Buckling Behavior of Imperfect Unstiffened and Stiffened Cylindrical Shells under External Pressure

This study numerically investigates the linear and nonlinear buckling behavior of unstiffened and stiffened cylindrical shells under uniform external pressure. Linear buckling analysis accurately captured the buckling mode shapes, which closely matched published experimental observations; however, the corresponding buckling pressures differed from the experimental values. To improve prediction accuracy, a nonlinear buckling analysis (NLA) was performed on both perfect and imperfect geometries, accounting for large deflection effects and eigenmode-based geometric imperfections. For unstiffened shells, the NLA results with a 50% geometric imperfection showed excellent agreement with experimental buckling strengths and deformation modes, confirming the accuracy of the finite-element model. In contrast, for stiffened shells, a 5% geometric imperfection yielded the best correlation with experimental results. A parametric study was also conducted to evaluate the influence of stiffener geometry while maintaining a constant cross-sectional area. The results demonstrated that thinner, taller stiffeners significantly enhance the buckling strength, particularly for specimens exhibiting global buckling modes. These findings provide valuable insights into the design optimization of thin-walled cylindrical shells under external pressure, offering practical guidance to improve buckling resistance and structural efficiency.