The Research On Ultimate Bearing Capacity Of Large-scale Welded Hollow Spherical Joint

In recent years, as many international events were successfully held, Large-span spatial structure is quickly developed in China. And the development of large-span spatial structure is closely related to the development of joints. With a history of about 50years, welded hollow spherical joints are widely used in China, the research of which is also very well. But with the development of new structures, new problems should be studied.At present, for spherical joints whose diameter is larger than 500mm, because of the discreteness of quantity and test results, the reduction factor 0.9 should be considered in designing the bearing capacity to guarantee the safety, and tests should also be done in projects. But the illustration in the code is not very clear, though the wall-thickness of steel pipe should be increased is mentioned in the code, but how to realize it is not illustrated. And the experimental study of three rows of welded hollow spherical joints shows, the steel pipes yield to axial compressive load before the yield of hollow spheres.Using ANSYS finite element program, through the analysis of 131 joints with different parameters, the failure model and corresponding ultimate bearing capacity were obtained. And a necessary increase of wall-thickness of steel pipe which matches joints with radius of 800mm is suggested.Additionally, past tests shows, the two steel pipes nearly have no influence to each other when their distance was big enough, so the bearing capacity of the joint under biaxial loads is decided by the one axial load case, and there is still no specific analysis.Through the finite element analysis of 124 models, the bearing capacity of welded hollow spherical joints under biaxial loads was acquired. The research shows, the influence to the bearing capacity of spherical joints is obvious by changing the degree of the angle between two pipes, when the angle is small. When the angle between two pipes is smaller than 70 degree, the bearing capacity of the joint decreases linearly with the increase of the diameter of the steel pipe. When the angle is between 70 degree to 90 degree, with the increase of the diameter of the steel pipe, bearing capacity of joints is nearly changeless.