Analysis Of Cable-Strut Structure Redundancy And Its Characteristic

Generally, Cable-strut System is a kind of structure constituted by tensional cables and struts, which can be classified to Pin-jointed Bar Structure System consisting of only struts, Cable-net Structure consisting of only tensional cables, and Cable-Strut Tensile Structure System consisting of both tensional cables and struts. For this system the nodes are pin-connected. Only axial force can be transferred and external forces can only be applied on nodes, therefore elements bear only compressive or tensile force. Hook's Law should be satisfied. For pin-jointed bar structure, stiffness comes from geometric constitution and material strength, which is classified to rigid structure. The stiffness of rigid structure is therefore called elastic stiffness. Apart from traditional rigid structure, the main source of stiffness for flexible tensile structure is prestressed. As a result, the stiffness of tensile structure can be divided to elastic stiffness and geometric stiffness, and prestress condition mainly influences the latter.The analysis of structure geometric stability is an important problem in the field of structure system analysis, which has not been perfectly solved so far. With the coming forth of innovative structure systems, it is very necessary to find new theory and method. In this paper, redundancy as well as characteristic of pin-jointed bar structures, cable-net structures and cable-strut tensile structures was investigated. Conceptions of elastic redundancy and geometric redundancy were introduced, and structure system is analyzed using its redundancy.First, the definition of redundancy of pin-jointed bar structure system was presented. Formulation of elastic redundancy for pin-jointed bar structures was deduced based on the potential energy equation mathematically, and the conception of redundancy and its physical significance were interpreted. Then this formulation was achieved by MATLAB programming. After that, two-degree and three-degree static-indeterminate plane truss, as well as octahedron special unit were investigated with the consideration of redundancy.Based on the former derivation, the elastic redundancy for cable-net structure was derived, which was also achieved by MATLAB programming. However, the geometric redundancy was calculated by Easy 9.2. Redundancy values of different kinds of cable-net structure were calculated and analyzed, and the features demonstrated by elastic redundancy and geometric redundancy were discussed.Finally, numerical examples of tensegrity structure and cable domes structure were carried out to analyze the redundancy of cable-strut tensile structure and its feature demonstrated by elastic redundancy and geometric redundancy.