WT 12X58.5 vs Tee 305×305×90
WT 12X58.5 is an WT section from the American AISC Shapes Database; Tee 305×305×90 is the closest equivalent in the UK Blue Book (SCI P363). Tee 305×305×90 carries more bending: 656 cm³ of plastic modulus against 642.37 cm³, 2.1% more. WT 12X58.5 is the lighter of the two at 87.1 kg/m against 89.5 kg/m, a saving of 2.7% on steel weight. Both are about 309 mm deep, so either fits the same construction zone.
| Property | WT 12X58.5 WT | Tee 305×305×90 Tees (from UB) | Difference |
|---|---|---|---|
| Mass | 87.1 kg/m | 89.5 kg/m | -2.7% |
| Depth | 307.3 mm | 310 mm | -0.9% |
| Width | 325.1 mm | 307.1 mm | +5.9% |
| Web thickness | 14 mm | 14.1 mm | -0.7% |
| Flange thickness | 21.6 mm | 23.6 mm | -8.5% |
| Area | 111 cm² | 114 cm² | -2.6% |
| Second moment, major (Iy) | 8,824 cm⁴ | 9,040 cm⁴ | -2.4% |
| Plastic modulus, major (Wpl,y) | 642.37 cm³ | 656 cm³ | -2.1% |
| Elastic modulus, major (Wel,y) | 365.43 cm³ | 372 cm³ | -1.8% |
| Second moment, minor (Iz) | 6,202 cm⁴ | 5,700 cm⁴ | +8.8% |
| Plastic modulus, minor (Wpl,z) | 585.02 cm³ | 572 cm³ | +2.3% |
| Radius of gyration, minor (iz) | 7.47 cm | 7.07 cm | +5.7% |
| Torsion constant (It) | 139.4 cm⁴ | 170 cm⁴ | -18.0% |
WT 12X58.5 to AISC Shapes Database v16.0; Tee 305×305×90 to BS EN 10365:2017. Difference is expressed relative to Tee 305×305×90.
How to choose between them
On stiffness, Tee 305×305×90 has the larger second moment of area: 9,040 cm⁴ against 8,824 cm⁴, a difference of 2.4%. 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 (7.4 against 7.3 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 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 2.7% weight.
In short, Tee 305×305×90 is the stronger section and WT 12X58.5 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.