The Upper Bound of the Buckling Stress of Axially Compressed Carbon Steel Circular Cylindrical Shells

The buckling stress of axially compressed circular cylindrical shells (CCSs) is highly sensitive to imperfections. Perfect CCSs are an idealization unattainable in reality. In practice, imperfections are always present and significantly reduce the load-carrying capacity. Accordingly, shell designers are encouraged by the Eurocode EN 1993:1-6 to conduct geometric and material nonlinear with imperfections analysis (GMNIA) considering different possible forms of imperfections for the shell under design. As GMNIA type of analysis is difficult and requires highly skilled engineers, knowledge of the upper limit of the buckling stress serves as a guide and prevents overestimation of the shell buckling resistance. It also encourages average skilled designers to attempt GMNIA as far as the maximum possible limit is known. Thus, the objective of this study is to provide the upper bound of the buckling stress of carbon steel CCSs. Geometric and material nonlinear analysis (GMNA) of perfect CCSs for a wide range of R/t ratio is conducted. It has been found that for cases of small and intermediate R/t values the buckling stress can be predicted by GMNA while the elastic buckling controls those of larger R/t values. The limiting R/t values depend on the steel grade and have been derived for the available standard grades of carbon steel. The obtained results are presented in terms of simplified formulas and a design chart to be used by engineers. Application of the proposed upper bound in simplified design approaches using knock down factor (KDFs) has also been discussed.