Concrete Beam Design to AS 3600

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The Concrete Beam to AS 3600 calculator computes the design capacities of a reinforced concrete beam to meet flexural and shear design requirements to ultimate limit state design (ULS) methods.

All calculations are performed in accordance with AS3600:2018.

What are the main changes to AS3600:2018 compared to the previous edition AS3600:2009?

There has been significant updates and changes since the 2009 edition, mainly concerning:

• Rectangular stress-block configuration (Section 8.1.3)
• Values of the capacity reduction factor Φ, for different action effects (Table 2.2.2)
• Shear and torsion design (Section 8.2)

What is the role of the rectangular stress-block in concrete beam design to AS3600:2018?

The flexural (also referred to as 'bending' or 'moment') capacity of a beam cross-section is determined using the Rectangular Stress Block method (Section 8.1.2). The compressive stress distribution in concrete under bending is curved in reality, however it can be converted to an equivalent rectangular stress block by the use of reduction factors α2 and γ.

How do you design a concrete beam against shear to AS3600:2018?

The total shear capacity of a section is the combination of the shear strength contributed by concrete and shear reinforcement. AS3600 (similar to other international codes) use a truss analogy of shear resistance, where the diagonal concrete strut is in compression and the vertical tie (provided by shear reinforcement) is in tension. The strut angle θv affects the distribution of shear resistance:

• a smaller θv means the strut crosses more shear ligs and therefore a smaller area of shear ligs is needed
• a larger θv means more of the applied shear force is taken by the vertical tie (shear ligs) and therefore a larger area of shear ligs is needed

The code limits θv ≥ 36° to ensure the required shear reinforcement is not under-conservative.

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