Optimum Design — Minimum Weight Versus Fully Stressed

The substitute problem of fully stressed design or simultaneous failure modes design is often solved in place of the minimum weight design. A method is presented which can be used to determine the validity of the substitute problem of fully stressed or simultaneous failure modes design. The equivalence of these two solutions can be demonstrated for a large class of discrete and continuous structures subjected to a single load condition. This equivalence can also be extended to a stress limited determinate truss subjected to several independent mechanical loads. However, it can also be shown that the simultaneous failure modes is not necessarily the minimum weight design for waffle plates subjected to a multiplicity of biaxial loads.