Wind on 12" Masonry w/4" Veneer 2

[EIT2]

Designing an exterior cavity wall consisting of 12" concrete masonry unit, 2" rigid insulation and 4" concrete masonry veneer.

To resist 20 psf wind, should the wall be designed as 12" concrete masonry, 16" concrete masonry, or 18" concrete masonry due to a 2" cavity?

The question is this: Can the 4" veneer contribute to the structural wall thickness, if properly tied with horizontal, ladder-type, wire reinforcing.

Thank you!

 

[DaveAtkins]

The wall should be designed as 12" CMU. The wall ties cannot develop enough shear capacity, especially across a wall cavity, to make the wall composite.

DaveAtkins

 

[TFL]

I agree!! the wall should be designed utilizing only the width of the cmu portion.

At service loads the veneer probably contributes something to the stiffness of the wall. However, at the design loads the ties could not transfer the required sheer to develop composite action

 

[cap4000]

First, the 4 inch veneer must be able to withstand the 20 psf wind load through the ties to the 12 inch CMU. IF the cavity was real small and or filled solid essentially the "collar joint" would justify a composite wall design. Your situation clearly calls for only the 12 cmu inch to stand alone. P.S. The minor additional strength obtained from the tied back brick veneer would be your insurance against any potential cracking. Good Luck.

 

[CSEllc]

The 12" CMU wall should be designed to resisit the wind load. Adequate ties should be installed to transfer the wind lod to the 12" wall.

 

[CABaker]

20 psf is less than 1 kPa in SI, which is typical in some cases but low in terms of lateral load failure. Is this a URM section? Have you considered 8'' block with a little reinforcement?

More and more there is less call for cavity walls, just veneer with a block backup with the backup designed to take the full load. Even if you want to include the veneer as load resisting, if it is ever subject to a high wind storm and it cracks, you've lost a lot of its benefit for coupling with the backup, and you're back to a veneer wall.