Tee 178×203×30 vs WT 8X20
Tee 178×203×30 is an Tees (from UB) section from the UK Blue Book (SCI P363); WT 8X20 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 157 cm³ against 154.53 cm³ of plastic modulus, a difference of 1.6%. They weigh essentially the same, 30 kg/m and 29.8 kg/m. Both are about 203 mm deep, so either fits the same construction zone.
| Property | Tee 178×203×30 Tees (from UB) | WT 8X20 WT | Difference |
|---|---|---|---|
| Mass | 30 kg/m | 29.8 kg/m | +0.7% |
| Depth | 203.1 mm | 203.5 mm | -0.2% |
| Width | 177.9 mm | 177.8 mm | +0.1% |
| Web thickness | 7.9 mm | 7.7 mm | +2.6% |
| Flange thickness | 12.8 mm | 12.8 mm | same |
| Area | 38.3 cm² | 38 cm² | +0.8% |
| Second moment, major (Iy) | 1,400 cm⁴ | 1,378 cm⁴ | +1.6% |
| Plastic modulus, major (Wpl,y) | 157 cm³ | 154.53 cm³ | +1.6% |
| Elastic modulus, major (Wel,y) | 89 cm³ | 87.671 cm³ | +1.5% |
| Second moment, minor (Iz) | 602 cm⁴ | 599.4 cm⁴ | +0.4% |
| Plastic modulus, minor (Wpl,z) | 104 cm³ | 104.22 cm³ | -0.2% |
| Radius of gyration, minor (iz) | 3.97 cm | 3.96 cm | +0.3% |
| Torsion constant (It) | 16.6 cm⁴ | 16.48 cm⁴ | +0.7% |
Tee 178×203×30 to BS EN 10365:2017; WT 8X20 to AISC Shapes Database v16.0. Difference is expressed relative to WT 8X20.
How to choose between them
On stiffness, Tee 178×203×30 has the larger second moment of area: 1,400 cm⁴ against 1,378 cm⁴, a difference of 1.6%. 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 (5.2 against 5.2 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. Tees (from UB) sections are specified to BS EN 10365:2017 and WT 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, these two are genuine equivalents. Pick whichever your supplier stocks and the rest of the frame already uses.