The present paper describes a series of test on slender model cantilever beams containing a set of rectangular or circular openings along the center line of the beam, in which the size and spacing of the opening were varied. The beams were subjected to tip shear loads, and results are given to illustrate the influence of the relative size of the openings on the buckling loads which were determined by a modified Southwell Plot. The experimental results have been compared with approximate theoretical values based on an equivalent beam flexural rigidity.