W 21X101 vs IPE V 550
W 21X101 is an W section from the American AISC Shapes Database; IPE V 550 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 4145.9 cm³ against 4200 cm³ of plastic modulus, a difference of 1.3%. W 21X101 is the lighter of the two at 150.3 kg/m against 159 kg/m, a saving of 5.5% on steel weight. IPE V 550 is deeper, 566 mm against 543.6 mm, which matters where the floor zone is tight.
| Property | W 21X101 W | IPE V 550 IPE | Difference |
|---|---|---|---|
| Mass | 150.3 kg/m | 159 kg/m | -5.5% |
| Depth | 543.6 mm | 566 mm | -4.0% |
| Width | 312.4 mm | 216 mm | +44.6% |
| Web thickness | 12.7 mm | 17.1 mm | -25.7% |
| Flange thickness | 20.3 mm | 25.2 mm | -19.4% |
| Area | 192.3 cm² | 202 cm² | -4.8% |
| Second moment, major (Iy) | 100,728 cm⁴ | 102,000 cm⁴ | -1.2% |
| Plastic modulus, major (Wpl,y) | 4,145.9 cm³ | 4,200 cm³ | -1.3% |
| Elastic modulus, major (Wel,y) | 3,719.9 cm³ | 3,620 cm³ | +2.8% |
| Second moment, minor (Iz) | 10,323 cm⁴ | 4,260 cm⁴ | +142.3% |
| Plastic modulus, minor (Wpl,z) | 1,011.1 cm³ | 632 cm³ | +60.0% |
| Radius of gyration, minor (iz) | 7.34 cm | 4.59 cm | +59.9% |
| Torsion constant (It) | 216.9 cm⁴ | 372 cm⁴ | -41.7% |
W 21X101 to AISC Shapes Database v16.0; IPE V 550 to EN 10365 · Continental Steel. Difference is expressed relative to IPE V 550.
How to choose between them
On stiffness, IPE V 550 has the larger second moment of area: 102,000 cm⁴ against 100,728 cm⁴, a difference of 1.2%. 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 21X101 is the more efficient section: 27.6 against 26.4 cm³ per kg/m, 4.4% 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 21X101 has 1011.1 cm³ of minor-axis plastic modulus against 632 cm³, 60.0% 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. W sections are specified to AISC Shapes Database v16.0 and IPE 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 5.5% weight.
In short, IPE V 550 is the stronger section and W 21X101 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.