Governor Cuomo of New York now has the privilege of having two 16,000-ft-long bridges named in his father's honor. These two structures linking Tarrytown, N.Y., to South Nyack, N.Y., over the Hudson River will help streamline traffic while also adding an element of beauty to the river scene. “The bridge has been honored by the communities it serves by being recognized as a ‘Work of Art’ by the county art organization and council,” says Jamey Barbas, project director, New York State Thruway Authority.
Constructing this river crossing was no small effort. The nearly $4 billion project was the largest construction project in the history of the New York State Thruway Authority, and one of the largest bridge projects in the nation. “The key challenge on the project was simply one of sheer size,” Barbas says. “The bridges cross over one of the widest points of the Hudson River, covering a distance of 3.1 miles.” Using precast concrete elements helped the designer tackle this challenge while keeping scalability in mind. “Applying the efficiencies of precasting was pivotal to delivering this mega-project,” he says.
The project involves 6 linear miles of bridge composed of 85% approach viaducts and 15% cable-stayed structures. “The project used a vast amount of precast concrete materials, including pile caps, pier caps, road deck panels, and crossbeams between its eight iconic towers,” Barbas says. Almost all (95%) of the piers and their foundations are waterborne, which made construction difficult.
To expedite construction and limit the amount of fabrication/casting performed over water, the designer developed precasting techniques to reduce on-site construction. The four 60- and 70-ft-long crossbeams, which weigh nearly 3000 tons in total, were cast on a floating barge in Chesapeake, Va., and transported by barge directly to the main span for installation. Instead of using sheet-pile cofferdams for pile caps, which would have been a labor-intensive method with an unacceptable environmental impact, the designers developed a permanent precast concrete tub system as a form for the waterline pile caps. The tubs, which weighed an estimated 360 tons each, were shipped by barge to the project site and lifted into place over previously driven piles.
“This strategy yielded a huge benefit in terms of the schedule, reduced volume of in situ concrete placement, enhanced worker safety, and a reduction in the environmental risks otherwise associated with pile cap construction using cofferdams,” Barba says.
To manage the giant precast concrete elements, the project used of one of the largest lifting cranes in the United States, and a 16-acre staging area at the Port of Coeymans in Albany County, N.Y. “The location of these staging yards alongside the Hudson River allowed the builder to readily barge the materials directly to the project site for installation with this large crane,” Barba explains. The project met all of its goals and has resulted in a signature structure that will serve more than 50 million travelers annually for decades to come.