Concrete Column Design to AS 3600

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The Concrete Column to AS 3600 performs ultimate limit state (ULS) capacity checks for a concrete section subjected to axial load. It checks combined compression-flexural actions by plotting the interaction diagram, and it also checks the shear capacity.

All calculations are performed in accordance with AS3600:2018.

For an in-depth guide about how to produce the interaction diagram, check out our Concrete Column Design Guide.

What is an interaction diagram?

An interaction diagram is a graphical representation of the ultimate strength of a column's cross-section. In the Australian Standards, it is defined by four critical points which form the boundary of failure for a section subject to combined bending and axial load. The critical points are called:

• Squash load
• Decompression point
• Balanced point
• Pure bending

Each point on the boundary of an interaction diagram describe a value for the axial capacity and bending capacity for a given reinforcement arrangement based on a specific neutral axis depth.

How do I produce an interaction diagram to AS3600:2018?

You can produce the interaction diagram in two ways: by hand (conservative approach) or by using a software package (accurate approach).

• By hand: calculate the axial capacity and flexural capacity of the four critical points identified in clause 10.6.2, then draw a line of best fit through the four points.
• Using a computer: define a list of values of the neutral axis depth from close to zero to the section depth, and for each value of neutral axis depth, calculate the axial capacity and bending capacity.

Using a computer with many increments of neutral axis depth, will produce a curved diagram as oppose to one with straight lines. Doing so proves more capacity of a concrete section close to the boundary of it's interaction diagram.

Do I need to design a concrete column for shear?

Shear is not usually a design concern in columns because it's applied compression load increases the shear resistance of the concrete section. However, shear reinforcement (called 'links', 'ligs' or 'fitments') are often included in concrete columns in reality to ensure the longitudinal reinforcement bars don't buckle, and also to ensure stability of the reinforcement cage during construction. Nonetheless, our calculator does a quick shear capacity check on the concrete section.

How to prepare an engineering report

Engineering reports require a balance of clarity, precision, and professionalism. Here are some best practices for preparing a report we use at CalcTree:

• Clear and visual: Use heading types to establish a logical structure, add diagrams for clarity.
• Integrate sources: Map data from your calculation tools such as spreadsheet or Python to your report.
• Units: Assign units to physical quantities.
• Compliance: State and hyperlink the relevant codes of practices.
• Peer review: Share a link to your page with team members for reviews and feedback.

For more on verification, see CalcTree’s internal methods.