UK Section Types — Overview
UK structural steel sections are designated per BS 4-1 and the SCI Blue Book (P363):
| Section Designation | Full Name | Standard | Typical Depth Range |
|---|---|---|---|
| UB | Universal Beam | BS 4-1 | 127 x 76 to 1016 x 305 |
| UC | Universal Column | BS 4-1 | 152 x 152 to 356 x 406 |
| PFC | Parallel Flange Channel | BS 4-1 | 100 x 50 to 430 x 100 |
| SHS | Square Hollow Section | BS EN 10210-2 | 40 x 40 to 400 x 400 |
| RHS | Rectangular Hollow Section | BS EN 10210-2 | 50 x 30 to 500 x 300 |
| CHS | Circular Hollow Section | BS EN 10210-2 | 21.3 to 508.0 OD |
| RSA | Rolled Steel Angle (Equal) | BS EN 10056-1 | 25 x 25 to 250 x 250 |
Universal Beams (UB) — Selection Guide
Designation format: Depth (mm) x Width (mm) x Mass (kg/m) — e.g., 457 x 191 UB 74
| Depth Series | Width Range (mm) | Typical UK Application | Span Range |
|---|---|---|---|
| 127-178 UB | 76-102 | Secondary beams, purlins, lintels | 2-5 m |
| 203-254 UB | 102-146 | Floor beams (secondary), portal rafter (short span) | 4-8 m |
| 305-356 UB | 127-171 | Floor beams (primary), portal rafter (medium) | 6-12 m |
| 406-457 UB | 178-191 | Portal rafter (long), heavy floor beams | 8-18 m |
| 533-610 UB | 210-229 | Portal rafter (long span), transfer beams | 10-25 m |
| 686-762 UB | 254-267 | Crane girders, transfer beams, long-span portals | 15-30 m |
| 838-914 UB | 292-305 | Heavy transfer beams, bridge girders | 20-35 m |
| 1016 UB | 305 | Bridge girders, very heavy transfer | 25-40 m |
Selection rule of thumb for UB floor beams (simply supported, UDL):
- Span/depth ratio: 18-25 for standard floor loading (5-7.5 kN/m2 imposed)
- Deeper for longer spans: L/25 for 5 m span, L/18 for 15 m span
- Wider flanges (heavier in series) for LTB resistance when unrestrained
- 457UB and 533UB are the workhorse UK floor beam sections
Universal Columns (UC) — Selection Guide
Designation format: Depth (mm) x Width (mm) x Mass (kg/m) — e.g., 254 x 254 UC 73
| Depth Series | Width Range (mm) | Typical UK Application | Axial Load Range |
|---|---|---|---|
| 152 UC | 152 | Light columns, posts, secondary compression members | 200-600 kN |
| 203 UC | 203 | Internal columns in 2-3 storey frames | 500-1,200 kN |
| 254 UC | 254 | Internal/external columns, 3-6 storey frames | 800-2,200 kN |
| 305 UC | 305 | Primary columns, 5-12 storey frames | 1,500-4,000 kN |
| 356 UC | 368-406 | Heavy columns, portal legs, high-rise | 3,000-7,000 kN |
Key UC properties for UK design:
- h/b ratio approximately 1.0 (near-square) — efficient for compression in both axes
- Typically governed by minor-axis buckling (z-z axis) for pinned-pinned columns
- UC 203 and 254 are the most commonly specified UK column sections
- For storey heights 3-5 m, a 254UC typically provides economical utilisation
Parallel Flange Channels (PFC) — Selection Guide
UK PFC sections are used for secondary members, bracing, and edge beams where the channel shape suits the connection geometry:
| Depth Series | Typical UK Application |
|---|---|
| 100-150 PFC | Purlins, side rails, light bracing |
| 180-230 PFC | Secondary edge beams, lintels, bracing struts |
| 260-300 PFC | Crane runway beams (light), stair stringers |
| 380-430 PFC | Heavy edge beams, portal frame side rails (long span) |
PFC sections are asymmetric — the shear centre lies outside the section, producing torsion under transverse loading. For beams, ensure the load passes through the shear centre (web stiffeners may be required). For bracing, PFC sections work well in tension and compression.
Structural Hollow Sections — Selection Guide
Hot-finished SHS and RHS to BS EN 10210-2:
| Section | Size Range (mm) | Wall Thickness (mm) | Typical UK Application |
|---|---|---|---|
| SHS | 40 x 40 to 400 x 400 | 3.0 to 16.0 | Columns, truss chords, bracing, architectural |
| RHS | 50 x 30 to 500 x 300 | 3.0 to 16.0 | Portal rafter (short span), truss members, beams |
| CHS | 21.3 to 508.0 OD | 2.3 to 16.0 | Tension members, bracing (architectural), circular columns |
Advantages of hollow sections for UK design:
- Torsional stiffness: SHS/RHS have high torsion constants (It) — excellent for members subject to torsion (edge beams, crane runway beams)
- No weak axis: buckling resistance identical in both axes (curve a for hot-finished hollow sections — the most favourable curve)
- Clean appearance: often specified for visible architectural steelwork in UK buildings
- Lower fire protection requirements: lower section factor A_p/V than equivalent open sections
- Higher fabrication cost: end preparation, profiling, and welding are more expensive than for open sections
UK Steel Section Databases
SCI P363 (Blue Book) — the definitive source for UK hot-rolled section properties. Available in print, PDF, and as an Excel spreadsheet. Contains:
- Dimensions and mass per metre
- Section properties (A, Iy, Iz, Wel, Wpl, It, Iw, Av)
- Buckling parameters (lambda_bar tables for common spans)
- Torsion and warping properties
Tata Steel Sections Interactive "Blue Book" online — free web tool from Tata Steel (formerly Corus/ British Steel) providing section properties for current UK production ranges.
