RHS 200×120×8 vs CF RHS 200×100×10
RHS 200×120×8 is an RHS Hot-finished section from the UK Blue Book (SCI P363); CF RHS 200×100×10 is the closest equivalent in the UK Blue Book (SCI P363). They are close to interchangeable in bending: 313 cm³ against 318 cm³ of plastic modulus, a difference of 1.6%. RHS 200×120×8 is the lighter of the two at 37.6 kg/m against 41.3 kg/m, a saving of 9.0% on steel weight. Both are about 200 mm deep, so either fits the same construction zone.
| Property | RHS 200×120×8 RHS Hot-finished | CF RHS 200×100×10 RHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 37.6 kg/m | 41.3 kg/m | -9.0% |
| Depth | 200 mm | 200 mm | same |
| Width | 120 mm | 100 mm | +20.0% |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 48 cm² | 52.6 cm² | -8.7% |
| Second moment, major (Iy) | 2,530 cm⁴ | 2,440 cm⁴ | +3.7% |
| Plastic modulus, major (Wpl,y) | 313 cm³ | 318 cm³ | -1.6% |
| Elastic modulus, major (Wel,y) | 253 cm³ | 244 cm³ | +3.7% |
| Second moment, minor (Iz) | 1,130 cm⁴ | 818 cm⁴ | +38.1% |
| Plastic modulus, minor (Wpl,z) | 218 cm³ | 195 cm³ | +11.8% |
| Radius of gyration, minor (iz) | 4.85 cm | 3.94 cm | +23.1% |
| Torsion constant (It) | 2,500 cm⁴ | 2,150 cm⁴ | +16.3% |
RHS 200×120×8 to BS EN 10210-2:2006; CF RHS 200×100×10 to BS EN 10219-2:2006. Difference is expressed relative to CF RHS 200×100×10.
How to choose between them
On stiffness, RHS 200×120×8 has the larger second moment of area: 2,530 cm⁴ against 2,440 cm⁴, a difference of 3.7%. 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 of steel, RHS 200×120×8 is the more efficient section: 8.3 against 7.7 cm³ per kg/m, 8.1% better. Over a floor of repeated beams that difference is real tonnage, though it is often outweighed by whichever section the fabricator can actually source.
The two diverge much more about the minor axis: RHS 200×120×8 has 218 cm³ of minor-axis plastic modulus against 195 cm³, 11.8% more. If the member sees any minor-axis bending, or if it is unrestrained over a long length and lateral-torsional buckling governs, that gap decides the comparison even though the major-axis numbers looked equivalent.
In short, CF RHS 200×100×10 is the stronger section and RHS 200×120×8 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.