Buckling of imperfect unstiffened and stiffened cylindrical shells under external pressure

Liquid storage tanks facilitate a variety of functions, including the storage of water, oils, chemicals, agricultural and food products. These storage tanks are often subjected to natural forces which may lead to severe damage, leakage of stored items, and production stoppage for certain times. Thin-walled cylindrical shell structures are prone to shell buckling. Stiffened thin-walled shell structures built as a combination of thin plates and strong stiffeners are often used to enhance buckling resistance. This research presents numerical results on the linear and nonlinear buckling behavior of unstiffened and stiffened cylindrical shells under external pressure. The analysis revealed that stiffened cylindrical shells exhibited less sensitivity to imperfections compared to unstiffened shells. An optimization study was conducted to achieve the optimal stiffener dimensions by considering 182 specimens such that the overall cylindrical weight remained the same for all specimens. It reveals that linear buckling pressure improves by considering optimum stiffener dimensions. A further parametric study was conducted by considering 350 sample specimens with different radius-to-thickness (R/t) ratios, stiffener's area/tank radius, l/R, and shell thicknesses. A parametric study reveals that the stiffened cylindrical shells with a lower R/t ratio give higher buckling strength; however, linear buckling strength significantly decreases as the R/t ratio increases. Moreover, the linear buckling strength can be gained by increasing the stiffener area and by increasing the shell thickness, with a more pronounced effect observed in tubular specimens. Shell thickness, R/t ratio, and relative stiffener area are the most critical parameters affecting the buckling strength.