Mechanical behavior of welded hollow spherical joints with diameter exceeding 1.0 m

Abstract

The welded hollow spherical joint (WHSJ) with diameter greater than 1.0 m is commonly employed in long-span tubular transmission towers. It has a relatively higher ratio of diameter to thickness compared to traditional spherical joints, since the larger thickness leads to difficulties in fabricating a spherical joint with a diameter of more than 1.0 meter, and will also lead to deterioration of mechanical properties of materials. Therefore, longitudinal and transverse stiffeners are usually set inside to avoid local buckling and improve bearing capacity. In this study, experimental tests and finite element (FE) analyses of full-scale WHSJs with a diameter of 1400 mm under the multi-axial load are conducted. The results indicate that all specimens have similar failure modes, namely the indentation of the hollow sphere near the main tube, and the failure of the longitudinal stiffeners at the same position. In addition, the setup of longitudinal stiffeners would obviously improve the ultimate bearing capacity (UBC) of WHSJ. After the validity of the FE model is verified, the parametric study is carried out. The results indicate that the UBC of stiffened WHSJ can be approximated by the sum of the resistances of the corresponding unstiffened WHSJ and the stiffeners. Accordingly, design equations are proposed for stiffened WHSJs with diameter greater than 1.0 m. The results obtained by proposed equations are compared with that obtained by tests and FE analyses. They are basically in good agreement, which shows the validity of the equations.