UC 356×368×129 vs W 14X90
UC 356×368×129 is an UC section from the UK Blue Book (SCI P363); W 14X90 is the closest equivalent in the American AISC Shapes Database. W 14X90 carries more bending: 2572.8 cm³ of plastic modulus against 2480 cm³, 3.6% more. UC 356×368×129 is the lighter of the two at 129 kg/m against 133.9 kg/m, a saving of 3.7% on steel weight. Both are about 356 mm deep, so either fits the same construction zone.
| Property | UC 356×368×129 UC | W 14X90 W | Difference |
|---|---|---|---|
| Mass | 129 kg/m | 133.9 kg/m | -3.7% |
| Depth | 355.6 mm | 355.6 mm | same |
| Width | 368.6 mm | 368.3 mm | +0.1% |
| Web thickness | 10.4 mm | 11.2 mm | -7.1% |
| Flange thickness | 17.5 mm | 18 mm | -2.8% |
| Area | 164 cm² | 171 cm² | -4.1% |
| Second moment, major (Iy) | 40,200 cm⁴ | 41,582 cm⁴ | -3.3% |
| Plastic modulus, major (Wpl,y) | 2,480 cm³ | 2,572.8 cm³ | -3.6% |
| Elastic modulus, major (Wel,y) | 2,260 cm³ | 2,343.4 cm³ | -3.6% |
| Second moment, minor (Iz) | 14,600 cm⁴ | 15,068 cm⁴ | -3.1% |
| Plastic modulus, minor (Wpl,z) | 1,200 cm³ | 1,238.9 cm³ | -3.1% |
| Radius of gyration, minor (iz) | 9.43 cm | 9.4 cm | +0.3% |
| Torsion constant (It) | 153 cm⁴ | 169 cm⁴ | -9.5% |
UC 356×368×129 to BS EN 10365:2017; W 14X90 to AISC Shapes Database v16.0. Difference is expressed relative to W 14X90.
How to choose between them
On stiffness, W 14X90 has the larger second moment of area: 41,582 cm⁴ against 40,200 cm⁴, a difference of 3.3%. 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, the two are equally efficient (19.2 against 19.2 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.
These come from different catalogues, so treat the swap as a design change rather than a like-for-like substitution. UC 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 3.7% weight.
In short, W 14X90 is the stronger section and UC 356×368×129 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.