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Corrosion Weighed in Mall Disaster

Wednesday, June 27, 2012

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As two bodies were pulled Wednesday from the rubble of a collapsed Canadian shopping mall, reports painted a troubled history of salt seepage, corrosion, leaks and mold in the 30-year-old structure

The victims, who were not identified, had been trapped in the wreckage since about 2:20 p.m. Saturday, when a 40-by-80-foot section of the rooftop parking lot at Algo Shopping Centre in Elliot Lake collapsed, raining down tons of concrete and steel.

 The ceiling where Saturday’s collapse occurred also suffered a collapse in February, when this photo was taken.

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The ceiling where Saturday’s collapse occurred also suffered a collapse in February, when this photo was taken.

The roof section smashed into the mall’s second floor, part of which then crashed through to the first floor.

The rooftop section that failed was a parking area for customers and mall staff. A witness said cars had fallen through the roof near the escalators and some were hanging inside.

Officials said the two victims recovered Wednesday were expected to be the accident’s only fatalities, although many more had originally been feared.

More than two dozen people were in the food court area before the collapsed area. About 22 were treated for injuries at area hospitals.

Complaints and Inspections

Built in the 1980s, the mall has been the subject of multiple complaints about leaks and mold in recent years, according to Ontario’s Ministry of Labour.

Ministry inspectors visited the site six times in the last three years due to complaints about leaky pipes, a leaky roof, mold and an unsafe escalator, The Canadian Press reported.

In 2009, the ministry issued a stop work order related to inadequate training in the use of a skyjack lifting device to paint structural beams outside the mall, the newspaper said.

The entire piping system was being replaced while an inspector visited in November 2010, the ministry said.

Another inspection followed in January 2011, to confirm completion of that work. On June 1, 2011, an inspector visited again on the basis of a complaint about leaks and mold.

 Rooftop lot immediately after the collapse.
A photo supplied to several news organizations shows the rooftop lot immediately after the collapse.

No violations related to that complaint were noted, but the inspector did issue two citations related to training violations of workers handling hazardous material and the reporting of the materials.

The most recent inspection occurred Jan. 11, 2012, in response to a complaint about the roof, but no orders were issued, the ministry told The Press.

Mall manager Rhonda Bear told Canada’s CBC News that repairs had been conducted on the building but not on the section that collapsed. She said that an engineering and structural study completed in May had turned up nothing unusual.

Corrosion Weighed

Initial speculation about the cause of the collapse has centered on structural corrosion.

A Queen’s University civil engineering professor told the Kingston Whig-Standard that rebar corrosion in the 30-year-old structure was a leading suspect in the factors that led to the collapse.

Because the roof served as a parking lot, corrosion could have been an even greater issue because of the salt used to clear the surface of ice during winter, said Professor Mark Green.

Green said it was also possible that the design of the building may have included an aspect that made it more susceptible to collapse, although he did not elaborate.

De-Icing Salt

Nalliah Thayabharan, of Building Experts Canada Ltd., noted in an online posting Wednesday that business owners in the mall were complaining about leaking water damage to their stores in 2009. One bank had to close temporarily to make repairs.

“Sudden failure of normal reinforced concrete is very rare,” wrote Thayabharan. “Provided regular inspections are made, the condition of the concrete can be observed and ongoing deterioration noted.”

Like Green and other experts, Thayabharan noted that because the roof was used as a parking area, freeze-thaw cycles and salt damage could have accelerated corrosion. In Canada, he wrote, “de-icing road salt” is “the most common cause of concrete deterioration.”

“Highly corrosive salt water reach[es] the steel reinforcing of the parking decks through cracks, and by permeating the concrete,” Thayabharan wrote. “Due to high amounts of salt, the reinforcing steel rusts. When rebar corrodes, the oxidation products (rust) expand and tend to flake, cracking the concrete and unbonding the rebar from the concrete.”

Thayabharan also notes that calcium chloride was once commonly used as an admixture to promote rapid set-up of concrete and in the mistaken belief that it would prevent freezing.

In fact, he adds, the practice backfired, because high concentrations of chlorides are now known to promote corrosion of embedded steel.

   

Tagged categories: Accidents; Commercial Buildings; Corrosion; Rebar; Structural steel

Comment from Mary Chollet, (6/28/2012, 2:44 PM)

Editor's Note: In the June 28 issue of PaintSquare News, the headline on this article incorrectly cites "painting" as a possible contributing factor to the mall collapse. Although, as the story correctly notes, a painting job at the mall was shut down temporarily in 2009, that issue has not been tied to Saturday's roof collapse. PaintSquare News apologizes for this error.


Comment from Glenn Summers, (6/28/2012, 3:14 PM)

Someone had to have been asleep at the wheel for a long time not to have seen signs of corrosion of a magnitude to cause a catostrophic collapse such as this. Where were the people responsible for maintenance and operation of this mall? A real waste of Life !!


Comment from jeff truman, (6/28/2012, 3:20 PM)

The roof structure is coreslab on steel beams - there is no reinforced concrete. The original design flaw is using coreslab in northern ontario - all the joints in the slab require sealants - and a double layer of them. Better would have been an RC slab, which would then receive a membrane. Failure was most likely at the bolts, which are higher strength and more susceptible to stress corrosion cracking, exacerbated by the salts. The joints in the coreslab line up over the support beams, and water constantly dripped onto the beams. (I grew up in Elliot Lake, am a structural engineer, and investigated the mall 15 years ago.)


Comment from Robert Gallant, (6/29/2012, 4:32 PM)

Concerning the collapsed roof of the shopping mall in Elliot Lake it is interesting that the media and others are not reporting the root cause of the failure. It appears by looking at the photo they used hollow-core post tensioned concrete panels as opposed to reinforced concrete. Hollow-core post tension slabs are generally used as structural units for roofs with proper membranes but should not be used in corrosive environments such a parking with high chlorides from road salts. The reason being is that reinforced concrete when subjected to over stress conditions due to loadings and corrosion will show distress by cracking and spalling first, good example see Montreal road infrastructure. Hollow-core post tension panels are less forgiving they are designed using small diameter tendons that have zero tolerance for corrosion, catastrophic shear failure will result


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