When a documentary crew wanted to film the emergency glow-strips that line the expansive stairwells in 7 World Trade Center, Dara McQuillan called down to the security desk and asked them to flick off the lights. Moments after the stairwell went dark, however, a backup power system switched on and ruined the shot.
Mr. McQuillan, vice president of communications for the building, called again, but when the security desk shut down the backup system, this time a battery-powered generator flooded the stairs with light. The crew never got its dramatic glow-in-the-dark shot.
It has been hailed as the safest building in the world, its 52-stories of glass elegance belying a concrete core built to be a bunker in the sky. It is the first skyscraper to be completed at the World Trade Center site, and as it approaches its second anniversary, its innovative architecture and endlessly redundant security features – most of them designed from the lessons of the Twin Towers catastrophic collapse – offer a template for high-rise buildings in a post-9/11 world.
"The biggest change in high-rise construction now is this sealed, hardened core," says Dr. Herb Hauser, president of New York-based Midtown Technologies, a firm that specializes in security technologies for
buildings. "This means that the structure around the core can go down, or be on fire, or be invested with a biological or chemical problem, but the actual core itself will be protected." [Editor's note: The original version incorrectly stated that Dr. Hauser worked with architects designing new buildings for the World Trade Center site in New York. He didn't.]
At least three skyscrapers under construction that will surpass the height of the world's tallest building, Taipei 101 in Taiwan, are using the concrete-core technique (as well as a number of others under proposal in Russia and Korea). Indeed, the 1,776-foot high Freedom Tower, the anchor of the World Trade Center site, will in many ways simply be a larger version of the adjacent 7 WTC. The Chicago Spire, at 2,000 feet high, and Burj Dubai, soon to be the tallest building in the world at a staggering 2,700 feet, will also each have hollow concrete spines anchoring floors that will cascade and twist around them.
Making buildings with a concrete core isn't a new idea, but the cost of constructing them in the past has been prohibitive. "The main drawback at one time was that a steel frame was so much faster to build," says Mir Ali, professor of architecture at the University of Illinois at Urbana-Champaign. "It took you approximately three to four days to build a steel-frame floor. With concrete, it used to take 10 to 14 days a floor."
But with advances in construction techniques – better and cheaper concrete, more powerful pumps, easy-to-assemble slip and fly forms – crews can now put up a concrete core as fast as a steel frame. Moreover, very tall steel-frame buildings like the former World Trade Center towers and the Sears Tower often shimmy and sway in the wind. The top floor of a concrete-core high rise is as solid as a first-floor lobby.
And yet, since such buildings are, in part, towering symbols of power and strength, and therefore important symbolic targets, the question persists: Will tenants want to work in them? Ellis Rubinstein, president of the New York Academy of Sciences, the first organization to sign a lease at 7 WTC, recalls a number of board members and employees who were wary of working in a high rise at the site. "But the reverse was also quite true, actually. There was a great deal of pride that we were standing for the revitalization of the area," he says.
In addition to 7 WTC and the Freedom Tower, Larry Silverstein, the leaseholder of the site, is planning three more massive skyscrapers in the area. "Larry's big gamble in building over 7 million square feet of office space without tenants is that people will soon want more out of their buildings," says McQuillan.
Old Wall Street buildings, forming the "canyons" of 1930s-era high rises, often choke off the signals for legions of BlackBerrys, and just aren't built for the high-tech business needs of today. In 10 years, Mr. Silverstein believes, Wall Street firms will head a few blocks west to Greenwich Street, near the World Trade Center site, leaving the historic business district to the luxury loft renovators. But first he must convince them these state-of-the-art buildings are state-of-the-art safe.
The sense of security architects tried to build into the hollow spine of 7 WTC, which has tenants on 30 of 42 available floors, starts with the glow-strip lined stairs. Stadiumlike in size, the stairwells allow a space where evacuees can rest or the wheelchair-bound can wait for assistance. They are also pressurized to force out smoke, and engineers have incorporated dual standpipes and extra water storage for the sprinkler system.
But beyond the concrete core, 7 WTC has a host of other security features. The building's skin is made almost entirely of glass, and since the foundation is designed like a diamond parallelogram, the structure gives off a crystalline appearance – hardly the look of a concrete bunker in the sky.
The glazing process incorporates new bomb-resistant technologies into the glass that eliminate flying shards – and actually shield the structure from an explosion, deflecting the energy of a blast. Windows are double-paned, laminated, and layered with a new plastic polymer. The windows near the lobby are reinforced with inner cables that would, like a rubber band, absorb a blast and snap back.
The lobby features another use of "new" glass. A 65-by-14-foot art installation behind the reception desk doubles as a bomb shield for the elevator lobby. The installation has two laminated glass walls. Each wall is a series of vertical panes that tilt inward, like a giant hinge, and spring back in the event of an explosion. Designed by James Carpenter and conceptual artist Jenny Holzer, the display flashes illuminated poetry and prose.
"It's quite robust in its strength, although it's relatively delicate in terms of its visual presence," says Mr. Carpenter, a sculptor and architect at James Carpenter Design Associates here.
Throughout 7 WTC, architects have tried to convey openness and optimism rather than a fortress mentality. Even the first eight floors, which are windowless and house a utility substation, are wrapped in a stainless-steel screen that glows a faint blue after dusk. The wall contains light sensors that create a drifting illumination whenever a pedestrian walks near it. "We're always trying to harness two things," says Carpenter, "performance and visual aesthetics."
Indeed, as four larger towers begin to rise at Ground Zero, architects in a post-9/11 world must balance safety with art, commerce, and community interests. "There's no doubt in anyone's mind that as they're building these towers," says Hauser, "somebody overseas is thinking about how to take them down again."