WT 10.5X34 vs ST 10X33
WT 10.5X34 is an WT section from the American AISC Shapes Database; ST 10X33 is the closest equivalent in the American AISC Shapes Database. ST 10X33 carries more bending: 383.46 cm³ of plastic modulus against 375.26 cm³, 2.1% more. ST 10X33 is the lighter of the two at 49.1 kg/m against 50.6 kg/m, a saving of 3.1% on steel weight. WT 10.5X34 is deeper, 269.2 mm against 254 mm, which matters where the floor zone is tight.
| Property | WT 10.5X34 WT | ST 10X33 ST | Difference |
|---|---|---|---|
| Mass | 50.6 kg/m | 49.1 kg/m | +3.1% |
| Depth | 269.2 mm | 254 mm | +6.0% |
| Width | 210.1 mm | 159 mm | +32.1% |
| Web thickness | 10.9 mm | 12.8 mm | -14.8% |
| Flange thickness | 17.4 mm | 20.2 mm | -13.9% |
| Area | 64.5 cm² | 62.6 cm² | +3.0% |
| Second moment, major (Iy) | 4,287 cm⁴ | 3,867 cm⁴ | +10.9% |
| Plastic modulus, major (Wpl,y) | 375.26 cm³ | 383.46 cm³ | -2.1% |
| Elastic modulus, major (Wel,y) | 211.39 cm³ | 211.39 cm³ | same |
| Second moment, minor (Iz) | 1,349 cm⁴ | 570.2 cm⁴ | +136.6% |
| Plastic modulus, minor (Wpl,z) | 199.92 cm³ | 126.18 cm³ | +58.4% |
| Radius of gyration, minor (iz) | 4.57 cm | 3.02 cm | +51.3% |
| Torsion constant (It) | 50.78 cm⁴ | 74.09 cm⁴ | -31.5% |
WT 10.5X34 to AISC Shapes Database v16.0; ST 10X33 to AISC Shapes Database v16.0. Difference is expressed relative to ST 10X33.
How to choose between them
On stiffness, WT 10.5X34 has the larger second moment of area: 4,287 cm⁴ against 3,867 cm⁴, a difference of 10.9%. 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 10X33 is the more efficient section: 7.8 against 7.4 cm³ per kg/m, 5.0% 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 10.5X34 has 199.92 cm³ of minor-axis plastic modulus against 126.18 cm³, 58.4% 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 10X33 is the stronger section and ST 10X33 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.