This work presents the experimental assessment of the joint behaviour of five steel beam-to-column end-plate joint configurations to assess (i) the effect of minor axis end plate joints in the behaviour of major axis end plate joints, and (ii) the interaction of two minor axis end plate joints. The experimental tests were performed with true size cruciform sub-frames specimens with boundary conditions intended to simulate unbraced frames. The sub-fames, with one to three beams, were loaded introducing multiple 3D stress states in the column unstiffened web, causing an interaction between the mechanical behaviour of two or three major and minor axis joints. The interactions were assessed in terms of the moment-rotation relations of joints, connections and column web. It was found that, for the slenderness of the column web tested, (i) the minor-axis joints have only a relevant influence on the stiffnesses of the major-axis joints and (ii) that, when two minor axis joints are present, their mutual interation increases both their stiffness and strength.