Concrete Wall Footing

How it calculates

The Concrete Wall Footing calculator designs continuous strip footings supporting a concrete or masonry wall to AS 3600:2018 (Amdt 2). The footing is modelled as a unit-length strip (1 m) with the wall positioned either at the centre or along one edge, subjected to vertical load and a uniaxial bending moment parallel to the wall.

Applied loads and load cases

Loads are entered as axial force per unit length (G and Q) and bending moment per unit length about the axis parallel to the wall. The calculator generates strength load cases per AS/NZS 1170.0 (1.35G; 1.2G + 1.5Q; and combinations with wind where entered) and working load cases for the bearing check. Self-weight of the footing concrete is computed automatically from the footing geometry.

Bearing stress check (working loads)

Under the governing working load case, the net eccentricity of the resultant vertical force is determined. The bearing stress distribution (trapezoidal or triangular, depending on whether the resultant falls inside or outside the kern) is compared to the allowable bearing capacity q_a entered by the engineer:

q_max ≤ q_a

A warning is flagged if the resultant falls outside the footing, indicating the footing would partially lift and the bearing stress would exceed the uniform assumption.

Moment demand and capacity (AS 3600:2018, Cl. 8.1)

The critical section for bending is at the face of the wall. The cantilever moment demand M_u at the critical section is calculated from the net upward soil pressure on the toe side under the governing strength load case:

utilization = M_u / (phi × M_n) ≤ 1.0

where phi = 0.85 for bending and M_n is calculated from the reinforcement area, bar depth, and concrete compressive strength. Minimum reinforcement per AS 3600:2018 Cl. 8.1.6 is also verified.

Shear demand and capacity (AS 3600:2018, Cl. 8.2)

One-way shear is checked at a distance d_v from the face of the wall. Shear capacity is calculated using the simplified method per AS 3600:2018 Cl. 8.2.4 without shear reinforcement (Asv = 0):

utilization = V_u / (phi × V_n) ≤ 1.0

where phi = 0.75 for shear.

Assumptions and scope

The footing is a continuous strip with unit breadth (1 m). Only vertical loads and uniaxial moments parallel to the wall are considered. Lateral loads on the footing, bi-directional eccentricity, and detailed deflection checks are outside the scope of this calculator. The footing is assumed to be in contact with the soil over its full base length (no uplift beyond the kern check).