UC 305×305×97 vs H-300x300x15x15
UC 305×305×97 is an UC section from the UK Blue Book (SCI P363); H-300x300x15x15 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 1590 cm³ against 1596 cm³ of plastic modulus, a difference of 0.4%. UC 305×305×97 is the lighter of the two at 96.9 kg/m against 105 kg/m, a saving of 7.7% on steel weight. UC 305×305×97 is deeper, 307.9 mm against 300 mm, which matters where the floor zone is tight.
| Property | UC 305×305×97 UC | H-300x300x15x15 MB & MC | Difference |
|---|---|---|---|
| Mass | 96.9 kg/m | 105 kg/m | -7.7% |
| Depth | 307.9 mm | 300 mm | +2.6% |
| Width | 305.3 mm | 305 mm | +0.1% |
| Web thickness | 9.9 mm | 15 mm | -34.0% |
| Flange thickness | 15.4 mm | 15 mm | +2.7% |
| Area | 123 cm² | 133 cm² | -7.5% |
| Second moment, major (Iy) | 22,200 cm⁴ | 21,310 cm⁴ | +4.2% |
| Plastic modulus, major (Wpl,y) | 1,590 cm³ | 1,596 cm³ | -0.4% |
| Elastic modulus, major (Wel,y) | 1,450 cm³ | 1,421 cm³ | +2.0% |
| Second moment, minor (Iz) | 7,310 cm⁴ | 7,103 cm⁴ | +2.9% |
| Plastic modulus, minor (Wpl,z) | 726 cm³ | 714 cm³ | +1.7% |
| Radius of gyration, minor (iz) | 7.69 cm | 7.3 cm | +5.3% |
| Torsion constant (It) | 91.2 cm⁴ | 109 cm⁴ | -16.3% |
UC 305×305×97 to BS EN 10365:2017; H-300x300x15x15 to Continental Steel. Difference is expressed relative to H-300x300x15x15.
How to choose between them
On stiffness, UC 305×305×97 has the larger second moment of area: 22,200 cm⁴ against 21,310 cm⁴, a difference of 4.2%. 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, UC 305×305×97 is the more efficient section: 16.4 against 15.2 cm³ per kg/m, 8.0% 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 7.7% weight.
In short, H-300x300x15x15 is the stronger section and UC 305×305×97 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.