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RE: cmu wall control joints

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Here is your chance to educate me....

If you don't need horizontal reinforcement for shear loads in the form of
bed reinforcement or bar reinforcement.... and you don't have multiwythe
construction that you are tying together with bed reinforcement.....you
would put bed reinforcement in to help control expansion/contraction?

Thanks,

Mark D. Baker
Baker Engineering

-----Original Message-----
From: Lutz, James [mailto:James.Lutz(--nospam--at)earthtech.com] 
Sent: Friday, March 04, 2005 11:39 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: cmu wall control joints

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
Spacing(ft)
None
2				40
24
2.5				45	
16
3				52
8
4				60

I get the same from an old NCMA detailing manual. The aspect ratios are
not-to-exceed.

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)earthlink.net]
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.

 

Thanks,

 

Mark D. Baker

Baker Engineering

 


				
			 
	
		 
	
			 
 

 
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