SHS 300×300×8.8 vs SHS 300×300×9
SHS 300×300×8.8 is an SHS Hot-finished section from the UK Blue Book (SCI P363); SHS 300×300×9 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 1110 cm³ against 1102 cm³ of plastic modulus, a difference of 0.7%. They weigh essentially the same, 79.8 kg/m and 80.6 kg/m. Both are about 300 mm deep, so either fits the same construction zone.
| Property | SHS 300×300×8.8 SHS Hot-finished | SHS 300×300×9 SHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 79.8 kg/m | 80.6 kg/m | -1.0% |
| Depth | 300 mm | 300 mm | same |
| Width | 300 mm | 300 mm | same |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 102 cm² | 102 cm² | same |
| Second moment, major (Iy) | 14,300 cm⁴ | 14,180 cm⁴ | +0.8% |
| Plastic modulus, major (Wpl,y) | 1,110 cm³ | 1,102 cm³ | +0.7% |
| Elastic modulus, major (Wel,y) | 954 cm³ | 946 cm³ | +0.8% |
| Second moment, minor (Iz) | 14,300 cm⁴ | 14,180 cm⁴ | +0.8% |
| Plastic modulus, minor (Wpl,z) | 1,110 cm³ | 1,102 cm³ | +0.7% |
| Radius of gyration, minor (iz) | 11.9 cm | 11.8 cm | +0.8% |
| Torsion constant (It) | 22,100 cm⁴ | 22,660 cm⁴ | -2.5% |
SHS 300×300×8.8 to BS EN 10210-2:2006; SHS 300×300×9 to EN 10219 · Continental Steel. Difference is expressed relative to SHS 300×300×9.
How to choose between them
On stiffness, SHS 300×300×8.8 has the larger second moment of area: 14,300 cm⁴ against 14,180 cm⁴, a difference of 0.8%. 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, the two are equally efficient (13.9 against 13.7 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 a marginal amount of weight.
In short, these two are genuine equivalents. Pick whichever your supplier stocks and the rest of the frame already uses.