#### Input Data

 Slab Thickness, t = in. Concrete Strength, f 'c = 3000350040004500500055006000 psi Subgrade Modulus, k = pci Wall Load, P = in.

#### Result :

Design Parameters:
Modulus of Rupture, MR = psi MR = 9*SQRT(f 'c)
Allow. Bending Stress, Fb = psi Fb = 1.6*SQRT(f 'c) (as recommended in reference below)
Factor of Safety, FS =   FS = MR/Fb
Section Modulus, S = in.^3/ft. S = b*t^2/6
Modulus of Elasticity, Ec = psi Ec = 57000*SQRT(f 'c)
Width, b = in. b = 12" (assumed)
Moment of Inertia, I = in.^4 I = b*t^3/12
Stiffness Factor, l =   l = (k*b/(4*Ec*I))^(0.25)
Coefficient, Blx =   Blx = coefficient from "Beams on Elastic Foundations" by M. Hetenyi
Wall Load Near Center of Slab or Keyed/Doweled Joints:
Allowable Wall Load, Pc = lb./ft. Pc = 4*Fb*S*l
= 12.8*SQRT(f 'c)*t^2*(k/(19000*SQRT(f 'c)*t^3))^(0.25)

Wall Load Near Free Edge of Slab: psf Pe = Fb*S*l/Blx
= 9.9256*SQRT(f 'c)*t^2*(k/(19000*SQRT(f 'c)*t^3))^(0.25)

Min. req'd. slab thk. for center or keyed/doweled joints:
t(min) = in. Set Pc(allow) = 12.8*SQRT(f 'c)*t^2*(k/(19000*SQRT(f 'c)*t^3))^(0.25)
t(min) = in. Set Pe(allow) = 9.9256*SQRT(f 'c)*t^2*(k/(19000*SQRT(f 'c)*t^3))^(0.25)

References:
Army Technical Manual TM 5-809-12, Air Force Manual AFM 88-3, Chapter 15 (1987)

Type of Soil Support Provided k Values Range (pci)

Fine-grained soils in which
silt and clay-size particles
predominate
Low50 - 120

Sands and sand-gravel
mixtures with moderate
amounts of silt and clay
Medium 130 - 170

Sands and sand-gravel
mixtures relatively free
of plastic fines
High 180 - 220

Cement-treated subbases Very high 250 - 400
Note: direct solution for t(min) has been rounded up to nearest 1/4" thickness.
Note: direct solution for t(min) has been rounded up to nearest 1/4" thickness.

Disclaimer: This calculator is not intended to be used for the design of actual structures, but only for schematic (preliminary) understanding of structural design principals. For the design of an actual structure, a competent professional should be consulted.

‘Calculations courtesy of Alex Tomanovich, PE ’