Abstract: peculiar multi-variable approximate function which has good numerical stability is proposed. By combining the approximate function with the two-level, multi-point approaching concept, a more perfect relative optimum algorithm is formed.The method is applied to optimum design of frames, and without any special intermediate variable,the cross-sectional dimensions of frames are directly selected as design variables.The results of numerical examples show that the present method is of satisfactory efficiency,which also testifies the wide adaptability of the method.

Key words: structural optimization, numerical approximation, optimum method