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RE: cmu wall control joints

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I have seen guidelines to control joint spacing based upon how much bed
reinforcement you use in the wall. These aren't real consistent.

>From an ancient copy of PCA's Concrete Masonry Handbook, for unreinforced
CMU, they suggest the following maximum joint spacings:

9 GA bed joint reinforcement spacing (in)		Length/Height	Max
2				40
2.5				45	
3				52
4				60

I get the same from an old NCMA detailing manual. The aspect ratios are

Another detailing manual suggests a maximum spacing of 25 ft for block, 20
ft for veneer, with bed reinforcement at 16".

A more recent  NWCMA Tek Note suggests a maximum of 46 ft for reinforced
CMU, 26 ft for veneer, with maximum aspect ratios of 3 and 1.5 respectively.
For solid grouted walls, they recommend reducing the spacing to 40 feet for
CMU with a maximum aspect ratio of 2.5.

I have typically gone 40 ft max with bed reinforcement at 16" on 8" block
with no problems. This is in addition to bond beam steel. I wouldn't think
you would need a control joint for a wall of your dimensions, but I would
definitely include some bed joint reinforcement. 

-----Original Message-----
From: Mark D. Baker [mailto:shake4bake(--nospam--at)]
Sent: Friday, March 04, 2005 10:50 AM
To: seaint
Subject: cmu wall control joints

For any cmu experts out there..


I have a 30'x30'x20' tall, 8" cmu building. I am thinking these dimensions
would be acceptable without any control joints in walls and would like some
other opinions.




Mark D. Baker

Baker Engineering



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