Australian Steel Sections Guide — UB, UC, PFC, EA, UA per AS/NZS 3679.1

Complete reference for Australian hot-rolled structural steel sections. Covers Universal Beams (UB), Universal Columns (UC), Parallel Flange Channels (PFC), Equal Angles (EA), and Unequal Angles (UA) as manufactured to AS/NZS 3679.1:2016 Grade 300PLUS. Includes section designation conventions, dimensional ranges, selection guidance for common framing applications, and comparison tables showing mass per metre and key geometric properties.

Quick access: AS 4100 Beam Sizes | Section Properties Search | AS 4100 Beam Design Example | Beam Capacity Calculator

Section Designation System

Australian hot-rolled sections follow a systematic naming convention that encodes section type, nominal depth, and mass per metre:

The nominal depth is approximate. Actual section depth varies slightly between serial sizes within each mass group. Tolerances are specified in AS/NZS 3679.1:2016 Clause 7, with depth tolerance typically +/-2 mm for depths up to 300 mm and +/-3 mm for depths 300–600 mm.

Universal Beams (UB)

Universal Beams are the workhorse of Australian steel construction. With a depth-to-flange-width ratio typically between 1.3 and 2.5, UBs are optimised for bending resistance about the major (x-x) axis. Their relatively slender webs and generous flange widths provide efficient section moduli while minimising self-weight.

Dimensional Range

UB sections available in Australia range from 150UB14.0 (the smallest standard UB) to 610UB125 (the largest standard rolled section produced locally). Imported sections up to 1000 mm depth are available for special projects.

Note: Values are nominal from ASI handbook. Actual mill certificates may differ slightly. Use the online Section Properties Search for the full database of all serial sizes.

Selection Guidelines for UB

Floor beams (typical span 6–12 m): Start with 310UB to 410UB range. For a simply supported floor beam at 3 m tributary width with 5 kPa floor load, a 310UB40.4 typically works for 7 m span. Increase to 410UB53.7 for 9 m spans, and 460UB67.1 for 10 m spans. Always check serviceability deflection (span/250 for total load, span/500 for live load only per AS 4100 Table C1).

Portal frame rafters (typical span 15–30 m): Start with 460UB to 610UB range depending on spacing and roof pitch. A 25 m clear-span portal frame at 6 m bay spacing with 0.5 kPa roof live load typically requires 530UB82.0 rafters and 460UB67.1 columns (pin-base). Haunched connections at the eaves significantly reduce rafter sizes by increasing section depth at the maximum moment region.

Crane runway beams: Use heavier UB sections (410UB to 610UB) with a cap channel for lateral stiffness. Fatigue considerations per AS 4100 Section 11 may govern when the crane operates more than 500,000 cycles. The lateral deflection limit is typically span/600 for electric overhead travelling cranes.

Universal Columns (UC)

Universal Columns have approximately equal depth and width with thicker flanges than UBs of comparable mass. The near-square cross-section provides similar buckling resistance about both axes, making UCs efficient for axial compression. The flange thickness can be up to 50% greater than a comparable-mass UB, providing significantly higher minor-axis stiffness.

Dimensional Range

UC sections range from 150UC23.4 to 310UC158. Larger fabricated sections (welded box columns, built-up H-sections) are used when rolled UC dimensions are insufficient.

UC Selection for Columns

For a typical multi-storey column at 8 m grid with 5 kPa floor load:

• 4 storeys (axial load ~1,600 kN): 200UC46.2 at 3.5 m floor height gives nominal capacity φN_s ≈ 1,700 kN (adequate for braced frame, k_e = 0.85).
• 8 storeys (axial load ~3,200 kN): 250UC89.5 at 3.5 m floor height gives φN_s ≈ 3,400 kN.
• 12 storeys (axial load ~4,800 kN): 310UC137 at 3.5 m floor height gives φN_s ≈ 5,200 kN.

Always check combined actions if the column is part of a moment-resisting frame. The interaction check per AS 4100 Clause 8.4 may govern over pure axial capacity when bending moments exceed 15–20% of the section moment capacity.

Parallel Flange Channels (PFC)

PFC sections have a C-shaped cross-section with parallel flanges, distinguishing them from older tapered-flange channels. They are primarily used as bracing members, girts, purlins, and secondary framing elements. The shear centre lies outside the web, producing torsion under transverse loads applied through the web — always account for this in connection detailing.

Dimensional Range

PFC Application Notes

Bracing members: PFC sections are the default choice for roof and wall bracing in portal frame buildings. They are typically connected through the web using a single bolt or welded gusset plate connection. When subject to compression, the unbraced length for buckling about the minor axis controls capacity. The effective length factor k_e for bracing members is typically 1.0 unless end restraint can be demonstrated.

