PFC 150×75×18 vs PFC 150×75
PFC 150×75×18 is a PFC section from the UK Blue Book (SCI P363); PFC 150×75 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 132 cm³ against 132 cm³ of plastic modulus, a difference of 0.0%. They weigh essentially the same, 17.9 kg/m and 17.9 kg/m. Both are about 150 mm deep, so either fits the same construction zone.
| Property | PFC 150×75×18 PFC | PFC 150×75 PFC | Difference |
|---|---|---|---|
| Mass | 17.9 kg/m | 17.9 kg/m | same |
| Depth | 150 mm | 150 mm | same |
| Width | 75 mm | 75 mm | same |
| Web thickness | 5.5 mm | 5.5 mm | same |
| Flange thickness | 10 mm | 10 mm | same |
| Area | 22.8 cm² | 22.8 cm² | same |
| Second moment, major (Iy) | 861 cm⁴ | 861 cm⁴ | same |
| Plastic modulus, major (Wpl,y) | 132 cm³ | 132 cm³ | same |
| Elastic modulus, major (Wel,y) | 115 cm³ | 115 cm³ | same |
| Second moment, minor (Iz) | 131 cm⁴ | 131 cm⁴ | same |
| Plastic modulus, minor (Wpl,z) | 47.2 cm³ | 47.2 cm³ | same |
| Radius of gyration, minor (iz) | 2.4 cm | 2.4 cm | same |
| Torsion constant (It) | 6.1 cm⁴ | 6.1 cm⁴ | same |
PFC 150×75×18 to BS EN 1993-1-1:2005 / BS 4-1:2005; PFC 150×75 to Continental Steel. Difference is expressed relative to PFC 150×75.
How to choose between them
On stiffness, PFC 150×75 has the larger second moment of area: 861 cm⁴ against 861 cm⁴, a difference of 0.0%. 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, the two are equally efficient (7.4 against 7.4 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.
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 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 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.