PFC 430×100×64 vs MC 18X42.7
PFC 430×100×64 is an PFC section from the UK Blue Book (SCI P363); MC 18X42.7 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 1220 cm³ against 1230.7 cm³ of plastic modulus, a difference of 0.9%. They weigh essentially the same, 64.4 kg/m and 63.5 kg/m. MC 18X42.7 is deeper, 457.2 mm against 430 mm, which matters where the floor zone is tight.
| Property | PFC 430×100×64 PFC | MC 18X42.7 MC | Difference |
|---|---|---|---|
| Mass | 64.4 kg/m | 63.5 kg/m | +1.4% |
| Depth | 430 mm | 457.2 mm | -5.9% |
| Width | 100 mm | 100.3 mm | -0.3% |
| Web thickness | 11 mm | 11.4 mm | -3.5% |
| Flange thickness | 19 mm | 15.9 mm | +19.5% |
| Area | 82.1 cm² | 81.3 cm² | +1.0% |
| Second moment, major (Iy) | 21,900 cm⁴ | 23,059 cm⁴ | -5.0% |
| Plastic modulus, major (Wpl,y) | 1,220 cm³ | 1,230.7 cm³ | -0.9% |
| Elastic modulus, major (Wel,y) | 1,020 cm³ | 1,007.8 cm³ | +1.2% |
| Second moment, minor (Iz) | 722 cm⁴ | 595.2 cm⁴ | +21.3% |
| Plastic modulus, minor (Wpl,z) | 176 cm³ | 144.53 cm³ | +21.8% |
| Radius of gyration, minor (iz) | 2.97 cm | 2.72 cm | +9.2% |
| Torsion constant (It) | 63 cm⁴ | 51.2 cm⁴ | +23.0% |
PFC 430×100×64 to BS EN 1993-1-1:2005 / BS 4-1:2005; MC 18X42.7 to AISC Shapes Database v16.0. Difference is expressed relative to MC 18X42.7.
How to choose between them
On stiffness, MC 18X42.7 has the larger second moment of area: 23,059 cm⁴ against 21,900 cm⁴, a difference of 5.0%. 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, MC 18X42.7 is the more efficient section: 19.4 against 18.9 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.
The two diverge much more about the minor axis: PFC 430×100×64 has 176 cm³ of minor-axis plastic modulus against 144.53 cm³, 21.8% 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.