SHS 40×40×3.6 vs SHS 40×40×4
SHS 40×40×3.6 is an SHS Hot-finished section from the UK Blue Book (SCI P363); SHS 40×40×4 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 6.88 cm³ against 7.01 cm³ of plastic modulus, a difference of 1.9%. SHS 40×40×3.6 is the lighter of the two at 4.01 kg/m against 4.2 kg/m, a saving of 4.5% on steel weight. Both are about 40 mm deep, so either fits the same construction zone.
| Property | SHS 40×40×3.6 SHS Hot-finished | SHS 40×40×4 SHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 4 kg/m | 4.2 kg/m | -4.5% |
| Depth | 40 mm | 40 mm | same |
| Width | 40 mm | 40 mm | same |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 5.1 cm² | 5.3 cm² | -4.7% |
| Second moment, major (Iy) | 11.1 cm⁴ | 11.1 cm⁴ | same |
| Plastic modulus, major (Wpl,y) | 6.88 cm³ | 7.01 cm³ | -1.9% |
| Elastic modulus, major (Wel,y) | 5.54 cm³ | 5.54 cm³ | same |
| Second moment, minor (Iz) | 11.1 cm⁴ | 11.1 cm⁴ | same |
| Plastic modulus, minor (Wpl,z) | 6.88 cm³ | 7.01 cm³ | -1.9% |
| Radius of gyration, minor (iz) | 1.47 cm | 1.44 cm | +2.1% |
| Torsion constant (It) | 18.1 cm⁴ | 19.4 cm⁴ | -6.7% |
SHS 40×40×3.6 to BS EN 10210-2:2006; SHS 40×40×4 to EN 10219 · Continental Steel. Difference is expressed relative to SHS 40×40×4.
How to choose between them
On stiffness, SHS 40×40×4 has the larger second moment of area: 11.1 cm⁴ against 11.1 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 of steel, SHS 40×40×3.6 is the more efficient section: 1.7 against 1.7 cm³ per kg/m, 2.8% 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.
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 4.5% weight.
In short, SHS 40×40×4 is the stronger section and SHS 40×40×3.6 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.