UK Steel Section Guide — UB, UC, PFC, CHS, SHS

UK structural steel construction relies on a standardised family of hot-rolled sections defined by BS EN 10365 and detailed in the SCI P363 Blue Book. Choosing the right section type for your application — beam, column, bracing, or hollow section — is the first step in any efficient steel design. This guide covers each UK section family, its typical applications, how it compares to European section series, and how to select the right section for your structural design.

UK Section Families at a Glance

Universal Beams (UB)

Universal Beams, designated UKB in the latest BS EN 10365 revision, are the most common section type in UK steel construction. They have a narrower flange relative to depth, making them efficient for bending about the major axis.

UB Designation System

A UB is denoted by approximate depth × flange width × mass per metre:

• 152×89×16 UB: approximately 152 mm deep, 89 mm wide, 16 kg/m
• 457×191×67 UB: approximately 457 mm deep, 191 mm wide, 67 kg/m
• 610×229×113 UB: approximately 610 mm deep, 229 mm wide, 113 kg/m

Typical Span Ranges for UB Sections

These are indicative only. Actual maximum span depends on loading, deflection limits, lateral restraint, and the design standard. Always verify using the Beam Capacity Calculator.

When to Use UB vs UC

Universal Columns (UC)

Universal Columns (UKC) have nearly equal depth and width with thicker flanges than UB sections. This geometry maximises compression resistance and gives similar stiffness about both axes — essential for columns where buckling can occur about either axis.

UC Designation System

A UC is denoted by depth × width × mass per metre:

• 152×152×23 UC: approximately 152 mm square, 23 kg/m
• 203×203×52 UC: approximately 203 mm square, 52 kg/m
• 254×254×89 UC: approximately 254 mm square, 89 kg/m
• 305×305×137 UC: approximately 305 mm square, 137 kg/m
• 356×368×153 UC: approximately 356 × 368 mm, 153 kg/m (slightly wider than deep)

Axial Capacity Guide for UC Sections (S355)

Values are approximate for flexural buckling buckling about the minor axis (governs for UC sections with equal depth and width). Use the Column Capacity Calculator for precise design.

Parallel Flange Channels (PFC)

PFC sections are C-shaped channels with parallel flanges (the modern replacement for the tapered-flange RSC channels). Key characteristics:

• Shear centre is offset from the centroid — PFC sections in bending experience torsion unless laterally restrained
• Weak torsional stiffness — avoid using PFC as primary beams without lateral restraint
• Common in pairs — two PFC sections back-to-back form a built-up I-section with high torsional resistance

PFC Applications

Hollow Sections — CHS, SHS, RHS

Structural hollow sections (SHS/RHS/CHS) are increasingly popular in UK construction, particularly for exposed architectural steelwork and highly efficient structural systems.

Circular Hollow Sections (CHS)

CHS sections offer the best strength-to-weight ratio in compression, the highest torsional stiffness of any open section, and reduced wind drag for exposed structures. Typical applications:

• Columns in atrium spaces and exposed frames
• Lattice truss chords and web members
• Bracing in concentric braced frames (CBF)
• Offshore and marine structures

Square Hollow Sections (SHS)

SHS sections provide equal bending stiffness about both axes with a clean architectural appearance. Typical applications:

• Columns in exposed steel frames
• Beams with biaxial bending
• Truss chords and web members
• Transfer truss elements

Rectangular Hollow Sections (RHS)

RHS sections are deeper than they are wide, optimising bending stiffness about one axis. Typical applications:

• Rafters in portal frames (hot-finished S355J2H)
• Edge beams with simple connections
• Lattice girder chords
• Composite beams with shear connectors

Hot-Finished vs Cold-Formed Hollow Sections

For UK structural applications, hot-finished SHS/RHS to BS EN 10210 S355J2H is the preferred specification because the lower residual stresses give better buckling resistance and the tighter tolerances suit architecturally exposed steelwork (AES).

UK Sections vs European IPE / HEA / HEB

Engineers working across UK and European projects often need to compare section families. Here is how they differ:

Key Differences When Substituting

1. Flange width affects connections. A 457×191×67 UB has a 191mm flange, but an IPE 450 has only 190mm — close, but bolt gauge distances differ. Always check the connection detailing when substituting.

2. Depth-to-span ratios differ. An IPE section has slightly greater depth than a UB of similar load capacity, which may affect floor-to-floor heights and cladding dimensions.

3. Buckling curves differ. Under the UK National Annex, a UB in S355 follows buckling curve a (strong axis), while an equivalent HEA or HEB would follow curves a or b depending on the European NA. This changes column capacity calculations.

4. Hollow sections follow different standards. UK hollow sections are specified to BS EN 10210 (hot-finished) or BS EN 10219 (cold-formed). European hollow sections may follow EN 10210-2 or national standards. Properties are similar but not identical.

