The lateral energy absorbing characteristics of axially loaded structural members were investigated from a qualitative point of view based on the energy balance equations of the inelastic column model with single degree of freedom, and its stability and response characteristics were discussed in the general. Furthermore the limitations of the method of rigidplastic analysis for the present problem were studied by the comparison of the rigid-plastic solutions with the elasto-plastic solutions. The obtained results are summarized as follows :
(1) The equations of the elastic critical energy and the stable critical energy were derived and the stability diagrams were presented.
(2) The equations of the elastic maximum displacement and the elasto-plastic maximum displacement were derived and the response diagrams were presented.
(3) It was shown that the accuracy of the rigid-plastic solutions is determined by the ratio of the axial load to the elastic buckling load (p/q) by the comparison of the solutions with respect to the critical energy and the maximum displacement response.