Friday, November 7, 2008

RE: Slab on grade

As previously stated, a SOG is not reinforced concrete and the provisions of ACI 318 are not applicable, but you should be aware of the recommendations from CRSI and the WRI.  It is recommended that reinforcement be placed 2 inches below the slab surface or within the upper third of the slab thickness, whichever is closer to the surface.  ACI 360 states that it is a common practice to place the reinforcing 1.5 to 2 inches below the top surface or at least 1/3 the slab depth below the surface. 
 
If 2 inches cover to the top surface is used in your scenario, the bottom would only have 1 inch clear for the #4 bars.  Bear in mind that the tolerance for reinforcing for SOG per ACI 117 is plus or minus 3/4".  This creates the potential for 1/4" cover. 
 
It would be my suggestion to use WWR in a 4" slab and if you choose to use #4 bars, I would suggest that you use a minimum of a 5" slab.  I generally prefer to go to a 4" WWR to make it easy to walk on the surface of the WWR once the sheets are placed on dobies.   I like going to 24 " or 18" o.c. for rebar to accommodate walking in the spaces. 
 
Again, it is not a safety or code issue, and it is not "reinforced" concrete, it is more of a serviceability issue. 
 
The election is over, my usual fees are applicable,
Regards, Harold Sprague





Subject: RE: Slab on grade
Date: Fri, 7 Nov 2008 11:57:51 -0700
From: jason@wcaeng.com
To: seaint@seaint.org


Thanks!

 

Jason

 

From: Jerry Coombs [mailto:JCoombs@carollo.com]
Sent: Friday, November 07, 2008 11:54 AM
To: seaint@seaint.org
Subject: RE: Slab on grade

 

Scope.  ACI 318  1.1.6 

>>> "Jason Christensen" <jason@wcaeng.com> 11/7/2008 12:50 PM >>>

Where is this exclusion?  I would like to show the BO.

 

Jason

 

From: Jerry Coombs [mailto:JCoombs@carollo.com]
Sent: Friday, November 07, 2008 11:45 AM
To: seaint@seaint.org
Subject: Re: Slab on grade

 

3" clear is not req'd.  ACI 318 specifically excludes non-structural, SOGs.

>>> "Jason Christensen" <jason@wcaeng.com> 11/7/2008 12:29 PM >>>

For our typical 4" slab on grade (non-structural slab) we call out #4 at 24"o.c. each way.

 

We just got by a building official plan review for not meeting the 3" min. clearance for concrete cast next to earth.  For a non-structural slab I have never worried about the bottom clearance, maybe I should be?

 

Any thoughts?  Is there a exception for non-structural concrete not needing the 3" clearance?

 

Jason


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