Design of non-linear steel frames for stress and displacement constraints with semi-rigid connections via genetic optimization

A genetic-algorithm-based optimum design method is presented for non-linear steel frames with semi-rigid connections and column bases. 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 the optimization method, which utilizes reproduction, crossover and mutation operators. Displacement and stress constraints of AISC Allowable Stress Design (ASD) specification and size constraints for beams and columns are imposed on the frame. The algorithm requires a large number of non-linear analyses of frames. The analyses cover both the non-linear behavior of beam-to-column connection and P-Δ effects of beam-column members. The Frye and Morris polynomial model is used for modeling semi-rigid connections. Two design examples with various types of connections are presented to demonstrate the application of the algorithm. The semi-rigid connection and column base modeling results in more economical solutions than rigid connection modeling, but increases the sway of frames.