UC 305×305×118 vs H-300x300x13x20
UC 305×305×118 is an UC section from the UK Blue Book (SCI P363); H-300x300x13x20 is the closest equivalent in the European (Continental) range. H-300x300x13x20 carries more bending: 2031 cm³ of plastic modulus against 1960 cm³, 3.5% more. UC 305×305×118 is the lighter of the two at 117.9 kg/m against 125 kg/m, a saving of 5.7% on steel weight. Both are about 312 mm deep, so either fits the same construction zone.
| Property | UC 305×305×118 UC | H-300x300x13x20 MB & MC | Difference |
|---|---|---|---|
| Mass | 117.9 kg/m | 125 kg/m | -5.7% |
| Depth | 314.5 mm | 310 mm | +1.5% |
| Width | 307.4 mm | 303 mm | +1.5% |
| Web thickness | 12 mm | 13 mm | -7.7% |
| Flange thickness | 18.7 mm | 20 mm | -6.5% |
| Area | 150 cm² | 159 cm² | -5.7% |
| Second moment, major (Iy) | 27,700 cm⁴ | 28,130 cm⁴ | -1.5% |
| Plastic modulus, major (Wpl,y) | 1,960 cm³ | 2,031 cm³ | -3.5% |
| Elastic modulus, major (Wel,y) | 1,760 cm³ | 1,815 cm³ | -3.0% |
| Second moment, minor (Iz) | 9,060 cm⁴ | 9,282 cm⁴ | -2.4% |
| Plastic modulus, minor (Wpl,z) | 895 cm³ | 932 cm³ | -4.0% |
| Radius of gyration, minor (iz) | 7.77 cm | 7.64 cm | +1.7% |
| Torsion constant (It) | 161 cm⁴ | 200 cm⁴ | -19.5% |
UC 305×305×118 to BS EN 10365:2017; H-300x300x13x20 to Continental Steel. Difference is expressed relative to H-300x300x13x20.
How to choose between them
On stiffness, H-300x300x13x20 has the larger second moment of area: 28,130 cm⁴ against 27,700 cm⁴, a difference of 1.5%. 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 305×305×118 is the more efficient section: 16.6 against 16.2 cm³ per kg/m, 2.3% 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 5.7% weight.
In short, H-300x300x13x20 is the stronger section and UC 305×305×118 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.