On direct and stepped optimization problems of flexural steel frame and their numerical realization considering strength and stiffness conditions

Abstract

Optimization of flexural steel frame responding to loading in elastic-plastic range via direct and stepped methods is considered. Both methods employ structural elastic response values, finally conditioning the optimized parameters of the structure. It enables the problem to be solved iteratively by recalculating the above values for running optimization problem solutions and is continued until problem’s convergence. The formulation of stepped optimization problem via optimization cycles, containing subsequent solution of analysis and optimization problems, allows to avoid direct evaluation of complementarity con-ditions being included in the direct optimization problem. A noncorrect choosing of bounding constraints, the starting point values essentially complicate the iterative and/or stepped procedures or even makes the problem to be the unsolvable one. An intelligent handling of stepped process procedures ensures an efficient and successful convergence of the problem with significant computing resources sav-ings in respect of direct optimization procedures. The pro-posed techniques are illustrated via the solution of ten-storey steel frame, designed from standard steel sections.