UB 457×191×133 vs W 18X86
UB 457×191×133 is an UB section from the UK Blue Book (SCI P363); W 18X86 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 3070 cm³ against 3048 cm³ of plastic modulus, a difference of 0.7%. W 18X86 is the lighter of the two at 128 kg/m against 133.3 kg/m, a saving of 4.1% on steel weight. UB 457×191×133 is deeper, 480.6 mm against 467.4 mm, which matters where the floor zone is tight.
| Property | UB 457×191×133 UB | W 18X86 W | Difference |
|---|---|---|---|
| Mass | 133.3 kg/m | 128 kg/m | +4.1% |
| Depth | 480.6 mm | 467.4 mm | +2.8% |
| Width | 196.7 mm | 281.9 mm | -30.2% |
| Web thickness | 15.3 mm | 12.2 mm | +25.4% |
| Flange thickness | 26.3 mm | 19.6 mm | +34.2% |
| Area | 170 cm² | 163.2 cm² | +4.2% |
| Second moment, major (Iy) | 63,800 cm⁴ | 63,683 cm⁴ | +0.2% |
| Plastic modulus, major (Wpl,y) | 3,070 cm³ | 3,048 cm³ | +0.7% |
| Elastic modulus, major (Wel,y) | 2,660 cm³ | 2,720.3 cm³ | -2.2% |
| Second moment, minor (Iz) | 3,350 cm⁴ | 7,284 cm⁴ | -54.0% |
| Plastic modulus, minor (Wpl,z) | 535 cm³ | 793.13 cm³ | -32.5% |
| Radius of gyration, minor (iz) | 4.44 cm | 6.68 cm | -33.5% |
| Torsion constant (It) | 292 cm⁴ | 170.7 cm⁴ | +71.1% |
UB 457×191×133 to BS EN 10365:2017; W 18X86 to AISC Shapes Database v16.0. Difference is expressed relative to W 18X86.
How to choose between them
On stiffness, UB 457×191×133 has the larger second moment of area: 63,800 cm⁴ against 63,683 cm⁴, a difference of 0.2%. 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, W 18X86 is the more efficient section: 23.8 against 23.0 cm³ per kg/m, 3.3% 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: W 18X86 has 793.13 cm³ of minor-axis plastic modulus against 535 cm³, 32.5% 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 4.1% weight.
In short, UB 457×191×133 is the stronger section and W 18X86 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.