Elliot Lake: Algo Centre Mall Roof Collapse

On June 23, 2012, the town of Elliot Lake, along Highway 108 in Ontario was struck with a horrific disaster, the partial collapse of the roof structure of the Algo Centre Mall. The roof section, part of the parking deck section of the structure collapsed through the room and food court area down to the ground floor of the two story main building. The collapse injured more than 20 people, and resulted in the deaths of two people where were buried in rubble for four days before being found by rescuers. The remains of the mall will be demolished, and a new shopping centre is currently under construction for opening in late 2013. Over the intervening months since the collapse, investigations into the structural design, monitoring, and approvals of the mall have been regular pieces in the news, and class action lawsuits are also in the works.
Reports from investigating engineering firms have shown continual negligence which led to the accident, and are drawing attention to the threats of under-design and shortcuts to get in a low bid. Investigations have shown that the cause of collapse was the structural failure of a welded joint in the steel framing of the lower parking level, immediately above the second shopping level of the four storey building. The weld was severely corroded by salt water leaking through the concrete slab floor of the parking level, a design consideration that would seem to be an obvious issue in the Canadian climate.
A waterproofing system was designed for the structure but it was grossly unprepared for the conditions present, and was ultimately a significant contribution to the failure. The parking level consisted of precast hollow concrete slabs measuring eight inches deep, four feet wide, and commonly up to 30 feet long, which were then laid on steel beams. Design calculations required the slabs to withstand loads of up to 120 pounds per square foot, but the slabs were not rated for that kind of loading by the manufacturer unless a composite concrete top layer was also applied. The engineer from the concrete company that eventually won the bid for the project and built the slabs also stated their system could support the 120 pound loads (despite their company specs stating that the maximum capacity was 87 pounds per square foot). Despite all this confusion, a concrete top layer was put in as part of the construction – but for the purpose of waterproofing the system, not for structural stability.
While it wasn’t the actual concrete that failed in the collapse, the realisation that the slabs could be under-designed led to the decision to not fix the waterproofing system. It was feared that increasing the concrete layer used for waterproofing would overload the already strained flooring system. Unfortunately, this decision led to rapid deterioration of the steel structure beneath the floor, to the point where inspectors analyzing the debris described many of the steel boats as being so corroded that they resembled something from a “marine environment”. This kind of damage should have been noticed in inspections done year after year within the building, but every person who toured the building gave the structure a clean bill of health. Troubling images from before the collapse show tarps permanently installed in the anchor Walmart store to control constant leaking. How this was not identified as a concern is a worrying mystery. Structural testing submitted by NORR Ltd. stated that the welded steel connection that failed had deteriorated to the point where it could only support 13% of its original capacity.
The investigations into this tragedy are still ongoing, and new developments seem to being coming up every few weeks. The engineers involved showed gross negligence over the course of the years the mall was open to the public, and the incident has severely damaged the opinion of the professional integrity involved. While there are many opinions and reports around describing the way local’s complaints were completely ignored, there is also the problem of engineers who advised action (increased waterproofing, alternate parking structures, in-depth structural testing) but it was never carried out by the owner.
Every licenced engineer takes the responsibility for human life into their hands, and incidents like the Elliot Lake Algo Centre Mall show the serious consequences that can come when that responsibility is neglected or the message behind it ignored. While new regulations for building inspections are now coming out as a result of the collapse, this is an tragedy that could have been prevented, and should have been.