New York State’s $3.98 billion New NY Bridge project to replace the 3.1 mile, 61-year-old Tappan Zee Bridge saw another milestone before Christmas, when its eight iconic main span towers reached their full 419-foot heights. At that juncture—and with more than 90% of support structures in place, more than 1,000 piles installed and more than 3,000 roadway panels set—the project was within its strict 62-month schedule and on budget.
Four years before the towers’ topping, consortium Tappan Zee Constructors, LLC (TZC)—Fluor Enterprises Inc., American Bridge Company (prime subcontractor for the current bridge), Granite Construction Northeast Inc., and Traylor Bros. Inc.—received an executed contract for a twin-span, cable-stayed bridge with a walking/bicycle path. TZC’s secret weapon was the Left Coast Lifter super crane (later nicknamed I Lift NY) built upon a 384-foot marine barge high in the water that reduces dredging needs by 50% and saves the state $1 billion. (TZC bid at least 20% less than competitors.).
With a 328-foot boom (reach) and lifting capacity greater than 1,900 tons, the super crane is lifting and placing concrete deck panels and 110,000 tons of U.S.-made steel, among other tasks, and will help dismantle the current bridge this year.
Multi-layered Subcontract Project
Jamey Barbas, project director for New NY Bridge owner the New York State Thruway Authority, oversees the Empire State’s first design-build, and largest, infrastructure endeavor, calling it “an exceptional engineering marvel that continues New York’s legacy of building extraordinary transportation networks.”
"Designing and constructing a bridge requires coordination between the owner, design engineers, contractors, suppliers, fabricators, erectors, inspectors, and construction workers,” Andrew Herrmann, emeritus member of consulting engineers Hardesty & Hanover, explained. Aiding the process is BIM (building information modeling), which “creates digital images early in the design process, which can allow participants to see projects in full or partial view,” Herrmann said. “This can help identify potential problems sooner, which can then be addressed more quickly during the design process.”
TZC hired Maxon Industries Inc. and Putzmeister America Inc., Wisconsin-based companies that collaborate on worldwide civil projects, to mix and place the more than 300,000 cubic yards of concrete required, including for foundations, piers, platforms and the towers. Two floating concrete plants, each producing up to 75 yards per hour, were onsite by summer and fall 2014. A third plant capable of producing 180 yards per hour, with a placing boom that extended more than 130 feet and a conveyor belt, was onsite the following June. Putzmeister stationary pump, placing boom, and tower, and Maxon remix surge hoppers are among its machinery.
Concrete Precision and Timing
While the mix design was not specific to this project, Bob Weiglein, Putzmeister general manager at Telebelts, special projects, explained, it specified a very high-strength concrete that included a high percentage of chemical additives and a very low water-cement ratio. “The concept of designing a mix that will last 100 years both below and above water was a critical issue,” Maxon president Bill Maxon agreed. Raw materials—slag, fly ash and cement—were barged to the project site and held in the batch plants' silos, then mixed proportionally with sand, stone, and water from nearby barges and delivered through a large placement boom.
“In appearance, the mix was very wet; however, in performance, there were very few fines to create the boundary layer within the pipeline to facilitate pumping,” Weiglein said. “Ongoing changes to the aggregate and chemical content modified the actual pumpability characteristics as the project advanced.”
Maxon acknowledged the drawback to producing concrete in-river—saving up to two hours from on-land production to pouring at the location—“is that you put a manufacturing plant and complex systems of equipment on the water.”
“The floating batch plants have been one of the most important parts of this project,” said Neil Napolitano, TZC area manager for the project’s approach spans. “In addition to keeping the 22,400 (trips by) concrete trucks, required to transport 202,000 yards of concrete, off local roadways, (the floating plants) provide us the flexibility to conduct complicated operations in a challenging environment.”
The Bridge’s Structure
Forty-three pairs of concrete piers, all except two in the water, 350 feet apart begin with cages of galvanized reinforcing steel. After a hot-dip galvanizing process (molten zinc coating) to ensure against rust, the rebar is placed in the formwork. Semi-liquid concrete is poured into the forms, its temperature carefully monitored and maintained as it cures and turns from dark gray to a uniform light gray. Factoid: The shortest piers, a few feet above water level, are on the Rockland approach; while the tallest piers, near the main span, are more than 130 feet high. EFCO Corp. of Marlboro, N.J. supplied formwork for the giant precast pile caps and for the anchor and approach pier/columns.
“Part of the challenge was the high pour rate that Tappan Zee Constructors was looking to accomplish on the piers,” vice president, northeast regional manager Joe Capozzi said. EFCO successfully met that requirement by providing “high pressure custom Plate Girder Panels with a one-quarter-inch steel face sheet along with custom guying platforms and access ladders.”
In late August 2015, TZC began building four towers to support the stay cables each atop two giant foundations—each 14 feet thick, 360 feet long, and 60 feet wide and filled with 11,000 cubic yards of concrete—using self-climbing concrete jump forms, tower cranes, and catwalks. After assembling rebar cages for each tower, crews poured 26 lifts of concrete ranging from 12 to 18 feet high. As each lift placement was completed, the jump forms were raised higher into the air via a screw jack system so the next segment could be build upon it. When the westbound towers reached their full 419-foot heights, crews removed the self-climbing forms to reveal chamfered (angled) tops.
Supporting the Main Road
Last summer, crews installed the first few stay cables to the main span towers, “a major milestone in the construction of this critical project,” Barbas said. Twelve pairs of cables varying from 190 to 623 feet long are anchored into each side of the towers and tensioned to outside sections of structural steel. The cables contain bundles of high-strength steel strands covered in protective sheaths; placed end-to-end the total is 14 miles of sheathing encasing 700 miles of strands.
Cable bundles increase in size as they move away from the towers to support the 74-million-pound main span road. About 100 of the total 192 cables were attached and tensioned by February 2017, and the westbound spans neared completion by mid-March, when two 375-ton sections of steel joined its main road with the Westchester and Rockland approaches.
This time last year, crews installed the first of four crossbeams, each secured by temporary steelwork while crews connected them. At 26 feet high and 16 feet, 6 inches wide, the eastbound span’s crossbeams are 60 feet long, and the westbound span’s are 70 feet long to allow for the walking/bicycle path. Coastal Precast System in Chesapeake, Va.. fabricated the 645-ton eastbound crossbeams and the 742-ton westbound crossbeams. Last summer, crews installed the first 40-foot-long steel sections and prefabricated road deck panels across the main span crossbeams, working outward in each direction.
Barged into position near the appropriate crane, the panels are rigged to the crane’s lifting arm, after which an operator controls the machine, working with signal crews at the roadway level, communicating via radio as the panels are hoisted to their final position.
Securing the Deck Panels and Looking Ahead
While they are bonded to structural steel panels using 1,800–amp heating guns with 9-inch-long studs, the panels are also designed to connect with one another via the rebar that extends from each panel. These connect with additional steel before concrete from the batch plants is poured between them to seal the panels together.
NAlmost 6,000 steel-reinforced concrete deck panels will cover the approach spans’ structural steel; the main span road will have 973 panels. A 1-inch durable polymer overlay atop the deck panels will be the final driving surface.
Two-way traffic will temporarily switch to the new westbound span’s eight lanes by spring/summer. Crews will then dismantle the current bridge so the eastbound span can be completed and attached to the Westchester and Rockland landings.
The full bridge and its walking/bicycle path should open in 2018.