By Mike McGraw, McClatchy Newspapers –
JOPLIN, Mo. — The Joplin Home Depot store, where seven people died May 22 when the building catastrophically collapsed during an EF-5 tornado, reopened Wednesday with a unique feature.
The new store, rebuilt much like the old structure, is the only Home Depot in the nation with a reinforced interior room made of precast concrete with a concrete roof, and that room can hold at least 150 people, according to plans filed with the city.
But Home Depot officials insisted it is not a storm shelter.
“We don’t hold our stores out to be storm shelters,” said spokesman Stephen Holmes. “It is a reinforced room. We felt it was appropriate given the events of the past at this store and the sentiment of the community.”
The store’s reopening featured a mostly upbeat ceremony with cheerleaders, a drum corps and speeches by Home Depot officials and Joplin Mayor Michael Woolston. The company also presented a $500,000 check to the Joplin Recovery Fund.
A plaque at the front of the store, however, was a somber reminder of those who died last year and is dedicated to “the future of rebuilding in their memory.”
Federal agencies and structural engineers hope to learn from the Home Depot collapse and other building failures resulting from Joplin’s devastating tornado, which killed a total of 161 people and destroyed 8,500 structures. Many of those studies aimed at preventing or limiting future tragedies are expected to be released this spring.
Engineers with the National Institute of Standards and Technology are studying drawings from the original Home Depot building and other so-called “big-box” stores where employees and customers were injured or killed. Studies by the Federal Emergency Management Agency and regional and national engineering groups also are under way.
The Kansas City Star reported in June that some engineers and tornado experts are concerned how such big-box buildings withstand tornadic activity. Many of those structures are built with heavy concrete or block walls tied together with a relatively lightweight roofing system. Previous post-disaster studies have shown that the roofing systems and roof-to-wall connections can be weak links that can lead to catastrophic failures.
While many such structures in hurricane-prone areas are required to sustain winds as high as 150 mph, the same buildings throughout tornado alley — including the new Home Depot store — must meet only a 90-mph standard.
No one knows for sure how powerful the winds were during Joplin’s tornado, but some estimates run as high as 200 to 250 mph or higher.
The Star in June also reported that some engineers have specific concerns about a construction method called “tilt-up” — used in the original Home Depot store in Joplin and elsewhere as well as thousands of other big-box buildings across America.
A young father, his two small children and four other people died at the Home Depot when the roof failed and the walls tumbled as a result of the tornado, crushing them beneath a 100,000-pound concrete panel.
Tilt-up buildings rely on a relatively economical process in which concrete wall sections are poured on the ground, then lifted into place and tied together at the top, often with a relatively lightweight roofing system.
Larry Tanner, an engineer and tornado expert from Texas Tech University, told The Star that he was “aghast” at the extent of the Home Depot damage. He said there are numerous issues with tilt-up buildings that should be addressed.
Tanner and other engineers interviewed said that if the local building code had required Home Depot to have stronger roof-to-wall connections, it might have sustained less damage, even in extremely heavy winds.
However, the Tilt-Up Concrete Association, which researches and promotes tilt-up wall construction, said Tanner unfairly criticized their industry, arguing that it’s no different than other big-box construction methods.
The association assembled nine engineers, including Jeffrey Needham of Lenexa, to study the Joplin collapse. Their report could be released to association members as early as next week.
But Needham said that their engineers found that the tilt-up panels themselves did not fail and there is nothing common to tilt-up construction that makes it any more vulnerable to tornadic winds than any other method.
“There are no smoking guns here, there is nothing flawed about tilt-up construction,” Needham said. “The collapse at Home Depot is as bad as you will ever see,” he added, “but the building was directly in the path of some of most intense stages of the tornado.”
Instead, Needham said the association’s investigation found that the failure point at Home Depot was its relatively lightweight roof system.
Eyewitness accounts indicated that the front entrance of the building blew off first. Once the building lost its enclosure, internal pressures increased rapidly, and the entire building began to “vibrate or pulsate,” then came down in a matter of seconds. Huge sections of all four walls collapsed — inward at the front of the store, where the tornado first hit, and outward at the rear.
Noting that pressures in the building were much higher than anyone would have predicted, Needham said, “this building initially failed near the center … the roof deck almost certainly failed where it was attached to the bar joists that support it.”
While the building complied with local codes, he said, those roof connections were almost certainly a weak link.
But Needham said the Home Depot roof system is “very typical” of other big-box systems nationwide. He said one area of concern for panel members was the welded connections between the metal roof deck and the joists that helped support it, adding that an alternative, such as self-tapping screws, might hold better.
The new Joplin store’s design, which city inspectors signed off on last week and granted an occupancy permit, is similar to tilt-up construction but allowed for quicker completion. However, the chain’s spokesman declined to give any additional details about the new building design, other than it was built to local codes, which as before, require the ability to withstand winds up to 90 mph.
“Our focus is on ensuring our stores are prepared to deal with these storms by getting customers to the safest area of the store, which saved more than 20 lives when the storm hit Joplin,” Holmes, the Home Depot spokesman, said this week.
Steve Cope, Joplin’s chief building inspector, said there were no post-tornado changes to local codes affecting such buildings, and that drawings indicate the roof of the new building is similar to the one in the original structure.
Wayne Lischka, an architectural engineer hired by The Star to examine the building’s plans, said the new Home Depot appeared to be more sturdy.
“This new design concept will make a stronger structure for normal wind loads. It is not reasonable to design a structure to take a direct hit by a major tornado,” Lischka said.
Whether codes are ultimately toughened or not, shelters or hardened rooms may be the most economical solutions to the weaknesses in such buildings, according to many engineers and such groups as the Tilt-Up Association.
In a message on the association’s website, executive director Ed Sauter noted that design changes on new buildings to meet such extreme events are unlikely because of the high cost.
“But that doesn’t mean we should ignore the problem,” he noted, adding one option might be a “safe room” such as the one at the new Joplin Home Depot.
