Tee 165×152×27 vs ST 6X15.9
Tee 165×152×27 is an Tees (from UB) section from the UK Blue Book (SCI P363); ST 6X15.9 is the closest equivalent in the American AISC Shapes Database. ST 6X15.9 carries more bending: 97.339 cm³ of plastic modulus against 92.8 cm³, 4.7% more. ST 6X15.9 is the lighter of the two at 23.7 kg/m against 27 kg/m, a saving of 13.9% on steel weight. Both are about 154 mm deep, so either fits the same construction zone.
| Property | Tee 165×152×27 Tees (from UB) | ST 6X15.9 ST | Difference |
|---|---|---|---|
| Mass | 27 kg/m | 23.7 kg/m | +13.9% |
| Depth | 155.1 mm | 152.4 mm | +1.8% |
| Width | 166.9 mm | 127 mm | +31.4% |
| Web thickness | 7.9 mm | 8.9 mm | -11.2% |
| Flange thickness | 13.7 mm | 13.8 mm | -0.7% |
| Area | 34.4 cm² | 30 cm² | +14.7% |
| Second moment, major (Iy) | 642 cm⁴ | 616 cm⁴ | +4.2% |
| Plastic modulus, major (Wpl,y) | 92.8 cm³ | 97.339 cm³ | -4.7% |
| Elastic modulus, major (Wel,y) | 52.2 cm³ | 54.077 cm³ | -3.5% |
| Second moment, minor (Iz) | 531 cm⁴ | 194 cm⁴ | +173.7% |
| Plastic modulus, minor (Wpl,z) | 97.8 cm³ | 52.766 cm³ | +85.3% |
| Radius of gyration, minor (iz) | 3.93 cm | 2.54 cm | +54.7% |
| Torsion constant (It) | 17.3 cm⁴ | 18.23 cm⁴ | -5.1% |
Tee 165×152×27 to BS EN 10365:2017; ST 6X15.9 to AISC Shapes Database v16.0. Difference is expressed relative to ST 6X15.9.
How to choose between them
On stiffness, Tee 165×152×27 has the larger second moment of area: 642 cm⁴ against 616 cm⁴, a difference of 4.2%. 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, ST 6X15.9 is the more efficient section: 4.1 against 3.4 cm³ per kg/m, 16.3% 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: Tee 165×152×27 has 97.8 cm³ of minor-axis plastic modulus against 52.766 cm³, 85.3% 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 ST 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 13.9% weight.
In short, ST 6X15.9 is the stronger section and ST 6X15.9 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.