Exterior Load Bearing CMU wall with Sill Block Transition Detail

[structuralengr89]

I have a client that wants to use a detail as in the attached sketch for an exposed, exterior load bearing cmu wall. He has a 12" block transitioning to an 8" block with a sill block that is 6" wide (nominal dimensions). He is showing a 6" wide CMU block adjacent to the 6" wide sill block.

It appears as though there is inadequate clearance between the rebar centered in the 8" cmu above and the face shell of the 6" block for grouting.

Has anyone every detailed a cmu wall similar to this? Should the face shell of the 6" cmu block be knocked out to allow clearance for the grout around the rebar?

Thanks!

 

[JAE]

I realize that the standard is to have at least 1/2" of clearance off the inside face of the block- but in this case it is only one course high and the reasoning behind having good clearance is two-fold - 1) to help ensure that grout can get down through the cells into cells below and 2) to ensure good bond - i.e. development length - between the grout and rebar.

For 1) - if you have them grout the lower courses first, prior to settint the 6" block you should be OK

For 2) - the one block with a lack of bond wouldn't create a significant problem in my view.


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[KootK]

From a mechanics standpoint, I'm not sure that I'd care if you got no grout at all in that one cell. I'd argue that the flexural performance would remain unchanged so long as the compression block falls within the face shell thickness. Shear capacity and corrosion potential in that transition cell might warrant some extra attention. Breaking the face shells does sound like a good idea if it doesn't incur too much cost.

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.

 

[dhengr]

Structuralengr89:
Grout the 5 courses of 12" conc. blk. Set the sill blk. in a full bed of mortar, and at the same time, cut the inner face off the 6" conc. blk. and set it with the inner face and cross shells bedded in mortar. Then continue the 8" conc. blk. Put horiz. ladder reinforcing in the joints below and above the sill blk. You probably couldn’t high lift grout this wall arrangement in any case.