Equivalent geometric imperfections for the numerical buckling strength verification of steel shell structures subject to axial compression

The most sophisticated method of a numerical buckling strength verification of steel shell structures is a geometrically and materially non-linear analysis with imperfections included (GMNIA). By this way, equivalent geometric imperfections, which have to cover the influence of all deviations from the nominal dates of the resistance parameters, are fundamental for the quality of the buckling strength verification. The problem of equivalent geometric imperfections includes the problems of their shape and size. Eigenmode-affine, single wavy axisymmetric imperfections and multi-wavy axisymmetric imperfections are analysed in the paper and compared with respect to their influence on the load bearing capacity. Besides the hints regarding the imperfection mode, the Eurocode makes statements about the imperfection amplitudes, which are to be adopted. Using these imperfection amplitudes, partly substantial differences between numerically and experimentally determined buckling resistances arise for several geometries. Possibilities are discussed to overcome these inconsistencies also thin-walled shells, keeping up the framework of the Eurocode to use only geometric equivalent imperfections.