Finite Element Analysis Of Welded Spherical Joint's Stiffness

Welded hollow spherical joints have been extensively used as a node pattern in spatial structures in recent years. They have some excellences which contain simple structure, definiteness of load transferring and convenient connection. The research about this node pattern is major in elastic extent. But the joints stiffness which is an important factor influencing the lattice structure is rarely involved. This thesis makes further finite element calculation and analysis on welded spherical joint's stiffness based on past research results, then some reasonable calculation formulas and corresponding suggestions on their design were given.As for the welded hollow spherical joints subject to single-direction load, this paper chooses many different kinds of models which diameter are larger than 400mm to calculate by using the elastic-plastic shell element. Then the comparatively ideal formulas about the axial flexibility and flexural stiffness are given. It provides reference data for correlatively analysis in joints stiffness.This paper also calculates axial flexibility and flexural stiffness of different rib stiffeners. Compared with the non-rib hollow spherical joints' stiffness, then the methods of calculation about the axial flexibility and flexural stiffness under different rib stiffeners styles are given. Meanwhile some suggestions have been brought forward about it during practical applications. In practical projects, joints are usually subject to bi-directional and even multi-directional forces. Finite element analyses are carried out for the simplest four-tube orthogonal and bi-directional joints in the thesis. We catch some rule conclusion about the change of the stiffness and make some illuminates combine the real situations by investigating one axial joint's stiffness influence from the other.At last, based on the multilinear isotropic hardening plastic model and the Von-Mises yielding criterion, a finite element model for the analysis of welded hollow spherical joints is established, in which the effect of geometric nonlinearity is also taken into account. Through making nonlinear analysis on model's suffer axial compression and bending by using Arc-length method and Newton-rapshon method respectively. Compare the data of past experiments to make sure the calculation methods of this thesis is effective. It also provides some valuable reference data for the research on considering the joints' stiffness at phase of elastic-plasticity.