Australian Universal Column Guide — UC Sizes and Compression Design

Complete engineering reference for Australian universal column (UC) sections manufactured to AS/NZS 3679.1:2016. Covers the full size range with section properties, axial capacities, buckling classification, column design workflow per AS 4100:2020 Clause 6, and worked examples. All values in metric units consistent with AS 4100.

Related pages: AU Universal Beam Guide | Column Design Worked Example | Column Buckling Reference | Base Plate Design

Universal Column Section Properties — Full Range

Australian UC sections are designated by nominal depth (mm) followed by mass per metre (kg/m). The designation 200UC46.2 indicates a universal column approximately 200 mm deep with a mass of 46.2 kg/m. Unlike UBs, UC sections have depth and flange width approximately equal (d/bf ~ 1.0), providing balanced radii of gyration in both axes.

150 UC Series

200 UC Series

250 UC Series

310 UC Series

Typical Applications by UC Size

Column Buckling Curves — AS 4100 Clause 6.3.3

The member capacity reduction factor alpha_c depends on the modified slenderness lambda_n and the section shape constant alpha_b:

UC sections use alpha_b = 0 (hot-rolled UB/UC sections per Table 6.3.3(2)).

Comparison: Australian UC vs International Column Sections

Effective Length Factors for Typical Column Conditions

Worked Example: UC Column Design for Multi-Storey Building

Problem: Design an internal column for a 6-storey office building. The column is 3.8 m floor-to-floor with moment-resisting connections at each end. Factored axial load N* = 2,150 kN. Assume Grade 300 steel (fy = 300 MPa). The column is part of a braced frame.

Step 1: Determine effective length

ke = 0.85 (braced frame, rotational restraint at each end per AS 4100 Clause 4.6.3.3)

Le = ke x L = 0.85 x 3800 = 3230 mm

Step 2: Trial section

Try 250UC89.5: A_g = 11,400 mm^2, ry = 68.7 mm, kf = 1.0 (compact section)

Step 3: Calculate modified slenderness

lambda_n = (Le / ry) x sqrt(kf) x sqrt(fy / 250) = (3230 / 68.7) x 1.0 x sqrt(300/250) = 47.0 x 1.095 = 51.5

Step 4: Determine alpha_c

For alpha_b = 0 (hot-rolled UC), at lambda_n = 51.5: alpha_c = 0.91 (from table)

Step 5: Calculate member capacity

Ns = kf x An x fy = 1.0 x 11,400 x 300 / 1000 = 3,420 kN

Nc = alpha_c x Ns = 0.91 x 3,420 = 3,112 kN

phi Nc = 0.90 x 3,112 = 2,801 kN > 2,150 kN — OK.

Step 6: Check lighter section

Try 250UC72.9: A_g = 9,280 mm^2, ry = 68.3 mm

lambda_n = (3230 / 68.3) x 1.095 = 51.8, alpha_c = 0.91

Ns = 1.0 x 9,280 x 300 / 1000 = 2,784 kN

Nc = 0.91 x 2,784 = 2,533 kN

phi Nc = 0.90 x 2,533 = 2,280 kN > 2,150 kN — OK.

Result: 250UC72.9 Grade 300 is adequate with utilisation = 2,150 / 2,280 = 0.943.

Frequently Asked Questions

Can I weld stiffeners to a UC section without compromising the column capacity?

Yes, but the welding procedure must follow AS/NZS 1554.1 for structural welding. Stiffeners (continuity plates, web doubler plates, or cap plates) are routinely welded to UC sections in Australian fabrication practice. The heat-affected zone (HAZ) does not reduce the column capacity provided that: (1) the stiffener is proportioned to match the force being transferred, (2) the weld is sized for the full stiffener force, and (3) the welding sequence minimises distortion. For heavy UC sections (flange thickness > 20 mm), preheat (typically 75-100 degree C for Grade 300) may be required to prevent hydrogen cracking.

What is the typical splice detail for UC columns?

UC column splices in multi-storey construction typically use flange cover plates and web splice plates, bolted with Grade 8.8/S bolts. For 250UC72.9 columns, a typical splice uses 10 mm thick flange cover plates with 6x M20 bolts per flange, and a 10 mm web splice plate with 4x M20 bolts. The splice is designed to transfer the full column capacity in compression (bearing on prepared contact surfaces) and a nominal tension of 25% of the column capacity for robustness.

How does fire rating affect UC column selection?

For columns requiring fire resistance, AS 4100 Clause 12 provides methods for determining capacity at elevated temperatures. The key factor is the section factor (exposed perimeter / cross-sectional area) in m^-1. UC sections have a lower section factor than UB sections of equivalent mass because their compact shape minimises exposed surface area. For a 1-hour FRL, unprotected 250UC72.9 columns can typically carry 60-70% of their ambient capacity depending on the load ratio.

Can UC sections be used horizontally as beams?

UC sections can be used as beams, particularly where lateral-torsional buckling restraint is limited, because their wider flange provides greater minor-axis stiffness. A 250UC72.9 used as a beam has Zx = 980 x 10^3 mm^3 (comparable to a 410UB53.7 with Zx = 647 x 10^3 mm^3), but at 72.9 kg/m versus 53.7 kg/m. The UC is 36% heavier for the same bending capacity — not economical for standard beam applications. UCs as beams are justified only when the wider flange is needed for connection detailing or lateral stability.

Educational reference only. All design values must be verified against the current edition of AS 4100:2020 and the project specification. This information does not constitute professional engineering advice. Always consult a qualified structural engineer for design decisions.

Disclaimer: This content is for educational purposes only. Results must be verified by a licensed professional engineer. Steel Calculator provides preliminary design tools — NOT a substitute for professional engineering judgment.