Theoretical Research On Tensegrity Torus And Load-Carrying Capacity And Practical Calculation Method For Welded Hollow Spherical Joints Subject To Planar Tri-Directional Combined Loading Of Axial Forces And Bending Moments

The work of this thesis includes two parts. One is about theoretical research on tensegrity torus, and the other is about load-carrying capacity and practical calculation method for welded hollow spherical joints subject to planar tri-directional combined loading of axial forces and bending moments. These two parts will be introduced respectively as follows.Tensegrity structures are a class of truss structures consisting of a continuous set of cables (tension members) and a discrete set of bars (compression members). The word tensegrity is a contraction of tensile and integrity, firstly conceived by Fuller. With Snelson's work in 1948, much research work on different types of tensegrity modules and systems has been carried out during the past 60 years. Cylindrical and spherical tensegrity modules are two basic modules extensively studied by now. In Nishimura and Sultan's work, detailed research on various cylindrical and spherical tensegrity modules was carried out and analytical solutions for form-finding were derived.However, as another kind of basic geometric modules, tensegrity torus modules received little attention from scholars and engineers. This thesis presents a kind of tensegrity torus with a new topology.First, this thesis presents a detailed study on topology and form-finding method of the new kind of tensegrity torus. And a general form-finding procedure of tensegrity torus is developed and a close-formed solution is derived for a simple tensegrity torus. Then, static and dynamic behaviors of tensegrity torus are preliminarily studied. Furthermore, a new cable dome with a tensegrity torus as its ring beam is proposed. And the form-finding method and structural behaviors of the new dome are investigated. Based on the topology of tensegrity torus, several new kinds of tensegrity structures are finally proposed, such as a new kind of cyclic right-cylindrical tensegrity with a new topology, tensegrity arch, and tensegrity shell.Welded hollow spherical joints have been extensively used in latticed spatial structures. In practical single-layer lattice shells, welded hollow spherical joints always bear planar tri-directional combined loading of axial forces and bending moments. With the development of science and technology in engineering, some novel spatial structures are developed, such as Chinese National Swimming Center 'Water Cube', in which members bear large axial forces and bending moments at the same time. It brings new research topics and challenges in the design of welded hollow joints.Theoretical and experimental researches on load-carrying capacity of welded hollow joints subject to unidirectional axial loads or unidirectional combined loading of axial forces and bending moments have been carried out for many years. However the load-carrying capacity and practical calculation method for welded hollow spherical joints subject to planar tri-directional combined loading of axial forces and bending moments are little involved.Based on the fact that in practical single-layer lattice shells welded hollow spherical joints always bear planar tri-directional axial forces or planar tri-directional combined loading of axial forces and bending moments, finite element analyzes of welded hollow spherical joints are carried out by adopting the hexahedral solid element SOLID45 with eight nodes, the elastic-perfectly plastic stress-strain curve and the Von-Mises yield criterion. The effect of geometric nonlinearity is also taken into account. By summarizing the results of a great amount of finite element analyses, a practical calculation method is proposed for the load-carrying capacity of the joints. The results from the study can be applied for direct design use, and also provide a reference for the revision of relevant design codes.