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RE: Minimum reinforcing in mat slab foundation

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Thank you.  My bending requirements will exceed .0018 therefore from that perspective I am probably o.k.  I couldn’t find if there were more stringent minimum requirements for a mat due to the large square footage.  Like I said ACI 350 increases the minimum for distances between joints, but that is for “environmental structures”.  I was using those values, but due to the dimensions of the slab I was getting a lot of temp and shrinkage steel.  Since it is not a “containment” structure and there probably isn’t a ground water problem, I can probably back off some.

Thanks again,



Joseph R. Grill, PE

Verde Valley Engineering, PLLC

email: VVEng(--nospam--at)


From: David Topete [mailto:d.topete73(--nospam--at)]
Sent: Friday, July 30, 2010 12:25 PM
To: seaint(--nospam--at)
Subject: Re: Minimum reinforcing in mat slab foundation


I have checked for min. temp and shrinkage steel, which typically governs over bending and shear requirements in (thicker) mats.  So, I'll check for 0.0018 Ag.  For an 18" thick mat, for example, the minimum steel needed would be 0.0018*18"*12" = 0.39 in^2 per foot of mat width.  In that case, #4 @ 12"o.c., top & bottom.  Depending how thick, I've added intermediate steel.


No one has called me on it yet.

On Fri, Jul 30, 2010 at 10:52 AM, Joseph R. Grill <vveng(--nospam--at)> wrote:

I am designing a buried structure to be used as a shelter.  The depth of the structure and the soil conditions have required the design of a mat foundation (my first).  Not having software that directly designs the mat, I have set up a model on Risa3D (I don’t have Risa Foundation yet).  I have checked punching shear and sized reinforcing for flexure.  What is the minimum temperature shrinkage requirements for the mat.  ACI 350 suggests some parameters based on joint spacing which I would like to do without.  But the ACI 350 suggestions require a lot of minimum steel and probably warranted.  The slab is 26 ft. x 54 ft. and will probably have no issues with groundwater.


Thanks, Joe


Joseph R. Grill, PE

Verde Valley Engineering, PLLC

email: VVEng(--nospam--at)


David Topete, SE