UB 305×165×54 vs W 12X35
UB 305×165×54 is an UB section from the UK Blue Book (SCI P363); W 12X35 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 846 cm³ against 839.02 cm³ of plastic modulus, a difference of 0.8%. W 12X35 is the lighter of the two at 52.1 kg/m against 54 kg/m, a saving of 3.6% on steel weight. W 12X35 is deeper, 317.5 mm against 310.4 mm, which matters where the floor zone is tight.
| Property | UB 305×165×54 UB | W 12X35 W | Difference |
|---|---|---|---|
| Mass | 54 kg/m | 52.1 kg/m | +3.6% |
| Depth | 310.4 mm | 317.5 mm | -2.2% |
| Width | 166.9 mm | 166.6 mm | +0.2% |
| Web thickness | 7.9 mm | 7.6 mm | +3.9% |
| Flange thickness | 13.7 mm | 13.2 mm | +3.8% |
| Area | 68.8 cm² | 66.5 cm² | +3.5% |
| Second moment, major (Iy) | 11,700 cm⁴ | 11,863 cm⁴ | -1.4% |
| Plastic modulus, major (Wpl,y) | 846 cm³ | 839.02 cm³ | +0.8% |
| Elastic modulus, major (Wel,y) | 754 cm³ | 747.25 cm³ | +0.9% |
| Second moment, minor (Iz) | 1,060 cm⁴ | 1,020 cm⁴ | +3.9% |
| Plastic modulus, minor (Wpl,z) | 196 cm³ | 188.45 cm³ | +4.0% |
| Radius of gyration, minor (iz) | 3.93 cm | 3.91 cm | +0.5% |
| Torsion constant (It) | 34.8 cm⁴ | 30.84 cm⁴ | +12.8% |
UB 305×165×54 to BS EN 10365:2017; W 12X35 to AISC Shapes Database v16.0. Difference is expressed relative to W 12X35.
How to choose between them
On stiffness, W 12X35 has the larger second moment of area: 11,863 cm⁴ against 11,700 cm⁴, a difference of 1.4%. 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, W 12X35 is the more efficient section: 16.1 against 15.7 cm³ per kg/m, 2.7% 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. UB sections are specified to BS EN 10365:2017 and W to AISC Shapes Database v16.0; 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 3.6% weight.
In short, UB 305×165×54 is the stronger section and W 12X35 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.