Parking deck collapse is a puzzle for engineers
Parking deck collapse is a puzzle for engineers
Parking deck collapse is a puzzle for engineers
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<strong>Parking</strong> <strong>deck</strong> <strong>collapse</strong> <strong>is</strong> a <strong>puzzle</strong> <strong>for</strong> <strong>engineers</strong><br />
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<strong>Parking</strong> <strong>deck</strong> <strong>collapse</strong> <strong>is</strong> a <strong>puzzle</strong> <strong>for</strong> <strong>engineers</strong><br />
By Leon Staf<strong>for</strong>d<br />
The Atlanta Journal-Constitution<br />
Wednesday, July 01, 2009<br />
On the surface, designing a parking <strong>deck</strong> seems a simple business: four walls, some ramps, painted spaces and<br />
tons of concrete and steel.<br />
But structural <strong>engineers</strong> say the design specifications of a parking garage are just as exacting and important as<br />
those <strong>for</strong> a 100-story signature building. Even using the wrong size bolt on support beams or changing the angle of<br />
a joint can one day reduce a parking <strong>deck</strong> to concrete pancakes.<br />
Monday’s partial <strong>collapse</strong> of the Centergy parking <strong>deck</strong> on 5th and Spring Streets in Midtown drove that message<br />
home as officials began to turn their focus from the recovery of crushed vehicles to why the structure caved in.<br />
David Tyndall, head of Gateway Development, which owns the <strong>deck</strong>s, told WSB-TV Wednesday the floors<br />
<strong>collapse</strong>d because a “spandrel” beam — an exterior beam that extends from column to column and marks the<br />
floor level between stories — “popped out.”<br />
What Tyndall couldn’t explain <strong>is</strong>, what <strong>for</strong>ced the spandrel beam out.<br />
That d<strong>is</strong>covery will be critical, structural engineering experts said. <strong>Parking</strong> lots, like most structures, are “overdesigned”<br />
to handle weight that <strong>is</strong> much more than designated, to allow <strong>for</strong> increased stress and to allow <strong>for</strong> small<br />
m<strong>is</strong>takes during construction.<br />
“In the design phase, we try to allow <strong>for</strong> some tolerances,” said Roberto Leon, a professor of civil engineering at<br />
Georgia Tech. For instance, an engineer may allow <strong>for</strong> a floor to be off-plumb by one-quarter to one-half inch.<br />
“We design <strong>for</strong> a stronger structure than it ought to be,” he said.<br />
But beyond that, deviation from the design specifications — choosing a less expensive bolt or using a support<br />
designed <strong>for</strong> a different weight — can lead to devastating consequences, experts said. “All of a sudden, the<br />
details of a connection become important,” said Tom Leslie, director of external affairs <strong>for</strong> the Georgia<br />
Engineering Alliance.<br />
For precedent, Leslie pointed to the 1981 walkway <strong>collapse</strong> at the Hyatt Regency in Kansas City that killed more
<strong>Parking</strong> <strong>deck</strong> <strong>collapse</strong> <strong>is</strong> a <strong>puzzle</strong> <strong>for</strong> <strong>engineers</strong><br />
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2 of 3 7/2/2009 5:37 AM<br />
than 100 people and injured 200 others at a hotel dance. The builder deviated from the original engineering design<br />
that called <strong>for</strong> beams and rods to support individual walkways suspended above the floor below. The builder<br />
constructed beams that supported several walkways simultaneously, which eventually gave way under the stress<br />
of the partygoers.<br />
“People live and learn from failure,” Leslie said.<br />
The challenge in the Centergy <strong>collapse</strong> will be in solving what experts see as an anomaly. Generally, they said, a<br />
garage will <strong>collapse</strong> either during construction, within its first year of use or when it’s older and deteriorating.<br />
The Centergy <strong>deck</strong>, however, was fin<strong>is</strong>hed in 2004, a short five years in operation. It had not been inspected since<br />
receiving its certificate of occupancy that year. City officials said they had received no complaints about the<br />
structure, which <strong>is</strong> the only way another inspection would have been prompted.<br />
Leon said inspections can be cost-prohibitive. “The <strong>is</strong>sue <strong>is</strong>, who bears the cost of doing that and who <strong>is</strong><br />
responsible <strong>for</strong> doing that,” he said.<br />
Other structures get more attention. The state Department of Transportation, which has built bridges over<br />
countless creeks and rivers using concrete, requires that its inspectors re-examine all of them at least once every<br />
two years. Inspectors are directed to a wide range of <strong>is</strong>sues including the condition of bolts, connecting plates and<br />
concrete, and problems like cracks or rigidity.<br />
So what happened in Midtown? Danielle Kleinhans and Steven Smith of Illino<strong>is</strong>-based CTL group, which<br />
investigates <strong>collapse</strong>s, said they would look <strong>for</strong> signs such as changes in the use of the structure or the load it was<br />
expected to support. Re-striping to accommodate more cars, maintenance activity or moved heavy equipment<br />
could suggest changes that had an unexpected impact.<br />
“It’s wide ranging,” Smith said. “Sometimes it can be construction-related. It could be rein<strong>for</strong>ced steel was placed<br />
incorrectly during building to the [point of] deterioration.”<br />
Others pointed to other possibilities — soil erosion, stress on concrete panels, shallow spandrel beams that made<br />
the structure “roll” a bit more than it should have.<br />
“When <strong>engineers</strong> design these types of structures, they design <strong>for</strong> worst-case scenarios,” said Claude Goguen,<br />
director of technical services <strong>for</strong> the National Precast Concrete Association. “It could be one thing or it could be<br />
a combination of things.”<br />
He said precast concrete <strong>is</strong> used in a majority of parking lot projects — especially in areas where it <strong>is</strong> cold —<br />
because it saves cost and time.<br />
“The bottom line <strong>is</strong> it’s very unusual that there are any [precast] problems,” he said. “Concrete continues to get<br />
stronger all the time. Most of the time, it <strong>is</strong> a very, very reliable material.”<br />
Atlanta-based Hardin Construction Co., the lead contractor on the project, pledged Monday to “make ourselves<br />
available” to investigators looking into the parking <strong>deck</strong> <strong>collapse</strong>. Hardin was also the builder of a walkway that<br />
<strong>collapse</strong>d last year at Atlanta Botanical Garden that killed one and injured 18.<br />
Metromont Corp., which built the Centergy garage, said in a statement Tuesday, “Metromont has an unwavering<br />
commitment to quality building construction. Our professional <strong>engineers</strong> participate in and support the continuous<br />
quality improvement programs of the Precast/Prestressed Concrete Institute. All construction <strong>is</strong> per<strong>for</strong>med in<br />
accordance with its publ<strong>is</strong>hed specifications and in strict compliance with the International Building Code.”<br />
Metromont has operated <strong>for</strong> more than 75 years and has projects in 25 states, including the other parking garages<br />
at Atlantic Station, the World of Coca-Cola and at the University of Georgia, which said Wednesday it <strong>is</strong><br />
inspecting all its garages in wake of the Centergy <strong>collapse</strong>.
<strong>Parking</strong> <strong>deck</strong> <strong>collapse</strong> <strong>is</strong> a <strong>puzzle</strong> <strong>for</strong> <strong>engineers</strong><br />
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— Staff writer Ariel Hart contributed to th<strong>is</strong> report.<br />
Find th<strong>is</strong> article at:<br />
http://www.ajc.com/metro/content/metro/atlanta/stories/2009/07/01/<strong>collapse</strong>_why_<strong>engineers</strong>.html?cxntlid=homepage_tab_newstab<br />
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