The
era of the signature building may very well have ended on Sept.
11, 2001.
Two different
attack sites in two different cities—one with its buildings
arranged vertically, in celebration of America's towering supremacy,
the other horizontally, crouched symbolically in defense—have
posed two very different challenges for the rescue teams at work
there. And after the rubble is cleared, they will provoke two
very different responses from architects and engineers.
The twin
World Trade Center towers provided a large amount of office space
on a relatively small plot of land. The risks inherent in such
a design became dramatically clear on September 11, not so much
during but after the airplane attacks, when the towers succumbed
to the heat and collapsed upon themselves.
The Pentagon,
by contrast, is an example of how millions of square feet of office
space can be constructed close to the ground. The building continued
to burn two days later, but the weight of the rest of the structure
did not bear down on the affected area. Firefighters were able
to tackle the blaze right away—even if with the wrong equipment—rather
than remaining helplessly on the street, 80-odd stories below
the point of impact and the resulting conflagration.
The Pentagon
will very likely be restored to its full geometry long before
any decision is made about what to do with the land on which the
World Trade Center once stood. Indeed, the terrorist attack on
the towers may well mark the end of new skyscraper construction
for the foreseeable future.
Computer
and other models can test a design's strengths and weaknesses—thereby
obviating many potential disasters—but sometimes it takes
a life-changing event to demonstrate a structure's true vulnerabilities.
Just as the 1986 explosion of the space shuttle Challenger—the
haunting images of which came to mind again last week—led
to missions being postponed until the spacecraft was redesigned
with improved safety features, so, too, new skyscrapers will probably
remain on the drawing board until their designs have been reconsidered.
It is not
that structural engineers cannot build tall buildings to withstand
the impact of an airplane. That they could was proved as long
ago as 1945, when the Empire State Building survived being struck
by a bomber flying off-course in fog. The World Trade Center attacks
demonstrated that even newer, taller buildings can take the impact
of large aircraft. What the twin towers could not survive was
the ensuing inferno fed by enormous amounts of jet fuel.
Can any skyscraper
be designed to stand up to what the World Trade Center towers
could not? Perhaps. Most super-tall buildings are made of steel,
but other materials are more fire-tolerant. The concrete-lined
Channel Tunnel connecting England and France was able to withstand
a horrendous fire in 1996. Nontraditional structural materials,
such as ceramics, might someday provide the framework for new
fire-resistant skyscrapers. And current research into nanotechnology—the
manipulation of structures on the atomic scale—might in the
distant future yield new materials suitable for building toward
the sky. But ceramics are much more brittle than steel, more susceptible
to snapping under impact; and nanotechnology is still in its infancy.
Furthermore,
the engineering of tall buildings involves much more than just
structural materials. Tall buildings present enormous problems
in vertical transportation when fire breaks out, for example,
and elevators stop working. In the wake of the 1993 World Trade
Center bombing, people had to find their way down dark and smoke-filled
stairwells, which called attention to the importance of evacuation
plans. Kuala Lumpur's twin Petronas towers, the tallest in the
world, are concrete structures, completed in 1996 with a sky bridge
between them—an alternative exit from the highest floors.
The World
Trade Center tragedy is likely to affect future building plans
in even more fundamental ways. What business will want to rent
space in a new skyscraper if the very word evokes images of airplanes
flying into the upper stories and deaths numbering in the thousands?
Will employees be constantly on the lookout for a surprise attack?
Will clients want to visit an office in which they fear they may
be trapped?
Then there
is the question of why anyone would want to build in the heavily
populated city at all. Now that the Internet and World Wide Web
have provided the means for efficient and instantaneous communications
throughout the world, there is a diminished need for compact contiguous
space. There may no longer be any reason to build super-tall structures,
raising above surrounding rooftops the most easily recognizable
and tempting targets for terrorists.
The era of
the signature building may very well have ended on Sept. 11, 2001,
and America's skylines—as well as many others around the
world—may remain for the next several decades as they are
today. It is not likely that the competition to build the world's
tallest building will draw many participants while terrorists
are the architects of disaster.
Henry Petroski, A.S. Vesic Professor of Civil Engineering and
a professor of history at Duke University, is the author of "Remaking
the World: Adventures in Engineering."
Reprinted
from the Washington Post
