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RE: Ground bearing slabs without control joints

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Based on an old (1978) Concrete Floors on Ground by Ralph Spears, PCA

As = FLW/2fs

                        As = effective cross-sectional area of steel, in square inches per foot of width of section

F = coefficient of subgrade friction which may vary from 1.0 to 2.5.  1.5 is recommended

L = distance between free ends, in feet.  A free end is any joint free to move in a horizontal plane    

W = weight of slan in pounds per square foot based on 150 pcf.

fs = allowable unit tensile stress in the reinforcement in psi


Gary Loomis, PE


-----Original Message-----
From: Mark L. Puccio [mailto:mpuccio(--nospam--at)]
Tuesday, November 14, 2006 4:46 PM
To: seaint(--nospam--at)
Subject: Ground bearing slabs without control joints


We have a project in which for various reasons we wish to have a slab on ground without control joints. Section 7.12 of ACI discusses minimum temp and shrinkage steel for structural slabs but the commentary states this is not intended for SOG. Would using the minimum areas of steel p = 0.0018 be conservative?  If section & 9.2.7 (for restrained slabs) is followed how would you practically quantify the force of shrinkage?


The floor area is about 150x 65 and we could probably divided this up into thirds with moving construction joints.


Thanks for your thoughts.


Mark L. Puccio P.E., S.E.