Concrete Member (Design Only)

How it calculates

The calculator performs a capacity design of a reinforced concrete member to AS 3600:2018 from design actions the engineer supplies directly. It suits members whose forces come from a separate analysis, such as a 3D structural model, and reports each action as a demand-versus-capacity check with the governing clause shown.

Axial capacity

For members carrying axial load, the ultimate squash load is found from the concrete and reinforcement areas using the uniform compressive stress block (Cl 10.3, 10.6.2.2). Slenderness is then addressed through the axial buckling capacity (Cl 10.4): the calculator classifies the column as braced or sway about each axis, computes the buckling load, and applies a moment magnifier that amplifies the design moment for second-order effects.

Bending and axial interaction

Moment capacity is evaluated with the axial demand acting simultaneously. For each axis the calculator constructs the interaction curve from key points: the decompression point (Cl 10.6.2.3), the balanced failure point (Cl 10.6.2.5), the pure bending capacity (Cl 8.1), and the general combined axial-and-moment condition (Cl 10.6.2.4-5). At each point it resolves the neutral axis location and parameter, the depth of the concrete compressive stress block, the concrete compression force, and the corresponding capacity reduction factor, giving the factored ultimate moment capacity at the applied axial load.

Biaxial bending

When bending acts about both axes at once, the biaxial moment and axial interaction is checked with the power-law rule of Cl 10.6.4. The power coefficient is derived from the axial utilisation, and the combined utilisation about the two axes must be 1.0 or less.

Shear

Shear about each axis is checked with the sectional design method (Cl 8.2). The calculator computes the effective shear depth and breadth, the angle of the compression strut, the web crushing limit, the concrete shear strength contribution, and the reinforcement contribution from the fitments, then reports the factored shear capacity against the shear demand. The simplified concrete shear method is valid when the concrete strength is 65 MPa or less with no prestressing, tension, or torsion.

Tension

For members in net axial tension the ultimate tensile load is taken from the reinforcement yield capacity with the relevant capacity factor, and checked against the tension demand.

Deflection: creep and shrinkage

Serviceability uses the simplified deflection method (Cl 8.5.3). The calculator derives the drying, autogenous, and total shrinkage strains (Cl 3.1.7) and the creep factor (Cl 3.1.8) from the concrete age at loading, member geometry, and climate environment. Cracked and uncracked second moments of area are combined into an effective second moment of area, and short- and long-term deflections are compared against the entered deflection and extension limits.

Assumptions

Torsion, prestressing, and post-tensioning are not considered, and detailing requirements (covered by Cl 4, 5, and 8.3, among others) are checked separately. For columns, the worst-case compression and moment actions are not necessarily from the same load combination, transmission of axial force through floor systems (Cl 10.8) is not checked, and columns in net tension are excluded. All utilisation ratios must be 1.0 or less for the design to pass.