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RE: S.O.G.

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Andrew,

Question:
Harold, you said to use rebar in SOG, so are you using #3, about 1.5" or 1/3
from the top of the slab? And since it is agreed that even this won't
prevent cracking, however, it should hold the widths to acceptable limits.
And do you design the reinforcement ACI 360R-21, EQ (6-3) and the thickness
according to one of the methods listed in Chapter 5 (PCA, WRI, or COE
methods)??

Answer:
It depends.  If I can do the controls to get a uniform sub base with a
definitive slip plane (no thickened slabs, other slab restraints, and use
PNA dowels at the perimeter) I will use the Subgrade drag method from
Designing Floor Slabs on Grade by Ringo Sect 1.5.1.3.  Keep in mind that
this is NOT reinforced concrete in the conventional sense where
reinforcement is used to resist flexural bending.  The rebar is a tension
element used to resist the shrinkage effects.  

I will also investigate the other methods of determining rebar in Ringo's
book, depending on the perceived required strength.

I generally use #4 @ 18" EW and have them place it so that I have the bar
about 1/3 from the top.  If I am doing a COE project, I check the slab using
the COE standards just to get the "deemed to comply" stamp of approval.  

Regards,
Harold O. Sprague


-----Original Message-----
From: Andrew Kester [mailto:andrew(--nospam--at)baeonline.com] 
Sent: Friday, July 18, 2003 8:54 AM
To: seaint(--nospam--at)seaint.org
Subject: S.O.G.


Thanks to Harold and Scott for their great advice on slabs on grade.

As Scott said, the ACI does address the base material between the vapor
retarder and the slab. This is a good read- ACI 4.1.5, but see the Addendum
at the end of the Chapter, 302.1R-96, Vapor Retarder Location, and the
accompanying flow chart. This has been a real eye opener and I hope to
reevaluate the way we design and specify SOG. It is very dependent on the
expected/known finish floor material...

I guess it is a bit simpler on exterior slabs where you do not need a vapor
retarder.

Harold, you said to use rebar in SOG, so are you using #3, about 1.5" or 1/3
from the top of the slab? And since it is agreed that even this won't
prevent cracking, however, it should hold the widths to acceptable limits.
And do you design the reinforcement ACI 360R-21, EQ (6-3) and the thickness
according to one of the methods listed in Chapter 5 (PCA, WRI, or COE
methods)??

Thanks again for all of the input.

Andrew Kester, EI
Longwood, FL


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