WT 4X10.5 vs ST 4X9.2
WT 4X10.5 is an WT section from the American AISC Shapes Database; ST 4X9.2 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 34.577 cm³ against 33.921 cm³ of plastic modulus, a difference of 1.9%. ST 4X9.2 is the lighter of the two at 13.7 kg/m against 15.6 kg/m, a saving of 13.9% on steel weight. WT 4X10.5 is deeper, 105.2 mm against 101.6 mm, which matters where the floor zone is tight.
| Property | WT 4X10.5 WT | ST 4X9.2 ST | Difference |
|---|---|---|---|
| Mass | 15.6 kg/m | 13.7 kg/m | +13.9% |
| Depth | 105.2 mm | 101.6 mm | +3.5% |
| Width | 133.9 mm | 101.6 mm | +31.8% |
| Web thickness | 6.4 mm | 6.9 mm | -7.2% |
| Flange thickness | 10.2 mm | 10.8 mm | -5.6% |
| Area | 19.9 cm² | 17.4 cm² | +14.4% |
| Second moment, major (Iy) | 162.3 cm⁴ | 145.3 cm⁴ | +11.7% |
| Plastic modulus, major (Wpl,y) | 34.577 cm³ | 33.921 cm³ | +1.9% |
| Elastic modulus, major (Wel,y) | 19.337 cm³ | 18.681 cm³ | +3.5% |
| Second moment, minor (Iz) | 203.1 cm⁴ | 76.59 cm⁴ | +165.2% |
| Plastic modulus, minor (Wpl,z) | 46.539 cm³ | 26.055 cm³ | +78.6% |
| Radius of gyration, minor (iz) | 3.2 cm | 2.1 cm | +52.4% |
| Torsion constant (It) | 5.87 cm⁴ | 6.95 cm⁴ | -15.5% |
WT 4X10.5 to AISC Shapes Database v16.0; ST 4X9.2 to AISC Shapes Database v16.0. Difference is expressed relative to ST 4X9.2.
How to choose between them
On stiffness, WT 4X10.5 has the larger second moment of area: 162.3 cm⁴ against 145.3 cm⁴, a difference of 11.7%. 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 4X9.2 is the more efficient section: 2.5 against 2.2 cm³ per kg/m, 10.5% 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 4X10.5 has 46.539 cm³ of minor-axis plastic modulus against 26.055 cm³, 78.6% 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, WT 4X10.5 is the stronger section and ST 4X9.2 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.