Masonry Wall 2

[bpstruct]

I'm working on a 2-story building project, and the architect is wanting to use an unconventional wall system. It is a combo 4-inch cmu, grout (2-inches) core, and brick. All would be tied together with wire ties. I don't like the idea, primarily because I'm unfamiliar with this kind of construction. And I feel like I would probably have to back into some method for checking strength that I'm not confident in. To complicate matters, one of the long walls is littered with overhead garage doors. So there are really short segments of wall...not sure how well these would work as shear walls - which I need. See attached. Any thoughts would be appreciated.

 

[oldestguy]

What does your building code require? Any tests first? What about corrosion potential? Those "wires" and possible corrosion staining problems? Similar use elsewhere?

 

[kipfoot]

I think you'll find some useful information if you search 'composite masonry wall'. There's the general material issue that concrete block shrinks and brick expands, but the NCMA has at least a couple items in their TEK series: TEK 16-1A and TEK 16-2B. (these are based on old codes)

Traditional multi-wythe walls were constructed with a row-lock course to tie the inner and outer wythe together, where you'd have steel reinforcing and a collar joint.

I think you're right to identify the large openings with skinny piers as the problem area.

 

[dik]

You'd think that Architects were better educted... Concrete block will shrink slightly over time and fired clay brick will expand...

Dik

 

[concretemasonry]

That is definitely a composite wall that resists the load totally and not with the individual wythes.

The 2" grout is just like a collar joint. The 8' to 11" grout should be placed every 4' of height. As the grout consolidates, the excess grout moisture is sucked into the masonry units creating a homogeneous or unified masonry wall. NCMA TEKS are a great references due to the NCMA research and panel testing that was done.

The people at the NCMA and the others (BIA, MCAA TMS, etc.) that wrote the current ACI 530 code/specifications also did the testing/research.

This method is certainly far superior to the old brick and block header system since a proper grout(8" to 11" slump) is used rather than slopping wet mortar into the irregular space.

Dick



Engineer and international traveler interested in construction techniques, problems and proper design.

 

[XR250]

CM,
Like others, I would be concerned about the differential expansion/contraction between the wythes.
What are your thoughts on this?

 

[concretemasonry]

The stresses in the fully grouted assembly are very small and distributed over a long period of time.

The "classic"/typical concerns about the different material properties are for the classic block/brick wall with the voids connected with wire. There is a limit is a limit on that type of construction that requires angle ledgers, just as you would uses with a reinforced concrete structur with a brick veneer (3 or 4 stories).

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[XR250]

The stresses in the fully grouted assembly are very small and distributed over a long period of time.

It still scares me. It is probably reasonable to expect the brick to grow 1/4" over a 20 ft. height. It seems unlikely the CMU can restrain that. So it would either crack the CMU or the wall would try to bow outwards.

 

[bpstruct]

Thank you all for the responses!

 

[hokie66]

XR250,

Some brick grows more than others, and you can only determine it by testing. But to avoid the problem, it would be best to use brick both faces. I don't like 4" CMU for anything.