Heavy Lifting – Concrete Products

BAYSHORE CONCRETE, COASTAL PRECAST SHIP NEAR-RECORD SCALE MEMBERS THAT PROVE INSTRUMENTAL IN NEW NY BRIDGE SCHEDULING, ECONOMY AND SITE SAFETY PLAN

By Ken Stadden

Bayshore Concrete Products built the pile cap tub forms at its Cape Charles steel fabrication shop. The producer enlisted a rebar subcontractor for the pile cap tub cages, fabricated mainly with galvanized steel, but some stainless steel for conditions with the potential for exposure to Hudson River flows. The 340- to 490-ton tubs were cast in half sections and designed as stay-in-place forms for the finished pile caps. The products have been tandem-towed, four at a time, two per barge, to the Hudson River project site.

In the second and concluding part of “In With The New” (Concrete Products, August cover feature), visits to two Chesapeake Bay precast/prestressed operations underscore the astute engineering and colossal concrete schedule behind the Empire State’s largest bridge contract to date. The 3.1-mile, cable-stayed, double span New NY Bridge, linking Rochester and Westchester Counties across the Hudson River, will replace the Tappan Zee Bridge in 2017-2018 phases. Work proceeds under Tappan Zee Constructors LLC (TZC), a design-build joint venture of American Bridge Co., Fluor Enterprises, Granite Construction Northeast, and Traylor Bros. TZC is running the project from a Tarrytown, N.Y., field office about 15 miles upriver from New York City.

TWO BRIDGES REPLACE ONE

The New NY Bridge is actually two parallel bridges connected by emergency crossovers and designed to accommodate a future, centrally-located light rail transit deck with no additional reinforcement. The twin spans will provide eight full-time traffic lanes at least 12 ft. wide with full shoulders, two express/emergency lanes, and a 12-ft.-wide bicycle and pedestrian path.

While the project calls for abundant use of steel girders on approach and main spans, the most impressive horizontal load-bearing members are precast concrete. Bayshore Concrete Products Corp. and Coastal Precast Systems LLC are producing massive tubs for 60 pile caps and 59 pier caps, respectively, in their Virginia operations. The caps are designed as stay-in-place formwork and will greatly curtail the need for forming crews to work at the water line, far from shore, or at high elevations above the pier foundations. Although operating with a “lighter” load than Bayshore Concrete and Coastal Precast, Massachusetts-based Unistress Corp. holds TZC’s largest precast contract: A $70 million order for 6,000 prestressed deck panels measuring 40- x 12-ft.

Bayshore Concrete Products has fabricated 60 footer boxes for approach span pile caps at its 90-acre, Cape Charles, Va., facility. The tubs are produced in four sizes, the smallest of which are 30- x 73-ft., weighing 320 tons, up to 36- x 84-ft., weighing 490 tons. “We can stage up to 13 units,” says Bayshore Plant Manager Chuck Hook, “and we send two units per barge in tandem tow, with about a 10-day turnaround.”

A subcontractor ties reinforcing cages on site using four truckloads of galvanized steel or stainless steel rebar, the latter specified where the pier will be below the waterline due to micro-flexing of the tub at high tide. Bayshore’s fab shop built the steel tub forms. “First we pour the floor, 106 yards,” says Hook. “The next day, we pour the walls.”

The initial pour takes 3.5 to four hours using pump trucks, notes Bayshore’s TZC Project Manager Thomas James. On the second day the walls are poured. After curing, a waterproofing epoxy is applied to the floor-wall joint. Finally, robust plastic fendering systems are bolted in place. The finished tub has cylindrical holes in its floor that allow a 9-in. gap around the piles.

A 600-ton, rubber-tired gantry crane was rented for the project to transport the finished tubs through the bustling yard to the staging area and barge slip. Bayshore Concrete approached mid-2015 with production and shipping on schedule, tub fabrication wrapping up by August.

