Imagination takes off in design of new SFO control tower

No Bay Area building shows the engineered reality of today’s architectural scene — or rather, keeps it under wraps — quite like the new flight control tower at San Francisco International Airport.

The first impression is effortless, a flared silver beacon topped by a glass swirl within which the controllers do their job. What we don’t see is the work behind the lyrical flourish: a concrete spine rising from a concrete mat 7 feet thick, concealed by the aluminum skin and topped by 75,000 pounds of steel weights calibrated to thwart high winds and earthquakes.

The expressive show brings a smile — it’s a vertical counterpoint to SFO’s sprawl of terminals and support buildings. But the hidden exertions deserve a nod, if only to remind us that it takes more than hitting the “print” button to conjure up architectural moves that look so easy on a computer screen.

The new tower, which SFO will hand off next month to the Federal Aviation Administration, is a 212-foot-tall shaft that pops from the narrow hinge between terminals 1 and 2. Its peak is only 42 feet higher than the current observation post from 1981. Where that vantage point is the stocky culmination of a broad administrative building, though, the newcomer is like a freestanding torch.

The upward motion is accented by the conceptual design from HNTB, which was completed by the design-build team of Fentress Architects and Hensel Phelps — the shaft tapers as it climbs, then widens at the crest. The metal skin uses angled vertical panels to emphasize the ascension all the more, with three-panel-high ventilation shafts near the peak.

Bracing all this visually is a central recessed “trunk” of opaque glass, its straight lines a counterpoint to the tailored curves — and the one hint of the actual bracing that goes on behind the scenes.

The rounded opaque skin hugs the concrete core within, a tube punctured only by the entries to the central elevator with fire stairs on either side. The tower is wrapped in steel cables and tied to the concrete mat, a foundation that in turn rests on piers locked into bedrock roughly 140 feet below.

Most of the funding for the $120 million tower came from the FAA, which needs a perch tall enough to take in all the runways at a glance and strong enough to shrug off a magnitude 8 earthquake. The shaft also must stand rigid, so that it doesn’t sway in high winds and make the controllers up top queasy. Hence the steel weights just below the crest: two dampers, each 37,400 pounds, one of them hidden in the ceiling above a break room, absorbing the pressures that otherwise would send the shaft whipping back and forth.

With all these requirements, it’s easy to imagine a brawny tower hulking over SFO, rather than the curvy cone sliding up into the sky. The efficiency with which the tall structure fits into the tight site is a tribute to the engineering firms involved: Walter P Moore, Rutherford + Chekene and Maffei Structural Engineering.

Deceptive? In some ways, yes. There’s also a stilted feel to the sculptural flow. Though cool beyond a doubt, the tower lacks the fluid ebullience of a gem like Frank Gehry’s Disney Hall in Los Angeles.

On the other hand, deception has been part of the architectural game going back centuries to all those churches with arches carved to look as though they’re being propped up by angels.

The important thing here is the effort that went into the make-believe. There’s real care in blending the different demands — even the need to drape a thin net of braided aluminum cables on the exterior, each leading to a slender spike. The FAA (understandably) wanted to lessen any chance of a lightning bolt causing damage. The design team made sure that as much as possible, the cables trace the edges of individual metal panels, hidden paths to lightning rods.

Benjamin Franklin would be proud.

Before construction began in 2012, architect Alejandro Ogata of HNTB explained how the flared form itself is a response to the narrow site and the control tower’s reason for being: “All the activities need to be at the top of the building, but nobody wanted a lollipop on a stick.”

Instead of a lollipop, or the funky glass nests that topped SFO in its days before the jet era, we have a slender torch that wants to be an icon. If it isn’t a landmark-in-waiting, it’s an ambitious piece of contemporary design showing us that unexpected architecture can enliven our surroundings rather than mess them up.

All in all, not a bad trade.