Effects of Mode Interaction on Collapse of Short, Imperfect, Thin-Walled Columns

The present paper deals with the design of beneficial geometric imperfections of short, thin-walled columns in order to maximize their energy absorption. The investigation was motivated by the experimental finding that under axial compressive load, the symmetric mode (which has a higher buckling load than the antisymmetric mode) actually has a much higher energy absorption than the antisymmetric mode as measured by the area under the curve of applied load versus end-shortening curve. Thus, an attempt is made to introduce imperfections in the beneficial symmetric mode so that the mode shapes of extremely large deflection in plastic collapse will also be of the symmetric type. The two-mode stability problem is studied using Koiter’s theory of elastic stability.