Concrete Rectangular Footing Designer to AS3600

Verified by the CalcTree engineering team on August 2, 2024
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This calculator allows the user to design an isolated reinforced concrete footing supporting a single load-carrying column, that can be eccentric. It includes the section design to AS3600-2018 and checks for overturning, sliding, uplift and soil bearing at the four corners of the footing.
Detailed explanation of the behaviour of footings and required checks can be found in CalcTree's Design Guide: Concrete Footing to AS3600.
All calculations are performed in accordance with AS3600-2018.
CalculationAssumptions
InputsMaterial Properties
Footing Geometry and Reinforcement
Column Geometry
Loads
OutputResultant Forces and Eccentricities
Geotechnical Checks (Stability)
﻿﻿Factor of Safety
:3​
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Bearing Check
Overturning Check
Uplift Check
Sliding Check
Structural Checks (ULS)
ExplanationThis section focuses on the limit state design principles of footing 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.
Note
Design ConsiderationsFooting design is an iterative process; it requires an initial judgement from the engineer on the required thickness and reinforcement, then repeating structural analysis until the desired strength is achieved.
The initial 'guess' of the footing size is governed by two things:
Applied load and allowable bearing pressure - this determines bearing area i.e. length and width
Required development length column reinforcement in the footing, and the concrete shear strength without shear reinforcement - this determines the depth
The required bearing area can be calculated by dividing the total applied load on the footing by the allowable bearing pressure:
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A =FqallowableA\ =\large \frac{F}{q_{allowable}}A =qallowable​F​
Although there are many combinations of lengths and widths that can achieve the same bearing area, squarer footings are better as they produce a more even pressure distribution than a rectangular one.
Longitudinal reinforcement from columns are required to continue into the footing to achieve sufficient development length for structural continuity and load transfer. Generally, at column-footing interface, these bars are cogged at 90° and extend parallel to the footing surface.
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Columns are mostly in compression and hence the reinforcement is also in compression. AS3600 Cl. 13.1.5 provides the following formula for calculating the development length of bars in compression:
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Lsy.cb=0.22fsyfc′db≥0.0435fsydbor 200mm, whichever is greaterL_{\mathrm{sy} . \mathrm{cb}}=\frac{0.22 f_{\mathrm{sy}}}{\sqrt{f_{\mathrm{c}}^{\prime}}} d_{\mathrm{b}} \geq 0.0435 f_{\mathrm{sy}} d_{\mathrm{b}}\\ \text{or\ 200mm,\ whichever\ is\ greater}Lsy.cb​=fc′​​0.22fsy​​db​≥0.0435fsy​db​or 200mm, whichever is greater
Considering that the minimum development length is 200mm, the required footing depth would generally be around 300mm or higher.
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Isolated pad footing under construction (Source: TR Construction)
Related ResourcesDesign Guide: Concrete Footing to AS3600-2018
Concrete Slab-on-Grade Designer to AS3600
Foundation Bearing Failure Modes and Capacities
Rectangular Spread Footing Design to ACI-384
Concrete Slab-on-grade Calculator to ACI 360R-10
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