UB 914×419×388 vs HE 900 x 391
UB 914×419×388 is an UB section from the UK Blue Book (SCI P363); HE 900 x 391 is the closest equivalent in the European (Continental) range. UB 914×419×388 carries more bending: 17700 cm³ of plastic modulus against 17000 cm³, 4.1% more. They weigh essentially the same, 388 kg/m and 391 kg/m. Both are about 922 mm deep, so either fits the same construction zone.
| Property | UB 914×419×388 UB | HE 900 x 391 HE | Difference |
|---|---|---|---|
| Mass | 388 kg/m | 391 kg/m | -0.8% |
| Depth | 921 mm | 922 mm | -0.1% |
| Width | 420.5 mm | 307 mm | +37.0% |
| Web thickness | 21.4 mm | 25 mm | -14.4% |
| Flange thickness | 36.6 mm | 46 mm | -20.4% |
| Area | 494 cm² | 498 cm² | -0.8% |
| Second moment, major (Iy) | 720,000 cm⁴ | 674,000 cm⁴ | +6.8% |
| Plastic modulus, major (Wpl,y) | 17,700 cm³ | 17,000 cm³ | +4.1% |
| Elastic modulus, major (Wel,y) | 15,600 cm³ | 14,600 cm³ | +6.8% |
| Second moment, minor (Iz) | 45,400 cm⁴ | 22,300 cm⁴ | +103.6% |
| Plastic modulus, minor (Wpl,z) | 3,340 cm³ | 2,310 cm³ | +44.6% |
| Radius of gyration, minor (iz) | 9.59 cm | 6.7 cm | +43.1% |
| Torsion constant (It) | 1,730 cm⁴ | 2,600 cm⁴ | -33.5% |
UB 914×419×388 to BS EN 10365:2017; HE 900 x 391 to EN 10365 · Continental Steel. Difference is expressed relative to HE 900 x 391.
How to choose between them
On stiffness, UB 914×419×388 has the larger second moment of area: 720,000 cm⁴ against 674,000 cm⁴, a difference of 6.8%. 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, UB 914×419×388 is the more efficient section: 45.6 against 43.5 cm³ per kg/m, 4.9% 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: UB 914×419×388 has 3340 cm³ of minor-axis plastic modulus against 2310 cm³, 44.6% 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 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, UB 914×419×388 is the stronger section and UB 914×419×388 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.