After braving a "perfect storm" of construction challenges—including mucky conditions and seismic- and wind-load concerns—the builders behind Clemson University's first-of-its-kind wind-turbine drivetrain testing facility in North Charleston, S.C., have finally found safe harbor as the university prepares to begin commissioning.
"We had heavy loads on muck in a seismic area with flooding potential and high wind loads due to hurricanes on a brownfield site," says James Tuten, program manager for the Clemson University Restoration Institute (CURI), the project owner. Indeed, project officials would have been hard-pressed to find a more challenging site for constructing the roughly $100-million testing facility, which was financed in part by a $47-million Dept. of Energy grant using stimulus funds.
Adding to the challenge was the need to build the state-of-the-art facility—housing some of the world's largest equipment of its kind—within an existing structure, as required as part of CURI's sustainability mission of revitalizing historic and urban structures.
To retrofit the 1980s-era Navy warehouse to today's codes for wind and seismic loads, contractors first redid the existing building foundation. They installed 432 steel H-piles, ranging from 46 ft to 57 ft in length, and placed 980 cu yd of concrete. To beef up the vertical structure, crews added 1,200 tons of steel columns and beams.
Keeping it Steady
As a platform for testing drivetrain equipment, the heart of the center revolves around its two test-rig systems, which are designed to deliver 20-year-life loads to drivetrains within a roughly six-month span. Essentially, each of its two test beds is a "big vibrating piece of equipment," Tuten says, with each generating forces in an unsteady, cyclic fashion.
Moreover, the two test structures are among the most powerful in the world. The smaller of the two is driven by a 7.5-MW gearbox, while the larger features a 15-MW, 341-ton gearbox that is considered to be the world's largest. Designed as secured, independent systems, the rigs can simultaneously accommodate confidential drivetrain testing by competing manufacturers.
Whether working separately or simultaneously, the dynamos will produce "tremendous" dynamic loads, says Tuten. The two separate bays for these systems—measuring 26 ft by 86 ft and 50 ft by 100 ft, respectively—feature dynamic, independent foundations.
The engineer of record, AEC Engineering, opted for a complex system utilizing friction piles, which project officials believe is a first for this type of facility.
"We are unaware of anybody else who has ever built a dynamic piece of equipment on friction piles," says Tuten. He adds that the approach required extra analysis. "We couldn't let [the testbed] become a vibrator and watch it just vibrate its way down."
As independent, isolated structures, the test-bed foundations had to be able to avoid transferring any vibrations, explains Thomas Lorentz, senior vice president with AEC Engineering.
"The foundations required isolation from the existing structure such that external vibrations were not induced into the test specimen and that test vibrations were not transmitted to the facility structure," he says.