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Floor slabs on grade should be analyzed for
adequate structural live loads. Since floor slabs maybe
designed for moving and extreme live loads, the design should
be checked for stationary live loading conditions as well. The
following equation may be used to find allowable loads.
where
w = the maximum allowable distributed
stationary live load, pounds per square foot
s = the allowable extreme fiber stress in
tension excluding shrinkage stress and is assumed to be equal
to one-half the normal 28-day concrete flexural strength,
pounds per square inch
k = the modulus of subgrade reaction, pounds
per cubic inch
h = the slab thickness, inches
E = the modulus of elasticity for the
slab ( typically 4.0 x 106 pounds per square inch)
257.876 = Conversion constant
Further safety may be obtained by reducing
allowable extreme fiber stress to a smaller percentage of the
concrete flexural strength. The design should be
examined for the possibility of differential settlements which
could result from non-uniform subgrade support. Also,
consideration of the effects of long-term overall settlement
for stationary live loads may be necessary for compressible
soils.
Reference: Army Corps of Engineers, TM
5-809-12/AFM 88-3, Chap. 15
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