Optimum Design Using Available Sections

Conventional optimum structural design methods assume that a continuous spectrum of member sizes is available to the designer. For example, in the minimum weight rigid-plastic design of stiff-jointed frameworks, it is usually assumed that the weight per unit length of frame members is a linear function of their fully plastic moment. In actual fact, the sections available consist of a finite range of discrete member sizes. By making use of discrete programming techniques, it is possible to derive design methods which do not depend on theoretical weight-strength functions, but instead work directly with the available discrete sections. Two classes of design problem are considered: (1) The design of stiff jointed frameworks using rigid-plastic theory; and (2) the elastic design of statically determinate triangulated frameworks subject to deflection constraints.