WT 12X81 vs ST 12X60.5
WT 12X81 is an WT section from the American AISC Shapes Database; ST 12X60.5 is the closest equivalent in the American AISC Shapes Database. ST 12X60.5 carries more bending: 893.09 cm³ of plastic modulus against 873.43 cm³, 2.2% more. ST 12X60.5 is the lighter of the two at 90 kg/m against 120.5 kg/m, a saving of 33.9% on steel weight. Both are about 315 mm deep, so either fits the same construction zone.
| Property | WT 12X81 WT | ST 12X60.5 ST | Difference |
|---|---|---|---|
| Mass | 120.5 kg/m | 90 kg/m | +33.9% |
| Depth | 317.5 mm | 312.4 mm | +1.6% |
| Width | 330.2 mm | 204.5 mm | +61.5% |
| Web thickness | 17.9 mm | 20.3 mm | -11.8% |
| Flange thickness | 31 mm | 27.7 mm | +11.9% |
| Area | 154.2 cm² | 114.8 cm² | +34.3% |
| Second moment, major (Iy) | 12,196 cm⁴ | 10,780 cm⁴ | +13.1% |
| Plastic modulus, major (Wpl,y) | 873.43 cm³ | 893.09 cm³ | -2.2% |
| Elastic modulus, major (Wel,y) | 489.97 cm³ | 493.25 cm³ | -0.7% |
| Second moment, minor (Iz) | 9,199 cm⁴ | 1,727 cm⁴ | +432.7% |
| Plastic modulus, minor (Wpl,z) | 861.96 cm³ | 296.61 cm³ | +190.6% |
| Radius of gyration, minor (iz) | 7.75 cm | 3.89 cm | +99.2% |
| Torsion constant (It) | 383.8 cm⁴ | 265.6 cm⁴ | +44.5% |
WT 12X81 to AISC Shapes Database v16.0; ST 12X60.5 to AISC Shapes Database v16.0. Difference is expressed relative to ST 12X60.5.
How to choose between them
On stiffness, WT 12X81 has the larger second moment of area: 12,196 cm⁴ against 10,780 cm⁴, a difference of 13.1%. 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, ST 12X60.5 is the more efficient section: 9.9 against 7.2 cm³ per kg/m, 27.0% 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 12X81 has 861.96 cm³ of minor-axis plastic modulus against 296.61 cm³, 190.6% 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.
In short, ST 12X60.5 is the stronger section and ST 12X60.5 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.