Metrodome Collapses In Minneapolis

I like when science and sports meet...just an FYI article

http://www.scientificamerican.com/artic ... afe&page=2
Tearing into the Metrodome: Are Other Air-Pressurized Stadiums Unsafe and Outmoded?
Conventional air-pressurized stadiums such as the Metrodome, whose inflatable roof collapsed under the weight of snow in December, are rare in the U.S.--and may be accidents waiting to happen
By Laurie Wiegler | January 20, 2011
What happened in Minneapolis

At the Metrodome last month, the main problem was the weight of the snow, says civil engineer Dario Gasparini of Case Western Reserve University. The Metrodome's roof—which is Teflon-coated fiberglass and weighs approximately 265 metric tons—is inspected every three years by tensile structure contractor Birdair, Inc., in Amherst, N.Y. About 5 A.M. on December 12, one of the roof's triangular fabric panels located on the west side of the building ruptured and "then it appears that then the roof started to come down—and then sequentially two adjacent (diamond-shaped) panels failed," Maki says. "We had an additional diamond panel rupture suddenly on the Wednesday night [December 15] after initial deflation."

"Finally," he says, "we had a diamond panel that was extremely loaded that we knew could fail any time. The inner liner has drain holes which were not lining up with the outer fabric so the panel was not draining as we heated the building. We attempted to drain it by shooting the lowest point with a shotgun slug; however, that action caused the panel to rupture anyway."

Although investigations are ongoing, Maki says the first panel tear was "obviously" snow-related, and then a shift of strain to the center of the dome caused the next two ruptures.

Larry Griffis of the American Society of Civil Engineers and principal engineer with Walter P. Moore, an engineering and consultancy firm in Houston, has been retained to investigate the Metrodome incident, but is not allowed to comment. He says, however, that Geiger—whom Griffis called a "brilliant" engineer—would have agreed that air-pressurized dome technology is outdated.

Even though such structures have advantages—particularly, being lightweight, of high strength and low cost—maintaining such facilities is not nearly as attractive as it was a couple decades ago.