Joplin Home Depot building design under scrutiny
Tuesday, June 28, 2011
JOPLIN, Mo. (AP) — A Home Depot store that was leveled by the deadly tornado that ripped through Joplin last month was especially vulnerable to catastrophic damage because of the way its walls were constructed, according to engineers who studied the aftermath of the May 22 twister.
At least seven people were killed when they took shelter in the Home Depot store as the tornado bore down. A popular construction method called “tilt-up wall” met city building codes, but it proved deadly in the extreme conditions when the giant concrete walls fell like a row of dominoes, The Kansas City Star reported over the weekend.
The design is used in thousands of warehouses, stores and schools across the country, but engineers believe it has weak links that often fail even in winds much less severe than those that hit Joplin.
“Once you lose one (wall) panel, then the dominoes all start to fall, so the failure becomes increasingly more catastrophic,” said Larry Tanner, a tornado expert and part of a team of engineers that traveled to Joplin to study the Home Depot collapse and other building failures for the Federal Emergency Management Agency. “I was aghast at how extensive Home Depot’s failure was.”
In tilt-up wall building, the structures are erected with concrete walls that are poured on site and lifted into place with cranes. The walls are held upright by critical connections to a relatively lightweight roof system.
Some engineers interviewed by the newspaper said building codes for big-box stores need to be strengthened, or the stores should have internal storm shelters when they’re built.
Across the street from the Home Depot, at least 200 people survived the storm in a Walmart when they huddled in the store’s safe area, a concrete block structure containing break rooms, restrooms and a customer service area. Three people were killed inside that store.
Home Depot officials originally told the newspaper that they were so confident in the tilt-up wall design that it would be used again when they rebuild the Joplin store. A few days later they said they would be using a different design similar to tilt-up construction that would allow quicker completion and still meet local building codes.
The company said it also would install a storm shelter, making the store the only Home Depot in the country with that feature.
The death toll from the Joplin tornado stands at 156, making it the most deadly U.S. tornado in 60 years. The twister cut a three-quarter-mile wide swath through the city, destroying roughly 8,000 homes and more than 500 businesses.
Tim Marshall, a meteorologist and engineer with Haag Engineering in Irving, Texas, said many local building codes are not good enough. But Joplin officials have steered clear of making them so overly restrictive that they sharply raise building costs and could force companies to locate somewhere else.
“This year I have seen so much carnage, and so many people who died who did not need to die,” Marshall said. “These strong tornadoes are no match for those kinds of safety rules.”
Joplin Fire Chief Mitch Randles said two other box stores in the same area, including the Walmart, were built of concrete blocks instead of tilt-up walls and didn’t sustain the same amount of damage as the Home Depot.
“Academy Sports’ roof is missing, but their walls are still standing, and most of what was missing at the Walmart was the roof,” Randles said. He added that the Home Depot took a direct hit from the tornado, but he wasn’t sure if the other buildings did.
Joplin city officials have discussed requiring fairly inexpensive changes to the local building code, such as metal reinforcing to better hold a home’s roof to its walls and beefed-up concrete block foundations. But they’ve not indicated whether they will require any major code changes, arguing they do not want to institute requirements that would be costly to homeowners and drive businesses away.
Missouri Gov. Jay Nixon said after the tornado that it could prompt discussion of stronger statewide building codes and other measures to protect the public. But he questioned whether codes could be written to prevent the kind of destruction that hit Joplin.
Marshall said it all boils down to what kind of risk a community is willing to accept.
“It’s acceptable risk in the center of the country,” he said. “We are at the mercy of building codes, and that is 90-mph winds, and anything above that, all bets are off.”
Information from: The Kansas City Star, http://www.kcstar.com