Load-carrying capacity and practical calculation method of welded hollow spherical joints connected with square steel tubes

New polyhedron space frame structure is adopted in the National Swimming Center "Water Cube".Circular hollow sections,square hollow sections and rectangular hollow sections are employed as structural members,while welded hollow spherical joints are employed to connect the members.This paper investigates the structural behavior and load-carrying capacity of welded hollow spherical joints connected with square steel tubes and subjected to axial forces, bending moments and combined loading of the two.Based on the elastic-perfectly plastic model and the Mises yield criterion,a finite element model for the analysis of these joints is established,in which the effect of geometric nonlinearity is taken into account.A major parametric study was then carried out employing this model.It is shown that when the welded spherical joint is subjected to combined axial forces and bending moments,the axial force-bending moment correlation is independent from their geometric parameters,such as the diameter and the wall thickness of the spherical joint,and the side length of the steel tube.Experiments on four typical full-scale joints were conducted to understand directly the structural behavior and the collapse mechanism of the joint,and also to validate the finite element model.A simplified theoretical solution is also derived for the loading-carrying capacity of the joint based on the punching shear failure model,and the basic form for the design equation is obtained.Finally,by utilizing the results from the simplified theoretical solution,finite element analysis and experimental study,