This paper proposed a novel form-finding method for irregular tensegrity structures base on matrix iteration. On the basis of two different forms of structural equilibrium equations, the estimated elemental self-stresses and nodal coordinates were constructed via the singular value decomposition of equilibrium matrix and eigenvalue decomposition of force density matrix, respectively. The configuration of tensegrity that satisfies the specified coordinates was determined through the iterative computation of self-stresses and nodal coordinates, and the constraint condition was introduced in the construction of the estimated nodal coordinates simultaneously. The detailed algorithm procedure was listed and the convergent criterion was also defined. In the end, several illustrated examples were given to prove the validity of the algorithm. Numerical examples and physical models showed that the proposed form-finding method was correct and efficient. The form-finding algorithm could be applied to find tensegrity structures that satisfied the given geometrical forms, and the creation of novel irregular tensegrity, as long as the topological relation and several known coordinate of nodes were given. Keywords: Irregular tensegrity, Form-finding, Equilibrium matrix, Force density matrix, Numerical method DOI: 10.18057/IJASC.2015.11.4.7
INTRODUCTIONTensegrity, a kind of self-balancing system where the cables are in continuous tensional status and a few of struts are located among the cables, is light-weight but efficient, in that they could be stiffened by specified inner prestressing. Tensegrity structures have been already applied to several research fields [1,2], such as mechanical control, aerospace, biology, etc.. In addition, an alternative form of tensegrity, i.e. cable dome, has been widely used in the large span structures in contemporary architecture.As a sort of form-sensitive structure, the superior mechanical property of tensegrity comes from its reasonable geometrical configuration. The topology, geometry and the prestressing both affect its stability and stiffness. Hence, form finding is the core of tensegrity researches [3]. The form-finding algorithms were divided into two categories by Tibert and Pellegrino [4], respectively static method and dynamic method, ranging from analytic method to force density method proposed by Schek and Linkwitz, and to dynamic relaxation method introduced earlier by Motro and Belkacem. These early form-finding algorithm gave more prominence to the research of reasonable topological relations. Accordingly, the form-finding results were mainly regular tensegrity structures, attaching little emphasis upon geometrical configuration. In recent decades, with the increasingly deeper researches, relevant scholars have made some improvements based on the classic algorithms and created several novel form-finding algorithms [5][6][7][8][9]. The irregular tensegrity and its geometrical configuration have achieved attention gradually. Meanwhile, the evolution theory began to be i...