UK Universal Beam Sizes — UB Section Table

Universal Beams (UB), now designated UKB under BS EN 10365:2017, are the primary hot-rolled section for bending members in UK steel construction. This reference provides a comprehensive table of UB section dimensions and properties, span-to-depth guidance, and EN 1993-1-1 design notes.

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UB Section Table

Dimensions and section properties for the most commonly specified Universal Beam sections. Standard steel grade: S355J2 to BS EN 10025-2 (Fy = 355 MPa for t ≤ 16 mm, Fy = 345 MPa for 16 < t ≤ 40 mm). All values from SCI P363 Blue Book and BS EN 10365:2017.

Source: SCI P363 — Steel Building Design: Design Data (Blue Book). Values for S275/S355 hot-rolled sections per BS EN 10365:2017. Verify against the current SCI edition.

How to Read the UB Designation

A UB designation follows the pattern: depth×width×mass

Example: 457×191×67 UB

• 457 = approximate section depth in mm (actual depth = 453.4 mm)
• 191 = approximate flange width in mm (actual width = 189.9 mm)
• 67 = mass per metre in kg/m (67.1 kg/m)

The depth and width are nominal labels from the serial size group, not exact dimensions. Use the actual values from the table for design calculations.

Span-to-Depth Ratios for UB Sections

For preliminary sizing of simply supported UB beams:

The UK National Annex to EN 1993-1-1 specifies L/200 as the general limit for floor beams carrying non-brittle finishes. This is significantly less restrictive than the AISC L/360 default, meaning UK-designed beams can be shallower than US-designed beams for the same span.

Quick Sizing Examples

• 8 m floor beam (no brittle finishes): Try depth = 8,000/20 = 400 mm → 406×178×60 UB
• 10 m floor beam (brittle finishes): Try depth = 10,000/18 = 556 mm → 533×210×92 UB
• 12 m roof beam: Try depth = 12,000/24 = 500 mm → 457×191×89 UB or 533×210×82 UB

Always verify with a full calculation including bending, shear, deflection, and lateral-torsional buckling checks.

EN 1993-1-1 Design Notes for UB Sections

Section Classification

UB sections in S355 steel are typically Class 1 in bending about the major axis — meaning they can develop full plastic moment capacity with sufficient rotation ductility for plastic analysis. Key classification limits per EN 1993-1-1 Table 5.2:

For the deepest heavy UB sections (e.g., 914×305×289), the web may classify as Class 2 depending on the cw/tw ratio. Check SCI P363 or use the Beam Capacity Calculator for section classification.

Lateral-Torsional Buckling (LTB)

LTB is usually the governing limit state for UB beams without continuous lateral restraint. The elastic critical moment Mcr is calculated per EN 1993-1-1 Clause 6.3.2.2:

• For simply supported beams with uniform moment: Mcr = (π² × E × Iz / Lcr²) × √(Iw/Iz + Lcr² × G × It / (π² × E × Iz))
• The reduction factor χLT depends on the slenderness λLT = √(Wy × fy / Mcr)
• Under the UK National Annex, buckling curve a applies to UB sections in S275 and S355 for strong-axis bending

Shear Check

UB sections have relatively thin webs compared to UC sections, so shear capacity should always be checked. Per EN 1993-1-1 Cl 6.2.6:

Vpl,Rd = Av × (fy / √3) / γM0

Where Av = A - 2btf + (tw + 2r)tf for rolled I-sections (but not less than η × hw × tw). The UK NA specifies η = 1.0 for shear area calculation.

Deflection Check

The UK National Annex specifies:

• General floors and roofs: δ ≤ L/200 (vertical deflection from variable actions)
• Floors supporting brittle finishes: δ ≤ L/360
• Cantilevers: δ ≤ L/180

Note: For office floors designed to L/200 (about 40 mm for an 8 m span), the deflection limit is rarely the governing criterion — strength or LTB typically governs for UB beams. This differs from US practice where L/360 usually governs.

Frequently Asked Questions

What is the difference between a 457×191×67 UB and a 457×191×74 UB? Both sections share the same nominal depth (457 mm) and width (191 mm), but the 74 kg/m version has a thicker web (9.0 mm vs 8.5 mm) and thicker flanges (14.5 mm vs 12.7 mm). This gives the heavier section 13% more plastic section modulus (1,660 cm³ vs 1,480 cm³) and 13% more second moment of area (33,300 cm⁴ vs 29,400 cm⁴). Use the 67 kg/m version for lightly loaded beams and the 74 kg/m version where slightly higher capacity is needed without moving to the next serial size.

What steel grade is standard for UK UB sections? S355J2 to BS EN 10025-2 is the standard grade. For thicknesses up to 16 mm, Fy = 355 MPa; for 16-40 mm, Fy = 345 MPa. S275J2 may be specified for cost savings on lightly loaded members. For heavy sections (flange thickness > 100 mm), grade S355J2 may have reduced yield strength per EN 10025-2 — check the mill certificate or specify S355K2 for fracture-critical applications.

How do I convert UB design from BS 5950 to EN 1993-1-1? The main changes are: (1) partial factors — γM0 = 1.00 (vs γm = 1.0 in BS 5950) and γM1 = 1.00 (buckling); (2) section classification follows EN 1993-1-1 Table 5.2 with different c/t limits; (3) LTB uses Mcr-based slenderness (χLT method) instead of the BS 5950 Pb method; (4) deflection limits from the UK NA (L/200 general vs BS 5950 Table 6 typical L/300). Use the Beam Capacity Calculator with EN 1993-1-1 selected for automatic conversion.

Related Pages

• UK Steel Section Guide — UB, UC, PFC, CHS, SHS
• UK Steel Beam Sizes — UB, UC, PFC Chart
• UK Steel Design Guide — BS EN 1993, National Annex & SCI
• EN 1993-1-1 Beam Design Guide
• European Beam Sizes — IPE, HEA, HEB
• Metric Steel Sections — IPE, HEA, HEB, UB, UC
• Steel Beam Capacity Calculator
• Full Section Properties Database
• How to Verify Calculator Results
• Disclaimer

This page is for educational reference only. All section data sourced from SCI P363 (Blue Book) and BS EN 10365:2017. Verify dimensions and properties against the current SCI edition, mill certificates, and the applicable National Annex before procurement or design. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent PE/SE or CEng verification.

Design Resources

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• Steel Beam Capacity Calculator
• Beam Deflection Calculator
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• Beam Span Table Tool

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• Steel Beam Calculator Guide
• Beam Capacity Worked Example
• Beam Deflection Worked Example
• Steel Beam Design Workflow
• Steel Beam Span Reference