UB 533×210×122 vs S 20X96
UB 533×210×122 is an UB section from the UK Blue Book (SCI P363); S 20X96 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 3200 cm³ against 3244.6 cm³ of plastic modulus, a difference of 1.4%. UB 533×210×122 is the lighter of the two at 122 kg/m against 142.9 kg/m, a saving of 14.6% on steel weight. UB 533×210×122 is deeper, 544.5 mm against 515.6 mm, which matters where the floor zone is tight.
| Property | UB 533×210×122 UB | S 20X96 S | Difference |
|---|---|---|---|
| Mass | 122 kg/m | 142.9 kg/m | -14.6% |
| Depth | 544.5 mm | 515.6 mm | +5.6% |
| Width | 211.9 mm | 182.9 mm | +15.9% |
| Web thickness | 12.7 mm | 20.3 mm | -37.4% |
| Flange thickness | 21.3 mm | 23.4 mm | -9.0% |
| Area | 155 cm² | 181.9 cm² | -14.8% |
| Second moment, major (Iy) | 76,000 cm⁴ | 69,511 cm⁴ | +9.3% |
| Plastic modulus, major (Wpl,y) | 3,200 cm³ | 3,244.6 cm³ | -1.4% |
| Elastic modulus, major (Wel,y) | 2,790 cm³ | 2,703.9 cm³ | +3.2% |
| Second moment, minor (Iz) | 3,390 cm⁴ | 2,077 cm⁴ | +63.2% |
| Plastic modulus, minor (Wpl,z) | 500 cm³ | 408.04 cm³ | +22.5% |
| Radius of gyration, minor (iz) | 4.67 cm | 3.38 cm | +38.2% |
| Torsion constant (It) | 178 cm⁴ | 349.6 cm⁴ | -49.1% |
UB 533×210×122 to BS EN 10365:2017; S 20X96 to AISC Shapes Database v16.0. Difference is expressed relative to S 20X96.
How to choose between them
On stiffness, UB 533×210×122 has the larger second moment of area: 76,000 cm⁴ against 69,511 cm⁴, a difference of 9.3%. 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 533×210×122 is the more efficient section: 26.2 against 22.7 cm³ per kg/m, 15.5% 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 533×210×122 has 500 cm³ of minor-axis plastic modulus against 408.04 cm³, 22.5% 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 S to AISC Shapes Database v16.0; 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 14.6% weight.
In short, S 20X96 is the stronger section and UB 533×210×122 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.