1. What is a "thin element"?

As the term "thin element" is being used more and more frequently, it is essential to clarify this notion before going any further. Depending on the context, or the interlocutor, in good faith and out of habit, it can take on a variety of meanings, leading to what is often a misuse of language.

As soon as the element becomes "long", as in the case of purlin, beam or joist profiles, it is more appropriate to consider it as thin when its length and the width of its constituent walls are greater than its thickness; the order of magnitude of 10...