The paper describes a design method for structures consisting of a heavily loaded masonry wall supported by a steel beam, taking account of the composite tied-arch behaviour of the wall and beam. The design approach is based on the assumption of triangular distributions of vertical stress at the wall–beam interface, the length of the distributions being a function of the beam-to-wall relative stiffness. In the design method the beam flexural stiffness is calculated to give an adequate distribution of the interface stress so that the maximum stress in the wall does not exceed allowable limits. The beam is also designed with flexural and shear strengths sufficient to resist the bending moment, tie force, and shear forees applied by the normal and shear interface loadings. Experimental evidence is cited to support the assumptions and the resulting design method.