UB 254×146×43 vs S 10X35
UB 254×146×43 is an UB section from the UK Blue Book (SCI P363); S 10X35 is the closest equivalent in the American AISC Shapes Database. S 10X35 carries more bending: 580.1 cm³ of plastic modulus against 566 cm³, 2.4% more. UB 254×146×43 is the lighter of the two at 43 kg/m against 52.1 kg/m, a saving of 17.5% on steel weight. UB 254×146×43 is deeper, 259.6 mm against 254 mm, which matters where the floor zone is tight.
| Property | UB 254×146×43 UB | S 10X35 S | Difference |
|---|---|---|---|
| Mass | 43 kg/m | 52.1 kg/m | -17.5% |
| Depth | 259.6 mm | 254 mm | +2.2% |
| Width | 147.3 mm | 125.5 mm | +17.4% |
| Web thickness | 7.2 mm | 15.1 mm | -52.3% |
| Flange thickness | 12.7 mm | 12.5 mm | +1.6% |
| Area | 54.8 cm² | 66.5 cm² | -17.6% |
| Second moment, major (Iy) | 6,540 cm⁴ | 6,119 cm⁴ | +6.9% |
| Plastic modulus, major (Wpl,y) | 566 cm³ | 580.1 cm³ | -2.4% |
| Elastic modulus, major (Wel,y) | 504 cm³ | 481.78 cm³ | +4.6% |
| Second moment, minor (Iz) | 677 cm⁴ | 345.5 cm⁴ | +95.9% |
| Plastic modulus, minor (Wpl,z) | 141 cm³ | 101.44 cm³ | +39.0% |
| Radius of gyration, minor (iz) | 3.52 cm | 2.28 cm | +54.4% |
| Torsion constant (It) | 23.9 cm⁴ | 53.69 cm⁴ | -55.5% |
UB 254×146×43 to BS EN 10365:2017; S 10X35 to AISC Shapes Database v16.0. Difference is expressed relative to S 10X35.
How to choose between them
On stiffness, UB 254×146×43 has the larger second moment of area: 6,540 cm⁴ against 6,119 cm⁴, a difference of 6.9%. 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 254×146×43 is the more efficient section: 13.2 against 11.1 cm³ per kg/m, 18.2% 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: UB 254×146×43 has 141 cm³ of minor-axis plastic modulus against 101.44 cm³, 39.0% 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 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 17.5% weight.
In short, S 10X35 is the stronger section and UB 254×146×43 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.