Foundation for Brick Veneer - vertical extension ok? 1

[MCurry]

I'm working on a 4 story bldg with exterior gage steel studs. Brick veneer runs from the foundation all the way up. Per ACI 530-02, 6.2.2.3.1.3, the height limitation for the veneer above the foundation is 30 feet, with veneer supported by relief angles at each floor above 30 feet.
Here's the rub. The veneer is double thickness for the first two stories. The inner wythe at the lower stories is 4" CMU. The concrete foundation extends up to the top of the first story (steel studs above that point).
The contractor argues that the CMU can be considered the foundation, so that the full height, single thickness veneer is less than 30 feet above the 'foundation' and no relief angles are required.
Can the 4 inch CMU be considered an vertical extension of the foundation this way? It makes some sense to me, but I'd like to get some feedback.

Thanks

 

[haynewp]

It sounds like he is trying to avoid putting in the angles. I have never heard of 4" cmu being called a vertical extension of the foundation.

 

[civilperson]

If the reinforcing is made continuous from the concrete into the 4" CMU with solid grout fill, then the CMU is part of the foundation.

 

[JAE]

But reinforcing 4" CMU with grout is very questionable - very small spaces. Also, the CMU "foundation" would, in my view, have to be self supporting to be considered a foundation. If the 4" CMU has lateral ties back to studs then that is simply anchored veneer per the code.

 

[MCurry]

All,
Thanks for looking at this. I'm in agreement with haynewp and jae. If the 4" cmu was to be a couple of feet high, I could justify reinforing it and calling it foundation. Of if I had solid masonry walls behind, I'd grout the collar joint and call it good. But in this case, I think I'm going to call for the relief/shelf angles.

Do any of you know the rationale behind the height limitation? Is it differential movement? Any links to industry/code docs that discuss the rationale?

Thanks again.

 

[csd72]

Dont try and play with loopholes in the building codes unless you are confident that it will actually work. We are engineers not lawyers.

The reason that the relief angles are installed is to allow for the expansion of the bricks as they absorb moisture. The higher the wall is without the relief angles the higher the differential between this expansion and the shrinkage of the concrete/timber backing.

This would mean that your veneer ties would not be horizontal and would not act as they are designed. Also in extreme cases it would cause cracking in windows e.t.c.

Get the builder to put these in or you could be blamed for any serviceability issues in this wall.

 

[haynewp]

You may already have this:

http://www.bia.org/BIA/technotes/T18a.pdf

 

[concretemasonry]

csd72 is correct.

Clay brick has an irreversible long term expansion. This is opposite to other materials that have srinkage or creep, especially under loads. Iy you were dealing with concrete brick, the situation does not exist.

The reason for the angles is to keep the exterior veneer in approximate vertical alignment with the structure. The typical problem down the road is usually evidenced at the upper part of the building where difference in height is the greatest. Wall ties have been known to break and leaks at windows are common.

To me, calling the 4" CMU backup a foundation is a stretch, unless there is something I do not see.

Proper use of the angles is prudent.

Dick

 

[MCurry]

Thanks to all. Good link haynewp - I'd looked at other tech notes, but somehow missed that one.
The Shelf angles are in.

 

[dik]

concretemasonry raises a very valid point about the expansion of clay brick products and the shrinkage of the concrete backup. I've done a few reports regarding brick masonry cracking for this very reason.

Dik

 

[jike]

Indeed, the clay brick will take on moisture and will expand vertically. This is, generally, incompatible with the shortening, creep or shrinkage of the backup structure or adjacent CMU. Relief angles in brick are required to prevent cracking or other damage.

 

[twinnell]

Sorry I am chiming in so late, but doesn't the height limitation only apply to either wood stud backup or light gage stud backup? ACI 530 doesn't put a limit on CMU backup. Please correct me if I am wrong.

 

[MCurry]

I agree twinnel. With CMU or concrete backup, there's no height limit. I've got steel stud backup once I get above the lower (garage) level.