Steel sway frames tested to collapse

The plastic collapse of a steel sway frame may take place in a mechanism containing one or more redundancies. If this does happen, a wide range of admissible bending moment distributions (i.e. satisfying both equilibrium and yield) is possible in the frame at collapse. The designer must decide which of these distributions to use in order to check the lateral (out-of-plane) stability of the columns. In 1973, Horne suggested that the frame would sway until the most favourable set of moments developed in it prior to collapse. In the present paper, tests designed to investigate this suggestion are described. The novel features of the loading rig are explained, followed by a description of the tests to failure of 18 model rectangular steel frames. The results do lend support to Horne's suggestion, a corollary of which is that designers may assume any admissible set of bending moments for the column stability check.