W 21X83 vs S 20X96
W 21X83 is an W section from the American AISC Shapes Database; S 20X96 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 3211.9 cm³ against 3244.6 cm³ of plastic modulus, a difference of 1.0%. W 21X83 is the lighter of the two at 123.5 kg/m against 142.9 kg/m, a saving of 13.6% on steel weight. W 21X83 is deeper, 543.6 mm against 515.6 mm, which matters where the floor zone is tight.
| Property | W 21X83 W | S 20X96 S | Difference |
|---|---|---|---|
| Mass | 123.5 kg/m | 142.9 kg/m | -13.6% |
| Depth | 543.6 mm | 515.6 mm | +5.4% |
| Width | 212.3 mm | 182.9 mm | +16.1% |
| Web thickness | 13.1 mm | 20.3 mm | -35.5% |
| Flange thickness | 21.2 mm | 23.4 mm | -9.4% |
| Area | 157.4 cm² | 181.9 cm² | -13.5% |
| Second moment, major (Iy) | 76,170 cm⁴ | 69,511 cm⁴ | +9.6% |
| Plastic modulus, major (Wpl,y) | 3,211.9 cm³ | 3,244.6 cm³ | -1.0% |
| Elastic modulus, major (Wel,y) | 2,802.2 cm³ | 2,703.9 cm³ | +3.6% |
| Second moment, minor (Iz) | 3,388 cm⁴ | 2,077 cm⁴ | +63.1% |
| Plastic modulus, minor (Wpl,z) | 499.81 cm³ | 408.04 cm³ | +22.5% |
| Radius of gyration, minor (iz) | 4.65 cm | 3.38 cm | +37.6% |
| Torsion constant (It) | 180.6 cm⁴ | 349.6 cm⁴ | -48.3% |
W 21X83 to AISC Shapes Database v16.0; S 20X96 to AISC Shapes Database v16.0. Difference is expressed relative to S 20X96.
How to choose between them
On stiffness, W 21X83 has the larger second moment of area: 76,170 cm⁴ against 69,511 cm⁴, a difference of 9.6%. 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 21X83 is the more efficient section: 26.0 against 22.7 cm³ per kg/m, 14.5% 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: W 21X83 has 499.81 cm³ of minor-axis plastic modulus against 408.04 cm³, 22.5% 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, S 20X96 is the stronger section and W 21X83 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.