A contribution to the optimisation of space trusses for 'flat plate' applications

摘要

Space trusses are in common use to support flat roofs, floors, exhibition platforms or temporary stages. Many structural configurations are adopted in practice. For instance, involving cubes, pyramidal or octahedral elements. The object of this study has been to make a contribution to the identification and optimisation of the most suitable morphology, since the cost will vary according to the selected member arrangement. For this purpose 11 different structural configurations for space trusses were investigated covering mass as well as cost for typical superimposed distributed loadings. The plan dimensions were restricted to square support grids, the slenderness ratios were kept to recommendations already researched by other authors. Strength, member stability and deflections were considered for medium column-free spans of up to 25 m with the sole object to establish design recommendations for the best structural solution. The costs for members, joints and the connection material were included. Ancillary costs for fire resistant treatments, corrosion protection and erection were assumed to be of similar magnitude in each case. The results appear in graphical format allowing for a given span and loading to conveniently select the cheapest design. Thus assisting the design engineer in practice to select from the beginning the best solution on a rational basis, obviating the need for an optimisation for each individual project. The associated structural analysis was undertaken with a commercially available computer program for space trusses, the detailed design follows the regulations of the German Steel Design Code, which is very similar to the equivalent European Standard. However, the results and general trends of the findings would also be valid when adopting other design codes.