UB 254×102×25 vs H-250x125x5x8-25.1
UB 254×102×25 is an UB section from the UK Blue Book (SCI P363); H-250x125x5x8-25.1 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 306 cm³ against 312 cm³ of plastic modulus, a difference of 1.9%. They weigh essentially the same, 25.2 kg/m and 25.1 kg/m. UB 254×102×25 is deeper, 257.2 mm against 248 mm, which matters where the floor zone is tight.
| Property | UB 254×102×25 UB | H-250x125x5x8-25.1 MB & MC | Difference |
|---|---|---|---|
| Mass | 25.2 kg/m | 25.1 kg/m | +0.4% |
| Depth | 257.2 mm | 248 mm | +3.7% |
| Width | 101.9 mm | 124 mm | -17.8% |
| Web thickness | 6 mm | 5 mm | +20.0% |
| Flange thickness | 8.4 mm | 8 mm | +5.0% |
| Area | 32 cm² | 32 cm² | same |
| Second moment, major (Iy) | 3,410 cm⁴ | 3,450 cm⁴ | -1.2% |
| Plastic modulus, major (Wpl,y) | 306 cm³ | 312 cm³ | -1.9% |
| Elastic modulus, major (Wel,y) | 266 cm³ | 278 cm³ | -4.3% |
| Second moment, minor (Iz) | 149 cm⁴ | 255 cm⁴ | -41.6% |
| Plastic modulus, minor (Wpl,z) | 46 cm³ | 63.2 cm³ | -27.2% |
| Radius of gyration, minor (iz) | 2.15 cm | 2.82 cm | -23.8% |
| Torsion constant (It) | 6.42 cm⁴ | 5.78 cm⁴ | +11.1% |
UB 254×102×25 to BS EN 10365:2017; H-250x125x5x8-25.1 to Continental Steel. Difference is expressed relative to H-250x125x5x8-25.1.
How to choose between them
On stiffness, H-250x125x5x8-25.1 has the larger second moment of area: 3,450 cm⁴ against 3,410 cm⁴, a difference of 1.2%. 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 of steel, H-250x125x5x8-25.1 is the more efficient section: 12.4 against 12.1 cm³ per kg/m, 2.3% 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.
The two diverge much more about the minor axis: H-250x125x5x8-25.1 has 63.2 cm³ of minor-axis plastic modulus against 46 cm³, 27.2% more. If the member sees any minor-axis bending, or if it is unrestrained over a long length and lateral-torsional buckling governs, that gap decides the comparison even though the major-axis numbers looked equivalent.
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.