Experimental test setup design for ultimate limit state evaluation of ductile wrapped composite KK‐joints

Complex circular hollow section double KK‐joints are widely used in, e.g. offshore wind turbine jackets. As an alternative to conventional welded joints of the CHS multi‐membered structures, wrapped composite joints have shown superior structural performance in previous pilot tests. Experimentally characterizing the joint behaviour under uniplanar loading can be complicated, because of the ductile failure mechanisms of wrapped composite joints and second‐order bending moments. This paper presents the design of a test frame in combination with a conventional tensile 2.5 MN test rig. Ductile joint failure, joint imperfections and second‐order effects are considered in the design. Structural finite element software SOFiSTiK is used to analyse the effects of wrapped joint behaviour and imperfections on the test system and interaction of joint, frame and loading rig behaviours. Non‐linear joint behaviour and misalignments of the braces increased the second‐order effects significantly. Mitigation strategies have been explored to reduce additional bending moments in the KK‐joint. A complete test setup is proposed to perform static experiments on double KK‐joints in uniplanar axial loading conditions.