PFC 300×100×46 vs MC 12X31
PFC 300×100×46 is an PFC section from the UK Blue Book (SCI P363); MC 12X31 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 641 cm³ against 650.57 cm³ of plastic modulus, a difference of 1.5%. They weigh essentially the same, 45.5 kg/m and 46.1 kg/m. Both are about 302 mm deep, so either fits the same construction zone.
| Property | PFC 300×100×46 PFC | MC 12X31 MC | Difference |
|---|---|---|---|
| Mass | 45.5 kg/m | 46.1 kg/m | -1.3% |
| Depth | 300 mm | 304.8 mm | -1.6% |
| Width | 100 mm | 93.2 mm | +7.3% |
| Web thickness | 9 mm | 9.4 mm | -4.3% |
| Flange thickness | 16.5 mm | 17.8 mm | -7.3% |
| Area | 58 cm² | 58.8 cm² | -1.4% |
| Second moment, major (Iy) | 8,230 cm⁴ | 8,408 cm⁴ | -2.1% |
| Plastic modulus, major (Wpl,y) | 641 cm³ | 650.57 cm³ | -1.5% |
| Elastic modulus, major (Wel,y) | 549 cm³ | 552.24 cm³ | -0.6% |
| Second moment, minor (Iz) | 568 cm⁴ | 470.3 cm⁴ | +20.8% |
| Plastic modulus, minor (Wpl,z) | 148 cm³ | 133.55 cm³ | +10.8% |
| Radius of gyration, minor (iz) | 3.13 cm | 2.82 cm | +11.0% |
| Torsion constant (It) | 36.8 cm⁴ | 41.62 cm⁴ | -11.6% |
PFC 300×100×46 to BS EN 1993-1-1:2005 / BS 4-1:2005; MC 12X31 to AISC Shapes Database v16.0. Difference is expressed relative to MC 12X31.
How to choose between them
On stiffness, MC 12X31 has the larger second moment of area: 8,408 cm⁴ against 8,230 cm⁴, a difference of 2.1%. 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 (14.1 against 14.1 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: PFC 300×100×46 has 148 cm³ of minor-axis plastic modulus against 133.55 cm³, 10.8% 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. PFC sections are specified to BS EN 1993-1-1:2005 / BS 4-1:2005 and MC to AISC Shapes Database v16.0; 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 a marginal amount of weight.
In short, these two are genuine equivalents. Pick whichever your supplier stocks and the rest of the frame already uses.