OPTIMUM DESIGN OF NONLINEAR ELASTIC FRAMED DOMES

In this paper, an algorithm is presented for the optimum design of thr ee-dimensional rigidly jointed frames which takes into account the non linear response due to the effect of axial forces in members. The stab ility functions for three-dimensional beam-columns are used to obtain the nonlinear response of the frame. These functions are derived by co nsidering the effect of axial force on flexural stiffness and effect o f flexure on axial stiffness. The optimum design algorithm considers d isplacement limitations and restricts combined stresses not to be more than yield stress. It employs the optimality criteria approach togeth er with nonlinear overall stiffness matrix to develop a recursive rela tionship for design variables in the case of dominant displacement con straints. The combined stress constraints are reduced into nonlinear e quations of design variables. The algorithm initiates the optimum desi gn at the selected load factor and carries out elastic instability ana lysis until the ultimate load factor is reached. During these iteratio ns checks of the overall stability of frame is conducted. If the nonli near response is obtained without loss of stability, the algorithm the n proceeds to the next design cycle. The method developed is applied t o the optimum design of a number of rigid space frames to demonstrate its versatility. (C) 1998 Elsevier Science Limited and Civil-Comp Limi ted. All rights reserved.