This calculator analyses the soil conditions below a concrete slab to determine the required thickness of the slab. The calculator checks the flexural, bearing and shear stresses in the slab and determines the minimum required slab thickness, the minimum required distribution reinforcement and the estimated crack width. The calculator also checks the bearing stress on the dowels at construction joints.

- Slab is idealized as a homogenous, isotropic material with uniform thickness and no discontinuities. Though in reality, a slab-on-ground is generally exposed to more rougher conditions during construction than others.
- The subgrade is represented by the modulus of subgrade, k and is modelled as a series of independent springs.
- All loads are assumed to be applied normal to the slab surface. Any braking or traction forces, which act at an angle to the surface, are not accounted for.
- Any contribution to flexural strength made by the reinforcement is neglected. The slab is only reinforced for crack width limit control due to shrinkage and temperature.
- Dowels are assumed to be plain bars.

Concentrated Load, P

:6000lbs

Factor of Safety, FoS

:5

Increase for 2nd Load, i (%)

:0

Slab Thickness, t

:8.00inch

Concrete Strength, f'c

:4000.00psi

Concrete Unit Weight, wc (pcf)

:150.00

Steel yield limit, fy

:60000.00psi

Contact Area, Ac

:144.00sqin

Temperature range of the slab, ΔT

:50.00degF

Subgrade Modulus, k (pci)

:500.00

Dowel diameter, db

:0.75inch

Dowel spacing, s

:12inches

Joint width, z

:0.25inches

Joint spacing, L

:20ft

Slab weight, W (psf)

:100

Modulus of Elasticity, Ec

:3.8e+6psi

Poisson's ratio, μ

:0.15

Modulus of Rupture, MR

:569.21psi

Cracking moment, Mr (ft-k/ft)

:6.07

Radius of relative stiffness, Lr

:24.05in

Friction factor, F

:1.5

Slab base friction adjustment, C

:1

Thermal expansion, α

:5.5e-6

Shrinkage coefficient, ε

:3.5e-4

Effective load radius, a

:6.77in

Equivalent radius, b

:6.32in

Shear perimeter, bo

:48.00in

Number of effective dowels, Ne

:2

Joint load, Pt

:3000.00lbs

Critical dowel load, Pc

:1495.05lbs

Modulus of dowel support, kc

:1.5e+6psi

Modulus of Elasticity for steel dowels, Eb

:2.9e+7psi

Inertia/Dowel Bar, Ib (in^4)

:0.0155

Relative Bar Stiffness, β

:0.889For single interior load:

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t(min) IL

:7.50inFor single corner load:

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t(min) CL

:8.00inFor single edge load (circular area):

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t(min) EL circular

:10.75inFor single edge load (semi-circular area):

t(min) EL (semi-circular)

:12.25in

💬 We'd love your feedback on this template! It takes 1 min!

A slab-on-ground, also referred to as slab-on-grade, is a slab supported by the ground whose main purpose is to support the applied loads by bearing on the ground.

The American and British Standards method for design is to compare "allowable stresses" against "actual stresses", where actual stresses are based upon characteristic loads with an overall Factor of Safety (FoS). The designer choses the FoS to minimise the likelihood of serviceability failure such as cracking and decrease to surface durability. In contrast, the Eurocode is based upon limit state design with partial factors of safety on materials and loads.

The design checks to ACI 360R-22 are based upon ensuring:

There are multiple failure modes of a slab-on-ground:

- Flexural failure of the slab, when the slab develops tension stresses in its soffit that exceed its flexural capacity
- Bearing failure of the slab, when the slab bearing stresses exceed its bearing strength
- Punching failure of the slab, when the slab shear stresses exceed its shear strength
- Bearing stress of dowels that causes the slab to fail, where the effectiveness of the dowel bars depend on the relative stiffness between the slab compared to its subgrade

Recommended values for some input parameters are provided:

This calculator is courtesy of Alex Tomanovich P.E.