Ultimate bearing capacity of the welded hollow spherical joints in spatial reticulated structures

The bearing capacity of the welded hollow spherical joints with a diameter limit of 500 mm has been presented in the Chinese Specification for Design and Construction of Reticulated Structures (JGJ7-91). In this specification, the collapse properties of the joint under tension loads are strength collapse but those under compression loads are stability failure. The bearing capacity of the joint under tension loads is related to the tension strength of the material, but that of the joint under compression loads is only related to the geometry of the joints, not the compression strength of the material. In this paper, the ultimate bearing capacity was calculated using three-dimensional degenerated curved shell elements. The tangent stiffness matrix and the elasto-plastic matrix of Dep were derived in detail. Based on the numerical analysis of the experimental data for the six tension joints and six compression joints using the multi-linear isotropic hardening model and Von-Mises yield criterion, the strength collapse criterion and ultimate criterion were put forward. The load-displacement curve under axial force was traced using sub-incremental cylindrical arc-length technology. The collapse was a strength problem under the axial tension load, but it was an elasto-plastic buckling collapse under the axial compression load. Both of them were related to the design strength of the material. The tension bearing capacity and the compression bearing capacity were different and generally the compression bearing capacity is much smaller than the tension bearing capacity. The formulas for the bearing capacity of the welded hollow balls were obtained on the basis of the regression of 64 different calculated data and the diameter limit has been developed to 900 mm. These two formulas were more accurate and valuable than the old ones and they were more useful to the engineers.