Answer:
Length LT represents the buckling length for torsional buckling and lateral-torsional buckling under systematic centric pressure. Length LT works similarly to Column D and Column G: a critical and buckling load are calculated for the design of a pure compressive force according to EN 1993‑1‑1, Section 6.3.1.4.On the other hand, length LW is not the effective length, but the length to which the moment and shear force distribution are related with the boundary conditions kz and kw (Column J and Column K) as well as the lateral intermediate supports. Generally, this length should not be changed.
