UB 356×171×57 vs H-350x175x8x13
UB 356×171×57 is an UB section from the UK Blue Book (SCI P363); H-350x175x8x13 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 1010 cm³ against 1022 cm³ of plastic modulus, a difference of 1.2%. They weigh essentially the same, 57 kg/m and 57.8 kg/m. Both are about 356 mm deep, so either fits the same construction zone.
| Property | UB 356×171×57 UB | H-350x175x8x13 MB & MC | Difference |
|---|---|---|---|
| Mass | 57 kg/m | 57.8 kg/m | -1.4% |
| Depth | 358 mm | 354 mm | +1.1% |
| Width | 172.2 mm | 176 mm | -2.2% |
| Web thickness | 8.1 mm | 8 mm | +1.2% |
| Flange thickness | 13 mm | 13 mm | same |
| Area | 72.6 cm² | 73.7 cm² | -1.5% |
| Second moment, major (Iy) | 16,000 cm⁴ | 16,100 cm⁴ | -0.6% |
| Plastic modulus, major (Wpl,y) | 1,010 cm³ | 1,022 cm³ | -1.2% |
| Elastic modulus, major (Wel,y) | 896 cm³ | 909 cm³ | -1.4% |
| Second moment, minor (Iz) | 1,110 cm⁴ | 1,184 cm⁴ | -6.3% |
| Plastic modulus, minor (Wpl,z) | 199 cm³ | 208 cm³ | -4.3% |
| Radius of gyration, minor (iz) | 3.91 cm | 4.01 cm | -2.5% |
| Torsion constant (It) | 33.4 cm⁴ | 36.1 cm⁴ | -7.5% |
UB 356×171×57 to BS EN 10365:2017; H-350x175x8x13 to Continental Steel. Difference is expressed relative to H-350x175x8x13.
How to choose between them
On stiffness, H-350x175x8x13 has the larger second moment of area: 16,100 cm⁴ against 16,000 cm⁴, a difference of 0.6%. 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, the two are equally efficient (17.7 against 17.7 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. UB sections are specified to BS EN 10365:2017 and MB & MC to 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.