C 15X40 vs PFC 380×100
C 15X40 is an C section from the American AISC Shapes Database; PFC 380×100 is the closest equivalent in the European (Continental) range. They are close to interchangeable in bending: 942.26 cm³ against 933 cm³ of plastic modulus, a difference of 1.0%. PFC 380×100 is the lighter of the two at 54 kg/m against 59.5 kg/m, a saving of 10.2% on steel weight. Both are about 381 mm deep, so either fits the same construction zone.
| Property | C 15X40 C | PFC 380×100 PFC | Difference |
|---|---|---|---|
| Mass | 59.5 kg/m | 54 kg/m | +10.2% |
| Depth | 381 mm | 380 mm | +0.3% |
| Width | 89.4 mm | 100 mm | -10.6% |
| Web thickness | 13.2 mm | 9.5 mm | +38.9% |
| Flange thickness | 16.5 mm | 17.5 mm | -5.7% |
| Area | 76.1 cm² | 68.7 cm² | +10.8% |
| Second moment, major (Iy) | 14,485 cm⁴ | 15,030 cm⁴ | -3.6% |
| Plastic modulus, major (Wpl,y) | 942.26 cm³ | 933 cm³ | +1.0% |
| Elastic modulus, major (Wel,y) | 762 cm³ | 791 cm³ | -3.7% |
| Second moment, minor (Iz) | 381.7 cm⁴ | 643 cm⁴ | -40.6% |
| Plastic modulus, minor (Wpl,z) | 112.09 cm³ | 161 cm³ | -30.4% |
| Radius of gyration, minor (iz) | 2.24 cm | 3.06 cm | -26.8% |
| Torsion constant (It) | 60.35 cm⁴ | 45.7 cm⁴ | +32.1% |
C 15X40 to AISC Shapes Database v16.0; PFC 380×100 to Continental Steel. Difference is expressed relative to PFC 380×100.
How to choose between them
On stiffness, PFC 380×100 has the larger second moment of area: 15,030 cm⁴ against 14,485 cm⁴, a difference of 3.6%. 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 380×100 is the more efficient section: 17.3 against 15.8 cm³ per kg/m, 8.3% 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 380×100 has 161 cm³ of minor-axis plastic modulus against 112.09 cm³, 30.4% 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 10.2% weight.
In short, C 15X40 is the stronger section and PFC 380×100 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.