PFC 125×65×15 vs PFC 125×65
PFC 125×65×15 is a PFC section from the UK Blue Book (SCI P363); PFC 125×65 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 89.9 cm³ against 89.9 cm³ of plastic modulus, a difference of 0.0%. They weigh essentially the same, 14.8 kg/m and 14.8 kg/m. Both are about 125 mm deep, so either fits the same construction zone.
| Property | PFC 125×65×15 PFC | PFC 125×65 PFC | Difference |
|---|---|---|---|
| Mass | 14.8 kg/m | 14.8 kg/m | same |
| Depth | 125 mm | 125 mm | same |
| Width | 65 mm | 65 mm | same |
| Web thickness | 5.5 mm | 5.5 mm | same |
| Flange thickness | 9.5 mm | 9.5 mm | same |
| Area | 18.8 cm² | 18.8 cm² | same |
| Second moment, major (Iy) | 483 cm⁴ | 483 cm⁴ | same |
| Plastic modulus, major (Wpl,y) | 89.9 cm³ | 89.9 cm³ | same |
| Elastic modulus, major (Wel,y) | 77.3 cm³ | 77.3 cm³ | same |
| Second moment, minor (Iz) | 80 cm⁴ | 80 cm⁴ | same |
| Plastic modulus, minor (Wpl,z) | 33.2 cm³ | 33.2 cm³ | same |
| Radius of gyration, minor (iz) | 2.06 cm | 2.06 cm | same |
| Torsion constant (It) | 4.72 cm⁴ | 4.72 cm⁴ | same |
PFC 125×65×15 to BS EN 1993-1-1:2005 / BS 4-1:2005; PFC 125×65 to Continental Steel. Difference is expressed relative to PFC 125×65.
How to choose between them
On stiffness, PFC 125×65 has the larger second moment of area: 483 cm⁴ against 483 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 (6.1 against 6.1 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.
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.