UB 356×171×51 vs IPE A 360
UB 356×171×51 is an UB section from the UK Blue Book (SCI P363); IPE A 360 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 896 cm³ against 907 cm³ of plastic modulus, a difference of 1.2%. They weigh essentially the same, 51 kg/m and 50.2 kg/m. Both are about 356 mm deep, so either fits the same construction zone.
| Property | UB 356×171×51 UB | IPE A 360 IPE | Difference |
|---|---|---|---|
| Mass | 51 kg/m | 50.2 kg/m | +1.6% |
| Depth | 355 mm | 357.6 mm | -0.7% |
| Width | 171.5 mm | 170 mm | +0.9% |
| Web thickness | 7.4 mm | 6.6 mm | +12.1% |
| Flange thickness | 11.5 mm | 11.5 mm | same |
| Area | 64.9 cm² | 64 cm² | +1.4% |
| Second moment, major (Iy) | 14,100 cm⁴ | 14,500 cm⁴ | -2.8% |
| Plastic modulus, major (Wpl,y) | 896 cm³ | 907 cm³ | -1.2% |
| Elastic modulus, major (Wel,y) | 796 cm³ | 812 cm³ | -2.0% |
| Second moment, minor (Iz) | 968 cm⁴ | 944 cm⁴ | +2.5% |
| Plastic modulus, minor (Wpl,z) | 174 cm³ | 172 cm³ | +1.2% |
| Radius of gyration, minor (iz) | 3.86 cm | 3.84 cm | +0.5% |
| Torsion constant (It) | 23.8 cm⁴ | 27.4 cm⁴ | -13.1% |
UB 356×171×51 to BS EN 10365:2017; IPE A 360 to EN 10365 · Continental Steel. Difference is expressed relative to IPE A 360.
How to choose between them
On stiffness, IPE A 360 has the larger second moment of area: 14,500 cm⁴ against 14,100 cm⁴, a difference of 2.8%. 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 of steel, IPE A 360 is the more efficient section: 18.1 against 17.6 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. UB sections are specified to BS EN 10365:2017 and IPE to EN 10365 · 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.