Tee 171×178×34 vs WT 7X26.5
Tee 171×178×34 is an Tees (from UB) section from the UK Blue Book (SCI P363); WT 7X26.5 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 145 cm³ against 145.35 cm³ of plastic modulus, a difference of 0.2%. Tee 171×178×34 is the lighter of the two at 33.5 kg/m against 39.4 kg/m, a saving of 15.0% on steel weight. Tee 171×178×34 is deeper, 181.6 mm against 176.8 mm, which matters where the floor zone is tight.
| Property | Tee 171×178×34 Tees (from UB) | WT 7X26.5 WT | Difference |
|---|---|---|---|
| Mass | 33.5 kg/m | 39.4 kg/m | -15.0% |
| Depth | 181.6 mm | 176.8 mm | +2.7% |
| Width | 173.2 mm | 204.7 mm | -15.4% |
| Web thickness | 9.1 mm | 9.4 mm | -3.2% |
| Flange thickness | 15.7 mm | 16.8 mm | -6.5% |
| Area | 42.7 cm² | 50.3 cm² | -15.1% |
| Second moment, major (Iy) | 1,150 cm⁴ | 1,149 cm⁴ | +0.1% |
| Plastic modulus, major (Wpl,y) | 145 cm³ | 145.35 cm³ | -0.2% |
| Elastic modulus, major (Wel,y) | 81.5 cm³ | 80.952 cm³ | +0.7% |
| Second moment, minor (Iz) | 681 cm⁴ | 1,199 cm⁴ | -43.2% |
| Plastic modulus, minor (Wpl,z) | 121 cm³ | 180.26 cm³ | -32.9% |
| Radius of gyration, minor (iz) | 3.99 cm | 4.88 cm | -18.2% |
| Torsion constant (It) | 27.8 cm⁴ | 40.25 cm⁴ | -30.9% |
Tee 171×178×34 to BS EN 10365:2017; WT 7X26.5 to AISC Shapes Database v16.0. Difference is expressed relative to WT 7X26.5.
How to choose between them
On stiffness, Tee 171×178×34 has the larger second moment of area: 1,150 cm⁴ against 1,149 cm⁴, a difference of 0.1%. 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 of steel, Tee 171×178×34 is the more efficient section: 4.3 against 3.7 cm³ per kg/m, 17.3% better. Over a floor of repeated beams that difference is real tonnage, though it is often outweighed by whichever section the fabricator can actually source.
The two diverge much more about the minor axis: WT 7X26.5 has 180.26 cm³ of minor-axis plastic modulus against 121 cm³, 32.9% more. If the member sees any minor-axis bending, or if it is unrestrained over a long length and lateral-torsional buckling governs, that gap decides the comparison even though the major-axis numbers looked equivalent.
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 15.0% weight.
In short, WT 7X26.5 is the stronger section and Tee 171×178×34 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.