W 24X104 vs UB 610×305×149
W 24X104 is an W section from the American AISC Shapes Database; UB 610×305×149 is the closest equivalent in the UK Blue Book (SCI P363). W 24X104 carries more bending: 4735.9 cm³ of plastic modulus against 4590 cm³, 3.2% more. UB 610×305×149 is the lighter of the two at 149.2 kg/m against 154.8 kg/m, a saving of 3.8% on steel weight. Both are about 612 mm deep, so either fits the same construction zone.
| Property | W 24X104 W | UB 610×305×149 UB | Difference |
|---|---|---|---|
| Mass | 154.8 kg/m | 149.2 kg/m | +3.8% |
| Depth | 612.1 mm | 612.4 mm | same |
| Width | 325.1 mm | 304.8 mm | +6.7% |
| Web thickness | 12.7 mm | 11.8 mm | +7.6% |
| Flange thickness | 19 mm | 19.7 mm | -3.6% |
| Area | 198.1 cm² | 190 cm² | +4.3% |
| Second moment, major (Iy) | 129,032 cm⁴ | 126,000 cm⁴ | +2.4% |
| Plastic modulus, major (Wpl,y) | 4,735.9 cm³ | 4,590 cm³ | +3.2% |
| Elastic modulus, major (Wel,y) | 4,227.9 cm³ | 4,110 cm³ | +2.9% |
| Second moment, minor (Iz) | 10,780 cm⁴ | 9,310 cm⁴ | +15.8% |
| Plastic modulus, minor (Wpl,z) | 1,022.6 cm³ | 937 cm³ | +9.1% |
| Radius of gyration, minor (iz) | 7.39 cm | 7 cm | +5.6% |
| Torsion constant (It) | 196.5 cm⁴ | 200 cm⁴ | -1.8% |
W 24X104 to AISC Shapes Database v16.0; UB 610×305×149 to BS EN 10365:2017. Difference is expressed relative to UB 610×305×149.
How to choose between them
On stiffness, W 24X104 has the larger second moment of area: 129,032 cm⁴ against 126,000 cm⁴, a difference of 2.4%. 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, the two are equally efficient (30.6 against 30.8 cm³ per kg/m), so on a pure steel-tonnage basis there is nothing to choose between them. The decision comes down to availability, connection detailing and what the rest of the frame uses.
The two diverge much more about the minor axis: W 24X104 has 1022.6 cm³ of minor-axis plastic modulus against 937 cm³, 9.1% 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. W sections are specified to AISC Shapes Database v16.0 and UB to BS EN 10365:2017; 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 3.8% weight.
In short, W 24X104 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.