SHS 400×400×8.8 vs SHS 400×400×9
SHS 400×400×8.8 is an SHS Hot-finished section from the UK Blue Book (SCI P363); SHS 400×400×9 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 2000 cm³ against 2009 cm³ of plastic modulus, a difference of 0.4%. They weigh essentially the same, 107 kg/m and 109 kg/m. Both are about 400 mm deep, so either fits the same construction zone.
| Property | SHS 400×400×8.8 SHS Hot-finished | SHS 400×400×9 SHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 107 kg/m | 109 kg/m | -1.8% |
| Depth | 400 mm | 400 mm | same |
| Width | 400 mm | 400 mm | same |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 137 cm² | 138 cm² | -0.7% |
| Second moment, major (Iy) | 34,800 cm⁴ | 34,790 cm⁴ | same |
| Plastic modulus, major (Wpl,y) | 2,000 cm³ | 2,009 cm³ | -0.4% |
| Elastic modulus, major (Wel,y) | 1,740 cm³ | 1,739 cm³ | +0.1% |
| Second moment, minor (Iz) | 34,800 cm⁴ | 34,790 cm⁴ | same |
| Plastic modulus, minor (Wpl,z) | 2,000 cm³ | 2,009 cm³ | -0.4% |
| Radius of gyration, minor (iz) | 15.9 cm | 15.9 cm | same |
| Torsion constant (It) | 53,300 cm⁴ | 54,720 cm⁴ | -2.6% |
SHS 400×400×8.8 to BS EN 10210-2:2006; SHS 400×400×9 to EN 10219 · Continental Steel. Difference is expressed relative to SHS 400×400×9.
How to choose between them
On stiffness, SHS 400×400×8.8 has the larger second moment of area: 34,800 cm⁴ against 34,790 cm⁴, a difference of 0.0%. 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 (18.7 against 18.4 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.