CHS 508×8 vs CF CHS 508×8
CHS 508×8 is an CHS Hot-finished section from the UK Blue Book (SCI P363); CF CHS 508×8 is the closest equivalent in the UK Blue Book (SCI P363). They are close to interchangeable in bending: 2000 cm³ against 2000 cm³ of plastic modulus, a difference of 0.0%. They weigh essentially the same, 98.6 kg/m and 98.6 kg/m. Both are about 508 mm deep, so either fits the same construction zone.
| Property | CHS 508×8 CHS Hot-finished | CF CHS 508×8 CHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 98.6 kg/m | 98.6 kg/m | same |
| Depth | 508 mm | 508 mm | same |
| Width | 508 mm | 508 mm | same |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 126 cm² | 126 cm² | same |
| Second moment, major (Iy) | 39,300 cm⁴ | 39,300 cm⁴ | same |
| Plastic modulus, major (Wpl,y) | 2,000 cm³ | 2,000 cm³ | same |
| Elastic modulus, major (Wel,y) | 1,550 cm³ | 1,550 cm³ | same |
| Second moment, minor (Iz) | 39,300 cm⁴ | 39,300 cm⁴ | same |
| Plastic modulus, minor (Wpl,z) | 2,000 cm³ | 2,000 cm³ | same |
| Radius of gyration, minor (iz) | 17.7 cm | 17.7 cm | same |
| Torsion constant (It) | 78,600 cm⁴ | 78,600 cm⁴ | same |
CHS 508×8 to BS EN 10210-2:2006; CF CHS 508×8 to BS EN 10219-2:2006. Difference is expressed relative to CF CHS 508×8.
How to choose between them
On stiffness, CF CHS 508×8 has the larger second moment of area: 39,300 cm⁴ against 39,300 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 (20.3 against 20.3 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.