Compressive performance of welded hollow spherical joints with external triangular ribs

This study addresses the axial compressive performance of welded hollow spherical (WHS) joints with external triangular ribs. External triangular ribs are able to postpone the local buckling of the joint during axial loading, and thus strengthen the compressive capacity of it. A simplified analytical model is proposed to elucidate the stress distribution on the hollow sphere of axial-loaded WHS joints with external triangular ribs. Then a simplified solution for the yield strength of axial-loaded WHS joints is deduced based on the elastic thin shell theory. The simplified solution indicates that the yield strength of WHS joints with external triangular ribs can be expressed by a coefficient related to the specifications of the ribs and the joints multiply by that of WHS joints without external ribs. Compression tests on 6 full-scale specimens of WHS joints with varied configurations of triangular ribs are conducted. It shows that the failure mode and the strength enhancement of the specimens vary as the specification of the triangular ribs change, and the triangular ribs enhance the strength of the joints up to 77 %. A refined FE model is established and calibrated against the findings from the experiments. Parametric studies on the design parameters which may affect the compressive response of the WHS joints with triangular ribs are fully investigated. It is shown that the compressive yield strength of the joint rises with the increase of the number, height and thickness of the triangular ribs, and decreases with the increase of the angle-of-elevation of the triangular ribs. It is also shown that the effect of the ratio of the diameter of the sphere to that of the steel tube on the compressive yield strength of the joint is much lighter than the others, and deemed as negligible. Regression analysis on the experimental and numerical data is carried out to obtain a practical formula for the compressive capacity of WHS joints with external triangular ribs. This formula is incorporated with the previously developed formula for the compressive capacity of WHS joints with external trapezoidal ribs, to form a general formula applicable for WHS joints with either external triangular ribs or external trapezoidal ribs.