THE FORM-FINDING METHOD BASED ON THE FORM OF COMPOSITION OF FORCES FOR SPOKE STRUCTURE

A spoke structure with a plane shape of an ellipse with a major axis of 237m，the minor axis of 230m and 54m in depth is adopted in Shenzhen Bao’an Stadium. The form-finding of the structure is the essential problem of the design. The mechanics analysis of a spoke structure is conducted and an important conclusion is drawn that the compositions of forces of both upper and lower cables form a virtual structure in a single layer. Based on the relationship between the balanced load and the form of the virtual structure and the horizontal components of the tensions, the FEM equation to calculate the form of the virtual structure is provided. The positions of the upper nodes and the lower nodes of flying columns can be calculated according to the ratios of the horizontal components of tensions of upper cables to the lower cables. The form of the spoke structure can be determined according to the end nodes of the cable-trusses and the loads as well as the horizontal components of the tensions of the cables.
The initial strains of the cables to calculate and to tense the structure as well as the method to deal with the deformation of the boundary part of the structure are described in the paper. The form-finding of the spoke structure of Shenzhen Bao’an Stadium is calculated. The method in the paper is easy to carry out and provides accurate results. It can be performed either by the program using the FEM equation of the paper or by the commercial FEM software.