UB 457×152×74 vs S 18X54.7
UB 457×152×74 is an UB section from the UK Blue Book (SCI P363); S 18X54.7 is the closest equivalent in the American AISC Shapes Database. S 18X54.7 carries more bending: 1704.3 cm³ of plastic modulus against 1630 cm³, 4.4% more. UB 457×152×74 is the lighter of the two at 74.2 kg/m against 81.4 kg/m, a saving of 8.8% on steel weight. Both are about 460 mm deep, so either fits the same construction zone.
| Property | UB 457×152×74 UB | S 18X54.7 S | Difference |
|---|---|---|---|
| Mass | 74.2 kg/m | 81.4 kg/m | -8.8% |
| Depth | 462 mm | 457.2 mm | +1.0% |
| Width | 154.4 mm | 152.4 mm | +1.3% |
| Web thickness | 9.6 mm | 11.7 mm | -17.9% |
| Flange thickness | 17 mm | 17.6 mm | -3.4% |
| Area | 94.5 cm² | 103.2 cm² | -8.4% |
| Second moment, major (Iy) | 32,700 cm⁴ | 33,340 cm⁴ | -1.9% |
| Plastic modulus, major (Wpl,y) | 1,630 cm³ | 1,704.3 cm³ | -4.4% |
| Elastic modulus, major (Wel,y) | 1,410 cm³ | 1,458.4 cm³ | -3.3% |
| Second moment, minor (Iz) | 1,050 cm⁴ | 861.6 cm⁴ | +21.9% |
| Plastic modulus, minor (Wpl,z) | 213 cm³ | 198.28 cm³ | +7.4% |
| Radius of gyration, minor (iz) | 3.33 cm | 2.9 cm | +14.8% |
| Torsion constant (It) | 65.9 cm⁴ | 96.98 cm⁴ | -32.0% |
UB 457×152×74 to BS EN 10365:2017; S 18X54.7 to AISC Shapes Database v16.0. Difference is expressed relative to S 18X54.7.
How to choose between them
On stiffness, S 18X54.7 has the larger second moment of area: 33,340 cm⁴ against 32,700 cm⁴, a difference of 1.9%. 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 of steel, UB 457×152×74 is the more efficient section: 22.0 against 20.9 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. UB sections are specified to BS EN 10365:2017 and S 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 8.8% weight.
In short, S 18X54.7 is the stronger section and UB 457×152×74 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.