UC 305×305×198 vs HE 320 C
UC 305×305×198 is an UC section from the UK Blue Book (SCI P363); HE 320 C is the closest equivalent in the European (Continental) range. UC 305×305×198 carries more bending: 3440 cm³ of plastic modulus against 3270 cm³, 5.2% more. HE 320 C is the lighter of the two at 186 kg/m against 198.1 kg/m, a saving of 6.5% on steel weight. Both are about 340 mm deep, so either fits the same construction zone.
| Property | UC 305×305×198 UC | HE 320 C HE | Difference |
|---|---|---|---|
| Mass | 198.1 kg/m | 186 kg/m | +6.5% |
| Depth | 339.9 mm | 340 mm | same |
| Width | 314.5 mm | 305 mm | +3.1% |
| Web thickness | 19.1 mm | 16 mm | +19.4% |
| Flange thickness | 31.4 mm | 30.5 mm | +3.0% |
| Area | 252 cm² | 237 cm² | +6.3% |
| Second moment, major (Iy) | 50,900 cm⁴ | 48,700 cm⁴ | +4.5% |
| Plastic modulus, major (Wpl,y) | 3,440 cm³ | 3,270 cm³ | +5.2% |
| Elastic modulus, major (Wel,y) | 3,000 cm³ | 2,860 cm³ | +4.9% |
| Second moment, minor (Iz) | 16,300 cm⁴ | 14,400 cm⁴ | +13.2% |
| Plastic modulus, minor (Wpl,z) | 1,580 cm³ | 1,440 cm³ | +9.7% |
| Radius of gyration, minor (iz) | 8.04 cm | 7.81 cm | +2.9% |
| Torsion constant (It) | 734 cm⁴ | 688 cm⁴ | +6.7% |
UC 305×305×198 to BS EN 10365:2017; HE 320 C to EN 10365 · Continental Steel. Difference is expressed relative to HE 320 C.
How to choose between them
On stiffness, UC 305×305×198 has the larger second moment of area: 50,900 cm⁴ against 48,700 cm⁴, a difference of 4.5%. 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, the two are equally efficient (17.4 against 17.6 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: UC 305×305×198 has 1580 cm³ of minor-axis plastic modulus against 1440 cm³, 9.7% 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. UC 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 6.5% weight.
In short, UC 305×305×198 is the stronger section and HE 320 C 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.