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Flat Slab Collapse in Windsor, Ontario, Canada

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Even if the boom lift did initiate this collapse, I'd say the cause is serious understrength.
There wasn't much spare capacity there, collapse would have happened anyway, sooner or later.
Rebar corrosion would have to be a suspect.
 
Agreed, the lift was probably the straw the broke the camel.

I've parked on that structure several times (my favorite thai restaurant is out front). I've never thought that the workmanship of the concrete looked very good. Should be interesting to see how this one turns out.
 
My eyesight is not as good as it used to be, but I can't see any reinforcement through the columns.

BA
 
I'd be thinking real hard about the other portion across the access road to the lower story that has not failed...yet - the one where the cars can still be driven off!

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
 
That's not the same one, Doug. That failure was some time ago, and was also discussed here.
 
Oh, sorry.

I thought it didn't look quite right, but with the yellow painted columns and Canadian location I thought it must be the same one.

Doug Jenkins
Interactive Design Services
 
There does seem to be a bit of a pattern. Canada, flat plate punching shear, parking structure, asphalt topping...
 
I wonder if the AC topping was an after thought, the weight not being incorporated into the original design.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
 
Isn't there a professor from a Canadian University that leads the way in punching shear reinforcement. I have just specified propriety stud-rails on a flat project that I am working on.
 
More info, the structure was built in 1948. From what I can gather, I think the adjacent level has been roped off, and the three buildings have also been evacuated.

asixth, you are probably speaking of Dr's. Dilger and Ghali out of the University of Alberta, they developed stud rails back in the 80s, and since they have been marketed throughout the world. They also developed the code equations used in the canadian concrete code for punching shear reinforcement.

the canadian code is actually pretty far along compared to ACI when it comes to punching shear, due to Dilger and Ghali's research being accepted there first. Although being built in 1948, this one obviously predates that..
 
If constructed in 1948, then it was designed using the older Working Stress Design and there is added safety for flexure and for shear in the method. In addition, I would have thought that there would be corrosion issues. The area uses a fair amount of salt de-icer and there could have been some degree of exfoliation of the concrete surface as well as reduction in steel area. There could have been added toppings to increase the dead load.

Dik
 
Looking at the top of the columns, I don’t see the failure cone that we assume in a two way shear check, i.e. d/2 from the face of the column. The failure plane here is exactly the perimeter of the column. Doesn’t that mean shear reinforcing would not be useful?
 
Good question, Ailmar, and I think you are right. The first thing I thought of in looking at those photos was that the columns may have been poured too high, reducing the slab depth. Punching shear has been studied to death, but I still don't believe in reinforcing against it. Using depth, better concrete, and larger effective perimeter are the better paths to take.

In the 1948 structure which failed, a lot of things could have contributed, including overloading, poor concrete, poor construction practice, deterioration due to salting, the list goes on. This appears to be a flat plate, and in 1948 I think this type floor was uncommon and perhaps ill understood by some. Flat plates in the early days were primarily used in lift slab construction.
 
The 50 psf live load we design for in these garages always seemed intuitively too light to me.

And now we've skinnied it down to 40 psf. A few inches of asphalt overlay and most of that's used up.
 
JLNJ... the 50 psf is adequate for cars and most trucks (not big ones) and some jurisdictions have reduced this to 40 psf. Realistic normal loading with vehicles parked bumper to bumper, and in all the drive isles as well as parking spots will yield a load of between 15 and 20 psf. A typical car space is about 300 sq.ft. Design loading is OK...

Dik
 
From what I can see, the whole portion of slab (with vehicles still in same relative positions)went down in one shot. With the boom/lift at one end, it is interesting that the complete slab appears to have collapsed. With the lift creating local concentrated loads, you would not expect that. So I agree it was probably the 'straw that broke the camels back', and led to a progressive, quick collapse. The date of the structure, lack of reinforcing, design (at that time), corrosion etc. created a scenario where punching shear was unfortunately illustrated as a textbook case. I am actually going to Windsor this afternoon for a family function and if I can sneak out.....might have a look.
 
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