WT 6X39.5 vs Tee 305×152×59
WT 6X39.5 is an WT section from the American AISC Shapes Database; Tee 305×152×59 is the closest equivalent in the UK Blue Book (SCI P363). They are close to interchangeable in bending: 155.51 cm³ against 156 cm³ of plastic modulus, a difference of 0.3%. They weigh essentially the same, 58.8 kg/m and 58.9 kg/m. Both are about 157 mm deep, so either fits the same construction zone.
| Property | WT 6X39.5 WT | Tee 305×152×59 Tees (from UC) | Difference |
|---|---|---|---|
| Mass | 58.8 kg/m | 58.9 kg/m | -0.2% |
| Depth | 157.2 mm | 157.2 mm | same |
| Width | 307.3 mm | 307.4 mm | same |
| Web thickness | 11.9 mm | 12 mm | -0.8% |
| Flange thickness | 18.7 mm | 18.7 mm | same |
| Area | 74.8 cm² | 75.1 cm² | -0.4% |
| Second moment, major (Iy) | 1,074 cm⁴ | 1,080 cm⁴ | -0.6% |
| Plastic modulus, major (Wpl,y) | 155.51 cm³ | 156 cm³ | -0.3% |
| Elastic modulus, major (Wel,y) | 82.427 cm³ | 82.8 cm³ | -0.5% |
| Second moment, minor (Iz) | 4,495 cm⁴ | 4,530 cm⁴ | -0.8% |
| Plastic modulus, minor (Wpl,z) | 444.09 cm³ | 448 cm³ | -0.9% |
| Radius of gyration, minor (iz) | 7.75 cm | 7.77 cm | -0.3% |
| Torsion constant (It) | 79.5 cm⁴ | 80.3 cm⁴ | -1.0% |
WT 6X39.5 to AISC Shapes Database v16.0; Tee 305×152×59 to BS EN 10365:2017. Difference is expressed relative to Tee 305×152×59.
How to choose between them
On stiffness, Tee 305×152×59 has the larger second moment of area: 1,080 cm⁴ against 1,074 cm⁴, a difference of 0.6%. 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 (2.6 against 2.6 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. WT sections are specified to AISC Shapes Database v16.0 and Tees (from UC) 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 a marginal amount of weight.
In short, these two are genuine equivalents. Pick whichever your supplier stocks and the rest of the frame already uses.