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re: bar spacing in a wall

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I should not post twice on the same subject, but I will be that guy because it is Friday and I am feeling chippy, hombre.


Riddle me this batman, why in one situation could I go with 8” CMU with #4@48” o.c. in solid grouted cells but ACI would require me to go 18” o.c. max for that same wall if it is 6” solid poured? I have done more than my fair share of CMU calcs so I understand the intricacies, I want a common sense type answer. Don’t blind me with your science. I think the answer is somewhere between a longstanding ACI minimum that gives people warm and fuzzies, and something to do with bond stress or the old Z factor or something? I don’t have my ACI around and I don’t have it memorized like Scott, but I bet he knows the answer.


But Jeff says the IRC table says 48” o.c. for 30 psf, which makes sense from a CMU perspective, and we all know about CMU being of much less compressive strength than solid concrete. I have also heard people in the ICF business throw 48” o.c. out there also. There has to be some science or testing behind this, but it from a residential wall standpoint it would seem about right. (I still would pay the extra for my house from a crack control perspective).


I digress. Rebar, we talkin about rebar? REBAR? REBAR? (Allen Iverson talkin about practice). How much more, anyone anyone anyone, can this 860sf addition cost either way for say about 20-30 more bars? Have the GC tell you, then bill him for your extra time on this list and doing research and call it even. Add in our time as “consulting and research”.


Its 100am where Conrad in Adelaide is, means we can all have a beer now right?



Andrew Kester, PE

Orlando, FL