UK Column Capacity Calculator — EN 1993 + UK National Annex

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Design per EN 1993-1-1 + UK National Annex

Check the compressive resistance and flexural buckling of UK steel columns per Eurocode 3 with UK National Annex modifications. Supports UB, UC sections in S275 and S355 steel grades.

Supported Sections and Grades

• UC sections (Universal Columns) — 152×152 UC to 356×406 UC, ideal for columns
• UB sections (Universal Beams) — 127×76 UB to 1016×305 UB (used as columns in light applications)
• Steel grades — S275, S355 (most common in UK), S460

Design Checks Performed

• Section classification — Class 1, 2, or 3 per EN 1993-1-1 Table 5.2 with UK NA modifications
• Cross-section compression resistance — Nc,Rd = A × fy / γM0 per Clause 6.2.4
• Flexural buckling resistance — Nb,Rd = χ × A × fy / γM1 per Clause 6.3.1
• UK NA buckling curves — Specific curve selection per UK NA to Table 6.2
• Combined compression and bending — Clause 6.3.3 interaction

Worked Example

Problem: Check a 203×203 UC 60 kg/m column in S355 steel with a 4.5 m effective length and a factored axial load of 1800 kN.

Solution:

• Section: 203×203 UC 60, S355 (fy = 355 MPa)
• Area A = 7640 mm², radius of gyration iy = 89.6 mm
• Cross-section resistance: Nc,Rd = 7640 × 355 / 1.0 = 2712 kN
• Non-dimensional slenderness: λ̄ = (4500/89.6) / (93.9 × 0.81) = 0.66
• UK NA buckling curve: UC section → curve 'c' (tf = 14.2 mm ≤ 40 mm) → χ = 0.79
• Buckling resistance: Nb,Rd = 0.79 × 7640 × 355 / 1.0 = 2143 kN
• Utilisation: 1800/2143 = 0.84 (84%) — OK

Result: 203×203 UC 60 in S355 is adequate. Buckling governs at 84% utilisation.

Related Resources

• UK Column Design Guide
• UK Column Buckling Guide
• UK Steel Design Guide
• UK Steel Grades

FAQ

What buckling curves does the UK NA specify? The UK National Annex specifies buckling curves based on section type and axis. For UC sections: curve 'b' for major axis, curve 'c' for minor axis (when tf ≤ 40 mm). For UB sections: curve 'a' for major axis, curve 'b' for minor axis.

How does the UK NA modify the slenderness calculation? The UK National Annex uses the same non-dimensional slenderness λ̄ = (Lcr/i)/(π√(E/fy)) as the core Eurocode 3. The key difference is in the selection of the appropriate buckling curve from Table 6.2.

Does the calculator handle UK NA modified γM factors? Yes. The UK National Annex specifies γM0 = 1.0 and γM1 = 1.0 (consistent with the recommended values in EN 1993-1-1).