WT 4X12 vs Tee 133×102×15
WT 4X12 is an WT section from the American AISC Shapes Database; Tee 133×102×15 is the closest equivalent in the UK Blue Book (SCI P363). Tee 133×102×15 carries more bending: 33.5 cm³ of plastic modulus against 32.446 cm³, 3.1% more. Tee 133×102×15 is the lighter of the two at 15 kg/m against 17.9 kg/m, a saving of 19.3% on steel weight. Tee 133×102×15 is deeper, 103.3 mm against 100.8 mm, which matters where the floor zone is tight.
| Property | WT 4X12 WT | Tee 133×102×15 Tees (from UB) | Difference |
|---|---|---|---|
| Mass | 17.9 kg/m | 15 kg/m | +19.3% |
| Depth | 100.8 mm | 103.3 mm | -2.4% |
| Width | 165.1 mm | 133.9 mm | +23.3% |
| Web thickness | 6.2 mm | 6.4 mm | -3.1% |
| Flange thickness | 10.2 mm | 9.6 mm | +6.2% |
| Area | 22.8 cm² | 19.1 cm² | +19.4% |
| Second moment, major (Iy) | 146.9 cm⁴ | 154 cm⁴ | -4.6% |
| Plastic modulus, major (Wpl,y) | 32.446 cm³ | 33.5 cm³ | -3.1% |
| Elastic modulus, major (Wel,y) | 17.698 cm³ | 18.8 cm³ | -5.9% |
| Second moment, minor (Iz) | 380.4 cm⁴ | 192 cm⁴ | +98.1% |
| Plastic modulus, minor (Wpl,z) | 70.137 cm³ | 44.1 cm³ | +59.0% |
| Radius of gyration, minor (iz) | 4.09 cm | 3.17 cm | +29.0% |
| Torsion constant (It) | 7.2 cm⁴ | 5.13 cm⁴ | +40.4% |
WT 4X12 to AISC Shapes Database v16.0; Tee 133×102×15 to BS EN 10365:2017. Difference is expressed relative to Tee 133×102×15.
How to choose between them
On stiffness, Tee 133×102×15 has the larger second moment of area: 154 cm⁴ against 146.9 cm⁴, a difference of 4.6%. 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 of steel, Tee 133×102×15 is the more efficient section: 2.2 against 1.8 cm³ per kg/m, 18.8% 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 4X12 has 70.137 cm³ of minor-axis plastic modulus against 44.1 cm³, 59.0% 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. WT sections are specified to AISC Shapes Database v16.0 and Tees (from UB) 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 19.3% weight.
In short, Tee 133×102×15 is the stronger section and Tee 133×102×15 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.