Tee 305×305×75 vs WT 12X42
Tee 305×305×75 is an Tees (from UB) section from the UK Blue Book (SCI P363); WT 12X42 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 538 cm³ against 532.58 cm³ of plastic modulus, a difference of 1.0%. WT 12X42 is the lighter of the two at 62.5 kg/m against 74.6 kg/m, a saving of 19.4% on steel weight. Both are about 307 mm deep, so either fits the same construction zone.
| Property | Tee 305×305×75 Tees (from UB) | WT 12X42 WT | Difference |
|---|---|---|---|
| Mass | 74.6 kg/m | 62.5 kg/m | +19.4% |
| Depth | 306.1 mm | 307.3 mm | -0.4% |
| Width | 304.8 mm | 229.1 mm | +33.0% |
| Web thickness | 11.8 mm | 11.9 mm | -0.8% |
| Flange thickness | 19.7 mm | 19.6 mm | +0.5% |
| Area | 95 cm² | 80 cm² | +18.8% |
| Second moment, major (Iy) | 7,410 cm⁴ | 6,909 cm⁴ | +7.3% |
| Plastic modulus, major (Wpl,y) | 538 cm³ | 532.58 cm³ | +1.0% |
| Elastic modulus, major (Wel,y) | 307 cm³ | 299.88 cm³ | +2.4% |
| Second moment, minor (Iz) | 4,650 cm⁴ | 1,965 cm⁴ | +136.6% |
| Plastic modulus, minor (Wpl,z) | 469 cm³ | 267.11 cm³ | +75.6% |
| Radius of gyration, minor (iz) | 7 cm | 4.95 cm | +41.4% |
| Torsion constant (It) | 99.8 cm⁴ | 76.59 cm⁴ | +30.3% |
Tee 305×305×75 to BS EN 10365:2017; WT 12X42 to AISC Shapes Database v16.0. Difference is expressed relative to WT 12X42.
How to choose between them
On stiffness, Tee 305×305×75 has the larger second moment of area: 7,410 cm⁴ against 6,909 cm⁴, a difference of 7.3%. 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 of steel, WT 12X42 is the more efficient section: 8.5 against 7.2 cm³ per kg/m, 15.4% 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: Tee 305×305×75 has 469 cm³ of minor-axis plastic modulus against 267.11 cm³, 75.6% 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 19.4% weight.
In short, Tee 305×305×75 is the stronger section and WT 12X42 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.