Wednesday, November 14, 2007

First take 862 large pieces of glass, individually cut so that each is unique. Connect them with steel, and the result is a glass canopy stretching 38,000 square feet, an area nearly as big as a football field without the end zones.

That's how large the new glass covering is over the courtyard shared by the National Portrait Gallery and the Smithsonian American Art Museum. The courtyard opens Sunday.

Building such a canopy might seem a fairly low-tech job. Not so. Without advanced computer technology, it would not have been possible, architects say.

The canopy seems to float 90 feet above the ground. Underneath are a new cafe, trees and other plants, and a stream one-quarter-inch deep that visitors can walk in or run their fingers through. The covering "looks curvaceous, but it's made out of flat things" (glass and steel) that had to be mapped out by computer model to fit together, says Dan Sibert of Foster + Partners, an architectural firm in England.

"Advances in computer technology are really the only thing that allows really complex constructions to be designed and . . . built," he says. Similar technology has been used to design cars and planes.

The courtyard project was "like connecting a vast piece of origami," Sibert says. Computers directed the cutting of each pane of glass and the making of the steel frame in Germany. The steel plant "was fun to visit," architect Graham Collingridge says, because of "all the sparks and red lights flashing" on the laser-cutter.

The pieces were shipped to the United States and trucked to Washington. The canopy was assembled upside down to make it easier for workers welding the pieces together. Having solid welds was crucial in making the canopy "perfect in all three dimensions," says Nancy K. Novak of Hensel Phelps, contractor for the project.

The canopy rolls through the air in a wave with three domes. The location of the valleys and domes, and thus the shape of each glass piece, was plotted out mathematically by computer. Every time the design changed, the computer code had to be rewritten.

It took about six months to develop the code, says Collingridge, but changes could be made in seconds because the technology is so sophisticated.

Doing the same work by hand would be "almost impossible," Sibert says. The drawings alone would take about 10 years.

Smithsonian officials didn't want the canopy to rest on either of the historic museums, so it is atop eight large columns with deep underground pilings that support its weight. The canopy's shape "is actually what's keeping it up," Sibert says. The pieces fit together like a jigsaw puzzle.

A scale model of the canopy was tested to see where snow would collect. Drains in the columns allow rain and melting snow to run off.

Builders like computer-assisted design because it saves so much time. The architects are "almost like artists" making shapes with computer code, Sibert says; behind it all is "an understanding of basic mathematical principles."

In other words, pay attention in math class!

-- Sandra Fleishman