Load-Carrying Capacity And Practical Calculation Method Of Welded Hollow Spherical Joints Subject To Combined Axial Force And Bending Moment

Welded hollow spherical joints are the earliest used kind of joints in our country, and are widely used for their simple structure, definiteness of load transferring and convenient connection. A great deal of experimental and theoretical studies have been made for the ultimate load-carrying capacity of the joints by many domestic and foreign researchers, and many empirical and theoretical criteria for the load-carrying capacity were proposed. However, the knowledge about the welded hollow spherical joints is generally shallow and non-overall. With the development of the utilization of the practical engineering, such limitations are gradually coming out. For instance, the welded hollow spherical joints in the polyhedron space frame structure for National Swimming Center "Water Cube" are subject to both axial forces and large bending moments. However, no provision has been provided by current design codes for welded hollow spherical joints subject to combined loading. So based on the summarization of the former work, theoretical and experimental researches are made on the ultimate load-carrying capacity of the welded hollow spherical joints subject to axial forces, bending moments and combined loading of the two kinds.Based on the elastic-perfectly plastic model and the Von-Mises yielding criterion, a finite element model for the analysis of welded hollow spherical joints is established, in which the effect of geometric nonlinearity is also taken into account. Employing the nonlinear finite element model, a great deal of parametric studies are carried out on the welded hollow spherical joints subject to axial forces, bending moments and combined loading of the two kinds. By the researches on the stresses and deformation of the joints, structural behavior and the collapse mechanism are investigated for the welded hollow spherical joints subject to various combinatorial loading. The arc-length iterative method is used to follow the loading-deformation curve of the node, and the ultimate load-carrying capacity for different types of joints subject to various combinatorial loading is obtained.Combined the simplified boundary conditions of the joints and the moment theory of elastic shell, the distributions of the internal force, displacement and the stress of the joints under axial force are derived. An example is given to validate the conformity between the theoretical and the finite element results. The maximum load-carrying capacity of the joints in the elastic stage is also obtained according to the Von-Mises yielding criterion.By the summarization of the former work and the finite element analyses in the thesis, and based on the punching shear failure model and the shear stress controlled condition, a simplified theoretical solution is also proposed in this thesis for the loading-carrying capacity of the joint under the combination of axial force and bending moment.Experiments on five typical full-scale joints are conducted to provide directly the evidence of the ultimate load-carrying capacity for the joint, and also to validate the finite element model.Finally, by summarizing the results from the simplified theoretical solution, finite element analyses and experimental study, a practical calculation method is proposed for the load-carrying capacity of the joints subject to combined loading. The results from this study can be applied for direct design use, and also provide a reference for the revision of relevant design codes.At last, as the welded hollow spherical joints in practical engineering are usually multi-directional in the space, finite element analyses are carried out for the simplest four-tube orthogonal and bidirectional joints in the thesis. Some rules are obtained for the load-carrying capacity of the bidirectional joints. The practical calculation method is modified and the expression of the modified coefficient is also proposed.