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
Concrete strength grade, f'c
:40MPa
Concrete unit weight
:24kN/m3
Concrete modulus of elasticity, Ec
:32800 MPa
Concrete flexural tensile strength, f'ct.f
:3.79 MPa
Concrete uniaxial tensile strength, f'ct.f
:2.28 MPa
Reinforcement
Steel yield strength, fsy
:500MPa
Steel modulus of elasticity, Es
:200,000MPa
Soil
Coefficient of soil friction, μ
:0
Slab-on-grade Geometry
Slab-on-grade length, L
:2.5m
Slab-on-grade width, B
:2.5m
Slab-on-grade thickness, T
:0.2m
Section x-x
(x) Cover
:50mm
(x) Reinforcement size
:16mm
(x) Number of bars
:50
(x) Reinforcement spacing
:49 mm
Section y-y
(y) Cover
:50mm
(y) Reinforcement size
:16mm
(y) Number of bars
:50
(y) Reinforcement spacing
:49 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
Uniform Surcharge
Q
:0kPa
FoS and Capacity Reduction Factors
Factor of Safety
:2
ϕ shall be selected as per AS3600 Table 2.2.2.
Capacity reduction factor, ϕ (bending)
:0.85
Capacity reduction factor, ϕ (shear)
:0.7
⬆️ Outputs
Resultant Forces and Eccentricities
Slab self-weight
:30 kN
Total vertical force, ΣPz
:289 kN
ex
:0.05 m
ey
:0.05 m
Bearing Check
Different cases of biaxial bearing pressure
Bearing corner pressures
Uniaxial
46.22
57.32
46.22
35.13
2.5
2.5
100
Maximum bearing pressure, qmax
:57.32 kPa
Bearing check
:PASS
Overturning
ΣMo=Total overturning momentΣMr=Total resisting moment
Section x-x
(x) ΣMr
:361 kNm
(x) ΣMo
:-14 kNm
Section y-y
(y) ΣMr
:361 kNm
(y) ΣMo
:14 kNm
Overturning check
:PASS
Uplift Check
Total downward load, ΣPz
:349 kN
Total uplift load, ΣPu
:60 kN
Uplift check
:PASS
Sliding Check
Ff=Frictional resistanceF∗=Pushing force=applied shear in the direction being considered
Section x-x
(x) Ff
:116 kN
(x) F*
:5 kN
Section y-y
(y) Ff
:116 kN
(y) F*
:5 kN
Sliding check
:PASS
ULS Capacity Checks
Beam Shear
Vu=kvbwdvfc′
Section x-x
(x) V*
:64 kN
(x) kv
:0.15
(x) dv
:102.2 mm
(x) ϕVu/m
:68 kN
(x) V*/ϕVu
:0.9353816256456007
Section y-y
(y) V*
:64 kN
(y) kv
:0.15
(y) dv
:102.2
(y) ϕVu/m
:68 kN
(y) V*/ϕVu
:0.9353816256456007
Flexure
Mu=Astfsy(do−2γkudo)
Rectangular stress block factor, α2
:0.79
Rectangular stress block factor, γ
:0.77
Section x-x
(x) M*
:45 kNm
(x) ku
:0.582
(x) do
:142 mm
(x) ϕMu
:188 kNm
(x) M* / ϕMu
:0.23779485821327626
Section y-y
(y) M*
:45 kNm
(y) ku
:0.582
(y) do
:142 mm
(y) ϕMu
:188 kNm
(y) M* / ϕMu
:0.23779485821327626
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.
Introduction
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:
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).
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.
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.
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.