RHS 200×100×8 vs CF RHS 200×150×6
RHS 200×100×8 is an RHS Hot-finished section from the UK Blue Book (SCI P363); CF RHS 200×150×6 is the closest equivalent in the UK Blue Book (SCI P363). RHS 200×100×8 carries more bending: 282 cm³ of plastic modulus against 271 cm³, 4.1% more. CF RHS 200×150×6 is the lighter of the two at 31.1 kg/m against 35.1 kg/m, a saving of 12.9% on steel weight. Both are about 200 mm deep, so either fits the same construction zone.
| Property | RHS 200×100×8 RHS Hot-finished | CF RHS 200×150×6 RHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 35.1 kg/m | 31.1 kg/m | +12.9% |
| Depth | 200 mm | 200 mm | same |
| Width | 100 mm | 150 mm | -33.3% |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 44.8 cm² | 39.6 cm² | +13.1% |
| Second moment, major (Iy) | 2,230 cm⁴ | 2,270 cm⁴ | -1.8% |
| Plastic modulus, major (Wpl,y) | 282 cm³ | 271 cm³ | +4.1% |
| Elastic modulus, major (Wel,y) | 223 cm³ | 227 cm³ | -1.8% |
| Second moment, minor (Iz) | 739 cm⁴ | 1,460 cm⁴ | -49.4% |
| Plastic modulus, minor (Wpl,z) | 172 cm³ | 223 cm³ | -22.9% |
| Radius of gyration, minor (iz) | 4.06 cm | 6.06 cm | -33.0% |
| Torsion constant (It) | 1,800 cm⁴ | 2,830 cm⁴ | -36.4% |
RHS 200×100×8 to BS EN 10210-2:2006; CF RHS 200×150×6 to BS EN 10219-2:2006. Difference is expressed relative to CF RHS 200×150×6.
How to choose between them
On stiffness, CF RHS 200×150×6 has the larger second moment of area: 2,270 cm⁴ against 2,230 cm⁴, a difference of 1.8%. 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, CF RHS 200×150×6 is the more efficient section: 8.7 against 8.0 cm³ per kg/m, 7.8% 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: CF RHS 200×150×6 has 223 cm³ of minor-axis plastic modulus against 172 cm³, 22.9% 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, RHS 200×100×8 is the stronger section and CF RHS 200×150×6 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.