Cross sections optimization of plane trusses for various spans and depths
Sumayah, Abdulsalam Mustafa
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Steel trusses are widely utilized in real-world applications and a continuing motivation for research in optimal structural design exists. In civil engineering, weight optimized trusses are convenient since the easier transportation and less costly structural parts as well as construction work in connection with the build-up is simplified. One more advantage of developing a weight optimized truss is the fact that the minimum share of the load capacity is enrolled by the structure itself. Structural optimization is also very important in the aircraft and car industry whereas a much lighter structure often means a much better energy economy. Accordingly, a rich literature has advanced within the last two decades in analysis and design as well as optimization of truss. Still, only a diminutive number of researchers dealt with the problem of parameterization of the truss cross section. The optimization design of trusses needs to be carried out in accordance to two essential requirements. First the best geometrical layout for members and nodes requires being determined, and second the best adequate cross-sections need to be determined. Generally there is need to exist an optimum shape and a cross-section distribution that is definitely adapted for external loads. Many previous studies, use the areas of cross sections as a continuous design variable, although, the use of a continuous optimization procedure usually more accurate, but it will lead to non-available sizes and any trail to replace those values by the nearest available sizes can make the design unnecessarily heavier. Consequently, solution of the area will be adequate if the design procedure includes the use of cross-sectional areas as discrete design variable from available sizes, as well as if the design takes into account the effective cross section shape at the start of process. This is the topic of this paper, to study the effect of the cross section shape on the optimization of plane trusses problem. This is going to be done by using finite element method and simple linear element with the aid of steel structural analysis and design STAAD software. Four rolled steel sections (angle, tube, channel, and pipe) which are used in industrial roof trusses are applied for this purpose. Furthermore, in producing a structure element, the material properties is not the only factor considered, however, the geometry properties also is vital factor to be considered which is represented by component’s shape factor, that measures the efficiency of the material usage. Outcome results of this research prove that the chosen cross section shape has a significant effect on the optimum truss weight for exact same geometry of the truss type under the similar circumstances of loading and support. Pipe and tube section shapes offer least truss weight. The best truss shape and topology concerns with Mansard and Pratt truss topology at span over depth ratio of six.