UB 610×229×125 vs S 24X90
UB 610×229×125 is an UB section from the UK Blue Book (SCI P363); S 24X90 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 3680 cm³ against 3637.9 cm³ of plastic modulus, a difference of 1.2%. UB 610×229×125 is the lighter of the two at 125.1 kg/m against 133.9 kg/m, a saving of 6.6% on steel weight. Both are about 611 mm deep, so either fits the same construction zone.
| Property | UB 610×229×125 UB | S 24X90 S | Difference |
|---|---|---|---|
| Mass | 125.1 kg/m | 133.9 kg/m | -6.6% |
| Depth | 612.2 mm | 609.6 mm | +0.4% |
| Width | 229 mm | 181.1 mm | +26.4% |
| Web thickness | 11.9 mm | 15.9 mm | -25.2% |
| Flange thickness | 19.6 mm | 22.1 mm | -11.3% |
| Area | 159 cm² | 171 cm² | -7.0% |
| Second moment, major (Iy) | 98,600 cm⁴ | 93,652 cm⁴ | +5.3% |
| Plastic modulus, major (Wpl,y) | 3,680 cm³ | 3,637.9 cm³ | +1.2% |
| Elastic modulus, major (Wel,y) | 3,220 cm³ | 3,064.4 cm³ | +5.1% |
| Second moment, minor (Iz) | 3,930 cm⁴ | 1,861 cm⁴ | +111.2% |
| Plastic modulus, minor (Wpl,z) | 535 cm³ | 367.07 cm³ | +45.7% |
| Radius of gyration, minor (iz) | 4.97 cm | 3.3 cm | +50.6% |
| Torsion constant (It) | 154 cm⁴ | 251.8 cm⁴ | -38.8% |
UB 610×229×125 to BS EN 10365:2017; S 24X90 to AISC Shapes Database v16.0. Difference is expressed relative to S 24X90.
How to choose between them
On stiffness, UB 610×229×125 has the larger second moment of area: 98,600 cm⁴ against 93,652 cm⁴, a difference of 5.3%. 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 610×229×125 is the more efficient section: 29.4 against 27.2 cm³ per kg/m, 8.3% 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: UB 610×229×125 has 535 cm³ of minor-axis plastic modulus against 367.07 cm³, 45.7% 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 6.6% weight.
In short, UB 610×229×125 is the stronger section and UB 610×229×125 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.