Cantilevered vs. Simply Supported CMU wall? 1

[AnimusVox]

So,

I'm an EI and I just finished working on this small (about 10' deep x 10' tall x 16' wide) CMU enclosure to be added onto the side of an existing building. (It's basically an outside storage area for this retail store) Anyways, after I did my calcs I handed it over to a co-worker to glance over it and one of their marks was to analyze the walls & footing as a cantilevered system for the period of time in construction where they've built the wall and haven't attached the roofing to the top yet.

I've never done that in any other masonry structure and I'm really curious when others have taken the same approach.

Small note: the roof diaphragm consists of 3" deck that span from clip angles anchored into the existing wall spanning 10' onto the CMU wall.

Thanks!

EDIT: Thanks for the replies everyone.

 

[Teguci]

There should be something in your general notes that states that your design is for the final configuration and construction loads are the responsibility of the contractor. I would think this is more of a temporary bracing issue that the contractor needs to provide and not a final structural issue that needs to be in your design.

 

[msquared48]

You must be talking cantilevered for forces normal to the plane of the wall. If that is so, I would agree if the wall was not to be shored for a long length time before the roof diaphragm was added.

For the forces in the plane of the wall - lateral shear loads to the CMU wall as a shear element, however, it would be cantilevered, as opposed to fixed, anyway.

Mike McCann, PE, SE (WA)

 

[sandman21]

If you design the wall to span 10'-0" you would not need to check in the one direction as its 10'-0" as well. Typically we have notes about the responsibility of the contractor as Teguci stated. If you dont check the 16'-0" wall to span between intersecting wall walls. You wont need larger footings or change wall reinforcing.

 

[JAE]

We always assume what Teguci writes above.



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[KootK]

X4 for Teguci's approach. If you designed the wall as a cantilever, you'd need to design your footings to resist overturning to be consistent. You won't find may owners willing to foot the cost for that instead of simply temporarily bracing the walls.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[msquared48]

Very True...

Mike McCann, PE, SE (WA)