On the day the world Trade Center fell, the Empire State Building once again became the tallest building in New York City. In the months that followed, six of its commercial tenants ran off. They did not want to be in the tallest anything, anywhere, anymore. At a time when U.S. Vice President Dick Cheney was still being shuttled around to undisclosed locations, skyscrapers suddenly seemed like the most disclosed locations of all bull's-eyes with nice lobbies attached. Within weeks of 9/11, Donald Trump canceled plans to make his new apartment-office tower in Chicago the tallest in the world. It didn't help that the U.S. economy was turning south at the same time, leaving empty space in office towers everywhere. For a while, it looked as though the tall building, at least in the U.S., might be one more casualty of war.
Three years later, big is beautiful again. On July 4, New York Governor George Pataki and New York City Mayor Michael Bloomberg presided at the groundbreaking for the Freedom Tower, the office building that will rise at the World Trade Center site. New skyscraper projects are under way once more elsewhere in the city and around the U.S. Meanwhile, outside the States, where the taste for tall buildings never really abated, the skyscraper has also been poking its head up in very different ways, and not just for reasons having to do with security. Since the early '90s, tall buildings have been reshaped by a roster of global architecture stars whose vision is finally beginning to penetrate the more conservative American market.
Some of the best examples of that rethinking now fill two large galleries of the Museum of Modern Art's temporary outpost in Queens, New York City. Using 25 spectacular architectural models (some more than 4 m high), "Tall Buildings," a show that runs at moma through Sept. 27, looks at the ways in which the skyscraper has evolved since the early '90s, at least in the hands of its most gifted practitioners, the kind who are proposing and, hey, even producing, but usually in other nations buildings that don't resemble the bland boxes that crowd most American downtowns. Nobody wants to summon back the naive techno-optimism of the 1950s and '60s. All the same, spend an hour at moma, and you can't resist gathering these buildings into an imaginary skyline as sexy as anything from TV's space-age Jetsons cartoon. Remember when the future was fun? Perhaps it still is.
But scary fun all the same. After 9/11, skyscrapers first have to be places where people can feel comfortable on those high, exposed floors. Military-style security has re-entered the thinking of civilian architects in a way not seen since the Middle Ages, when every castle was a castle keep both a courtly residence and a defensible perimeter. Maybe no one has worried about security issues with more intensity than David Childs of the firm Skidmore, Owings & Merrill, the architect chiefly responsible for the final design of the new Freedom Tower. (That was supposed to be Daniel Libeskind, but that's another story.) "Like jazz, the skyscraper is a true American invention," says Childs. "Yet America is no longer a leader in the technology of high-rise buildings." He wants the building not only to symbolize rebirth at the Trade Center site but also to demonstrate that American thinking and construction can compare with the best new examples in Europe, Asia and elsewhere.
Probably the most ingenious thing about the Freedom Tower is how it manages to lay claim to being the tallest structure in the world without actually obliging anyone to work at its highest altitudes. Its offices stop at the 70th floor. Those are then topped by a tall "wind farm" an unpeopled latticework of windmills that can provide as much as 20% of the building's electrical power. If the building is constructed as envisioned, rising from that will be a spire that reaches the record height of 1,776 ft. (541.32 m), in honor of the year the American colonies declared their independence from Britain.
Down below, in the occupied floors, the building will incorporate a whole spectrum of new, post-9/11 defensive features. Exit stairways will be wider and will open directly onto the street. There will be dedicated stairwells for use by fire fighters. Air filters will block chemical or biological agents. The building "core" the part surrounding elevators, stairwells and safety systems will be solid concrete, not steel girders of the kind at the Trade Center that were easily sliced by the intruding planes. "There are many ways," says Childs, "that this building is responding to the exact event that caused the tragedy."
For its main structural support, the Freedom Tower will also employ an increasingly popular triangular-grid trusswork. From a defensive standpoint, structural strength, even more so than fire safety, is the most important consideration for tall buildings. "A square is not a geometrically stable shape," says Childs. "A triangle is stable because it has a diagonal." The Trade Center towers fell because intense fires eventually melted their interior steel. But their structural systems permitted both towers to remain standing after the initial impact of massive jetliners. So for the new 52-story headquarters of the New York Times, the architect Renzo Piano agreed to reinforce the connections joining columns on lower floors to support structures above called outrigger trusses. If a blast severs the columns, the floors above could still hang from the trusses.
But engineering isn't just what military strategists call a force enhancer. In the right hands, it's also a path to new kinds of beauty. Just look at Piano's diaphanous London Bridge Tower, a slender glass pyramid that forms a glistening stalagmite against the old city's skyline. The MOMA show is co-curated by Guy Nordenson, a well-known structural engineer, and Terence Riley, the museum's chief curator of architecture and design, who says he decided to do it after seeing the first Spider-Man. ("That was the first time since 9/11," he says, "that I saw tall buildings without cringing.") You get a grasp of what ingenious engineering is all about from the London headquarters of the insurance firm Swiss Re, designed by Norman Foster. Even before it opened in April, it was known as the gherkin because it rises against the sky like a plump green pickle. (And yes, nobody has missed the more phallic interpretations.) It too has a triangular steel trusswork, a structural necessity that doubles as a twirling surface pattern. But the building's signal feature is the inclusion of large interior gardens throughout. "Those become the lungs of the building," says Foster. "They allow fresh air, light and views into the interiors." But there's a dematerializing spirit even in a building that didn't require new feats of engineering the Arcos Bosques Corporativo in Mexico City, an arched tower with a vertical slot down its center that lightens the building's mass and brings the sky itself into play. The Spanish designer Santiago Calatrava is by training both an architect and an engineer, and his new high-rise projects wear their engineering on their sleeves. Turning Torso, an apartment and office tower under construction in Malmö, Sweden, spirals suavely around its central core like a plug of twisted toffee, producing a form that looks stable and unified but also pliant, voluptuous. And for a condo tower about to go up in lower Manhattan, Calatrava breaks its mass into curving segments, residential packages that cantilever outward and carousel around and down the central core. When the building is completed, it could be an inspiration to American architects. "Not only did America invent the skyscraper," says Calatrava, "it invented the skyline." But American skylines have got a little dull. With some work, the world's architects might bring them back to a very tall standard.