UB 457×191×67 vs W 18X46
UB 457×191×67 is an UB section from the UK Blue Book (SCI P363); W 18X46 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 1470 cm³ against 1486.3 cm³ of plastic modulus, a difference of 1.1%. UB 457×191×67 is the lighter of the two at 67.1 kg/m against 68.5 kg/m, a saving of 2.0% on steel weight. Both are about 457 mm deep, so either fits the same construction zone.
| Property | UB 457×191×67 UB | W 18X46 W | Difference |
|---|---|---|---|
| Mass | 67.1 kg/m | 68.5 kg/m | -2.0% |
| Depth | 453.4 mm | 459.7 mm | -1.4% |
| Width | 189.9 mm | 153.9 mm | +23.4% |
| Web thickness | 8.5 mm | 9.1 mm | -6.6% |
| Flange thickness | 12.7 mm | 15.4 mm | -17.5% |
| Area | 85.5 cm² | 87.1 cm² | -1.8% |
| Second moment, major (Iy) | 29,400 cm⁴ | 29,636 cm⁴ | -0.8% |
| Plastic modulus, major (Wpl,y) | 1,470 cm³ | 1,486.3 cm³ | -1.1% |
| Elastic modulus, major (Wel,y) | 1,300 cm³ | 1,291.3 cm³ | +0.7% |
| Second moment, minor (Iz) | 1,450 cm⁴ | 936.5 cm⁴ | +54.8% |
| Plastic modulus, minor (Wpl,z) | 237 cm³ | 191.73 cm³ | +23.6% |
| Radius of gyration, minor (iz) | 4.12 cm | 3.28 cm | +25.6% |
| Torsion constant (It) | 37.1 cm⁴ | 50.78 cm⁴ | -26.9% |
UB 457×191×67 to BS EN 10365:2017; W 18X46 to AISC Shapes Database v16.0. Difference is expressed relative to W 18X46.
How to choose between them
On stiffness, W 18X46 has the larger second moment of area: 29,636 cm⁴ against 29,400 cm⁴, a difference of 0.8%. 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 (21.9 against 21.7 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 457×191×67 has 237 cm³ of minor-axis plastic modulus against 191.73 cm³, 23.6% 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 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 2.0% weight.
In short, W 18X46 is the stronger section and UB 457×191×67 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.