RHS 160×80×5 vs CF RHS 160×80×5
RHS 160×80×5 is an RHS Hot-finished section from the UK Blue Book (SCI P363); CF RHS 160×80×5 is the closest equivalent in the UK Blue Book (SCI P363). RHS 160×80×5 carries more bending: 116 cm³ of plastic modulus against 113 cm³, 2.7% more. They weigh essentially the same, 17.8 kg/m and 17.5 kg/m. Both are about 160 mm deep, so either fits the same construction zone.
| Property | RHS 160×80×5 RHS Hot-finished | CF RHS 160×80×5 RHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 17.8 kg/m | 17.5 kg/m | +1.7% |
| Depth | 160 mm | 160 mm | same |
| Width | 80 mm | 80 mm | same |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 22.7 cm² | 22.4 cm² | +1.3% |
| Second moment, major (Iy) | 744 cm⁴ | 722 cm⁴ | +3.0% |
| Plastic modulus, major (Wpl,y) | 116 cm³ | 113 cm³ | +2.7% |
| Elastic modulus, major (Wel,y) | 93 cm³ | 90.2 cm³ | +3.1% |
| Second moment, minor (Iz) | 249 cm⁴ | 244 cm⁴ | +2.0% |
| Plastic modulus, minor (Wpl,z) | 71.1 cm³ | 69.7 cm³ | +2.0% |
| Radius of gyration, minor (iz) | 3.31 cm | 3.3 cm | +0.3% |
| Torsion constant (It) | 600 cm⁴ | 601 cm⁴ | -0.2% |
RHS 160×80×5 to BS EN 10210-2:2006; CF RHS 160×80×5 to BS EN 10219-2:2006. Difference is expressed relative to CF RHS 160×80×5.
How to choose between them
On stiffness, RHS 160×80×5 has the larger second moment of area: 744 cm⁴ against 722 cm⁴, a difference of 3.0%. 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 (6.5 against 6.5 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, RHS 160×80×5 is the stronger section and CF RHS 160×80×5 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.