Answer:
According to EN 1993‑1‑1 and DIN 18800 Part 2, it is necessary to specify the equivalent geometric imperfections for the second-order analysis to determine the geometric and structural imperfections as well. This pre-deformation should be applied as affine to the lowest buckling or lateral-torsional buckling mode.
Therefore, in the FE‑LTB program, the eigenvalue belonging to the smallest mode shape is calculated (preliminary eigenvalue analysis) and then selected as the initial deformation mode. The imperfection approach is then carried out by the user scaling the mode shape.
Thus, the pre-deformation is based on the mode shape in RF‑/FE‑LTB. The imperfections defined in RFEM/RSTAB are irrelevant and are therefore not adopted.
