Numerical Buckling Strength Verification of Cylindrical Steel Shell Structures Subject To Combined Loading

The inevitable deviations from the nominal data of the resistance parameters have to be included in a numerical calculation of the load-bearing capacity of shells, because these structures are very imperfection-sensitive. The assumed imperfections are fundamental for the numerical buckling strength verification, because they have to cover the influence of all accidental imperfections of the structure in a consistent manner. Consistent equivalent geometric imperfections have been developed during the last years for the basic buckling cases of the circular cylindrical steel shell. The situation at shells subject to combined loading is more difficult, because not so much experimental data is available. Fundamental problems and previous proposals for assuming equivalent imperfections at combined loading are discussed in the contribution. In particular, it is a moot point whether the equivalent geometric imperfections have to be chosen without regard to the load case, because imperfections of real shells are caused by manufacturing and not by loading. Reasons are given for, why this is not applicable at equivalent imperfections of a numerical simulation. The conception of quasi-collapse-affine imperfections, which has already been proved at the basic buckling cases, can also be applied to shells under combined loading.