Influence of Bolt Ball Joints on Buckling Eigenvalues of Steel Tubular Members

A finite element model for the combined component of bolted spherical nodes and steel pipe members was established with ANSYS software, and contact simulation method was utilized to calculate the buckling characteristic values of the bolted spherical steel pipe component. The effects of factors such as bolt radius, sleeve wall thickness, cover plate thickness, bolt head radius and sleeve length on the buckling characteristic values of members with different slenderness ratios were parametrically studied. Based on the Euler formula for member buckling, a formula for calculating the buckling characteristic values of bolted ball joints and steel pipe composite components considering the influence of node parameters and member slenderness ratio was obtained through regression analysis. The results show that the buckling characteristic value of the component increases significantly with the increase of bolt radius and sleeve wall thickness, while the influence of bolt head radius can be ignored. The increase in closure plate thickness and the decrease in sleeve length can also increase the buckling characteristic value of the component, but their influence is small. With the increase of the slenderness ratio of the rod, the influence of the above factors gradually decreases, and the constraint of the bolt ball node on the rod becomes stronger as the slenderness ratio of the rod increases. In addition, the calculated values of the buckling characteristic value formula for composite components obtained through regression analysis are close to the finite element results, and the trend of change with the node parameters and slenderness ratio of the rod is consistent, which can accurately calculate the buckling characteristic value.