Abstract
This paper presents a unified and efficient new optimum design method for nonlinear plane frame structures with box sections. In the primary design problem, the design variables are the upper and lower flange plate thicknesses of box sections of all member elements and the stress and displacement constraints are dealt with as behavior constraints. The primary optimum design problem is reformulated considering both the primary design constraints and the necessary conditions for analysis problem which are derived from the analysis problem expressed as the total complementary energy minimization problem. The reformulated optimum design problem is solved efficiently by using the gradient projection method. In the optimization process, the complementary energy sensitivity with respect to primary design variables is used, however the calculation of behavior sensitivity with respect to primary design variables is not necessary. The rigorousness, efficiency and reliability of the proposed method are demonstrated by comparing the results obtained by the dual method in which the behavior sensitivities are used.
