RHS 200×150×8.8 vs RHS 200×100×12
RHS 200×150×8.8 is an RHS Hot-finished section from the UK Blue Book (SCI P363); RHS 200×100×12 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 390 cm³ against 395 cm³ of plastic modulus, a difference of 1.3%. RHS 200×150×8.8 is the lighter of the two at 45.3 kg/m against 50.8 kg/m, a saving of 10.8% on steel weight. Both are about 200 mm deep, so either fits the same construction zone.
| Property | RHS 200×150×8.8 RHS Hot-finished | RHS 200×100×12 RHS | Difference |
|---|---|---|---|
| Mass | 45.3 kg/m | 50.8 kg/m | -10.8% |
| Depth | 200 mm | 200 mm | same |
| Width | 150 mm | 100 mm | +50.0% |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 57.7 cm² | 64.7 cm² | -10.8% |
| Second moment, major (Iy) | 3,220 cm⁴ | 3,047 cm⁴ | +5.7% |
| Plastic modulus, major (Wpl,y) | 390 cm³ | 395 cm³ | -1.3% |
| Elastic modulus, major (Wel,y) | 322 cm³ | 305 cm³ | +5.6% |
| Second moment, minor (Iz) | 2,050 cm⁴ | 979 cm⁴ | +109.4% |
| Plastic modulus, minor (Wpl,z) | 319 cm³ | 237 cm³ | +34.6% |
| Radius of gyration, minor (iz) | 5.96 cm | 3.89 cm | +53.2% |
| Torsion constant (It) | 3,960 cm⁴ | 2,469 cm⁴ | +60.4% |
RHS 200×150×8.8 to BS EN 10210-2:2006; RHS 200×100×12 to EN 10219 · Continental Steel. Difference is expressed relative to RHS 200×100×12.
How to choose between them
On stiffness, RHS 200×150×8.8 has the larger second moment of area: 3,220 cm⁴ against 3,047 cm⁴, a difference of 5.7%. 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 200×150×8.8 is the more efficient section: 8.6 against 7.8 cm³ per kg/m, 10.7% 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 200×150×8.8 has 319 cm³ of minor-axis plastic modulus against 237 cm³, 34.6% 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.
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 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 10.8% weight.
In short, RHS 200×100×12 is the stronger section and RHS 200×150×8.8 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.