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Can a prototype skyscraper made entirely of composite materials survive the post-9/11 mania for safety?
By Christopher Hawthorne
February 2003
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Architect Peter Testa's proposed new skyscraper--the form of which draws
from architecture, advanced engineering, material science, and
purpose-built software--would be supported by woven carbon fibers.
Courtesy Peter Testa Architects
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In October of last year Peter Testa--a 50-year-old architect who has worked
for Alvaro Siza, taught at MIT and Columbia, and now runs a small firm
in Southern California--headed back east to take part in an invitation-only
conference in Cambridge, Massachusetts. Sponsored by Cap Gemini Ernst &
Young's Center for Business Innovation, the two-day gathering brought together
30 corporate leaders, academics, and scientists from around the country.
Their charge, as the no-nonsense conference materials put it, was to "sense,
capture, and communicate signals that point to imminent change and to examine
nascent shifts that will come to transform all aspects of economic activity."
It seemed a perfect forum--freewheeling, speculative, and full of very smart
people--for Testa to talk about a project that first seized his imagination
about three years ago and has not let go since. The project is a prototype
40-story skyscraper made entirely of composite materials, mostly carbon
fiber. Such man-made composites, which also include better-known materials
like fiberglass and Kevlar, are increasingly used in industry and for
consumer goods--in everything from airplane fuselages to tennis rackets--because
they are strong, lightweight, and easily molded into an almost endless variety
of shapes. They're also slowly making their way into highway bridges and
other civil-engineering projects.
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The double-helix design (above) of the perimeter leaves interiors open,
so the usual central core is replaced by a distributed system of ramps
and elevators.
Courtesy Peter Testa Architects
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Although the materials seem well suited for architecture--in tension, carbon
fiber is five times stronger than steel--their use in buildings
has been rare. Testa, though, is convinced that composites will radically
transform architecture during the next decade or two. His carbon skyscraper,
which he likes to describe as a "woven building," is designed
to be not just less muscle-bound than the skyscrapers in which Americans
work today but also more beautiful, environmentally friendly, and cheap
to build.
At the conference Testa gave a short presentation that included renderings
of the tower. He told the group about the preliminary computer testing he's
done of the building's structure and materials with help from the New York
office of the engineering firm Arup & Partners and from CTEK,
a Santa Ana, California-based prototyping company. When Testa turned
to the audience he was expecting to field general questions about the
design and properties of the materials. He got something else.
"Everybody started asking, 'What if a plane flies into it?'"
Testa recalls. "At first I was resistant to frame the project
entirely relative to the World Trade Center. After all, we began it long
before September 11, and here we were more than a year after. But people
really thought I should be ready to explain what would happen in that kind
of situation. And the more I thought about that, the more I agreed."
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In this new approach to building construction the primary structure
would be woven from carbon fiber (above) and all the components,
including ramps leading to a typical office floor (below), would be
manufactured from composite materials.
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Courtesy Peter Testa Architects
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Before his trip to Cambridge Testa wasn't exactly naïve about the profound
changes the September 11 attacks had brought about in the way Americans
think about skyscrapers. He understood that he'd chosen an odd time to be
peddling a revolutionary new design for a tall building. But he never guessed
that a group of specialists gathered specifically for their talent
in looking boldly forward would focus on the collapse of the Twin Towers
at the expense, it seemed, of all other issues.
The comments also reminded Testa of a more general trend he found disturbing.
"There's been a real backlash," he argues, against new approaches
to structural engineering since September 11. "Everybody in the press
seems to be calling for very strong and robust-looking construction, like
the Empire State Building, with tight structural grids and thick, heavy
columns. I haven't read anything to suggest that maybe what we need instead
is new materials that will behave differently and better."
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Spiral ramps (above) offer both emergency egress and lateral bracing. As
this section (below) illustrates, the interior space is open, allowing for
displacement ventilation throughout the building, which minimizes energy
consumption. A lightweight resin membrane replaces the traditional curtain
wall.
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Courtesy Peter Testa Architects
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All of which leaves Testa in an odd position. The good news for him is that
during the last year and a half the public has developed strong, even passionate,
ideas about how skyscrapers ought to look in the future. The bad news is
that Testa's open and airy design is precisely not the sort of thing they
have in mind.
Testa's carbon tower is the product of ongoing research in computer-aided
engineering and material science; as a result, its design seems to change
on a weekly basis. But the basic form is not especially complex. Imagine,
first of all, a cylindrical building 40 stories high. Then picture
that cylinder strung together by 40 carbon-fiber strands, about 1 inch
wide and nearly 650 feet long, that are arrayed in a helicoidal, or crosshatch,
pattern. Filling in the structure between floors is an advanced glass
substitute (Testa's current favorite is called ETFE, a kind of transparent
foil). A pair of ramps on the exterior of the building offers circulation
and further stabilizes the structure.
That, in simplified form, is the carbon tower. Perhaps the most striking
thing about it is that every major element in the building, including the
floors and the exterior ramps, is made of some kind of composite material--there
is no steel, concrete (apart from the foundations), or conventional glass.
Yet just as important is the structural use of continuous carbon strands,
which are woven to form a structure that distributes its loads over its
entire surface. (Most contemporary skyscrapers use steel or concrete, or
both, in compression.) Taken together, the building's innovations open up
the potential for what Testa calls a new "organic minimalist aesthetic"--a
building whose surface and structure are one and the same.
The 24 strands will be fixed into shape by something called a robotic
pultrusion machine, which Testa envisions climbing up the structure like
a spider and weaving the strands on the side of the tower as it's built.
"You just bring a bundle of fibers and some plastic to the site,
and then you manufacture the building right there," he says. "Each
of the strands will have its own machine."
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