RHS 250×150×8.8 vs RHS 250×150×9
RHS 250×150×8.8 is an RHS Hot-finished section from the UK Blue Book (SCI P363); RHS 250×150×9 is the closest equivalent in the European (Continental) range. RHS 250×150×8.8 carries more bending: 545 cm³ of plastic modulus against 533 cm³, 2.3% more. They weigh essentially the same, 52.2 kg/m and 52.3 kg/m. Both are about 250 mm deep, so either fits the same construction zone.
| Property | RHS 250×150×8.8 RHS Hot-finished | RHS 250×150×9 RHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 52.2 kg/m | 52.3 kg/m | -0.2% |
| Depth | 250 mm | 250 mm | same |
| Width | 150 mm | 150 mm | same |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 66.5 cm² | 66 cm² | +0.8% |
| Second moment, major (Iy) | 5,550 cm⁴ | 5,369 cm⁴ | +3.4% |
| Plastic modulus, major (Wpl,y) | 545 cm³ | 533 cm³ | +2.3% |
| Elastic modulus, major (Wel,y) | 444 cm³ | 430 cm³ | +3.3% |
| Second moment, minor (Iz) | 2,490 cm⁴ | 2,433 cm⁴ | +2.3% |
| Plastic modulus, minor (Wpl,z) | 381 cm³ | 375 cm³ | +1.6% |
| Radius of gyration, minor (iz) | 6.12 cm | 6.07 cm | +0.8% |
| Torsion constant (It) | 5,460 cm⁴ | 5,596 cm⁴ | -2.4% |
RHS 250×150×8.8 to BS EN 10210-2:2006; RHS 250×150×9 to EN 10219 · Continental Steel. Difference is expressed relative to RHS 250×150×9.
How to choose between them
On stiffness, RHS 250×150×8.8 has the larger second moment of area: 5,550 cm⁴ against 5,369 cm⁴, a difference of 3.4%. 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 250×150×8.8 is the more efficient section: 10.4 against 10.2 cm³ per kg/m, 2.4% 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.
These come from different catalogues, so treat the swap as a design change rather than a like-for-like substitution. RHS Hot-finished sections are specified to BS EN 10210-2:2006 and RHS Cold-formed to EN 10219 · Continental Steel; the steel grades, tolerances and available lengths differ, connection details and bolt gauges are set out differently, and the two are rarely both stocked in the same market. Check availability before changing a section on a drawing to save a marginal amount of weight.
In short, RHS 250×150×8.8 is the stronger section and RHS 250×150×8.8 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.