MULTIPLE FULLY STRESSED STRUCTURAL DESIGNS AND THE STRESS RATIO METHOD

Some structures are capable of being proportioned in several different ways such that each one is a fully stressed design. This paper investigates the nature of these multiple fully stressed designs, the relationships that exist between them, and the behavior of the stress ratio method when applied to the sizing of such structures. "Basins of attraction" constructions are used to graphically portray the behavior of the stress ratio method and to compare it with those of alternative design techniques. It is shown that both attracting and repelling fully stressed designs coexist in the design space under the action of the stress ratio method. A simple modification of the stress ratio method is suggested for transforming repellers into attractors. Instances of limit cycle and chaotic behavior of the stress ratio method are also presented.

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