The Louisiana Superdome: What once served as a multi-purpose sports and exhibition facility in the central business district of New Orleans, will now be remembered as a “shelter of last resort” for those in the city unable to escape the clenches of Hurricane Katrina. In light of that, the question becomes, when all is said and done, will that historic landmark still be standing?
Constructed in the early 1970s, the Dome covers 13 acres (5.3 ha). It reaches 27 stories at its peak and rises 273-ft. (83.2 m) into the New Orleans skyline, forming the world’s largest steel construction room unobstructed by posts, filling more than 125 million cu. ft. (3,539,606 cu m). Approximately 20,000 tons (18,143 t) of steel and 150,000 cu. yds. (114,683 cu m) of concrete were required for its construction.
The Superdome was built to withstand most catastrophes. The roof — which measures 9.7 acres (3.9 ha) — was estimated to be able to survive winds with speeds up to 150 mph winds with 200 mph gusts. Flood waters, however, could still possibly reach the second level 20 ft. (6.1 m) from the ground, making the structure an unreliable shelter in severe wind and rain.
Survive it did. Even with her 145 mph winds, Katrina only managed to damage — not destroy — the Dome. Approximately 50 percent of the roof’s membrane was lost and some structural damage occurred where the original metal deck on the roof was sucked off in two locations.
“I think the building performed well considering it was a Category 4 Hurricane,” reported Larry Griffis, president of the structures division of the structural engineering firm of Walter P. Moore Associates Inc., of Houston, TX. “Some damage to the membrane is to be expected. In my opinion, the structural frame was never in doubt.”
Roof membrane is a single-ply membrane that apparently was a result of a re-roofing project in approximately 1988-1989, when a single-ply EDPM membrane roof was put on. The original roof was a fluid-applied elastomeric one.
“That is sort of the controversy,” Griffis, a stadium and wind design expert, said. “The district started to reconsider a new roof after 15 years. The roofing industry pounced on them, saying the building had an unconventional roof and a more conventional one should be considered. Consequently, an EDPM roof, a popular, single-ply membrane roof, was installed. For whatever reason, during Katrina the roof membrane pretty much got sucked off.”
According to Griffis, the other — fairly minor — structural damage involved some of the original metal deck. An approximately 20 by 5 ft. (6.1 by 1.5 m) section of the roof blew off in two locations, causing rain water to come in.
“That’s what scared everybody,” said Griffis. “Just because that happened didn’t mean the roof frame or the steel skeleton were in any danger. One of the characteristics of long-span roof design today is that wind tunnel studies are conducted. Using that model technique you can accurately predict what the wind pressures on the roof are for various levels of storms.
“The Houston Astrodome and the Superdome both used that same process. Knowing it was designed for 150 mph winds and that a wind level test was performed to determine the wind loads, gives me a great deal of comfort on the structural capability of that dome. I am confident that the Superdome’s roof is more than adequate with its steel skeleton frame to carry all those loads. I never felt the roof’s integrity was in question,” Griffis said.
When the Superdome was designed approximately 40 years ago the best wind design criteria for that time was employed. Since then, tremendous inroads have been made in building codes and wind tunnel studies have been refined. Griffis believes another structural analysis should be conducted using modern technology and software and new wind information, particularly if the facility is to be used as a hurricane shelter.
“It should be more of a design assessment because the state-of-the-art is much more advanced than it was in the late 1960s when the Dome was designed,” he said. “We have a greater knowledge of wind loads and what they do to roofs, what the loading patterns are. That all needs to be revisited plus the landscape has changed. The large number of high-rise buildings could impact how winds are felt on the roof. Even after conducting another assessment, however, I suspect the Dome will come out pretty good, but no one will know that until it’s done.”
The Louisiana Sports Commission currently is evaluating the Superdome’s damage. In addition to the exterior, the inside of the structure was flooded and there are millions of dollars worth of damage. It has to be decided whether to tear the Dome down, put considerable money into fixing it even if it’s not a state-of-the-art building or rebuild.
“The city has a lot of other things to spend their money on,” Griffis said. “There’s a major political question whether the entire city of New Orleans is going to survive. The Superdome is a small piece of that puzzle.” CEG