Note: The SCI Blue Book is updated periodically as production ranges change. Always verify that the section is current in production before specifying it. Tata Steel publishes a current production range list.
Selecting the Right UK Section — Decision Flow
For beams (predominantly bending):
- Estimate depth from span/depth ratio (L/18 to L/25 for floors, L/30 to L/45 for roofs)
- Select a UB section: flange width approximately 0.4-0.5 x depth for standard beams
- Check bending (Mc,Rd) and shear (Vpl,Rd) per Clause 6.2
- Check LTB (Mb,Rd) per Clause 6.3.2 if unrestrained
- Check deflection (SLS) — often governs for longer spans
- If deflection governs: increase depth (I scales with h3)
- If LTB governs: select a wider flange section in the same depth series
For columns (predominantly compression):
- Estimate required area: A_req approximately = NEd / (chi x fy), assume chi = 0.6-0.8 initially
- Select a UC section with A >= A_req
- Check cross-section classification (Class 1-3 for compression)
- Determine buckling length Lcr (effective length method, Clause 6.3.1)
- Calculate lambda_bar and chi per Clause 6.3.1.2 (curve c for z-z axis per UK NA)
- Check Nb,Rd = chi x A x fy / gamma_M1
- If utilisation < 0.6: consider a lighter section in the same depth or next depth down
- If utilisation > 1.0: increase section size (next mass in same depth, or next depth up)
Frequently Asked Questions
What is the difference between UB and UC sections in UK design?
UB (Universal Beam) sections have h/b > 1.5 (deep, narrow flanges) and are optimised for bending about the major axis. They are relatively inefficient in minor-axis bending and have low torsional stiffness. UC (Universal Column) sections have h/b approximately 1.0 (near-square) and are optimised for compression — they have similar buckling resistance in both axes and higher torsional stiffness. Use UB for beams, UC for columns. For beam-columns (portal frame rafters, crane columns), UB sections are typically used because bending governs over axial compression.
How do I convert between UB/UC and European IPE/HEA sections?
UB/UC sections do not have direct European equivalents — they are different rolling series. Approximate comparisons: 305UB is roughly comparable to IPE 300 (depth similar but weight differs); 254UC is roughly comparable to HEA 240 (depth similar, HEA wider). SCI P363 provides comparative tables. UK designers generally prefer UB/UC sections because they are domestically produced (Tata Steel, Scunthorpe) and more readily available than imported European sections. For European projects using UK design, the correct EN 1993-1-1 rules apply to European sections but the UK NA buckling curves are tied to UK production, not European.
Which hollow section standard should I specify — hot-finished or cold-formed?
Hot-finished hollow sections to BS EN 10210-2 are preferred for structural applications in the UK because: (1) they use buckling curve a (most favourable) versus curve c for cold-formed (BS EN 10219); (2) they are free from residual stresses from cold-forming; (3) they are available in S355 and S460 grades. Cold-formed hollow sections to BS EN 10219 are cheaper but have lower buckling resistance and are limited to S355J2H for thicknesses over 6 mm. For primary structural members, always specify hot-finished. Reserve cold-formed for secondary members and architectural applications.
Why does the SCI Blue Book show different properties for the same section designation from different UK producers?
Historically, the UK had multiple steel producers (British Steel, Corus, Tata Steel) and each had slight variations in section geometry within the BS 4-1 tolerances. The SCI Blue Book uses Tata Steel's current production geometry. For legacy structures (pre-2000), the section properties may differ slightly from current values — the original mill certificates or the Steelwork Design Guide to BS 5950 (the "Green Book") should be consulted. For new designs, always use the current SCI P363 edition (latest published 2019).
Related Pages
- UK UB and UC Section Properties — Detailed dimension tables
- UK Beam Sizes — Complete Guide — Section dimensions and properties
- UK Steel Grades Guide — S235, S275, S355, S460
- UK Steel Properties — Material characteristics
- UK Compact Section Limits — Cross-section classification
- UK HSS Section Properties — Hollow section design data
- UK Column Design Guide — UC section selection and design
Educational reference only. Section dimensions and properties are as published in SCI P363 (Steel Building Design: Design Data, 2019 edition) and BS 4-1:2005. Verify current availability with the UK steel producer (Tata Steel) before specifying. All design values must be independently verified by a Chartered Structural Engineer. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent professional verification.