Stantec Architecture was stumped, having gone down several dead ends trying to design a system to manage the 48 ft of flexible conduit in the crawl space under FLEXLAB's rotational green-systems test building in Berkeley, Calif. The team worried about the conduit slack, which allows the turntable to rotate without ripping out the electrical service, snaking around on the concrete slab and getting tangled up or damaged.
Without a solution, construction had begun on the $15.7-million FLEXLAB, which stands for "Facility for Low-Energy Experiments in Buildings." Finally, Geoff Adams, Stantec's project architect, approached mechanical engineer Tony Zavanelli, a Stantec principal.
Zavanelli—who engineers building mechanical systems, not widgets—saved the day. He devised a trolley-in-a-tray system that, like a lawn hose as it retracts into a reel, manages the flexible conduit. "The cable never slides. It is always going across a rolling surface, so there is no external wear," says Zavanelli.
The system—which was engineered with assistance from the 64-ft-dia turntable's fabricator-erector, Metalset Inc.—consists of an 11-ft-dia conduit guide ring attached to the underside of the turntable framing; a 20-ft-long steel tray attached to the crawl-space slab; and a trolley with a drum that moves back and forth in the tray. The drum is a horizontal cylinder with four sections, one for each conduit.
As it rotates with the turntable, the guide ring moves the trolley by means of a chain drive. The conduit slack loops halfway around the drum and either collects in the tray or is spooled out to the guide ring, depending on the direction of rotation.
The guide ring is made up of four rolled-steel angles, one for each conduit. The conduits wrap and unwrap around the guide ring as the building rotates.
At the zero point of rotation, there are no conduits wrapped on the ring. The zero point is the maximum slack position, with all the conduits in the tray—half in the bottom and half above—looped around the drum on the trolley, which is at the far back end of the tray, away from the guide ring.
As the building slowly rotates clockwise away from the zero position, the conduits are pulled around the guide ring, which, by means of the chain drive, simultaneously moves the trolley and drum forward in the tray, releasing the slack cable. The motion continues to the 270˚ point of maximum rotation, when all the conduits are wrapped around the guide ring, the trolley is in its fully forward position, and the slack is entirely out of the tray. The system works in reverse as the building rotates counterclockwise back toward zero.