UB 356×171×51 vs H-350x175x7x11-49.6
UB 356×171×51 is an UB section from the UK Blue Book (SCI P363); H-350x175x7x11-49.6 is the closest equivalent in the European (Continental) range. UB 356×171×51 carries more bending: 896 cm³ of plastic modulus against 868 cm³, 3.2% more. H-350x175x7x11-49.6 is the lighter of the two at 49.6 kg/m against 51 kg/m, a saving of 2.8% on steel weight. Both are about 353 mm deep, so either fits the same construction zone.
| Property | UB 356×171×51 UB | H-350x175x7x11-49.6 MB & MC | Difference |
|---|---|---|---|
| Mass | 51 kg/m | 49.6 kg/m | +2.8% |
| Depth | 355 mm | 350 mm | +1.4% |
| Width | 171.5 mm | 175 mm | -2.0% |
| Web thickness | 7.4 mm | 7 mm | +5.7% |
| Flange thickness | 11.5 mm | 11 mm | +4.5% |
| Area | 64.9 cm² | 63.1 cm² | +2.9% |
| Second moment, major (Iy) | 14,100 cm⁴ | 13,560 cm⁴ | +4.0% |
| Plastic modulus, major (Wpl,y) | 896 cm³ | 868 cm³ | +3.2% |
| Elastic modulus, major (Wel,y) | 796 cm³ | 775 cm³ | +2.7% |
| Second moment, minor (Iz) | 968 cm⁴ | 985 cm⁴ | -1.7% |
| Plastic modulus, minor (Wpl,z) | 174 cm³ | 174 cm³ | same |
| Radius of gyration, minor (iz) | 3.86 cm | 3.95 cm | -2.3% |
| Torsion constant (It) | 23.8 cm⁴ | 23 cm⁴ | +3.5% |
UB 356×171×51 to BS EN 10365:2017; H-350x175x7x11-49.6 to Continental Steel. Difference is expressed relative to H-350x175x7x11-49.6.
How to choose between them
On stiffness, UB 356×171×51 has the larger second moment of area: 14,100 cm⁴ against 13,560 cm⁴, a difference of 4.0%. 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, the two are equally efficient (17.6 against 17.5 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 2.8% weight.
In short, UB 356×171×51 is the stronger section and H-350x175x7x11-49.6 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.