Multicriteria Topology Optimization of Structures that Maximizes Stiffness and Minimizes Maximum Stress

Stiffness and strength of a structure are two vital and important parameters. Always designers try to find a method to produce equilibrium between these. Recent decade's investigations focused on optimization of stiffness. In these structures we can not ensure that structure has adequate strength or not. So survey of strength is a very important topic. To maximize the strength we have to minimize the maximum stress of the structures. In all of old researches stress is a constraint rather than objective in the optimization processes. Although this may guarantee the stress within a prescribed constraint (generally less than some limit), it cannot always make the maximum stress a minimum. In optimization of a single criterion (stiffness or strength), other criteria can not be maximum. Hence, multicriteria optimization is a logical method. In this research, we use Evolutionary Structural Optimization (ESO) method for size optimization to maximize stiffness and strength of structures. To obtain global criteria, we use weighting method and weight factors. A linear combination of both weighted criteria produces global criteria. In order to calculate suitable weight factors for any structure that we use in research, we examined different value of these and optimize the structures for this values. By comparison of the results, we select the best value of weight factors that can optimize strength and stiffness of the structure. This research has two important a) Thickness distribution at different positions of structure according to stiffness or strength alone does not optimize other criteria in order to have a structure with optimum stiffness and strength; we have to optimize two criteria simultaneously.b) Programming ESO method for multicriteria optimization is very easy and simple. We used a MATLAB code for the FE analysis and a loop for repeating the optimization procedure. Optimization of stiffness alone does not lead to a structure with adequate and vice versa. In order to have a structure with adequate stiffness and strength, we have to optimized the these criteria simultaneously. ESO is a very easy method for multicriteria optimization and programming. We optimize topology of the structures in this research.