Abstract: Nonlinear finite element analysis was used in the ultimate bearing capacity on planar XX-joints by ANSYS software. The stress distributions of the joints were demonstrated, the main failure modes of the joints were determined, and the influences of some fundamental geometric parameters on the ultimate strength were the research points. The results show β (diameter ratio of the branch to the chord), θ (axial angle of the chord and the branch), γ (the ratio of the diameter of the chord to the thickness of the walls of the chord) are the main factors of the bearing capacity on planar XX-joints; the failure modes mostly belong to plastic failure of the walls of the chord; the computational formula of the bearing capacity on planar XX-joints is multiplied by a correction parameter based on the design formula of the bearing capacity on K-joints.

Key words: planar XX-joints, the ultimate bearing capacity, finite element analysis, geometric parameters