MIXING & TESTING

Coastal Precast Systems demonstrated the proposed pier cap scheme with models (opposite page), ultimately providing TZC crews templates showing pin locations. CPS subcontractor Rodbusters in Westbury, N.Y., was able to turn one 32-ton cage (opposite page, right) per week during the pier cap fabrication schedule. After wet curing of interior surfaces, the 83- and 92-ft. pier tubs were removed from forms with a 400-ton crane (top) and transferred to staging area near the producer’s barge slip. Upon placement, the tubs serve as stay-in-place forms (above), the concrete mixes pumped from one of three TZC barge-based plants.

New NY Bridge precast and cast-in-place concrete structures have common equipment: BHS twin-shaft mixers at TZC’s three floating plants at the job site, and at the Bayshore and Coastal precast batch plants. Bayshore’s two twin-shaft models on line in 2008, replacing pan mixers in a Standley Batch Systems plant long on storage of a wide range of cementitious materials and aggregates. The mixers produce 5.5-yd. batches, discharging into Tuckerbilt sidewinders or Bayshore’s fleet of eight 12-yd. front-discharge mixer trucks. Every load is tested and, as with Coastal Precast, a New York State Thruway inspector has been on site full time.

“We had several different mix designs on file, with and without silica fume, and we tried several different fly ashes to see which would perform best,” says James. “We always use the silica fume in the walls, but we only used [it] on the floors in the winter to get the little extra boost in strength that we needed.”

Previously dosing it by the bag, Bayshore added a silo dedicated to silica fume and conveyed the ultra fine powder to a spare water batcher prior to discharge into the mixers. A seven-day wet cure was required, with a target of 6,000 psi. Form removal could occur at 2,500 psi, and picking at 4,000 psi.

Bayshore had to widen its barge slip from 58 to 62 feet to accommodate the TZC precast footer boxes. A new casting line, complete with fabric-enclosed, open-truss frame structures, consumed former storage area. “Once the TZC contract was awarded,” says Hook, “we excavated new footers and poured a 400-foot soffit, and fabricated the steel formwork in house. For the crane’s path to the pier, we excavated and put in 40 inches of compacted material.” About 35 to 40 personnel were added for the TZC project, he adds, though it was only one of three large projects that swelled employee ranks from 58 to 400 in one year.

COASTAL PRECAST: PIERS, PILES, PANELS & CAPS

Between April 2014 and May 2015, Coastal Precast Systems (CPS), LLC, Chesapeake, Va., produced soffit panels weighing up to 145 tons each as floor components of two enormous 360- x 60-ft. tubs for the foundations of the New NY Bridge’s two 419-ft. tower piers, as well as for two 324- x 35-ft. anchor pier foundation tubs. For the tower piers, 36 soffit panels were produced, 18 per tower, measuring 32- x 30-ft. and weighing over 65 tons. Eight 38- x 30-ft. end panels were also produced, weighing in excess of 95 tons. For the anchor pier tubs, CPS produced 18 soffit panels, 27- x 35-ft., weighing in excess of 90 tons, and four 43- x 35-ft. end panels weighing over 145 tons.

CPS operates on a parcel along the lower Chesapeake Bay, the waterway access essential to handling and delivery of New NY Bridge-scale product. The massive panels were barged north to the work site and assembled to form the tower pier tub floors, after which forming systems were attached for wall pours. Finished tubs were hydraulically lowered into the water to a depth of 9 feet and drained prior to rebar installation and placement of 11,000 yd. of concrete.

This floating-tub method was selected by TZC over traditional cofferdams and cast-in-place construction because the Hudson River is more than 40 feet deep, subject to 6-ft. tides, and has powerful currents in its navigation channel. Perhaps due to the fluid nature of the design-build process and pressures to remain on schedule, CPS President Paul Ogorchock was able to persuade TZC to substitute planned cast-in-place methods with the precast tubs for the 59 pier caps.

