OPTIMUM LOAD AND RESISTANCE FACTOR DESIGN OF STEEL SPACE-FRAME STRUCTURES

Minimum weight design of steel moment-resisting space frame structures with or without bracing subjected to the American Institute of Steel Construction (AISC) Load and Resistance Factor Design (LRFD) specifica tion is presented. The LRFD constraints for moment-resisting frames ar e highly nonlinear and implicit functions of design variables (cross-s ectional areas). The structure is subjected to wind loading according to the Uniform Building Code (UBC) in addition to the vertical loads d ue to dead and live loads. A scaling procedure is developed that resul ts in fast convergence. The algorithm is applied to minimum weight des ign of four large high-rise steel building structures ranging in heigh t from 20 to 81 stories and in size from 1,920 to 9,245 members. A com parison of designs of space moment-resisting frames based on the AISC LRFD code with those based on the AISC Allowable Stress Design (ASD) c ode shows the former results in a lighter structure for the examples p resented.