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Long-spans amplify the collaborative relationship between architects and engineers

By Sara Hart

“The Cabledome is technically not a tensegrity dome, because it relies on a continuous perimeter compression ring,” explains Geiger principal David Campbell. “Bucky’s tensegrity concept requires that all compression in the system be discontinuous. Bucky also patented a dome system that employed suspended, nested, annular frames, which he called the ‘Aspension Dome.’ In Bucky jargon, the Geiger Cabledome is really a tensegrity-type Aspension Dome.”

Geiger’s first long-span, cable-stiffened, pneumatic dome was the U.S. Pavilion at Expo 70 in Osaka (Davis, Brody & Associates; DeHarak and Chermayeff & Geismar). With a clear span of 465 by 265 feet, it was an engineering marvel. And at a cost of only $4.50 a square foot, it was economical. Inflated from the interior, the entire roof was held in tension and weighed only 1.5 pounds per square foot, compared with the Houston Astrodome, built five years earlier, which weighed in at a relatively hefty 30 pounds. Only four materials were needed for the primary structural system and enclosure: steel cables for the roof, which are attached to a reinforced-concrete ring beam, which is set into an earth berm, and, finally, vinyl-coated fiberglass fabric. The use of this particular fabric represents an early example of technology transfer. Geiger helped show off American ingenuity at the expo by choosing fire-resistant fiberglass developed by NASA for the roof.

His cable-stiffened dome for the fencing and gymnastics arenas at the 1988 Olympics in Seoul was a marvel as well. Here, he finally got away from the air-inflated domes, which rely on mechanical equipment for their structural integrity. Campbell reminds us that pneumatically supported structures can and do deflate: “The most significant was the Pontiac Silverdome deflation in 1985 due to snow, followed by a wind storm that resulted in almost all the roof fabric being ‘lost.’ ” At Seoul, Geiger lowered the roof profile, simplified the cable system, and delivered two self-supporting structures with 393-foot and 295-foot diameters at only $20 per square foot.

Spanning greater distances in more innovative ways has been a preoccupation of engineers and architects ever since—from the Georgia Dome (1992, Thompson, Ventulett, and Stainbeck; Matthys Levy; Weidlinger Associates) to the Millennium Dome (1999, Richard Rogers; Buro Happold) to the Eden Project (2002, Nicholas Grimshaw & Partners; Anthony Hunt Associates; Arup) [record, January 2002, page 92]. Not all long-span roofs are tensegrity types, as evidenced by the three projects shown here, but they all share some ancestry with the Fuller and Geiger. While these three examples boast the tag line of “world’s largest” in their respective categories, they also illustrate the harmonic convergence of architecture and engineering in exciting new ways.