SHS 150×150×7.1 vs SHS 150×150×8
SHS 150×150×7.1 is an SHS Hot-finished section from the UK Blue Book (SCI P363); SHS 150×150×8 is the closest equivalent in the European (Continental) range. SHS 150×150×8 carries more bending: 226 cm³ of plastic modulus against 213 cm³, 5.8% more. SHS 150×150×7.1 is the lighter of the two at 31.4 kg/m against 33.9 kg/m, a saving of 7.4% on steel weight. Both are about 150 mm deep, so either fits the same construction zone.
| Property | SHS 150×150×7.1 SHS Hot-finished | SHS 150×150×8 SHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 31.4 kg/m | 33.9 kg/m | -7.4% |
| Depth | 150 mm | 150 mm | same |
| Width | 150 mm | 150 mm | same |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 40 cm² | 43.2 cm² | -7.4% |
| Second moment, major (Iy) | 1,350 cm⁴ | 1,412 cm⁴ | -4.4% |
| Plastic modulus, major (Wpl,y) | 213 cm³ | 226 cm³ | -5.8% |
| Elastic modulus, major (Wel,y) | 180 cm³ | 188 cm³ | -4.3% |
| Second moment, minor (Iz) | 1,350 cm⁴ | 1,412 cm⁴ | -4.4% |
| Plastic modulus, minor (Wpl,z) | 213 cm³ | 226 cm³ | -5.8% |
| Radius of gyration, minor (iz) | 5.81 cm | 5.71 cm | +1.8% |
| Torsion constant (It) | 2,120 cm⁴ | 2,364 cm⁴ | -10.3% |
SHS 150×150×7.1 to BS EN 10210-2:2006; SHS 150×150×8 to EN 10219 · Continental Steel. Difference is expressed relative to SHS 150×150×8.
How to choose between them
On stiffness, SHS 150×150×8 has the larger second moment of area: 1,412 cm⁴ against 1,350 cm⁴, a difference of 4.4%. 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, the two are equally efficient (6.8 against 6.7 cm³ per kg/m), so on a pure steel-tonnage basis there is nothing to choose between them. The decision comes down to availability, connection detailing and what the rest of the frame uses.
These come from different catalogues, so treat the swap as a design change rather than a like-for-like substitution. SHS Hot-finished sections are specified to BS EN 10210-2:2006 and SHS 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 7.4% weight.
In short, SHS 150×150×8 is the stronger section and SHS 150×150×7.1 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.