RHS 300×150×8 vs RHS 300×100×10
RHS 300×150×8 is an RHS Hot-finished section from the UK Blue Book (SCI P363); RHS 300×100×10 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 663 cm³ against 666 cm³ of plastic modulus, a difference of 0.5%. RHS 300×150×8 is the lighter of the two at 54 kg/m against 58.8 kg/m, a saving of 8.2% on steel weight. Both are about 300 mm deep, so either fits the same construction zone.
| Property | RHS 300×150×8 RHS Hot-finished | RHS 300×100×10 RHS | Difference |
|---|---|---|---|
| Mass | 54 kg/m | 58.8 kg/m | -8.2% |
| Depth | 300 mm | 300 mm | same |
| Width | 150 mm | 100 mm | +50.0% |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 68.8 cm² | 74.9 cm² | -8.1% |
| Second moment, major (Iy) | 8,010 cm⁴ | 7,613 cm⁴ | +5.2% |
| Plastic modulus, major (Wpl,y) | 663 cm³ | 666 cm³ | -0.5% |
| Elastic modulus, major (Wel,y) | 534 cm³ | 508 cm³ | +5.1% |
| Second moment, minor (Iz) | 2,700 cm⁴ | 1,275 cm⁴ | +111.8% |
| Plastic modulus, minor (Wpl,z) | 407 cm³ | 296 cm³ | +37.5% |
| Radius of gyration, minor (iz) | 6.27 cm | 4.13 cm | +51.8% |
| Torsion constant (It) | 6,450 cm⁴ | 3,676 cm⁴ | +75.5% |
RHS 300×150×8 to BS EN 10210-2:2006; RHS 300×100×10 to EN 10219 · Continental Steel. Difference is expressed relative to RHS 300×100×10.
How to choose between them
On stiffness, RHS 300×150×8 has the larger second moment of area: 8,010 cm⁴ against 7,613 cm⁴, a difference of 5.2%. 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 300×150×8 is the more efficient section: 12.3 against 11.3 cm³ per kg/m, 8.4% 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.
The two diverge much more about the minor axis: RHS 300×150×8 has 407 cm³ of minor-axis plastic modulus against 296 cm³, 37.5% 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 8.2% weight.
In short, RHS 300×100×10 is the stronger section and RHS 300×150×8 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.