UB 686×254×152 vs HE 700 AA
UB 686×254×152 is an UB section from the UK Blue Book (SCI P363); HE 700 AA is the closest equivalent in the European (Continental) range. UB 686×254×152 carries more bending: 5000 cm³ of plastic modulus against 4840 cm³, 3.3% more. They weigh essentially the same, 152.4 kg/m and 150 kg/m. UB 686×254×152 is deeper, 687.5 mm against 670 mm, which matters where the floor zone is tight.
| Property | UB 686×254×152 UB | HE 700 AA HE | Difference |
|---|---|---|---|
| Mass | 152.4 kg/m | 150 kg/m | +1.6% |
| Depth | 687.5 mm | 670 mm | +2.6% |
| Width | 254.5 mm | 300 mm | -15.2% |
| Web thickness | 13.2 mm | 13 mm | +1.5% |
| Flange thickness | 21 mm | 17 mm | +23.5% |
| Area | 194 cm² | 191 cm² | +1.6% |
| Second moment, major (Iy) | 150,000 cm⁴ | 143,000 cm⁴ | +4.9% |
| Plastic modulus, major (Wpl,y) | 5,000 cm³ | 4,840 cm³ | +3.3% |
| Elastic modulus, major (Wel,y) | 4,370 cm³ | 4,260 cm³ | +2.6% |
| Second moment, minor (Iz) | 5,780 cm⁴ | 7,670 cm⁴ | -24.6% |
| Plastic modulus, minor (Wpl,z) | 710 cm³ | 800 cm³ | -11.3% |
| Radius of gyration, minor (iz) | 5.46 cm | 6.34 cm | -13.9% |
| Torsion constant (It) | 220 cm⁴ | 186 cm⁴ | +18.3% |
UB 686×254×152 to BS EN 10365:2017; HE 700 AA to EN 10365 · Continental Steel. Difference is expressed relative to HE 700 AA.
How to choose between them
On stiffness, UB 686×254×152 has the larger second moment of area: 150,000 cm⁴ against 143,000 cm⁴, a difference of 4.9%. 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 (32.8 against 32.3 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.
The two diverge much more about the minor axis: HE 700 AA has 800 cm³ of minor-axis plastic modulus against 710 cm³, 11.3% 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 686×254×152 is the stronger section and HE 700 AA 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.