Bending performance of planar DK-shaped diaphragm welded joints

The planar DK-shaped diaphragm welded joint possesses advantages such as avoiding weld overlap, reducing eccentric loads, and offering flexible connections. It is applied in the novel star-type floating photovoltaic system composed of pipes. Given the primary exposure to bending moment loads, it is necessary to investigate the bending capacity and reinforcement methods of planar DK-shaped diaphragm welded joints. Six specimens were designed and fabricated based on a scale ratio of 1:4 for experimental testing. Subsequently, the mechanical properties of the specimens, including failure modes, deformations, bearing capacities, and stress distributions, were obtained. The experimental results indicate that the failure modes and force transfer mechanisms of the unreinforced DK-shaped diaphragm welded joints vary under different bending moment load directions. This explains the differences in bearing capacity, stiffness, and ductility observed in the joints when subjected to out-of-plane and in-plane bending loads. Ring stiffeners and crossed stiffeners can enhance the bending bearing capacity and initial bending stiffness of the joints. Finite element models have been established to investigate the influence of geometric parameters, such as the diameter of the chord, the ratio of the section radius to wall thickness of the chord, and the ratio of the diaphragm thickness to the chord wall thickness, on the mechanical performance of the joints. A mechanical model for the planar DK-shaped diaphragm welded joint has been established, and a design formula for bending bearing capacity has been derived. The comparison between the experimental and numerical results shows that the established mechanical model meets the accuracy requirements.