AS 3600 designs a beam through its own ductility parameter kuo — a truly different notation to Eurocode 2's K/K′ or ACI 318's c/dt ratio, but checking the same underlying idea: keep the neutral axis shallow enough that the section stays ductile.
Every check above runs automatically inside the Structyze RCC Beam module, free to try online — change any input and every downstream number recalculates instantly, with the governing code clause shown next to each result.
The Example We'll Use
- Clear span 5 m, continuous both ends
- b × D = 300 × 500 mm, cover 30 mm
- Superimposed dead 5 kN/m, live 8 kN/m
- Concrete N32 (f′c = 32 MPa), steel 500N (fsy = 500 MPa)
- Main bars 4–N20; fitments N10 (2-leg) at 150 mm
Working Through It
Design load w* = max(1.35G, 1.2G+1.5Q) = max(11.6, 22.3) = 22.3 kN/m — the load-and-live-load combination governs. Support moment M− = 22.3(5)²/12 ≈ 46.5 kN·m governs over the span moment.
Working through α2 = 0.85 and γ = 0.826 (both f′c-dependent) gives a required As around 248 mm² — just above the Cl 8.1.6.1 minimum of 226 mm², so calculated demand narrowly governs here rather than the code floor. The ductility check kuo = 0.044, far below the 0.36 limit, confirms the section is comfortably ductile.
Shear demand V* = 45.8 kN at d from the support stays well under the concrete-alone capacity φVuc = 77.3 kN (using the simplified kv = 0.15 with minimum fitments), so only minimum fitments are required — N10 at 150 mm, well inside the 0.5D = 250 mm spacing limit.
What Governs, and Why
Concrete shear governs at utilisation 0.59, with fitment spacing close behind at 0.60. Because 500N steel matches Eurocode 2's B500 grade, the required steel area here tracks the Eurocode 2 volume closely for the same moment — and AS 3600's simplified kv = 0.15 gives a shear capacity that sits between the Eurocode and CSA A23.3 values for the identical section.
Where Structyze Takes Over
Every check above runs automatically inside the Structyze RCC Beam module, free to try online — change any input and every downstream number recalculates instantly, with the governing code clause shown next to each result.
The free trial covers a curated set of flagship modules including this one. For the full catalogue — RCC, Steel, Composite, Timber, Masonry and more, across 20+ design codes — buy the full Structyze desktop app or see everything it does on the Software page.
Quick FAQ
What is kuo checking, exactly?
It's the ratio of the neutral-axis depth (adjusted by γ) to the effective depth — keeping it under 0.36 ensures the section fails by steel yielding first (ductile) rather than sudden concrete crushing, the same underlying goal as Eurocode 2's K′ limit or ACI 318's tension-controlled strain check, just expressed through AS 3600's own notation.
Why compare AS 3600, Eurocode 2 and CSA A23.3 for the same beam?
All three use materially similar 500 MPa-class reinforcement and broadly comparable limit-state philosophies, so a side-by-side comparison on an identical span and section isolates how much each code's own partial factors and shear provisions shift the final steel quantity and margin.
Final Thoughts
AS 3600's kuo ductility parameter is functionally the same idea as Eurocode 2's K′ or ACI 318's strain check, dressed in different notation — worth recognising as the same underlying safeguard rather than three unrelated rules.