UB 356×171×67 vs H-350x175x9x15
UB 356×171×67 is an UB section from the UK Blue Book (SCI P363); H-350x175x9x15 is the closest equivalent in the European (Continental) range. UB 356×171×67 carries more bending: 1210 cm³ of plastic modulus against 1180 cm³, 2.5% more. They weigh essentially the same, 67.1 kg/m and 66.2 kg/m. Both are about 361 mm deep, so either fits the same construction zone.
| Property | UB 356×171×67 UB | H-350x175x9x15 MB & MC | Difference |
|---|---|---|---|
| Mass | 67.1 kg/m | 66.2 kg/m | +1.4% |
| Depth | 363.4 mm | 358 mm | +1.5% |
| Width | 173.2 mm | 177 mm | -2.1% |
| Web thickness | 9.1 mm | 9 mm | +1.1% |
| Flange thickness | 15.7 mm | 15 mm | +4.7% |
| Area | 85.5 cm² | 84.3 cm² | +1.4% |
| Second moment, major (Iy) | 19,500 cm⁴ | 18,710 cm⁴ | +4.2% |
| Plastic modulus, major (Wpl,y) | 1,210 cm³ | 1,180 cm³ | +2.5% |
| Elastic modulus, major (Wel,y) | 1,070 cm³ | 1,045 cm³ | +2.4% |
| Second moment, minor (Iz) | 1,360 cm⁴ | 1,390 cm⁴ | -2.2% |
| Plastic modulus, minor (Wpl,z) | 243 cm³ | 243 cm³ | same |
| Radius of gyration, minor (iz) | 3.99 cm | 4.06 cm | -1.7% |
| Torsion constant (It) | 55.7 cm⁴ | 53.6 cm⁴ | +3.9% |
UB 356×171×67 to BS EN 10365:2017; H-350x175x9x15 to Continental Steel. Difference is expressed relative to H-350x175x9x15.
How to choose between them
On stiffness, UB 356×171×67 has the larger second moment of area: 19,500 cm⁴ against 18,710 cm⁴, a difference of 4.2%. 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 (18.0 against 17.8 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, UB 356×171×67 is the stronger section and H-350x175x9x15 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.