Answer:
The cross-section class is defined according to EN 1993‑1‑1 and EN 1999‑1‑1 by the maximum width/width ratio c/t or b/t of the cross-section parts subjected to compression. EN 1993‑1‑1 or EN 1999‑1‑1 only cover various straight c/t or b/t parts. Therefore, the classification and determination of effective widths is not possible for the curved c/t or b/t sections.