Fatigue tests and design of welded hollow spherical joints in grid structures

Grid structures with welded hollow spherical (WHS) joints have been increasingly used in industrial buildings with suspension cranes. WHS joints are particularly prone to fatigue failure due to the cyclic loading from the crane. This paper investigated the fatigue behavior of WHS joints under cyclic axial loading. The constant-amplitude fatigue tests of full-scale WHS joints were carried out. Effective data of the weld toe in the sphere of the WHS joints were obtained and fitted to the corresponding S-N curve with the stress range as a parameter, and the test results were compared with other similar S-N curves. Then, the stress distribution and the fatigue failure location of WHS joints under tension were discussed using the finite element analysis. The fatigue failure mechanism was investigated through microscopic analysis. Finally, based on the obtained S-N curve, the fatigue design method was established for the weld toe in the sphere of WHS joints.