WT 9X53 vs ST 9X35
WT 9X53 is an WT section from the American AISC Shapes Database; ST 9X35 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 412.95 cm³ against 411.32 cm³ of plastic modulus, a difference of 0.4%. ST 9X35 is the lighter of the two at 52.1 kg/m against 78.9 kg/m, a saving of 51.4% on steel weight. WT 9X53 is deeper, 238 mm against 228.6 mm, which matters where the floor zone is tight.
| Property | WT 9X53 WT | ST 9X35 ST | Difference |
|---|---|---|---|
| Mass | 78.9 kg/m | 52.1 kg/m | +51.4% |
| Depth | 238 mm | 228.6 mm | +4.1% |
| Width | 284.5 mm | 158.8 mm | +79.2% |
| Web thickness | 15 mm | 18.1 mm | -17.1% |
| Flange thickness | 23.9 mm | 17.6 mm | +35.8% |
| Area | 100.6 cm² | 66.5 cm² | +51.3% |
| Second moment, major (Iy) | 4,329 cm⁴ | 3,517 cm⁴ | +23.1% |
| Plastic modulus, major (Wpl,y) | 412.95 cm³ | 411.32 cm³ | +0.4% |
| Elastic modulus, major (Wel,y) | 231.06 cm³ | 229.42 cm³ | +0.7% |
| Second moment, minor (Iz) | 4,579 cm⁴ | 499.5 cm⁴ | +816.7% |
| Plastic modulus, minor (Wpl,z) | 494.89 cm³ | 117.5 cm³ | +321.2% |
| Radius of gyration, minor (iz) | 6.76 cm | 2.74 cm | +146.7% |
| Torsion constant (It) | 155.3 cm⁴ | 84.08 cm⁴ | +84.7% |
WT 9X53 to AISC Shapes Database v16.0; ST 9X35 to AISC Shapes Database v16.0. Difference is expressed relative to ST 9X35.
How to choose between them
On stiffness, WT 9X53 has the larger second moment of area: 4,329 cm⁴ against 3,517 cm⁴, a difference of 23.1%. 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 9X35 is the more efficient section: 7.9 against 5.2 cm³ per kg/m, 33.7% 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 9X53 has 494.89 cm³ of minor-axis plastic modulus against 117.5 cm³, 321.2% 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 9X53 is the stronger section and ST 9X35 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.