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Re: SLAB - Control Joints in Concrete Slab on Grade

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I agree with Brian.  Typically, the slab on grade is not structural and we
place the rebar in the center.

The coverage does become an issue, though, when we have a structural slab on
grade, which we often use in areas where the soil is bad, or prone to
disappear such as at the beach.  In these cases, we do require the 3" cover on
the bottom of the slab.  Since typical slab coverage is only 1" or so, we then
ignore the bottom 2" of concrete when calculating our minimum slab thickness
based on span length (h = L/20 or whatever) as required by the Code.  We feel
that those 2" are cover only and not part of the structure in the sense that
the slab thickness equations intended it to be.  This does lead to a thicker
slab, which, of course, has to carry the weight of the 3" bottom cover so the
grade beams and piles get heavy, too.  But I didn't put the lousy soil there
in the first place.

Bruce Resnick, SE
Parker Resnick Str. Eng.