Steel · Columns & beam-columns

Steel column (AS 4100 compression + bending) calculator

Section and member compression capacity about both axes, moment capacities and combined-action utilisation for UB/UC sections.

Standard: AS 4100 Cl 6.2–6.3 (αc, λn, αb) · Cl 8.3–8.4 combined actions

Inputs in the worked example

The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.

Diagram for the worked example

kf = Ae/Ag from effective widths (flange outstand λey = 16, web λey = 45, HR)
λn = (Le/r)·√kf·√(fy/250)
αa = 2100(λn − 13.5)/(λn² − 15.3λn + 2050); λ = λn + αa·αb; η = 0.00326(λ − 13.5)
ξ = [(λ/90)² + 1 + η]/[2(λ/90)²]; αc = ξ[1 − √(1 − (90/ξλ)²)]
Mrx = 1.18Msx(1 − N*/φNs) ≤ Msx (compact doubly symmetric I)
Mix = Msx(1 − N*/φNcx) and Mox = Mbx(1 − N*/φNcy): simplified, conservative forms of Cl 8.4

Compression member: UB / UC (library) — Major and minor axis member capacity for library or custom I-sections, with independent effective lengths.
Compression member: SHS / RHS — SHS/RHS compression capacity computed from outside dimensions and thickness, with the local buckling form…
Compression member: CHS — CHS compression capacity computed from outside dimensions and thickness, with the local buckling form factor.
Compression member: single equal angle — Equal angle strut: area and minor principal radius rv from dimensions, local buckling kf and member capacity…
Compression member: PFC channel — Channel strut with properties computed from d, bf, tf, tw and capacity about both axes.
Beam-column interaction (I-section) — Section capacity reduced for axial load, in-plane member capacity and out-of-plane (lateral buckling)…
Rod bracing (tension-only) — Brace force from the bay shear and geometry with a prestress allowance, threaded rod capacity on the tensile…

For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.