In modern weight sensitive applications, especially in marine and offshore engineering, thin shells have been greatly used as structural components due to their efficient load-carrying capacities. Imperfection-sensitive buckling is a critical design factor for this kind of structures when they are under compression. Traditional design method purely relies on experimentally-derived lower-bounds to the scatter of test results and is suggested to be no longer tenable for the buckling design of thin shells with novel material applications and structural forms due to the multitude of additional material and geometric parameters. It is in this context that an analytical lower-bound design method, the so-called reduced stiffness method (RSM) is proposed. The RSM has been shown to be capable of predicting safe and reliable lower bounds for a range of metallic and stiffened shells. The RSM observes that mode coupling, precipitated by initial geometric imperfections, will in the postbuckling state annihilate the membrane energy which provides important contribution to shell's initial resistance to buckling. By dismissing these energy terms in a modified classical critical load analysis, an analytical lower bound to the imperfection sensitive buckling can be obtained. This paper intends to systematically present the method and validate it through carefully controlled finite element analysis by comparing with the results from other nonlinear buckling analysis.

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