Archer Western Contractors Ltd. is more than two-thirds finished with the reconstruction of the Interstate 77 twin bridges over the New River, the New River Trail State Park and Route 52 in Wythe County, VA.
Work on the contract, awarded by the Virginia Department of Transportation (VDOT), has been under way since April 2002. Archer Western’s Richmond, VA, office is responsible for the project, which is being built in four phases and should be completed by spring 2006.
The project involves building a new superstructure between the two existing bridges and widening each bridge by one additional lane. A full emergency shoulder lane also will be added to the inside of each bridge. When finished, each bridge will accommodate three 12-ft. (3.6 m) lanes and two 12-ft. (3.6 m) shoulders.
The southbound bridge measures 1,808 ft. (551 m), and the northbound bridge is 1,798 ft. (548 m) in length. To compensate for the variation in the two lengths, the abutments are staggered. Additionally, the approach slabs will have a joint to transition to the different lengths.
VDOT originally selected TAMS as consultant designer of the bridge. Now, its parent company, Earth Tech in Alexandria, VA, has taken over the role as consultant designer.
“The consultant designer was selected by VDOT rather than designing the bridge in- house,” said Brenda Waters, Bristol district public affairs manager.
The bridge’s design is compatible with planned future widening of I-77 to six lanes. Therefore, the inside lanes on the bridge will remain closed until that project takes place.
Chris Blevins, VDOT’s assistant district bridge engineer of the Bristol district, stated that once completed, “only two lanes will be striped, and extra wide, allowing for future construction.”
Steel plate girders fabricated at Carolina Steel Corporation’s Abingdon plant in Bristol are being delivered approximately 80 mi. (129 km) to the site for the construction of the new bridge. Archer Western will be installing the 1,800-ft. (549 m) long continuous plate girders, which vary from 8 to 12 ft. (2.4 to 3.6 m) in depth.
According to Robert Pode, project manager of Archer Western, “The 1,800-foot long girders incorporate a haunch design, and the girders are 12 feet at their deepest and reduced to 8 feet throughout the rest of the span.”
The bridge reconstruction has been divided into four phases. Phase one, consisting of the construction of a new section of bridge between the two existing structures, was completed spring 2004. The superstructure is 140 ft. (43 m) high and 1,800 ft. (549 m) in length. Phase one included the addition of new pier columns and rebuilding abutments.
Archer Western made use of two Mi-Jack 70-ton (63 t) gantry cranes during phase one construction. While straddling the existing bridge decks and positioned on top of rail tracks attached to the decks, the gantry cranes erected the structural steel beams. The Mi-Jack cranes also were fitted with four-wheel drive due to the 4.55 percent slope of the grade on the bridge.
“To my knowledge, it was the first time four-wheel drive had to be employed on the cranes,” said Pode.
The cranes also helped the contractor avoid aerial splices.
Phase two of the project, the reconstruction of the bridge in the southbound lanes, was completed March 5. Before phase three work begins, said Pode, workers will “construct new roadway transitions to shift traffic.” Traffic from the northbound lane will be diverted onto the new structure because during phase three the northbound lanes will be reconstructed, which will start in April.
Phase four, the final stage, includes the installation of a 50-in. (127 cm) tall median barrier between the northbound and southbound lanes. The contractor also will be performing approach roadway work for smooth transition.
In addition to the Mi-Jack cranes, Archer Western has rented three Manitowoc cranes for the demolition and reconstruction of the bridges. Essex Crane Rental Corp. is supplying a Manitowoc 999 275-ton (247.5 t) crane and, for girder erection, a Manitowoc 888 220-ton (200 t) crane equipped with a 170-ft. (52 m) main boom and a 110-ft. (33.5 cm) luffing jib. C.P. Buckner Steel Erection Inc., in Graham, NC, also is providing a Manitowoc 888 crane.
The bridge’s proximity to the New River Trail State Park and two historical sites, the Sander’s House and the Historic Shot Tower, have presented the biggest challenges so far on the project. Precautions are being taken to ensure that environmental resources are not disturbed and that access to the state park by the public is still available.
In order to not disrupt visitors’ access to the trail, work that will affect the trail will be performed, for the most part, between 10 p.m. and 6 a.m. Escorts also are on hand to guide visitors if any overhead work is occurring during normal operational hours. In addition, escorts are available in the water for canoes or any other small unmotorized watercraft trying to navigate the construction site.
The historical buildings are under constant monitoring for construction induced vibrations. Garry Lovins, VDOT Bristol District bridge engineer, explained that the contractor is using, “drill shafts to minimize vibration and no blasting or pile driving is allowed.”
Furthermore, Louisville, KY-based Vibratech is monitoring vibration levels with geophones and seismographs, while VDOT inspectors are only a phone call away.
The primary reason for the bridge reconstruction is the fatigue cracking of the old structure. Even though VDOT maintains that the bridges have always been safe for motorists, the cracking had to be fixed.
“We had a lot of cracking — in excess of 500 cracks in different locations,” Blevins said.
There were a limited number of cracks on the girders and floor beams; most were concentrated on the steel stringers.
“They were significant but not dangerous,” added Lovins.
VDOT continues with its regularly scheduled inspection of the bridges even during construction.
Despite delays in the beginning with awarding the contract, work is progressing nicely. After some revision of the original contract amount and overrun estimates, VDOT has calculated approximately $45 million for the cost of the I-77 twin bridge reconstruction. That figure includes not only the construction costs but also expenses related to engineering, overhead and inspections.