WT 10.5X55.5 vs ST 10X43
WT 10.5X55.5 is an WT section from the American AISC Shapes Database; ST 10X43 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 508 cm³ against 509.64 cm³ of plastic modulus, a difference of 0.3%. ST 10X43 is the lighter of the two at 64 kg/m against 82.6 kg/m, a saving of 29.1% on steel weight. WT 10.5X55.5 is deeper, 274.3 mm against 259.1 mm, which matters where the floor zone is tight.
| Property | WT 10.5X55.5 WT | ST 10X43 ST | Difference |
|---|---|---|---|
| Mass | 82.6 kg/m | 64 kg/m | +29.1% |
| Depth | 274.3 mm | 259.1 mm | +5.9% |
| Width | 312.4 mm | 179.3 mm | +74.2% |
| Web thickness | 14 mm | 16.8 mm | -16.7% |
| Flange thickness | 22.2 mm | 23.4 mm | -5.1% |
| Area | 105.2 cm² | 81.9 cm² | +28.4% |
| Second moment, major (Iy) | 6,243 cm⁴ | 5,161 cm⁴ | +21.0% |
| Plastic modulus, major (Wpl,y) | 508 cm³ | 509.64 cm³ | -0.3% |
| Elastic modulus, major (Wel,y) | 286.77 cm³ | 281.86 cm³ | +1.7% |
| Second moment, minor (Iz) | 5,702 cm⁴ | 969.8 cm⁴ | +488.0% |
| Plastic modulus, minor (Wpl,z) | 558.8 cm³ | 190.09 cm³ | +194.0% |
| Radius of gyration, minor (iz) | 7.37 cm | 3.45 cm | +113.6% |
| Torsion constant (It) | 141.5 cm⁴ | 137.4 cm⁴ | +3.0% |
WT 10.5X55.5 to AISC Shapes Database v16.0; ST 10X43 to AISC Shapes Database v16.0. Difference is expressed relative to ST 10X43.
How to choose between them
On stiffness, WT 10.5X55.5 has the larger second moment of area: 6,243 cm⁴ against 5,161 cm⁴, a difference of 21.0%. 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 10X43 is the more efficient section: 8.0 against 6.2 cm³ per kg/m, 22.8% 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 10.5X55.5 has 558.8 cm³ of minor-axis plastic modulus against 190.09 cm³, 194.0% 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 10X43 is the stronger section and ST 10X43 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.