UB 610×305×149 vs S 24X106
UB 610×305×149 is an UB section from the UK Blue Book (SCI P363); S 24X106 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 4590 cm³ against 4572 cm³ of plastic modulus, a difference of 0.4%. UB 610×305×149 is the lighter of the two at 149.2 kg/m against 157.7 kg/m, a saving of 5.4% on steel weight. Both are about 617 mm deep, so either fits the same construction zone.
| Property | UB 610×305×149 UB | S 24X106 S | Difference |
|---|---|---|---|
| Mass | 149.2 kg/m | 157.7 kg/m | -5.4% |
| Depth | 612.4 mm | 622.3 mm | -1.6% |
| Width | 304.8 mm | 199.9 mm | +52.5% |
| Web thickness | 11.8 mm | 15.7 mm | -24.8% |
| Flange thickness | 19.7 mm | 27.7 mm | -28.9% |
| Area | 190 cm² | 200.6 cm² | -5.3% |
| Second moment, major (Iy) | 126,000 cm⁴ | 122,372 cm⁴ | +3.0% |
| Plastic modulus, major (Wpl,y) | 4,590 cm³ | 4,572 cm³ | +0.4% |
| Elastic modulus, major (Wel,y) | 4,110 cm³ | 3,932.9 cm³ | +4.5% |
| Second moment, minor (Iz) | 9,310 cm⁴ | 3,197 cm⁴ | +191.2% |
| Plastic modulus, minor (Wpl,z) | 937 cm³ | 547.33 cm³ | +71.2% |
| Radius of gyration, minor (iz) | 7 cm | 3.99 cm | +75.4% |
| Torsion constant (It) | 200 cm⁴ | 420.4 cm⁴ | -52.4% |
UB 610×305×149 to BS EN 10365:2017; S 24X106 to AISC Shapes Database v16.0. Difference is expressed relative to S 24X106.
How to choose between them
On stiffness, UB 610×305×149 has the larger second moment of area: 126,000 cm⁴ against 122,372 cm⁴, a difference of 3.0%. 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 610×305×149 is the more efficient section: 30.8 against 29.0 cm³ per kg/m, 6.1% 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 610×305×149 has 937 cm³ of minor-axis plastic modulus against 547.33 cm³, 71.2% 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 5.4% weight.
In short, UB 610×305×149 is the stronger section and UB 610×305×149 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.