WT 12X73 vs ST 12X50
WT 12X73 is an WT section from the American AISC Shapes Database; ST 12X50 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 789.86 cm³ against 778.39 cm³ of plastic modulus, a difference of 1.5%. ST 12X50 is the lighter of the two at 74.4 kg/m against 108.6 kg/m, a saving of 46.0% on steel weight. WT 12X73 is deeper, 315 mm against 304.8 mm, which matters where the floor zone is tight.
| Property | WT 12X73 WT | ST 12X50 ST | Difference |
|---|---|---|---|
| Mass | 108.6 kg/m | 74.4 kg/m | +46.0% |
| Depth | 315 mm | 304.8 mm | +3.3% |
| Width | 327.7 mm | 184.1 mm | +78.0% |
| Web thickness | 16.5 mm | 18.9 mm | -12.7% |
| Flange thickness | 27.7 mm | 22.1 mm | +25.3% |
| Area | 138.7 cm² | 94.8 cm² | +46.3% |
| Second moment, major (Iy) | 10,989 cm⁴ | 8,949 cm⁴ | +22.8% |
| Plastic modulus, major (Wpl,y) | 789.86 cm³ | 778.39 cm³ | +1.5% |
| Elastic modulus, major (Wel,y) | 445.73 cm³ | 430.98 cm³ | +3.4% |
| Second moment, minor (Iz) | 8,117 cm⁴ | 986.5 cm⁴ | +722.8% |
| Plastic modulus, minor (Wpl,z) | 763.64 cm³ | 196.64 cm³ | +288.3% |
| Radius of gyration, minor (iz) | 7.65 cm | 3.23 cm | +136.8% |
| Torsion constant (It) | 278.9 cm⁴ | 156.5 cm⁴ | +78.2% |
WT 12X73 to AISC Shapes Database v16.0; ST 12X50 to AISC Shapes Database v16.0. Difference is expressed relative to ST 12X50.
How to choose between them
On stiffness, WT 12X73 has the larger second moment of area: 10,989 cm⁴ against 8,949 cm⁴, a difference of 22.8%. 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 12X50 is the more efficient section: 10.5 against 7.3 cm³ per kg/m, 30.5% 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 12X73 has 763.64 cm³ of minor-axis plastic modulus against 196.64 cm³, 288.3% 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.
In short, WT 12X73 is the stronger section and ST 12X50 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.