Optimization of large steel truss structures using standard cross sections

A multi-constraint optimality criteria discrete optimization algorithm is presented for minimum weight design of large steel truss structures subjected to stress, displacement, and buckling constraints. The structures are subjected to actual constraints of AISC Allowable Stress Design (ASD) and Load Resistance Factor Design (LRFD) specifications. A design linking strategy is used to reduce the number of design variables. An efficient integer mapping strategy is presented for mapping the computed cross-sectional areas to the available standard wide flange (W) shapes. The algorithm has been applied to minimum weight design of two structures: a 52-story structure with 848 members and an 80-story structure with 5860 members. This research also sheds some light on the comparison of the AISC ASD and LRFD specifications. For the examples presented, designs based on the LRFD specifications resulted in weight savings of 5 to 9 percent.