How to Select the Right Section

Step 1: Determine the Primary Action

Step 2: Estimate Required Size

For beams, start with the span-to-depth ratio:

Example: a 10 m floor beam → try depth ≈ 10,000/20 = 500 mm → 457×191×67 UB or 533×210×82 UB.

For columns, estimate from axial load:

• S355 steel: approximate capacity = 2.5 × cross-sectional area (mm²) / 1000 (kN) for stocky columns (KL ≈ 3 m)
• For a 2,000 kN load at 3 m effective length: area ≈ 2,000/2.5 = 800 mm² → try 203×203×60 UC (A = 76.6 cm² = 7,660 mm² — gives 2,660 kN capacity)

Step 3: Check Serviceability (Deflection)

Deflection almost always governs for UK floor beams. For a quick deflection check:

δ = 5 w L⁴ / (384 E I)

Where w is the serviceability load (not factored), L is span, E = 210,000 MPa for steel, and I is the second moment of area. The UK National Annex limit for floors is typically L/200 (general) or L/360 (brittle finishes) — much less restrictive than AISC L/360 for general floors.

Step 4: Consider Connections

Your section choice affects connection detailing:

• UB beams require end plates, fin plates, or cleats. Standardised SCI P358 "Green Book" connections cover most UB sizes.
• UC columns accept beam connections on both flanges and the web — versatile for multi-bay frames.
• CHS/SHS columns need blind fasteners (Hollo-Bolts, Lindapters) or welded brackets for beam connections — more expensive than open section connections.
• PFC sections connect with web cleats or gusset plates — the offset shear centre must be considered.

UK Steel Section Standards (BS EN 10365)

BS EN 10365:2017 replaced BS 4-1 as the standard for hot-rolled structural steel sections in the UK. The new standard:

• Introduced the UKB (Universal Beam) and UKC (Universal Column) designations alongside the legacy UB/UC labels
• Updated dimensional tolerances to align with European standards
• Added new section sizes including heavier UC sections (356×406×634 UC) and deeper UB sections (1016×305×584 UB)
• Harmonised with EN 10034 (dimensional tolerances) and EN 10025 (steel grades)

The SCI P363 Blue Book (6th edition, 2024) provides the definitive section property tables under BS EN 10365.

Frequently Asked Questions

What is the difference between a UB and an IPE section? UB sections have wider flanges relative to their depth compared to IPE sections. A 457×191×67 UB has a flange width of 191 mm, while an IPE 450 has a 190 mm flange — but the IPE has a thinner web (9.4 mm vs 8.5 mm) and a slightly narrower flange-to-depth ratio. UB sections are optimised for bending efficiency with wider flanges that improve lateral-torsional buckling resistance. IPE sections are lighter per unit depth but require tighter lateral restraint.

When should I use CHS instead of UC for a column? CHS columns offer higher torsional stiffness and a cleaner architectural appearance, making them ideal for exposed atrium columns and architecturally visible steelwork. However, CHS beam-to-column connections are more expensive than UC connections because they require blind fasteners, welded brackets, or through-plates. For concealed columns in a braced frame, UC sections are more economical. For exposed columns where rotation about the base is architecturally desirable, CHS is the better choice.

What is the standard steel grade for UK sections? S355J2 to BS EN 10025-2 is the default structural steel grade for UK buildings. It provides 355 MPa minimum yield strength (for thicknesses up to 16 mm) and 27 J Charpy impact toughness at -20°C. S275J2 may be used for lightly loaded secondary members. For high-strength applications, S460ML (thermomechanically rolled) is available but with longer lead times. Always confirm with the project specification and the UK National Annex to EN 1993-1-1.

How do I find section properties for a specific UB section? Use the Full Section Properties Database on steelcalculator.app, which covers all common UB, UC, PFC, SHS, RHS, and CHS sections. For the definitive UK source, refer to SCI P363 (Blue Book) or the Tata Steel sections catalogue. Our database is updated to match BS EN 10365:2017 section designations and includes all dimensions, Iy, Iz, Wel, Wpl, and radius of gyration values.

Related Guides and References

• UK Universal Beam Sizes — UB Section Table
• 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
• EN 1993 Column Buckling Guide
• European Beam Sizes — IPE, HEA, HEB
• Metric Steel Sections — IPE, HEA, HEB, UB, UC
• Beam Capacity Calculator
• Column Capacity Calculator
• How to Verify Calculator Results
• Disclaimer

This guide is for educational reference only and does not constitute professional engineering advice. All section properties should be verified against the current SCI P363 Blue Book, BS EN 10365:2017, and the project specification. Design to BS EN 1993-1-1 with the UK National Annex. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent verification by a Chartered Structural Engineer.