Australian Column Capacity Calculator — AS 4100

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Design per AS 4100:2020

This calculator checks steel column compressive capacity per AS 4100-2020 Clause 6 for Australian UC sections. Select "AS 4100" from the code selector to use Australian capacity factors and slenderness rules.

Section Capacity — Clause 6.2

φNs = φ × kf × An × fy (φ = 0.9)

kf = form factor (Ae/Ag) accounting for local buckling in slender sections. For compact sections, kf = 1.0.

Member Capacity — Clause 6.3

φNc = φ × αc × Ns ≤ φNs

αc = member slenderness reduction factor based on the modified slenderness:

λn = (le/r) × √(fy/250)

The αc factor follows the AS 4100 column curve, which uses the Perry-Robertson formulation with αb = 0.5 for hot-rolled UB and UC sections.

Worked Example

Problem: Check a 200UC52.2 column, Grade 300, 4.0 m effective length.

Axial load: N* = 800 kN (factored) | Steel: Grade 300 (fy = 300 MPa)

Solution:

  1. Section properties: Ag = 6660 mm², rx = 89.1 mm, ry = 50.8 mm (ry controls)
  2. Section capacity: φNs = 0.9 × 1.0 × 6660 × 300 × 10⁻³ = 1798 kN
  3. Modified slenderness: λn = (4000/50.8) × √(300/250) = 78.7 × 1.095 = 86.2
  4. αc factor: from AS 4100 Table 6.3.3(1), αc ≈ 0.726
  5. Member capacity: φNc = 0.726 × 1798 = 1305 kN
  6. Check: 800 ≤ 1305 → OK (usage: 61%)

Result: 200UC52.2 is adequate for compression.

How to Use

  1. Select "AS 4100" from the code selector
  2. Choose an Australian UC section
  3. Select Grade 300 or Grade 350
  4. Enter effective length (KL) in metres
  5. Enter the applied factored axial load
  6. Review φNs, φNc, and slenderness results

Related Australian Resources

FAQ

What is the form factor kf? The form factor kf = Ae/Ag accounts for local buckling in slender sections per AS 4100 Clause 6.2. For compact sections with λ ≤ λey, kf = 1.0. For slender elements, the effective area Ae is reduced based on the effective width per Clause 6.2.4.

What is αb for Australian UC sections? Hot-rolled UC, UB, and welded sections with fy ≤ 450 MPa use αb = 0.5 per AS 4100 Table 6.3.3(1). This corresponds to the AISC column curve. Cold-formed sections and very thick sections use different αb values.