W 33X241 vs UB 914×419×343
W 33X241 is an W section from the American AISC Shapes Database; UB 914×419×343 is the closest equivalent in the UK Blue Book (SCI P363). They are close to interchangeable in bending: 15403.8 cm³ against 15500 cm³ of plastic modulus, a difference of 0.6%. UB 914×419×343 is the lighter of the two at 343.3 kg/m against 358.6 kg/m, a saving of 4.5% on steel weight. UB 914×419×343 is deeper, 911.8 mm against 868.7 mm, which matters where the floor zone is tight.
| Property | W 33X241 W | UB 914×419×343 UB | Difference |
|---|---|---|---|
| Mass | 358.6 kg/m | 343.3 kg/m | +4.5% |
| Depth | 868.7 mm | 911.8 mm | -4.7% |
| Width | 403.9 mm | 418.5 mm | -3.5% |
| Web thickness | 21.1 mm | 19.4 mm | +8.8% |
| Flange thickness | 35.6 mm | 32 mm | +11.3% |
| Area | 458.7 cm² | 437 cm² | +5.0% |
| Second moment, major (Iy) | 591,049 cm⁴ | 626,000 cm⁴ | -5.6% |
| Plastic modulus, major (Wpl,y) | 15,403.8 cm³ | 15,500 cm³ | -0.6% |
| Elastic modulus, major (Wel,y) | 13,617.7 cm³ | 13,700 cm³ | -0.6% |
| Second moment, minor (Iz) | 38,834 cm⁴ | 39,200 cm⁴ | -0.9% |
| Plastic modulus, minor (Wpl,z) | 2,982.4 cm³ | 2,890 cm³ | +3.2% |
| Radius of gyration, minor (iz) | 9.19 cm | 9.46 cm | -2.9% |
| Torsion constant (It) | 1,507 cm⁴ | 1,190 cm⁴ | +26.6% |
W 33X241 to AISC Shapes Database v16.0; UB 914×419×343 to BS EN 10365:2017. Difference is expressed relative to UB 914×419×343.
How to choose between them
On stiffness, UB 914×419×343 has the larger second moment of area: 626,000 cm⁴ against 591,049 cm⁴, a difference of 5.6%. 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, UB 914×419×343 is the more efficient section: 45.2 against 43.0 cm³ per kg/m, 4.9% 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.
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 4.5% weight.
In short, UB 914×419×343 is the stronger section and UB 914×419×343 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.