W 24X84 vs S 24X90
W 24X84 is an W section from the American AISC Shapes Database; S 24X90 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 3670.7 cm³ against 3637.9 cm³ of plastic modulus, a difference of 0.9%. W 24X84 is the lighter of the two at 125 kg/m against 133.9 kg/m, a saving of 6.6% on steel weight. Both are about 611 mm deep, so either fits the same construction zone.
| Property | W 24X84 W | S 24X90 S | Difference |
|---|---|---|---|
| Mass | 125 kg/m | 133.9 kg/m | -6.6% |
| Depth | 612.1 mm | 609.6 mm | +0.4% |
| Width | 229.1 mm | 181.1 mm | +26.5% |
| Web thickness | 11.9 mm | 15.9 mm | -25.2% |
| Flange thickness | 19.6 mm | 22.1 mm | -11.3% |
| Area | 159.4 cm² | 171 cm² | -6.8% |
| Second moment, major (Iy) | 98,647 cm⁴ | 93,652 cm⁴ | +5.3% |
| Plastic modulus, major (Wpl,y) | 3,670.7 cm³ | 3,637.9 cm³ | +0.9% |
| Elastic modulus, major (Wel,y) | 3,211.9 cm³ | 3,064.4 cm³ | +4.8% |
| Second moment, minor (Iz) | 3,929 cm⁴ | 1,861 cm⁴ | +111.1% |
| Plastic modulus, minor (Wpl,z) | 534.22 cm³ | 367.07 cm³ | +45.5% |
| Radius of gyration, minor (iz) | 4.95 cm | 3.3 cm | +50.0% |
| Torsion constant (It) | 154 cm⁴ | 251.8 cm⁴ | -38.8% |
W 24X84 to AISC Shapes Database v16.0; S 24X90 to AISC Shapes Database v16.0. Difference is expressed relative to S 24X90.
How to choose between them
On stiffness, W 24X84 has the larger second moment of area: 98,647 cm⁴ against 93,652 cm⁴, a difference of 5.3%. 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, W 24X84 is the more efficient section: 29.4 against 27.2 cm³ per kg/m, 8.1% 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: W 24X84 has 534.22 cm³ of minor-axis plastic modulus against 367.07 cm³, 45.5% 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, W 24X84 is the stronger section and W 24X84 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.