UK Beam Capacity Calculator — EN 1993 + UK National Annex

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

Calculate the bending and shear resistance of UK steel sections per Eurocode 3 with UK National Annex modifications. The calculator supports UB (Universal Beams), UC (Universal Columns), and UK channel sections.

Supported Sections and Grades

UB sections (Universal Beams) — 127×76 UB to 1016×305 UB, the standard UK beam sections
UC sections (Universal Columns) — 152×152 UC to 356×406 UC, standard UK column sections
UK channels — PFC and channel sections per BS 4-1
Steel grades — S235, 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 limits
Bending moment resistance — Mc,Rd = Wpl × fy / γM0 per Clause 6.2.5
Lateral-torsional buckling — Mb,Rd = χLT × Wy × fy / γM1 per Clause 6.3.2, using UK NA buckling curves
Shear resistance — Vc,Rd = Av × (fy/√3) / γM0 per Clause 6.2.6
Bending and shear interaction — Reduced moment resistance when VEd > 0.5Vc,Rd (Clause 6.2.8)

UK National Annex Modifications

The UK National Annex to EN 1993-1-1 specifies:

Partial factors: γM0 = 1.0, γM1 = 1.0 (same as recommended)
LTB curve selection: UK NA specifies specific buckling curves for UB/UC sections
Lateral-torsional buckling: Simplified assessment method per UK NA Clause 6.3.2.2
Deflection limits: Span/200 for total deflection, span/250 for imposed loads (UK practice)

Worked Example

Problem: Check a 533×210 UB 92 kg/m beam in S355 steel for a 7.5 m simply supported span with a factored UDL of 40 kN/m.

Solution:

Section: 533×210 UB 92, S355 (fy = 355 MPa, tf = 15.6 mm)
Section class: Class 1 (compact)
Plastic modulus Wpl,y = 2360 cm³
Design moment: MEd = 40 × 7.5² / 8 = 281 kNm
Moment resistance: Mc,Rd = 2360 × 10³ × 355 / 1.0 = 838 kNm
Utilisation: 281/838 = 0.34 (34%) — OK
Design shear: VEd = 40 × 7.5 / 2 = 150 kN
Shear resistance: Vc,Rd = 5100 × (355/√3) / 1.0 = 1045 kN
Utilisation: 150/1045 = 0.14 (14%) — OK

Result: 533×210 UB 92 in S355 is adequate. Moment governs at 34% utilisation.

Related Resources

FAQ

What is the difference between UK and EU beam design? The UK uses EN 1993-1-1 with a UK National Annex that specifies modifications to partial factors, buckling curve selection, and LTB assessment methods. The core calculation methodology is the same as Eurocode 3.

Does the calculator use UK or European buckling curves? The calculator uses the UK National Annex recommended buckling curves for UK sections. UB sections typically use curve 'a' for minor axis buckling, while UC sections use curve 'b' or 'c' depending on flange thickness.

What steel grade is most common in UK construction? S355 is the most widely used structural steel grade in the UK, followed by S275 for lighter applications. S460 is available but less common in building structures.

Are UK and European sections the same? UK UB and UC sections are based on BS 4-1, which differs from European IPE/HEA/HEB sections. UB sections have a different flange width-to-depth ratio compared to European sections.