UB 406×178×85 vs IPE V 400
UB 406×178×85 is an UB section from the UK Blue Book (SCI P363); IPE V 400 is the closest equivalent in the European (Continental) range. UB 406×178×85 carries more bending: 1730 cm³ of plastic modulus against 1680 cm³, 3.0% more. They weigh essentially the same, 85.3 kg/m and 84 kg/m. UB 406×178×85 is deeper, 417.2 mm against 408 mm, which matters where the floor zone is tight.
| Property | UB 406×178×85 UB | IPE V 400 IPE | Difference |
|---|---|---|---|
| Mass | 85.3 kg/m | 84 kg/m | +1.5% |
| Depth | 417.2 mm | 408 mm | +2.3% |
| Width | 181.9 mm | 182 mm | -0.1% |
| Web thickness | 10.9 mm | 10.6 mm | +2.8% |
| Flange thickness | 18.2 mm | 17.5 mm | +4.0% |
| Area | 109 cm² | 107 cm² | +1.9% |
| Second moment, major (Iy) | 31,700 cm⁴ | 30,100 cm⁴ | +5.3% |
| Plastic modulus, major (Wpl,y) | 1,730 cm³ | 1,680 cm³ | +3.0% |
| Elastic modulus, major (Wel,y) | 1,520 cm³ | 1,480 cm³ | +2.7% |
| Second moment, minor (Iz) | 1,830 cm⁴ | 1,770 cm⁴ | +3.4% |
| Plastic modulus, minor (Wpl,z) | 313 cm³ | 304 cm³ | +3.0% |
| Radius of gyration, minor (iz) | 4.11 cm | 4.06 cm | +1.2% |
| Torsion constant (It) | 93 cm⁴ | 99.6 cm⁴ | -6.6% |
UB 406×178×85 to BS EN 10365:2017; IPE V 400 to EN 10365 · Continental Steel. Difference is expressed relative to IPE V 400.
How to choose between them
On stiffness, UB 406×178×85 has the larger second moment of area: 31,700 cm⁴ against 30,100 cm⁴, a difference of 5.3%. 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 (20.3 against 20.0 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 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, UB 406×178×85 is the stronger section and IPE V 400 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.