UC 305×305×198 vs W 12X136
UC 305×305×198 is an UC section from the UK Blue Book (SCI P363); W 12X136 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 3440 cm³ against 3506.8 cm³ of plastic modulus, a difference of 1.9%. UC 305×305×198 is the lighter of the two at 198.1 kg/m against 202.4 kg/m, a saving of 2.1% on steel weight. Both are about 340 mm deep, so either fits the same construction zone.
| Property | UC 305×305×198 UC | W 12X136 W | Difference |
|---|---|---|---|
| Mass | 198.1 kg/m | 202.4 kg/m | -2.1% |
| Depth | 339.9 mm | 340.4 mm | -0.1% |
| Width | 314.5 mm | 315 mm | -0.2% |
| Web thickness | 19.1 mm | 20.1 mm | -5.0% |
| Flange thickness | 31.4 mm | 31.8 mm | -1.3% |
| Area | 252 cm² | 257.4 cm² | -2.1% |
| Second moment, major (Iy) | 50,900 cm⁴ | 51,613 cm⁴ | -1.4% |
| Plastic modulus, major (Wpl,y) | 3,440 cm³ | 3,506.8 cm³ | -1.9% |
| Elastic modulus, major (Wel,y) | 3,000 cm³ | 3,048 cm³ | -1.6% |
| Second moment, minor (Iz) | 16,300 cm⁴ | 16,566 cm⁴ | -1.6% |
| Plastic modulus, minor (Wpl,z) | 1,580 cm³ | 1,605.9 cm³ | -1.6% |
| Radius of gyration, minor (iz) | 8.04 cm | 8.03 cm | +0.1% |
| Torsion constant (It) | 734 cm⁴ | 770 cm⁴ | -4.7% |
UC 305×305×198 to BS EN 10365:2017; W 12X136 to AISC Shapes Database v16.0. Difference is expressed relative to W 12X136.
How to choose between them
On stiffness, W 12X136 has the larger second moment of area: 51,613 cm⁴ against 50,900 cm⁴, a difference of 1.4%. 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 (17.4 against 17.3 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 2.1% weight.
In short, W 12X136 is the stronger section and UC 305×305×198 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.