180UB78 AS/NZS 3679.1 Grade 300 — Australian Universal Beam Section Properties

180UB78 is an Australian UB (Universal Beam) per AS/NZS 3679.1 hot-rolled structural steel section. Standard Australian UB dimensions. Verify against Liberty OneSteel / InfraBuild section catalog.

Dimensions (Metric)

Elastic Section Properties (Metric)

Torsional Properties

Section Profile Summary

This is a standard hot-rolled I-section profile covered by AS 4100. The tabulated section properties are computed from the nominal dimensions per the governing material standard. With Ix = 3,803 cm⁴, the strong-axis flexural stiffness is suitable for preliminary sizing of beams and beam-columns.

At 180 mm deep, this is a mid-range section for secondary beams, roof purlins, and bracing in standard framing.

Key Design Checks (AS 4100)

Design Notes

• Compactness: Verify flange and web slenderness against AS 4100 Table B4.1 classification limits for the governing load case (pure compression, pure flexure, or combined).
• Combined loading: For members under simultaneous axial force and bending, use the interaction equations in AS 4100 Section H. The governing equation depends on the ratio of required to available axial strength.
• Connection limit states: Check bolt bearing, tear-out, block shear, and weld strength at all connections. The governing connection limit state often controls the member size selection.

Verification (AS 4100): All designs using this section must be verified by a licensed Professional Engineer. Before finalizing member selection, check beam-column interaction (P-M), lateral-torsional buckling, serviceability deflections, and all connection limit states. See Engineering Disclaimer.

Worked Example: Office floor beam — 180ub78

Scenario: Commercial office floor — typical open-plan layout with raised floor. Simply supported I-section, 4.3 m span, 2.4 m tributary width. Service loads: 4.0 kPa dead + 3.0 kPa live (16.8 kN/m total).

Given:

• Span L = 4320 mm (4.3 m)
• Total service load w = 16.8 kN/m
• Live load portion w_L = 7.2 kN/m
• Section 180ub78: Ix = 38.0 × 10⁶ mm⁴, Sx = 423,000 mm³, Zx = 498,000 mm³
• Steel: fy = 300 MPa, E = 200,000 MPa
• Design moment resistance: φMn = 0.9 × Zx × fy = 134 kN·m

Step 1 — Live load deflection:

Δ_LL = 5 w_L L⁴ / (384 E Ix)

Δ_LL = 5 × 7.2 × (4320)⁴ / (384 × 200000 × 38,030,000)

Δ_LL = 4.3 mm

Step 2 — Deflection limit (L/300):

Δ_limit = L / 300 = 4320 / 300 = 14.4 mm

Step 3 — Dead + live deflection:

Δ_total = 10.0 mm

Step 4 — Design check:

✓ Live load deflection is within the L/300 limit.

Verify the design moment M*_Ed (from factored loads 1.35G + 1.5Q per AS 4100) does not exceed φMn = 134 kN·m. Also confirm shear resistance and bearing details at the supports.

Related Resources

• Steel Beam Capacity Calculator
• Column Capacity Calculator
• Beam Deflection Calculator
• Section Properties Calculator
• Steel Grades Reference
• Section Comparison Tool

Design Resources

• Section Properties Lookup — Compare with similar sections
• Steel Beam Sizes Reference — Standard beam dimensions

Educational reference only. Verify all section properties against the current AS 4100 Manual and mill certificates before design. Results are PRELIMINARY — NOT FOR CONSTRUCTION.