UB 610×178×100 vs IPE 550
UB 610×178×100 is an UB section from the UK Blue Book (SCI P363); IPE 550 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 2790 cm³ against 2790 cm³ of plastic modulus, a difference of 0.0%. UB 610×178×100 is the lighter of the two at 100.3 kg/m against 106 kg/m, a saving of 5.4% on steel weight. UB 610×178×100 is deeper, 607.4 mm against 550 mm, which matters where the floor zone is tight.
| Property | UB 610×178×100 UB | IPE 550 IPE | Difference |
|---|---|---|---|
| Mass | 100.3 kg/m | 106 kg/m | -5.4% |
| Depth | 607.4 mm | 550 mm | +10.4% |
| Width | 179.2 mm | 210 mm | -14.7% |
| Web thickness | 11.3 mm | 11.1 mm | +1.8% |
| Flange thickness | 17.2 mm | 17.2 mm | same |
| Area | 128 cm² | 134 cm² | -4.5% |
| Second moment, major (Iy) | 72,500 cm⁴ | 67,100 cm⁴ | +8.0% |
| Plastic modulus, major (Wpl,y) | 2,790 cm³ | 2,790 cm³ | same |
| Elastic modulus, major (Wel,y) | 2,390 cm³ | 2,440 cm³ | -2.0% |
| Second moment, minor (Iz) | 1,660 cm⁴ | 2,670 cm⁴ | -37.8% |
| Plastic modulus, minor (Wpl,z) | 296 cm³ | 401 cm³ | -26.2% |
| Radius of gyration, minor (iz) | 3.6 cm | 4.45 cm | -19.1% |
| Torsion constant (It) | 95 cm⁴ | 123 cm⁴ | -22.8% |
UB 610×178×100 to BS EN 10365:2017; IPE 550 to EN 10365 · Continental Steel. Difference is expressed relative to IPE 550.
How to choose between them
On stiffness, UB 610×178×100 has the larger second moment of area: 72,500 cm⁴ against 67,100 cm⁴, a difference of 8.0%. 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, UB 610×178×100 is the more efficient section: 27.8 against 26.3 cm³ per kg/m, 5.7% 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: IPE 550 has 401 cm³ of minor-axis plastic modulus against 296 cm³, 26.2% 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. UB sections are specified to BS EN 10365:2017 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 5.4% weight.
In short, IPE 550 is the stronger section and UB 610×178×100 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.