Optimum design of plane steel frame structures using second-order inelastic analysis and a genetic algorithm

A genetic algorithm (GA)-based optimum design algorithm and a program incorporated with the refined plastic hinge analysis method, one of the second-order inelastic analysis methods, are presented. In the refined plastic hinge analysis method, geometric nonlinearity is considered by using the stability functions of beam-column members, and the material nonlinearity is considered by using the gradual stiffness degradation model that includes the effects of residual stresses, moment redistributions by the occurrence of plastic hinges, and geometric imperfections of members. In the genetic algorithm, the tournament selection method and micro-GAs are employed. The fitness function for the genetic algorithm is expressed as an unconstrained function composed of objective and penalty functions. The objective and penalty functions are expressed, respectively, as the weight of steel frames and the constraint functions accounting for the requirements of load-carrying capacity, serviceability, ductility, and constructability. To verify the appropriateness of the proposed method, the optimum design results of several plane steel frames obtained by the present study incorporating the refined plastic hinge analysis method are compared with those by others incorporating the AISC-LRFD elastic, geometric nonlinear, and plastic zone analysis methods.