Optimum Design of Three‐Dimensional Framework Structures

Abstract

A method for optimal design of large‐scale framework structures is presented. The approach is based on a reanalysis technique in combination with suboptimization for each member group in the structure. The suboptimization is performed using a nonlinear programming algorithm based on sequential quadratic programming. Given the topology and material quality, the cross‐sectional dimensions of wide‐flange and hollow‐section members are treated as design variables and the minimum weight or cost solution is sought. The structural problem is formulated using the matrix displacement method. Large three‐dimensional rigidly jointed frames subjected to multiple loading cases are analyzed. Constraints can be imposed on maximum Von Mises stresses, beam stability, and the fatigue damage at nodal points. The approach is general, robust, and efficient in that it avoids numerous global structural analyses. The practical engineering utility of the method is emphasized. Case studies of an offshore deck module and a platform jacket structure are included. Future work should focus on a refined formulation of the fatigue constraint.