UB 457×191×161 vs H-500x300x13x21
UB 457×191×161 is an UB section from the UK Blue Book (SCI P363); H-500x300x13x21 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 3780 cm³ against 3792 cm³ of plastic modulus, a difference of 0.3%. H-500x300x13x21 is the lighter of the two at 150 kg/m against 161.4 kg/m, a saving of 7.6% on steel weight. Both are about 493 mm deep, so either fits the same construction zone.
| Property | UB 457×191×161 UB | H-500x300x13x21 MB & MC | Difference |
|---|---|---|---|
| Mass | 161.4 kg/m | 150 kg/m | +7.6% |
| Depth | 492 mm | 494 mm | -0.4% |
| Width | 199.4 mm | 302 mm | -34.0% |
| Web thickness | 18 mm | 13 mm | +38.5% |
| Flange thickness | 32 mm | 21 mm | +52.4% |
| Area | 206 cm² | 191 cm² | +7.9% |
| Second moment, major (Iy) | 79,800 cm⁴ | 83,810 cm⁴ | -4.8% |
| Plastic modulus, major (Wpl,y) | 3,780 cm³ | 3,792 cm³ | -0.3% |
| Elastic modulus, major (Wel,y) | 3,240 cm³ | 3,393 cm³ | -4.5% |
| Second moment, minor (Iz) | 4,250 cm⁴ | 9,663 cm⁴ | -56.0% |
| Plastic modulus, minor (Wpl,z) | 672 cm³ | 984 cm³ | -31.7% |
| Radius of gyration, minor (iz) | 4.55 cm | 7.11 cm | -36.0% |
| Torsion constant (It) | 515 cm⁴ | 265 cm⁴ | +94.3% |
UB 457×191×161 to BS EN 10365:2017; H-500x300x13x21 to Continental Steel. Difference is expressed relative to H-500x300x13x21.
How to choose between them
On stiffness, H-500x300x13x21 has the larger second moment of area: 83,810 cm⁴ against 79,800 cm⁴, a difference of 4.8%. 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 of steel, H-500x300x13x21 is the more efficient section: 25.3 against 23.4 cm³ per kg/m, 7.4% 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: H-500x300x13x21 has 984 cm³ of minor-axis plastic modulus against 672 cm³, 31.7% 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 MB & MC to 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 7.6% weight.
In short, H-500x300x13x21 is the stronger section and H-500x300x13x21 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.