"The foundations required isolation from the existing structure such that external vibrations were not induced into the test specimen and test vibrations were not transmitted to the facility," Thomas Lorentz, senior vice president with AEC Engineering, told ENR Southeast during construction.
The 7.5-MW rig required a 10-ft-deep concrete foundation, and the 15-MW unit needed a 13-ft-thick base. Supporting the 7.5-MW section are 40 35-ft-long steel shoring piles, 88 70-ft-long steel piles and an estimated 250 tons of reinforcement steel, ranging in size from No. 4 to No. 11 bars. For the larger test rig, 54 35-ft-long steel piles and 115 75-ft-long concrete piles form the base, along with 650 tons of reinforcement steel.
For the concrete placement, only self-consolidating concrete would work, says Chris Palmer, Choate's project manager.
"With that amount of rebar, it would prove impossible to get traditional concrete and vibrators down 13 ft and know you have a solid foundation," says Palmer. Concrete contractor Cooper River Contracting, which had used the method on another area project, sold AEC on the approach.
Without that method, "I don't think we would've gotten [the foundations] built," Palmer adds. The 7.5-MW section required 880 cu yd of concrete, while the larger one consumed more than 3,600 cu yd.
Also, due to the height of the existing building, the piles' depth required crews to modify the pile-driving rig to drive the piles 20 ft at a time. "We would then have to full-pin moment weld the next 20-ft section, which took about three hours per weld."
By summer 2012, the budgetary impact of the redesigned foundation systems began to sink in with project officials and brought about another "significant redesign," Tuten says. To get back under budget, CURI was forced to eliminate the planned second-floor mezzanine, which accommodated offices. The team also had to settle for a more "industrial" interior aesthetic, instead of the originally planned high-end laboratory finish.
An even bigger challenge was getting the gearboxes for the test rigs into the building. The equipment was so much bigger than originally planned that only the smaller of the two units barely fit within the existing structure.
To accommodate the larger rig's installation, the contractors left unbuilt a roughly 20-ft-by-20-ft portion of the facility. That meant that installing items such as flooring and utilities, located in the easternmost portion of the building, couldn't begin until the 341-ton, 15-MW gearbox—the mechanical centerpiece of the test rig—was in place.
Once the gearbox arrived at the nearby Port of Charleston, it took roughly one month to get it in place. Says Tuten, "A 341-ton gearbox does not go anywhere very fast, and if it does, you're in real trouble."
Construction of the 15-MW test rig's load application unit (LAU) structure—the vertical structure that houses the gearbox and drivetrains—was another feat, requiring extreme tolerances. "There were hundreds of individual components that went into building these, all of which had to relate back to each other to within one-sixteenth of an inch in every dimension: X, Y and Z," Palmer says. Failing to meet tolerances would result in the drivetrains not aligning with the test rigs, he adds.