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Re:slab on grade

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I would like to amplify others who have responded to you.  You should consult a
Geotechnical Engineer, since as you have indicated, subgrade conditions, not
loading, will control design.  I concur that temperature should also be
considered.  In arid southeastern California we have metastable soils, including
sands, that "collapse" when wetted.  "Collapse" is a geotechnical term for the
response of arid native soils in a dispersed deflocculated state, when wetted.
Will there be new irrigation around your slab?  This is just one of many
possible subgrade problems that could arise.  Sounds like you do not have to
worry about frost heave (unless your project is at Taos or somewhere like that).
 Yes I am a Geotechnical Engineer ("to a carpenter with a hammer, everything
looks like a nail").

Good luck,

Tom Benson at Lowney Associates, Pasadena, CA

____________________Reply Separator____________________
Subject:    slab on grade 
Author: <seaint(--nospam--at)>
Date:       1/4/99 11:34 AM

Happy New Year, y'all
I need to put in a good slab for outdoor basketball courts.  The client 
would like for them to be free of joints.  It will be an unloaded slab, no 
traffic.  The slabs will be 100' x 65'.  I can spec a proper subgrade spec. 
 How do I design for the slab thickness and reinforcing required to keep 
cracking controlled.  I have reviewed  ACI 302 and 360, and the PCA guide. 
 None really address the unloaded slab except for the "subgrade drag 
equation", which is not really a qualitative approach.  I'm willing to add 
fibers to get a good crack control, but how does one balance between that 
and steel?  How thick a slab?  How much steel?  How much fibers?  Any 
comments are appreciated.
Jerry D. Coombs, PE