The evolutionary structural optimization (ESO) is an evolutionary based method, which has been broadly used for structural optimization in recent years. The concept behind the simple ESO method is the removal of inefficient material from a structure in an iterative process. The process involves a number of selections like the choice of rejection ratio and evolutionary rate. On the other hand, in the finite element analysis (FEA) of the problem, the designer should decide about the size of the mesh and the type of the element used. The influence of the rejection ratio, evolutionary rate and the size of elements choice on the optimized shape of 2D and 3D continuum structures are investigated in this paper. Different mesh sizes and boundary conditions are considered. In all examined cases the rejection criterion for removing material (elements) is the von Mises stress level of the elements. The results show the ability of the ESO method for generating optimum 2D and 3D continuum structures with different boundary conditions. In a series of examples of 2D and 3D continuum structures, it is shown that different initial rejection ratios and evolutionary rates may have no significant effect on the maximum and minimum stresses histories and on the volume reduction histories as well, but have a significant effect on the resulted shape. Furthermore, the optimized topology is more sensitive to the evolutionary rate changes than the variation of initial rejection ratios. It is also concluded that the element sizes have a significant effect on the histories of minimum stress and the volume reduction. Moreover, the optimized shape is completely changed by variation of the element sizes.

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