Comparison of theoretical approaches to account for geometrical imperfections of unstiffened isotropic thin walled cylindrical shell structures under axial compression

•Comparison of three different theoretical imperfection modelling approaches.•Deriving a knock down factor equivalent imperfection magnitude.•Exposing the effect of triggering buckling modes.•Providing a possible cause for the constant collapse load when applying the SPLA.•Highlighting the importance of the way of load introduction on the collapse load.

Thin walled circular cylindrical shell structures are prone to buckle and very sensitive towards geometrical imperfections. The influence of imperfections on the load carrying capacity of shell structures, as they are applied in launcher vehicles is considered by reducing theoretical buckling loads with empirical knock down factors. In general, these knock down factors may lead to a conservative estimate of the load carrying capacity since a worst case scenario is considered. In order to exploit the lightweight design potential of a structure, theoretical approaches to account for geometrical imperfections may lead to more adequate buckling load predictions. Within this contribution different theoretical approaches to account for geometrical imperfections of isotropic shell structures subjected to axial compression are investigated, and the influence of these approaches on the buckling load obtained is studied.