UB 533×312×273 vs HE 550 M
UB 533×312×273 is an UB section from the UK Blue Book (SCI P363); HE 550 M is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 7870 cm³ against 7930 cm³ of plastic modulus, a difference of 0.8%. They weigh essentially the same, 273.3 kg/m and 278 kg/m. Both are about 575 mm deep, so either fits the same construction zone.
| Property | UB 533×312×273 UB | HE 550 M HE | Difference |
|---|---|---|---|
| Mass | 273.3 kg/m | 278 kg/m | -1.7% |
| Depth | 577.1 mm | 572 mm | +0.9% |
| Width | 320.2 mm | 306 mm | +4.6% |
| Web thickness | 21.1 mm | 21 mm | +0.5% |
| Flange thickness | 37.6 mm | 40 mm | -6.0% |
| Area | 348 cm² | 354 cm² | -1.7% |
| Second moment, major (Iy) | 199,000 cm⁴ | 198,000 cm⁴ | +0.5% |
| Plastic modulus, major (Wpl,y) | 7,870 cm³ | 7,930 cm³ | -0.8% |
| Elastic modulus, major (Wel,y) | 6,890 cm³ | 6,920 cm³ | -0.4% |
| Second moment, minor (Iz) | 20,600 cm⁴ | 19,200 cm⁴ | +7.3% |
| Plastic modulus, minor (Wpl,z) | 1,990 cm³ | 1,940 cm³ | +2.6% |
| Radius of gyration, minor (iz) | 7.69 cm | 7.35 cm | +4.6% |
| Torsion constant (It) | 1,290 cm⁴ | 1,560 cm⁴ | -17.3% |
UB 533×312×273 to BS EN 10365:2017; HE 550 M to EN 10365 · Continental Steel. Difference is expressed relative to HE 550 M.
How to choose between them
On stiffness, UB 533×312×273 has the larger second moment of area: 199,000 cm⁴ against 198,000 cm⁴, a difference of 0.5%. 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 (28.8 against 28.5 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. UB sections are specified to BS EN 10365:2017 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.