Cost Optimization of Structural Roof System

The development of a procedure for the optimum design of a roof system to yield minimum cost is reported herein. The roof system is composed of parallel chord, steel trusses, with purlins and decking. The variables considered are geometry, topology, and member size. The optimal values of the geometry and topology variables are determined by the application of Box's complex method. A fully stressed design criterion is employed in selecting the member sizes. Many calculations have shown convergence to a low cost region, although not necessarily to a global optimum. A cost model is developed that includes member-related costs and weight-related costs. Parameter studies demonstrate the importance of selecting the proper ratios of fixed and weight-related costs.