DISCRETE SIZING OF TRUSSES FOR OPTIMAL GEOMETRY

The optimal configuration and discrete member sizes are automatically determined to minimize the cost of three-dimensional indeterminate truss structures under multiple loading conditions. Member areas and joint coordinates are used as design variables. Design constraints include Euler buckling and specified limits on member stresses, member sizes, and joint displacements. Design variables may be linked and members can be deleted. The design process is separated into geometry modifications using the complex method and suboptimization using the stress ratio method and an analogous scaling procedure for displacement constraints. For each geometry change, discrete member sizes are selected from a table of allowable values. The method is applied to the cost minimization of a 25-member space truss using discrete steel angle sections that are chosen from a table satisfying AISC code requirements, and comparisons are made with minimum weight designs and with continuous variable methods.