bridge in the continental United States.
Construction of the longest cable-stayed bridge in the continental United States went horizontal this summer. With the substructure essentially complete, workers began erecting steel for the new U.S. Hwy. 82 Mississippi River bridge between Chicot County, Ark., and Washington County, Miss.
A joint venture of Massman Construction Co. of Kansas City, Mo., and Traylor Brothers Inc. of Evansville, Ind., is moving toward a March completion of phase one. The structure should be open to traffic in April 2008.
The $110.8 million phase one project will result in a 2,560-ft. bridge, divided by three spans and bearing four lanes of traffic. Two additional phases, let in separate contracts, will add more than 11,000 ft. of elevated approaches and 6,600 ft. of roadway.
A final contract will be awarded to dismantle the old bridge, located a half-mile upstream, after the new one is open to traffic. Massman Construction was the contractor for the original bridge built 65 years ago.
The old steel-through-truss bridge was designed by HNTB Corp. of Kansas City, Mo., which also designed the new structure.
"This is the probably in the top 10 percent of projects I've worked on in terms of complexity and is certainly one of the most interesting," said Steve Underwood, project manager with Massman.
Underwood said one complicated task involved getting the caissons sunk in the right position for the foundations of the two bridge towers. The tolerance for positioning the caissons on the river bottom was 12 in.
Building the caissons - set in dense, rocklike clay 200 ft. below the water - was a two-year process that began in late 2001. Pier 37, the Arkansas tower, was completed in February 2004 and was followed two months later by the Mississippi tower.
The towers, which resemble an H, are formed by two columns rising 400 ft. above the river joined by a bow-tie strut. The first strut was completed on the Arkansas tower in March with work on the Mississippi tower strut finished in May.
Each strut is a box of 2-ft.-thick steel-reinforced concrete that contain strands of steel cable. Pulled to tension by hydraulic jacks, the strut cables strengthen the towers to horizontal force caused by the tremendous weight of the stay cables.
Eventually, about 472 mi. of half-inch strand steel cable, coated with an anticorrosion lubricant and covered by a polyethylene skin, will be used to support the weight of the superstructure.
Additional components of the bridge work are composed of 95-ft.-wide and 48-ft.-long sections of preassembled edge girders and floor beams. As a new section is added by a barge-mounted crane and bolted in place, more cable is secured to anchor it to a tower.
Field sections are supported from the bridge towers by bundles of cable. The bundles contain between 27 and 68 strands of cable, depending on the location and load-bearing requirements.
The cables are pulled to predetermined tensions after strands within each bundle are strung between anchorages on the edge girders and bridge tower. Each field section will contain six, precast steel-reinforced concrete slabs measuring 15 ft. 9 in. wide and 47 ft. long to be used as the roadway base.
The panels, installed in rows of two, are linked internally by 1-3/8-in. steel bars that are post-tensioned after concrete used to close gaps between the slabs hardens.
Atop the deck, a 2-in. layer of a dense concrete called silica fume is laid for the roadway surface. The roadway will include lanes and an outside shoulder that are 12 ft. wide along with an 8-ft.-wide inside shoulder. The old bridge has only two lanes with no shoulders.
Construction of the field sections/deck will extend symmetrically in both directions from each tower, tying in with anchor piers on both sides of the river by year's end and finally joining between the towers.
"We hope to get everything erected within six to eight months," said Gowen Dishman, project engineer with HNTB Corp. Work on the superstructure was launched on the Arkansas tower June 1.
Phase two construction kicked off in April when a joint venture of Hill Bros. Construction Co. of Falkner, Miss., and Jensen Construction Co. of Des Moines, Iowa, began work on an $85.8 million contract to build the bridge approaches in Mississippi.
This project requires 4,602 ft. of approach bridge with 46 piers and 3,752 ft. of roadway.
Mark Buller, jobsite superintendent with Jensen, said juggling space limitations with the scheduling of materials is difficult in the phase 2 work.
"We don't have room to keep much material on site unless it's getting worked on," Buller said. "Materials must be ordered three weeks in advance before delivery, so timing is very critical.
"You don't want the material to arrive too soon because it gets in the way and you sure don't want it too arrive late."
He said the job will require 456 drilled shafts, 90,000 cu. yds. of concrete and 13.2 million lbs. of rebar. The piling work, which is averaging five to six placements of concrete per day, is keeping three drilling and rebar crews busy.
Buller said construction of roadway decking will start in late fall.
"The weather has been good to us," he added. "Hot but dry."
The Mississippi Department of Transportation is coordinating the overall development with the Arkansas Highway & Transportation Department. Total cost for the first three phases of the project, dubbed the Greenville Bridge, is estimated at about $245 million.
Of that, Mississippi is footing about $141.2 million, with Arkansas paying about $103.4 million. Phase one is split between the two states, with each picking up the tab for work within its borders for phases two and three.
A separate contract for the Arkansas bridge approaches (estimated at $48 million) is scheduled to be awarded before winter.
"I expect that to go off as scheduled," said Kevin Magee, resident engineer at the MDOT's Leland project office.
Phase three work will encompass 3,752 ft. of roadway and 4,602 ft. of approach bridge supported by 35 piers.
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