C 9X20 vs PFC 230×75
C 9X20 is an C section from the American AISC Shapes Database; PFC 230×75 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 276.94 cm³ against 278 cm³ of plastic modulus, a difference of 0.4%. PFC 230×75 is the lighter of the two at 25.7 kg/m against 29.8 kg/m, a saving of 16.0% on steel weight. Both are about 229 mm deep, so either fits the same construction zone.
| Property | C 9X20 C | PFC 230×75 PFC | Difference |
|---|---|---|---|
| Mass | 29.8 kg/m | 25.7 kg/m | +16.0% |
| Depth | 228.6 mm | 230 mm | -0.6% |
| Width | 67.3 mm | 75 mm | -10.3% |
| Web thickness | 11.4 mm | 6.5 mm | +75.4% |
| Flange thickness | 10.5 mm | 12.5 mm | -16.0% |
| Area | 37.9 cm² | 32.7 cm² | +15.9% |
| Second moment, major (Iy) | 2,535 cm⁴ | 2,748 cm⁴ | -7.8% |
| Plastic modulus, major (Wpl,y) | 276.94 cm³ | 278 cm³ | -0.4% |
| Elastic modulus, major (Wel,y) | 221.23 cm³ | 239 cm³ | -7.4% |
| Second moment, minor (Iz) | 100.3 cm⁴ | 181 cm⁴ | -44.6% |
| Plastic modulus, minor (Wpl,z) | 40.312 cm³ | 63.2 cm³ | -36.2% |
| Radius of gyration, minor (iz) | 1.63 cm | 2.35 cm | -30.6% |
| Torsion constant (It) | 17.77 cm⁴ | 11.8 cm⁴ | +50.6% |
C 9X20 to AISC Shapes Database v16.0; PFC 230×75 to Continental Steel. Difference is expressed relative to PFC 230×75.
How to choose between them
On stiffness, PFC 230×75 has the larger second moment of area: 2,748 cm⁴ against 2,535 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, PFC 230×75 is the more efficient section: 10.8 against 9.3 cm³ per kg/m, 14.1% 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: PFC 230×75 has 63.2 cm³ of minor-axis plastic modulus against 40.312 cm³, 36.2% 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. C sections are specified to AISC Shapes Database v16.0 and PFC 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 16.0% weight.
In short, PFC 230×75 is the stronger section and PFC 230×75 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.