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Concrete Slab-on-Grade Designer to AS3600
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This calculator allows the user to design a rectangular concrete slab on soil, supporting walls and columns or vehicle load. It includes section design to AS3600-2018.

Note

❗ This calculation has been written in accordance with AS3600-2018

Calculation

Inputs

Geometry nomenclature

Geometry and load nomenclature



Material Properties

Concrete


f'c
:41MPa​



Concrete unit weight
:24kN/m3​



Ec
:0 MPa​



f'ct.f
:3.84 MPa​



f'ct.f (1)
:2.31 MPa​

Reinforcement


fsy
:500MPa​



Es
:200,000MPa​

Soil


μ
:0​


Slab-on-grade Geometry



L
:5m​



B
:5m​



T
:0.5m​

Section x-x


(x) Cover
:50mm​



(x) Reinforcement size
:16mm​



(x) Number of bars
:50​



(x) Reinforcement spacing
:100 mm​

Section y-y


(y) Cover
:60mm​



(y) Reinforcement size
:16mm​



(y) Number of bars
:50​



(y) Reinforcement spacing
:99 mm​



Loads

Wall, columns or post loads
You may input up to four coincident design actions due to concentrated loads. Note, negative N* is compression

Vehicle Load
If the vehicle is longer than the slab, then the calculator positions the largest axle load in the middle of the slab as it produces the most critical bending moment.
Vehicle load configuration

If the vehicle can fit along the length of the slab, then the calculator positions the centreline of the axles to the centre of the slab.


Axle spacing
:3m​



Wheel spacing
:2m​



:Vehicle sits on slab​



Front axle load
:90kN​



Back axle load
:40kN​


Uniform Surcharge


Q
:0kPa​




FoS and Capacity Reduction Factors



Factor of Safety
:1.5​

ϕ shall be selected as per AS3600 Table 2.2.2.


ϕ (bending)
:0.85​



ϕ (shear)
:0.7​



Output

Resultant Forces and Eccentricities



Slab self-weight
:300 kNkN​



ΣPz
:430 kN​



ex
:-0.17 m​



ey
:0 m​



Bearing Check

Different cases of biaxial bearing pressure

Bearing corner pressures


Uniaxial​
13.69​
13.69​
20.71​
20.71​
5​
5​
100​


qmax
:20.71 kPa​



Bearing check
:PASS​



Overturning


ΣMo =Total overturning momentΣMr =Total resisting moment\small{ΣM_o}\ = \text{Total\ overturning\ moment}\\\small{ΣM_r\ =\text{Total\ resisting\ moment}}
Section x-x


(x) ΣMr
:750 kNm​



(x) ΣMo
:0 kNm​

Section y-y


(y) ΣMr
:750 kNm​



(y) ΣMo
:0 kNm​



Overturning check
:PASS​



Uplift Check



ΣPz (1)
:430 kN​



ΣPu
:0 kN​



Uplift check
:PASS​



Sliding Check


Ff = Frictional resistanceF∗ = Pushing force = applied shear in the direction being considered\small{F_f\ =\ \text{Frictional\ resistance}}\\\small{F^*\ =\ \text{Pushing\ force}\ =\ \text{applied\ shear\ in\ the\ direction\ being\ considered}}
Section x-x


(x) Ff
:172 kN​



(x) F*
:0 kN​

Section y-y


(y) Ff
:172 kN​



(y) F*
:0 kN​



Sliding check
:PASS​



ULS Capacity Checks

Beam Shear


Vu = kvbwdvfc′V_u\ =\ k_vb_wd_v\sqrt{f'_c}
Section x-x


(x) V*
:43 kN​



(x) kv
:0.15 ​



(x) dv
:318.2 mm​



(x) ϕVu/m
:214 kN​



(x) V*/ϕVu
:0.1991885228880588​

Section y-y


(y) V*
:43 kN​



(y) kv
:0.15 ​



(y) dv
:318.2 mm​



(y) ϕVu/m
:214 kN​



(y) V*/ϕVu
:0.20015639714893374​



Flexure


Mu = Astfsy(do−γkudo2)\large{M_u\ =\ A_{st}f_{sy}(d_o-\frac{{\gamma}k_{u}d_o}{2})}


α2
:0.7885​



γ
:0.7630000000000001​

Section x-x


(x) M*
:65 kNm​



(x) ku
:0.092​



(x) do
:442 mm​



(x) ϕMu
:364 kNm​



(x) M* / ϕMu
:0.17758912990481143​

Section y-y


(y) M*
:65 kNm​



(y) ku
:0.094​



(y) do
:432 mm​



(y) ϕMu
:356 kNm​



(y) M* / ϕMu
:0.18185346958971838​


Explanation

This section focuses more on the limit state design principles of slab design to AS3600. Detailed explanation of the behaviour of footings and required checks can be found in CalcTree's Design Guide: Concrete Footing to AS3600.
A slab-on-grade (also called slab-on-ground) is a type of foundation mainly used for lightly loaded structures such as residential and small commercial buildings. Concrete is poured directly onto the prepared ground, without any basement or crawl space beneath it. This concrete slab serves as both the foundation and the floor of the building.
Slab-on-grade for residential housing (Source: RAMJACK)


Design Considerations

Choosing the appropriate foundation type for the structure above is essential; each have their advantages and disadvantages, and every site has its own constraints. Slab-on-grade is generally used when the following conditions are met:
  1. Warm climate - heat-loss occurs quickly in buildings built on slab-on-grade, as there is no space provision for heating ducts under the floor (the slab).
  2. Utilities can be routed above ground - any underground gas and drainage pipes must surface may need to routed into the building externally, without penetrations in the slab.
  3. Ground profile is generally flat - uneven ground profile requires excavation, at which point it may be easier to utilise other types of foundations
Slab-on-grade is particularly advantageous for its fast and cheap construction. It requires minimal preparation for concrete pouring. As the slab is poured directly on ground, there’s little to no excavation required. Also, the fact that it sits on ground reduces the likelihood of moisture issues e.g. water infiltration, swelling, etc. which are common in embedded foundations.
Freshly poured slab-on-grade (Source: DesignwithFrank)

However, there are also disadvantages to using slab-on-grade. Underground utilities cannot be checked or maintained and any damage can only be detected after it has occurred e.g. leakage. Also, as the building is constructed on low elevation, it is exposed to structural damage during flooding events.
In regions where the ground temperature drops marginally lower than the interior temperature, significant heat losses can occur in the building. To prevent this, often insulation is put in between the slab and ground surface.

Related Resources

  1. Concrete Beam Design Calculator to AS3600-2018
  2. Concrete Column Design Calculator to AS3600-2018
  3. Design Guide: Concrete Footing to AS3600-2018
  4. Foundation Bearing Failure Modes and Capacities
  5. Rectangular Footing Design to AS3600
  6. Rectangular Spread Footing Design to ACI-384
  1. Slab Thickness Calculator to ACI 360R-10