Comparative Study Concerning the Methods of Calculation of the Critical Axial Buckling Load for Stiffened Cylindrical Shells

Abstract

As demonstrated in numerous theoretical and experimental studies [1], the buckling behaviour of stiffened cylindrical shells (SCS) is strongly influenced by the presence of geometric imperfections caused by the manufacturing process and/or exploitation. Therefore, the design norms recommend the use of reduction coefficients with very low values, resulting in a significant reduction of the maximum load applied. In order to calculate the critical buckling load as accurately as possible it is necessary to know the real geometry of SCS. In case of SCS, the structural analysis based on the use of the finite element method (FEM), using models that reflect the real geometry of the shell determined from measurements, lead to a better evaluation of the critical buckling load. The structural analysis with FEM is accepted more and more by standards, EN 1993-1-6:2007 [2] specifying the types of numerical analysis accepted for cylindrical shells. The aim of this study is to compare the results concerning the critical buckling load for SCS under axial compression, obtained with both the analytical and FEM methods for real geometries obtained from measurements. For this purpose, scale models of SCS were used, for which were determined, by measuring, the values of the deviations from the median radius at several points on the shells surface. These deviations were then incorporated in the numerical analysis with FEM and it was determined, for each cylindrical shell, the value of the critical axial buckling load, by using geometrically nonlinear analysis. In order to validate the results of the numerical analysis, the analysed SCS were subjected to axial compression within an experimental program and the experimental data were compared with the results established on the basis of analytical and numerical calculation.