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CMU filled cells as column support

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StrEng007

Structural
Aug 22, 2014
543
ACI 530 requires that masonry columns utilize a minimum of (4) vertical bars. However, it's common practice to use CMU filled cells as the vertical support at masonry openings. For example, imagine a corner condition where two beams are supported by (1) 1'-4" x 1'-4" x 8" CMU L-Shaped corner, fully grouted with (1) vertical bar in each cell (3 cells total).

Assuming those filled cells take the axial load and lateral wind from the attached fenestration, how does the (4) bar requirement get resolved. I've seen this in many corner conditions where the GC doesn't want to CIP.

Is that analysis based on the combined axial and lateral for a 16" wide strip of 8" CMU that is fully grouted? Is there any software to design these different arrangements?
 
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I would agree with your assessment that corners like that are really two, in wall pilaster rather than conventional columns and, as such, the four bar requirement can be circumvented. That said, in designing the two pilasters, one might take advantage of the fact that each will be significantly braced in the weak axis direction by the other.
 
KootK,
Would the approach be the same as a column design, ignoring the (4) bar requirement?

I still don’t see how this is actually code compliant, yet it’s located everywhere.

This condition is not a pier or pilaster.
 
Terminology is always a problem with this. I'd call what you're talking about either an in-wall pier or an in-wall pilaster. Either way, it's a local point of concentrated load resistance built into a wall rather than projecting beyond it as is the case with larger pilasters & columns. I don't have the relevant code provisions committed to memory but I believe that the design approach is to effectively treat these elements as beefy bits of wall designed like beefy bits of wall. Ergo no code requirement for four corner bars. As I'm sure you know, similar "column" elements are constructed often as jamb elements beside windows and doors and as in wall compression elements at the support of moderately loaded beams & girders.
 
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