SHS 160×160×7.1 vs CF SHS 160×160×8
SHS 160×160×7.1 is an SHS Hot-finished section from the UK Blue Book (SCI P363); CF SHS 160×160×8 is the closest equivalent in the UK Blue Book (SCI P363). CF SHS 160×160×8 carries more bending: 260 cm³ of plastic modulus against 245 cm³, 5.8% more. SHS 160×160×7.1 is the lighter of the two at 33.7 kg/m against 36.5 kg/m, a saving of 7.7% on steel weight. Both are about 160 mm deep, so either fits the same construction zone.
| Property | SHS 160×160×7.1 SHS Hot-finished | CF SHS 160×160×8 SHS Cold-formed | Difference |
|---|---|---|---|
| Mass | 33.7 kg/m | 36.5 kg/m | -7.7% |
| Depth | 160 mm | 160 mm | same |
| Width | 160 mm | 160 mm | same |
| Web thickness | 0 mm | 0 mm | same |
| Flange thickness | 0 mm | 0 mm | same |
| Area | 42.9 cm² | 46.4 cm² | -7.5% |
| Second moment, major (Iy) | 1,660 cm⁴ | 1,740 cm⁴ | -4.6% |
| Plastic modulus, major (Wpl,y) | 245 cm³ | 260 cm³ | -5.8% |
| Elastic modulus, major (Wel,y) | 207 cm³ | 218 cm³ | -5.0% |
| Second moment, minor (Iz) | 1,660 cm⁴ | 1,740 cm⁴ | -4.6% |
| Plastic modulus, minor (Wpl,z) | 245 cm³ | 260 cm³ | -5.8% |
| Radius of gyration, minor (iz) | 6.22 cm | 6.12 cm | +1.6% |
| Torsion constant (It) | 2,600 cm⁴ | 2,900 cm⁴ | -10.3% |
SHS 160×160×7.1 to BS EN 10210-2:2006; CF SHS 160×160×8 to BS EN 10219-2:2006. Difference is expressed relative to CF SHS 160×160×8.
How to choose between them
On stiffness, CF SHS 160×160×8 has the larger second moment of area: 1,740 cm⁴ against 1,660 cm⁴, a difference of 4.6%. 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 160×160×7.1 is the more efficient section: 7.3 against 7.1 cm³ per kg/m, 2.1% 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.
In short, CF SHS 160×160×8 is the stronger section and SHS 160×160×7.1 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.