CPS began producing the 83-ft. and 92-ft. long, 13.5-ft. tall, 10.5-ft. wide pier cap tubs in August 2014 at the rate of about one per week. There are two widths because eastbound and westbound decks are different sizes. A jig was used to stage 64,000 lb. of galvanized rebar on the ground before a crane lifted the reinforcement into one of two forms. The in-house designed forms and bracing withstand nearly 800,000 lb. of pressure from 0.6-in. diameter galvanized prestressing strand—18 strands per side and 20 strands on the bottom. “The whole thing’s prestressed like a big beam,” explains Ogorchock. The 59 tubs consumed a total of 7,600 yd. of concrete, averaging 129 yd. apiece.

CPS provided TZC a template to aid in pinning the 350-ton tubs to the piers, and mating has gone smoothly as a result. The first tub was picked by the 1,699-ton capacity “I Lift NY” Super Crane in April 2015. “They set their template up and it went down like nothing,” Ogorchock affirms.

Mixing & Testing

TZC boosted mix production capacity to pace New NY Bridge contract requirements and serve future work, adding a second BHS twin-shaft mixer to an existing model for split batching, and bringing peak output to 500 yd./day. Actual volume could be higher if not for a 90-second mixing requirement from the NYS Thruway Authority, as the mixers have produced concrete exhibiting 95 percent homogeneity within 30 seconds in tests. CPS crews pumped mixes into the forms for the pier cab tubs; for all other jobs, concrete is transferred from the plant into a fabrication enclosure in 4-yd. tubs carried by forklifts.

For the initial load and every 50 yards throughout the TZC contract, slump tests and compressive strength tests were performed, using 10 cylinders per batch. A full-time NYS Thruway inspector remained on site to oversee testing. “The concrete reach[ed] 6,500 psi in as little as 24 hours, eventually hardening to 10,000 psi,” says CPS Senior Project Manager John Pridgen.

Infrastructure Improvements

The pier caps have been staged about a dozen at a time near the water by a 400-ton rail crane purchased in never-used condition from NASA. “We widened it 10 feet and converted it from electric to hydraulic power, and added remote ground control,” Ogorchock says. Nine hundred feet of steel track was laid so the crane could transport the caps from production to a new 78- x 250-ft. load out slip. CPS’s barge, “Gayle Force,” rated at 3,700 tons for ocean travel and purchased several years ago for another job, has transported all precast units to the TZC project. Fully loaded with eight pier caps, the barge takes 2-½ days to reach the Hudson River construction site.

CPS has 195 employees at the Chesapeake location, of whom 30 have been tasked with TZC contract work. Across the fabrication window, Pridgen calculates that crews placed nearly 11,000 yd. of concrete for the tower pier soffits, anchor pier soffits and pier caps.

Pennsylvania-based Ken Stadden specializes in business-to-business marketing communications, and prepared the New NY Bridge report on assignment from BHS-Sonthofen Inc.

RIGHT COAST ARRIVAL

The I Lift NY Super Crane was purchased used and brought east from California, but remains registered with the Coast Guard as the Left Coast Lifter. TZC joint venture partners American Bridge and Fluor Enterprises had it built in 2008 to work on San Francisco Bay Bridge re-decking. Its heaviest pick to date has entailed a 600-ton precast concrete pile cap, to be followed by lifts of 900- to 1,100-ton members. I Lift NY will get more work when demolition of the original Tappan Zee Bridge commences in 2018. The equipment has a 1,699-ton lift capacity and 328-ft. main boom. A second crane, The Hank Hummel (see Concrete Products, August, page 32), named after an early Traylor Bros. vice president, plays second banana to the super crane, but is being used more consistently during construction. At 750-ton capacity, the Manitowoc 4600 is mounted with a ringer attachment welded to a 225- x 70-ft. crane barge, making it more versatile than I Lift NY, which doesn’t swivel.