This check is used for channel sections and plated sections with unequal flanges. Such sections can be Class 1, 2 or 3 Plastic, Compact or Semi-compact (Class 4 Slender sections are not included in this release).

Two formulae are provided in Clause 4.8.3.3.1, and are based on linear interaction of axial force and moments in the two orthogonal directions. These are a lower-bound (conservative) treatment of the surface of interaction defined by the real behaviour. This is why there are only two formulae as compared to three in Clause 4.8.3.3.2 and why they have a wider scope of applicability. Both formulae must be checked; the second is calculated twice – once for the top flange and once for the bottom flange. Results for each at the position of maximum utilization ratio are reported.