Minimum cost design of steel frames with semi-rigid connections and column bases via genetic optimization

In this paper, an optimum design method is presented for non-linear steel frames with semi-rigid connections and semi-rigid column bases using a genetic algorithm. The design algorithm obtains the minimum total cost which comprises total member plus connection costs by selecting suitable sections from a standard set of steel sections such as American Institute of Steel Construction (AISC) wide-flange (W) shapes. A genetic algorithm is employed as optimization method which utilizes reproduction, crossover and mutation operators. Displacement and stress constraints of AISC-Load and Resistance Factor Design (LRFD) specification and also size constraints for beams and columns are imposed on the frame. The Frye and Morris polynomial model and also a linear spring model are used for semi-rigid connections and column bases respectively. Three design examples with various type of connections are presented. The designs obtained using AISC-LRFD code are compared to those where AISC-Allowable Stress Design (ASD) is considered. The comparisons show that the former code yields frames with less costs. Moreover, the semi-rigid connection and column base modelling is compared to rigid connection modelling.