A plastic failure model that is based on the yield line theory of plates is developed to provide a means for predicting the plastic strength of double chord RHS K-joints with separated chords. The model accounts for both localized bending of the chord face and shearing of its inner and outer walls in the gap between the mated diagonals.The results of a series of 24 tests conducted on RHS twin shear beams are reported. Predictions of joint strength were compared with experimental results and were found to be generally in good agreement for both the RHS twin shear beams and isolated K-joint specimens of square hollow section from previous work. A study on the effect that varying the geometrical properties of the joint has on its strength is also presented. Key words: experiments, K-joints, mechanism, plastic analysis, rectangular hollow sections, steel, yield lines.