UB 610×178×100 vs W 24X68
UB 610×178×100 is an UB section from the UK Blue Book (SCI P363); W 24X68 is the closest equivalent in the American AISC Shapes Database. W 24X68 carries more bending: 2900.5 cm³ of plastic modulus against 2790 cm³, 3.8% more. They weigh essentially the same, 100.3 kg/m and 101.2 kg/m. Both are about 605 mm deep, so either fits the same construction zone.
| Property | UB 610×178×100 UB | W 24X68 W | Difference |
|---|---|---|---|
| Mass | 100.3 kg/m | 101.2 kg/m | -0.9% |
| Depth | 607.4 mm | 602 mm | +0.9% |
| Width | 179.2 mm | 227.8 mm | -21.3% |
| Web thickness | 11.3 mm | 10.5 mm | +7.6% |
| Flange thickness | 17.2 mm | 14.9 mm | +15.4% |
| Area | 128 cm² | 129.7 cm² | -1.3% |
| Second moment, major (Iy) | 72,500 cm⁴ | 76,170 cm⁴ | -4.8% |
| Plastic modulus, major (Wpl,y) | 2,790 cm³ | 2,900.5 cm³ | -3.8% |
| Elastic modulus, major (Wel,y) | 2,390 cm³ | 2,523.6 cm³ | -5.3% |
| Second moment, minor (Iz) | 1,660 cm⁴ | 2,930 cm⁴ | -43.3% |
| Plastic modulus, minor (Wpl,z) | 296 cm³ | 401.48 cm³ | -26.3% |
| Radius of gyration, minor (iz) | 3.6 cm | 4.75 cm | -24.2% |
| Torsion constant (It) | 95 cm⁴ | 77.84 cm⁴ | +22.0% |
UB 610×178×100 to BS EN 10365:2017; W 24X68 to AISC Shapes Database v16.0. Difference is expressed relative to W 24X68.
How to choose between them
On stiffness, W 24X68 has the larger second moment of area: 76,170 cm⁴ against 72,500 cm⁴, a difference of 4.8%. 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, W 24X68 is the more efficient section: 28.7 against 27.8 cm³ per kg/m, 2.9% 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.
The two diverge much more about the minor axis: W 24X68 has 401.48 cm³ of minor-axis plastic modulus against 296 cm³, 26.3% 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 W 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 a marginal amount of weight.
In short, W 24X68 is the stronger section and UB 610×178×100 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.