IPE 550 vs W 21X73
IPE 550 is an IPE section from the European (Continental) range; W 21X73 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 2790 cm³ against 2818.6 cm³ of plastic modulus, a difference of 1.0%. IPE 550 is the lighter of the two at 106 kg/m against 108.6 kg/m, a saving of 2.4% on steel weight. IPE 550 is deeper, 550 mm against 538.5 mm, which matters where the floor zone is tight.
| Property | IPE 550 IPE | W 21X73 W | Difference |
|---|---|---|---|
| Mass | 106 kg/m | 108.6 kg/m | -2.4% |
| Depth | 550 mm | 538.5 mm | +2.1% |
| Width | 210 mm | 210.8 mm | -0.4% |
| Web thickness | 11.1 mm | 11.6 mm | -4.3% |
| Flange thickness | 17.2 mm | 18.8 mm | -8.5% |
| Area | 134 cm² | 138.7 cm² | -3.4% |
| Second moment, major (Iy) | 67,100 cm⁴ | 66,597 cm⁴ | +0.8% |
| Plastic modulus, major (Wpl,y) | 2,790 cm³ | 2,818.6 cm³ | -1.0% |
| Elastic modulus, major (Wel,y) | 2,440 cm³ | 2,474.4 cm³ | -1.4% |
| Second moment, minor (Iz) | 2,670 cm⁴ | 2,939 cm⁴ | -9.2% |
| Plastic modulus, minor (Wpl,z) | 401 cm³ | 435.9 cm³ | -8.0% |
| Radius of gyration, minor (iz) | 4.45 cm | 4.6 cm | -3.3% |
| Torsion constant (It) | 123 cm⁴ | 125.7 cm⁴ | -2.1% |
IPE 550 to EN 10365 · Continental Steel; W 21X73 to AISC Shapes Database v16.0. Difference is expressed relative to W 21X73.
How to choose between them
On stiffness, IPE 550 has the larger second moment of area: 67,100 cm⁴ against 66,597 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 (26.3 against 26.0 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.
The two diverge much more about the minor axis: W 21X73 has 435.9 cm³ of minor-axis plastic modulus against 401 cm³, 8.0% 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.
These come from different catalogues, so treat the swap as a design change rather than a like-for-like substitution. IPE sections are specified to EN 10365 · Continental Steel and W to AISC Shapes Database v16.0; 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 2.4% weight.
In short, W 21X73 is the stronger section and IPE 550 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.