OPTIMUM DESIGN OF GEOMETRICALLY NONLINEAR ELASTIC PLASTIC STEEL FRAMES WITH TAPERED MEMBERS

Abstract

Steel frames having members with nonuniform cross-sections are preferred in design cases where the architectural constraints are flexible. In such cases they produce economical solutions. In this study an algorithm is presented for the optimum design of such frames in which linear variation of cross-sections is considered. Each member introduces two variables into the design problem provided that they are not linked together. The first is the cross-sectional area at one end and the other is the ratio of areas at both ends. The design algorithm is obtained by coupling the optimality criteria approach with large deformation analysis method of elastic-plastic frames. The optimality criteria method is used to develop a recursive relationship for design variables considering displacement constraints. This relationship requires nonlinear response of the frame at every design cycle which is computed by an algorithm based on Euclerian formulation including clastic-plastic effects. The design algorithm is outlined in steps and number of design examples are presented to demonstrate its application.