W 21X111 vs HE 550 A
W 21X111 is an W section from the American AISC Shapes Database; HE 550 A is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 4572 cm³ against 4620 cm³ of plastic modulus, a difference of 1.0%. They weigh essentially the same, 165.2 kg/m and 166 kg/m. Both are about 543 mm deep, so either fits the same construction zone.
| Property | W 21X111 W | HE 550 A HE | Difference |
|---|---|---|---|
| Mass | 165.2 kg/m | 166 kg/m | -0.5% |
| Depth | 546.1 mm | 540 mm | +1.1% |
| Width | 312.4 mm | 300 mm | +4.1% |
| Web thickness | 14 mm | 12.5 mm | +12.0% |
| Flange thickness | 22.2 mm | 24 mm | -7.5% |
| Area | 210.3 cm² | 212 cm² | -0.8% |
| Second moment, major (Iy) | 111,134 cm⁴ | 112,000 cm⁴ | -0.8% |
| Plastic modulus, major (Wpl,y) | 4,572 cm³ | 4,620 cm³ | -1.0% |
| Elastic modulus, major (Wel,y) | 4,080.4 cm³ | 4,150 cm³ | -1.7% |
| Second moment, minor (Iz) | 11,405 cm⁴ | 10,800 cm⁴ | +5.6% |
| Plastic modulus, minor (Wpl,z) | 1,117.6 cm³ | 1,110 cm³ | +0.7% |
| Radius of gyration, minor (iz) | 7.37 cm | 7.15 cm | +3.1% |
| Torsion constant (It) | 284.3 cm⁴ | 360 cm⁴ | -21.0% |
W 21X111 to AISC Shapes Database v16.0; HE 550 A to EN 10365 · Continental Steel. Difference is expressed relative to HE 550 A.
How to choose between them
On stiffness, HE 550 A has the larger second moment of area: 112,000 cm⁴ against 111,134 cm⁴, a difference of 0.8%. 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, the two are equally efficient (27.7 against 27.8 cm³ per kg/m), so on a pure steel-tonnage basis there is nothing to choose between them. The decision comes down to availability, connection detailing and what the rest of the frame uses.
These come from different catalogues, so treat the swap as a design change rather than a like-for-like substitution. W sections are specified to AISC Shapes Database v16.0 and HE to EN 10365 · Continental Steel; the steel grades, tolerances and available lengths differ, connection details and bolt gauges are set out differently, and the two are rarely both stocked in the same market. Check availability before changing a section on a drawing to save a marginal amount of weight.
In short, these two are genuine equivalents. Pick whichever your supplier stocks and the rest of the frame already uses.