UC 305×305×198 vs H-350x350x16x25
UC 305×305×198 is an UC section from the UK Blue Book (SCI P363); H-350x350x16x25 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 3440 cm³ against 3424 cm³ of plastic modulus, a difference of 0.5%. H-350x350x16x25 is the lighter of the two at 181 kg/m against 198.1 kg/m, a saving of 9.4% on steel weight. H-350x350x16x25 is deeper, 362 mm against 339.9 mm, which matters where the floor zone is tight.
| Property | UC 305×305×198 UC | H-350x350x16x25 MB & MC | Difference |
|---|---|---|---|
| Mass | 198.1 kg/m | 181 kg/m | +9.4% |
| Depth | 339.9 mm | 362 mm | -6.1% |
| Width | 314.5 mm | 354 mm | -11.2% |
| Web thickness | 19.1 mm | 16 mm | +19.4% |
| Flange thickness | 31.4 mm | 25 mm | +25.6% |
| Area | 252 cm² | 230 cm² | +9.6% |
| Second moment, major (Iy) | 50,900 cm⁴ | 55,190 cm⁴ | -7.8% |
| Plastic modulus, major (Wpl,y) | 3,440 cm³ | 3,424 cm³ | +0.5% |
| Elastic modulus, major (Wel,y) | 3,000 cm³ | 3,049 cm³ | -1.6% |
| Second moment, minor (Iz) | 16,300 cm⁴ | 18,500 cm⁴ | -11.9% |
| Plastic modulus, minor (Wpl,z) | 1,580 cm³ | 1,591 cm³ | -0.7% |
| Radius of gyration, minor (iz) | 8.04 cm | 8.96 cm | -10.3% |
| Torsion constant (It) | 734 cm⁴ | 445 cm⁴ | +64.9% |
UC 305×305×198 to BS EN 10365:2017; H-350x350x16x25 to Continental Steel. Difference is expressed relative to H-350x350x16x25.
How to choose between them
On stiffness, H-350x350x16x25 has the larger second moment of area: 55,190 cm⁴ against 50,900 cm⁴, a difference of 7.8%. 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-350x350x16x25 is the more efficient section: 18.9 against 17.4 cm³ per kg/m, 8.2% 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.
These come from different catalogues, so treat the swap as a design change rather than a like-for-like substitution. UC 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 9.4% weight.
In short, UC 305×305×198 is the stronger section and H-350x350x16x25 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.