On the Choice of Eigenmode Shapes for Interactive Cases of Local and Global Buckling of RHS/SHS and I‐Shaped Sections

Abstract

AbstractBetter and simpler possibilities of structural optimization due to increasing computational power but also for reasons of environmental sustainability, the use of materials and their reusability lead to greater acceptance towards more advanced numerically intensive, so‐called “design by analysis” methods like geometrically and materially nonlinear analyses with imperfections (GMNIA). The general choice of imperfections and their combination in such models, especially for slender cross‐sections of intermediate length prone to an interaction between a global and local plate‐buckling, is crucial in terms of the reached load‐bearing capacity. Annex C of EN 1993‐1‐5 make use of the “70%‐rule” for the combination of imperfection modes and amplitudes. This rule postulates that two GMNIA calculations should be carried out when local and global interactive buckling may be dominant; one with 100% + 70% of the maximum specified amplitude in either case. In addition, extended information is provided on the choice and combination of imperfections in the newly introduced and currently available draft of the prEN1993‐1‐14:2020 (Design assisted by finite element analysis). Although information is provided how the local and global imperfections should be combined, it is not stated when it is relevant to consider those. Based on carried out GMNIA simulations on SHS/RHS and I‐shaped sections, this paper presents a general decision support on the choice of equivalent imperfections. Based on numerical analysis, the developed flowchart and design routine allows for the decision whether the consideration of the interaction of local and global imperfections is required or not.