The CBC ran a story on Moncton engineer Hélène Thériault, who owned MATCH Engineering, and was fined, and lost her license for professional incompetence. She and her firm are also subject to at least 14 lawsuits over badly designed buildings.
The TLDR of the story was that when cracks formed in a new build slab, the building owner hired a new engineer to review the work. That engineer found the slab to be under designed, which they reported to the regulator. That complaint prompted a review of other buildings that the first engineer had worked on. As a result of that review, 22 buildings required emergency shoring, and permanent repairs to strengthen them.
From various articles that were written, it appears the majority of the involved builds are what are commonly known as 5 over 1’s These are a 4 or 5 story wood frame building constructed over a concrete parking garage, where the roof of the parking garage serves as the first floor slab. A transfer slab is hick, heavily reinforced concrete floor that redirects heavy vertical loads from upper columns to a different, unaligned column grid on the floors below. The transfer slab essentially works like a slab on grade, and carries the load of itself and the building above it to the walls and posts in the parking garage, and down to the soil under the building.
If the transfer slab were to fail, then the building above would fall into the garage. The seriousness of this cannot be overstated. This could have been a Surfside level event.
Surfside (a suburb of Miami FL) was a structural collapse of a condo building in June 2021, which killed 98 people. The investigation still has not issued its final report, but updates have indicated that an under designed and poorly built pool deck slab failed 40 years after construction, due to continuous overloading. The slab failure caused other parts of the sub structure to fail, bringing down a wing of the tower.
There were several warning signs in the weeks before the collapse, including new and larger cracks appearing around the pool deck, though the severity of the damage, and its potential impacts were all missed prior to the failure. While this was entirely a concrete structure, the initial failure mode is the same.
A modern concrete building is built with a 2 way spanning slab. Rather then having separate beams support the slab between the columns, the beams are integrated within the slab itself by increasing the amount of rebar. This has a number of advantages – its easier and faster to construct, and and it allows for consistent ceiling heights, without wasting space.
The problem with 2 way spanning slabs is that they can be prone to punching shear. Punching shear happens when the forces on the slab overcome the support of the column connections and they fail, causing the slab to collapse, and the columns remain standing. Punching shear often leads to large pancake collapses, where slabs collapse onto each other, leaving no voids, which makes survival unlikely. Punching shear would be a likely fail scenario for the transfer slab. Several photos of affected buildings show shoring posts around columns, which is exactly what would be done if there was concern over a punching shear failure.
There are 5 basic types of structural collapse. 4 of them generally happen in post and beam construction, where a wall or column fails, and the possibility of large void spaces exist. Given everything above the transfer slab in the affected buildings are platform framed wood structures, its likely a collapse would lead to void spaces in the normally occupied parts of the building. This is good, but significant loss of life would still be probable.
In this case 22 buildings were under built before this was caught. Since shoring was required in many of them, it suggests the structures were significantly under built, and could have been at serious risk of collapse.
Major Collapses in Canada
In 2019, the Lester B. Person civic centre Theatre in Elliot lake suffered a roof collapse, as a result of snow loading, and a newish hvac system that was installed on the roof. there was 1 minor injury. the building was demolished.
The Algo Center mall in Elliot lake suffered a partial collapse in 2012 after decades of water ingress caused a steal post and beam connection to fail due to corrosion, Causing a 40×80′ section of the roof to fall into the mall killing 2 people. The mall was built with a parking deck on the roof. it flexed, which allowed water ingress, which was never properly repaired, and was a constant problem over the life of the mall. This collapse and its response was the subject of a public Inquiry
The deadliest structural collapse in Canada occurred Sept 30, 2006, when a section of the Boulevard de la Concorde Overpass over Highway 19 in Laval (Montreal) collapsed, killing 5. The overpass dropped chunks of concrete onto the highway for at least an hour before it ultimately collapsed resulting in several 911 calls. an inquiry found that it was poorly designed and built, and used concrete that could not survive repeated freeze/thaw cycles and road salt.
In 1995, a section of roof of the Station Mall in Sault Ste Marie collapsed due to poor weds on a beam connection. The station mall was originally built by the same developers as the Algo Center mall, and used the same engineering firms. There were no injuries or fatalities and the mall reopened two months later.
The Burnaby BC Save on foods collapse occurred in 1988. At the stores grand opening, a 6400 square foot section of the parking deck collapsed into the store after a beam failed. The roof top parking was added during construction, and the added weight of cars caused an undersized beam to twist. Onset to collapse took 5 minutes, and there was sufficient time for shoppers to evacuate. there were no fatalities in this incident.