Tee 178×203×27 vs WT 8X18
Tee 178×203×27 is an Tees (from UB) section from the UK Blue Book (SCI P363); WT 8X18 is the closest equivalent in the American AISC Shapes Database. Tee 178×203×27 carries more bending: 150 cm³ of plastic modulus against 146.34 cm³, 2.5% more. They weigh essentially the same, 27 kg/m and 26.8 kg/m. Both are about 201 mm deep, so either fits the same construction zone.
| Property | Tee 178×203×27 Tees (from UB) | WT 8X18 WT | Difference |
|---|---|---|---|
| Mass | 27 kg/m | 26.8 kg/m | +0.7% |
| Depth | 201.2 mm | 201.4 mm | -0.1% |
| Width | 177.7 mm | 177.5 mm | +0.1% |
| Web thickness | 7.7 mm | 7.5 mm | +2.7% |
| Flange thickness | 10.9 mm | 10.9 mm | same |
| Area | 34.5 cm² | 34.1 cm² | +1.2% |
| Second moment, major (Iy) | 1,290 cm⁴ | 1,274 cm⁴ | +1.3% |
| Plastic modulus, major (Wpl,y) | 150 cm³ | 146.34 cm³ | +2.5% |
| Elastic modulus, major (Wel,y) | 84.6 cm³ | 82.755 cm³ | +2.2% |
| Second moment, minor (Iz) | 511 cm⁴ | 507.8 cm⁴ | +0.6% |
| Plastic modulus, minor (Wpl,z) | 89.1 cm³ | 88.818 cm³ | +0.3% |
| Radius of gyration, minor (iz) | 3.85 cm | 3.86 cm | -0.3% |
| Torsion constant (It) | 11.5 cm⁴ | 11.32 cm⁴ | +1.6% |
Tee 178×203×27 to BS EN 10365:2017; WT 8X18 to AISC Shapes Database v16.0. Difference is expressed relative to WT 8X18.
How to choose between them
On stiffness, Tee 178×203×27 has the larger second moment of area: 1,290 cm⁴ against 1,274 cm⁴, a difference of 1.3%. 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 (5.6 against 5.5 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, Tee 178×203×27 is the stronger section and WT 8X18 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.