Edited. sorry for Miami Herald paywalled article. It seemed free when I first opened it. Others are clear I believe
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Partial collapse of false Mansard roof at 17500 NW 68th Ave, northwest Miami-Dade County, Florida
- Thread starter AusG
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There's a picture illustrating the method that was used for the Mansard:
It appears there was a concrete wall built up to the height of the roof, with some sort of shelf inside to hold the roof rafters. The lower 40% of the Mansard could/should have been attached to it. The remaining 60% of the height was a stud wall placed on top of the concrete.
Some of the weight was returned with diagonal 2x's landing at the bottom of the concrete section. That would then appear to be the "point of rotation" for the assembly. I believe the only thing that was preventing that (or not) was the 90 degree "return walls" on the roof.
I don't see much evidence of significant attachment to the concrete to provide an anchor against the rotation.
But the Authority Having Jurisdiction thought it was fine........
spsalso
It appears there was a concrete wall built up to the height of the roof, with some sort of shelf inside to hold the roof rafters. The lower 40% of the Mansard could/should have been attached to it. The remaining 60% of the height was a stud wall placed on top of the concrete.
Some of the weight was returned with diagonal 2x's landing at the bottom of the concrete section. That would then appear to be the "point of rotation" for the assembly. I believe the only thing that was preventing that (or not) was the 90 degree "return walls" on the roof.
I don't see much evidence of significant attachment to the concrete to provide an anchor against the rotation.
But the Authority Having Jurisdiction thought it was fine........
spsalso
spsalso - that's a pretty common cantilevered truss detail. It isn't a 2x4 wall - it's part of the truss. It's stepped to produce a bearing seat so the vertical reaction is taken in bearing on top of the concrete wall while a connection at the base of the truss and the connection at the top of the wall take lateral forces as a couple to resist the moment and hold it in place (prevent rotation)
You're most welcome - and thank you.
The problem with this kind of truss is that the connections are concealed. You're relying on the roof and flashing to keep water from getting in there and rotting out the wood at the connectors. In a building with lots of water issues...yikes. Used for the front canopy on a shopping center with a vented soffit with access panels isn't that big of a deal since it's easy to inspect. But 30 to 40 feet off the ground? This is probably the first time anyone has laid eyes on those connections since they were installed 45 years ago.
The problem with this kind of truss is that the connections are concealed. You're relying on the roof and flashing to keep water from getting in there and rotting out the wood at the connectors. In a building with lots of water issues...yikes. Used for the front canopy on a shopping center with a vented soffit with access panels isn't that big of a deal since it's easy to inspect. But 30 to 40 feet off the ground? This is probably the first time anyone has laid eyes on those connections since they were installed 45 years ago.
That mansard probably wasn't considered "critical". And the results of this collapse sort of prove that point. Could it have been terrible if somebody had been on that balcony or walking out of a door or along the building? No question. But does its failure compromise the building's stability? No, it doesn't. I'm not saying that's correct, but I can see a sort of rationale behind it - particularly in a world where buildings around 40 to 45 years old don't collapse and kill scores of people (which was the world where this one had its 40 year review).
I'm not familiar with the 40 year review process. Anyone out there have any insights? (It's probably been covered in the Surfside thread, but I'm not going to sift through 1200 some odd posts to find it.)
I'm not familiar with the 40 year review process. Anyone out there have any insights? (It's probably been covered in the Surfside thread, but I'm not going to sift through 1200 some odd posts to find it.)
Oh. Why them instead of an electrical contractor? I believe electrical contractors have thumbs.
I would also think it more direct if the city/county hired those "subcontractors" directly. They, after all, are the ones who want this information--why not just go get it? Lack of money is a valid point, but I expect things like a "special inspection fee" would easily cover that.
spsalso
I would also think it more direct if the city/county hired those "subcontractors" directly. They, after all, are the ones who want this information--why not just go get it? Lack of money is a valid point, but I expect things like a "special inspection fee" would easily cover that.
spsalso
That mansard probably wasn't considered "critical". And the results of this collapse sort of prove that point.
Remind me not to hire anyone for any structural work who thinks that 100's of pounds of Mansard roof falling off or possibly falling is non-critical. In this case it was only due to luck that no-one was injured or killed.
Remind me not to hire anyone for any structural work who thinks that 100's of pounds of Mansard roof falling off or possibly falling is non-critical. In this case it was only due to luck that no-one was injured or killed.
- Thread starter
- #18
In this case the mansard looks like nothing more than a profiled cladding feature. Wasn't integral to the roof diaphragm or primary GFRS or LFRS. Granted, it has a very pronounced profile, so its design and connectivity warranted more attention on the engineering side than, say, corbeled brick veneer or a metal stud soffit.
That said, the failed mansard says nothing of the structure's stability or safety.
Glad nobody was hurt.
That said, the failed mansard says nothing of the structure's stability or safety.
Glad nobody was hurt.
apper.42 - that was my point. It was lucky. I also said that while that I disagree with that line of thought, I can see how somebody can justify it. I think Seppe did a much better job than I did explaining it than I did.
spsalso - if a PE signs off on the electrical side, then they're supposed to be an Electrical Engineer. Why not hire subs directly? Would you recommend somebody who has no idea how a building goes together hire a general contractor to build a new house, or try to hire each trade individually? Hiring a single entity to oversee the entire process simplifies things for the condo board and, ideally, ensures the right people are selected and coordinated to do the work.
spsalso - if a PE signs off on the electrical side, then they're supposed to be an Electrical Engineer. Why not hire subs directly? Would you recommend somebody who has no idea how a building goes together hire a general contractor to build a new house, or try to hire each trade individually? Hiring a single entity to oversee the entire process simplifies things for the condo board and, ideally, ensures the right people are selected and coordinated to do the work.
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