General contractor Thompson-Arthur, a division of APAC-Atlantic; Lynchburg, Virginia-based English Construction Company; and the North Carolina Department of Transportation have nearly completed the twin spans over West Friendly Avenue in Greensboro, N.C. The bridges, which are the longest single-span steel bridges in the state, are part of Greensboro's western Urban Loop, which runs from I-85 southwest of the city to just north of Bryan Boulevard. Constructed in two sections at a total cost of $218 million, the western Urban Loop is scheduled for completion in November.
Preliminary work on the bridges began 22 months ago when the piles were driven for the end bents and the retaining walls were constructed, according to English Construction's Mike Kendrick, bridge superintendent, and James (Sonny) Silvers, project superintendent. A total of 144 piles were driven to an average depth of 40 feet. Work on the retaining walls came next. A total of 150,000 cubic meters of unclassified material and borrow were used for the retaining walls and the road bed for the approaches to the bridges.
Concrete pours for the end bents came next, followed by the placement of the girders for the bridge spans. There are six girders on the southbound bridge to accommodate three traffic lanes, and seven girders on the northbound bridge to accommodate four lanes of traffic. Fabricated by Carolina Steel in Colfax, N.C., each span is composed of three girder sections, two shorter sections at each end bent and the long center girder over the roadway. An entire span weighs 150 tons.
Because of the length of the girders, state troopers escorted each one to the project site. "The shorter end girders were set on a Thursday or Friday so we could be ready to set the long spans on the weekends," says Kendrick.
With West Friendly Avenue shut down, English used a 110-ton Link-Belt crane and a 100-ton Terex crane to place the girders on the southbound bridge, and a 100-ton Terex and a 210-ton Terex to place the girders on the northbound bridge. With the cranes holding the long spans in position, they were then spliced to the shorter end girders with 762 bolts per splice. The project team completed two spans each weekend.
David Carr, Thompson-Arthur project manager, explains that the beams were designed with a certain amount of deflection because of their length and depth and to account for the weight of the superstructures and future traffic loads. The deflection allows the girders to flatten out as the 600 yards of concrete for each deck is poured. A joint in the concrete at the end of the bridge deck was intentionally left out to allow room for the girders to move into their final positions and not crack the deck. Once the girders have settled a closure pour will tie the joint into the deck.
Designed by Edward Wetherill of Wetherill Engineering, NCDOT decided to use the single-span bridge design to eliminate the need for a median on West Friendly Avenue and additional bridge piers. The single-span design allows the bridge to be part of a single-point urban diamond interchange. "Traffic is controlled by one traffic signal in the center of the interchange," says Darrell Ferguson, resident engineer with NCDOT. "This design moves a lot of traffic efficiently."
Designed and constructed for a total cost of $4.3 million, the southbound bridge is currently 95-percent complete, and the northbound bridge is nearly 90-percent complete.