WT 9X38 vs ST 9X27.35
WT 9X38 is an WT section from the American AISC Shapes Database; ST 9X27.35 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 283.5 cm³ against 283.5 cm³ of plastic modulus, a difference of 0.0%. ST 9X27.35 is the lighter of the two at 40.7 kg/m against 56.6 kg/m, a saving of 39.1% on steel weight. Both are about 230 mm deep, so either fits the same construction zone.
| Property | WT 9X38 WT | ST 9X27.35 ST | Difference |
|---|---|---|---|
| Mass | 56.6 kg/m | 40.7 kg/m | +39.1% |
| Depth | 231.4 mm | 228.6 mm | +1.2% |
| Width | 279.4 mm | 152.4 mm | +83.3% |
| Web thickness | 10.8 mm | 11.7 mm | -7.7% |
| Flange thickness | 17.3 mm | 17.6 mm | -1.7% |
| Area | 71.6 cm² | 51.7 cm² | +38.5% |
| Second moment, major (Iy) | 2,989 cm⁴ | 2,593 cm⁴ | +15.3% |
| Plastic modulus, major (Wpl,y) | 283.5 cm³ | 283.5 cm³ | same |
| Elastic modulus, major (Wel,y) | 161.08 cm³ | 157.32 cm³ | +2.4% |
| Second moment, minor (Iz) | 3,172 cm⁴ | 432.9 cm⁴ | +632.7% |
| Plastic modulus, minor (Wpl,z) | 345.77 cm³ | 99.306 cm³ | +248.2% |
| Radius of gyration, minor (iz) | 6.63 cm | 2.9 cm | +128.6% |
| Torsion constant (It) | 58.69 cm⁴ | 48.28 cm⁴ | +21.6% |
WT 9X38 to AISC Shapes Database v16.0; ST 9X27.35 to AISC Shapes Database v16.0. Difference is expressed relative to ST 9X27.35.
How to choose between them
On stiffness, WT 9X38 has the larger second moment of area: 2,989 cm⁴ against 2,593 cm⁴, a difference of 15.3%. 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 9X27.35 is the more efficient section: 7.0 against 5.0 cm³ per kg/m, 28.1% 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 9X38 has 345.77 cm³ of minor-axis plastic modulus against 99.306 cm³, 248.2% 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, ST 9X27.35 is the stronger section and ST 9X27.35 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.