W 36X256 vs UB 914×419×388
W 36X256 is an W section from the American AISC Shapes Database; UB 914×419×388 is the closest equivalent in the UK Blue Book (SCI P363). UB 914×419×388 carries more bending: 17700 cm³ of plastic modulus against 17042.5 cm³, 3.7% more. They weigh essentially the same, 381 kg/m and 388 kg/m. W 36X256 is deeper, 950 mm against 921 mm, which matters where the floor zone is tight.
| Property | W 36X256 W | UB 914×419×388 UB | Difference |
|---|---|---|---|
| Mass | 381 kg/m | 388 kg/m | -1.8% |
| Depth | 950 mm | 921 mm | +3.1% |
| Width | 309.9 mm | 420.5 mm | -26.3% |
| Web thickness | 24.4 mm | 21.4 mm | +14.0% |
| Flange thickness | 43.9 mm | 36.6 mm | +19.9% |
| Area | 485.8 cm² | 494 cm² | -1.7% |
| Second moment, major (Iy) | 699,269 cm⁴ | 720,000 cm⁴ | -2.9% |
| Plastic modulus, major (Wpl,y) | 17,042.5 cm³ | 17,700 cm³ | -3.7% |
| Elastic modulus, major (Wel,y) | 14,666.4 cm³ | 15,600 cm³ | -6.0% |
| Second moment, minor (Iz) | 21,977 cm⁴ | 45,400 cm⁴ | -51.6% |
| Plastic modulus, minor (Wpl,z) | 2,245 cm³ | 3,340 cm³ | -32.8% |
| Radius of gyration, minor (iz) | 6.73 cm | 9.59 cm | -29.8% |
| Torsion constant (It) | 2,202 cm⁴ | 1,730 cm⁴ | +27.3% |
W 36X256 to AISC Shapes Database v16.0; UB 914×419×388 to BS EN 10365:2017. Difference is expressed relative to UB 914×419×388.
How to choose between them
On stiffness, UB 914×419×388 has the larger second moment of area: 720,000 cm⁴ against 699,269 cm⁴, a difference of 2.9%. 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 (44.7 against 45.6 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.
The two diverge much more about the minor axis: UB 914×419×388 has 3340 cm³ of minor-axis plastic modulus against 2245 cm³, 32.8% 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. W sections are specified to AISC Shapes Database v16.0 and UB to BS EN 10365:2017; 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 914×419×388 is the stronger section and W 36X256 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.