Girts and purlins: PFCs spanning horizontally between portal frames act as girts (wall) or purlins (roof). For a 200PFC18.2 spanning 6 m at 1.8 m spacing, the section can carry approximately 0.6 kPa wind pressure in bending. At 7.5 m spacing, upgrade to 250PFC25.7 or use cold-formed Z-purlins with bridging for better efficiency.

Lintels: PFC sections above door and window openings carry brick/block veneer loads plus wind pressure. For a 2.4 m opening width with 2.0 m of brickwork above, a single 150PFC15.3 typically works. For wider openings or higher loads, pair two PFCs back-to-back or use a UB section for the lintel.

Equal Angles (EA)

Equal Angles have two legs of identical length meeting at 90 degrees. They are efficient for axially loaded truss webs and chords, bracing members, and connection cleats. The centroid lies off both legs, so connection eccentricity must be considered in tension member design per AS 4100 Clause 7.3.

Standard Sizes

EA Design Notes

For truss web members in tension, the effective net area after deducting bolt holes governs capacity. For a single 75x75x6 EA with one M20 bolt hole (22 mm diameter) in one leg, A_n = 874 - 22 x 6 = 742 mm^2. The design tensile capacity φN_t = 0.9 x A_n x f_u = 0.9 x 742 x 440 = 294 kN for Grade 300.

For compression members, the minimum radius of gyration r_min governs buckling. A 75x75x6 EA has r_min = 14.8 mm. At 2.0 m unbraced length, L_e / r = 2,000 / 14.8 = 135, giving α_c ≈ 0.30 from AS 4100 Table 6.3.3. The design compressive capacity is approximately φN_c = 0.9 x α_c x A_g x f_y = 0.9 x 0.30 x 874 x 300 = 71 kN.

Unequal Angles (UA)

Unequal Angles have legs of two different lengths, making them useful for lintels (long leg vertical), connection angles (long leg provides bolt access), and situations where loading is predominantly in one plane. The longer leg provides increased bending stiffness in one direction at a lower weight penalty than an equivalent equal angle.

Common Sizes

UA Application: Lintel Angles

For residential brick veneer lintels, a single 125x75x10 UA with the long leg vertical is common for openings up to 2.1 m. The long leg provides depth for bending, while the short leg supports the outer brick skin. For 2.4–3.0 m openings, use 150x90x10 UA or pair two angles back-to-back.

The bending capacity is calculated about the geometric axis (not principal axis) when the load is applied through the shear centre. AS 4100 Clause 5.2 permits simplified design using the geometric axis section modulus for loads applied in the plane of the long leg, provided the maximum slenderness ratio does not exceed 200.

Material Grade and Tolerances

All Australian hot-rolled sections listed above are supplied in Grade 300PLUS to AS/NZS 3679.1:2016 unless Grade 350 is specified. Key mechanical properties:

Rolling tolerances per AS/NZS 3679.1 Clause 7:

• Depth: +/-2 mm for d ≤ 300 mm; +/-3 mm for 300 < d ≤ 600 mm
• Flange width: +/-3 mm for b_f ≤ 150 mm; +/-4 mm for b_f > 150 mm
• Web thickness: +/-0.5 mm for t_w ≤ 5 mm; +/-0.8 mm for 5 < t_w ≤ 10 mm
• Mass: +/-4% of nominal mass

Section Selection Workflow

For efficient structural design with Australian sections, follow this systematic approach:

1. Determine the structural action: Is the member primarily in bending (beam), compression (column), combined actions (beam-column), or tension (brace)?

2. Select the section family: UB for beams, UC for columns, PFC for bracing and secondary members, EA for truss webs, UA for lintels and connection angles.

3. Estimate the required size: For beams, start with depth ≈ span/20 for simply supported, span/25 for continuous. For columns, start with a UC where the nominal depth approximately equals the lesser of the floor height/20 and the grid dimension/15.

4. Check strength limit states: Verify moment capacity φM_s, shear capacity φV_v, and combined actions per AS 4100 Clauses 5 and 8.

5. Check serviceability: Deflection limits per AS 4100 Table C1 (span/250 total load, span/500 live load for beams; height/300 for columns under wind).

6. Check connection geometry: Ensure bolt pitch and edge distances can be accommodated within the flange and web dimensions per AS 4100 Clause 9.5.

For automated section selection and capacity checking, use the Steel Calculator Section Properties tool with the AS 4100 design module.