CHS 406.4×8 vs CF CHS 406.4×8
CHS 406.4×8 is an CHS Hot-finished section from the UK Blue Book (SCI P363); CF CHS 406.4×8 is the closest equivalent in the UK Blue Book (SCI P363). They are close to interchangeable in bending: 1270 cm³ against 1270 cm³ of plastic modulus, a difference of 0.0%. They weigh essentially the same, 78.6 kg/m and 78.6 kg/m. Both are about 406 mm deep, so either fits the same construction zone.
| Property | CHS 406.4×8 CHS Hot-finished | CF CHS 406.4×8 CHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 78.6 kg/m | 78.6 kg/m | same |
| Depth | 406.4 mm | 406.4 mm | same |
| Width | 406.4 mm | 406.4 mm | same |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 100 cm² | 100 cm² | same |
| Second moment, major (Iy) | 19,900 cm⁴ | 19,900 cm⁴ | same |
| Plastic modulus, major (Wpl,y) | 1,270 cm³ | 1,270 cm³ | same |
| Elastic modulus, major (Wel,y) | 978 cm³ | 978 cm³ | same |
| Second moment, minor (Iz) | 19,900 cm⁴ | 19,900 cm⁴ | same |
| Plastic modulus, minor (Wpl,z) | 1,270 cm³ | 1,270 cm³ | same |
| Radius of gyration, minor (iz) | 14.1 cm | 14.1 cm | same |
| Torsion constant (It) | 39,700 cm⁴ | 39,700 cm⁴ | same |
CHS 406.4×8 to BS EN 10210-2:2006; CF CHS 406.4×8 to BS EN 10219-2:2006. Difference is expressed relative to CF CHS 406.4×8.
How to choose between them
On stiffness, CF CHS 406.4×8 has the larger second moment of area: 19,900 cm⁴ against 19,900 cm⁴, a difference of 0.0%. This matters more often than the strength comparison, because on normal floor spans deflection rather than bending capacity sets the beam size - so if the two are close on modulus but apart on inertia, the stiffer one is usually the better answer even when it is not the stronger one.
Measured as bending capacity per kilogram, the two are equally efficient (16.2 against 16.2 cm³ per kg/m), so on a pure steel-tonnage basis there is nothing to choose between them. The decision comes down to availability, connection detailing and what the rest of the frame uses.
In short, these two are genuine equivalents. Pick whichever your supplier stocks and the rest of the frame already uses.