SHS 350×350×12.5 vs CF SHS 350×350×12.5
SHS 350×350×12.5 is an SHS Hot-finished section from the UK Blue Book (SCI P363); CF SHS 350×350×12.5 is the closest equivalent in the UK Blue Book (SCI P363). SHS 350×350×12.5 carries more bending: 2110 cm³ of plastic modulus against 2020 cm³, 4.5% more. CF SHS 350×350×12.5 is the lighter of the two at 127 kg/m against 131 kg/m, a saving of 3.1% on steel weight. Both are about 350 mm deep, so either fits the same construction zone.
| Property | SHS 350×350×12.5 SHS Hot-finished | CF SHS 350×350×12.5 SHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 131 kg/m | 127 kg/m | +3.1% |
| Depth | 350 mm | 350 mm | same |
| Width | 350 mm | 350 mm | same |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 167 cm² | 162 cm² | +3.1% |
| Second moment, major (Iy) | 31,500 cm⁴ | 30,000 cm⁴ | +5.0% |
| Plastic modulus, major (Wpl,y) | 2,110 cm³ | 2,020 cm³ | +4.5% |
| Elastic modulus, major (Wel,y) | 1,800 cm³ | 1,720 cm³ | +4.7% |
| Second moment, minor (Iz) | 31,500 cm⁴ | 30,000 cm⁴ | +5.0% |
| Plastic modulus, minor (Wpl,z) | 2,110 cm³ | 2,020 cm³ | +4.5% |
| Radius of gyration, minor (iz) | 13.7 cm | 13.6 cm | +0.7% |
| Torsion constant (It) | 48,900 cm⁴ | 49,400 cm⁴ | -1.0% |
SHS 350×350×12.5 to BS EN 10210-2:2006; CF SHS 350×350×12.5 to BS EN 10219-2:2006. Difference is expressed relative to CF SHS 350×350×12.5.
How to choose between them
On stiffness, SHS 350×350×12.5 has the larger second moment of area: 31,500 cm⁴ against 30,000 cm⁴, a difference of 5.0%. 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 (16.1 against 15.9 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, SHS 350×350×12.5 is the stronger section and CF SHS 350×350×12.5 is the lighter one; where those are the same section, it is the clear choice, and where they are not, decide on whether your design is governed by capacity or by tonnage.