In recent decades, the resistance of a structure has been thought of as well defined by the outcome of a geometrically and materially nonlinear analysis with explicitly modelled imperfections (GMNIA). But when this is the only analysis that is performed on a complex structural system, it is sometimes difficult to interpret the result. The outcome must be seen in the context of those from simpler analyses, which can define appropriate reference quantities. Other analyses, like a small displacement theory materially nonlinear analysis (MNA) and a linear elastic bifurcation analysis (LBA) are very important in the interpretation of a GMNIA. The general capacity curve in the Eurocode for shell structures  provides a representation of these different analyses. Using this capacity curve, different identifiable key aspects of the structure's behaviour can be studied independently and understood in relation to the corresponding parameter of this curve. This unified representation allows an easy and meaningful characterisation of all elastic–plastic buckling problems. However, some care is needed when applying such a generalised curve to structures with particular features. This paper outlines the limitations of the simplest version of the curve, and develops an enhancement that permits it to be deployed without restriction.
Doerich-Stavridis, C., & Rotter, J. M. (2011). Generalised capacity curves for stability and plasticity: application and limitations. Thin-Walled Structures, 49(9), 1132-1140. https://doi.org/10.1016/j.tws.2011.04.005