During the last fifty years much experimental and theoretical work has been carried out on the subject of the failure of struts, i.e., rods under axial compression. Most of this work has been devoted to the case of struts pin-jointed at both ends and only a small part examined the behaviour of rigidly encastred struts. From these investigations we know that in case of very slender struts the critical load for rigid encastrement is the fourfold of that for pin-jointed ends. This difference becomes less with decreasing slenderness of the strut, but even for slenderness ratios usually attained in aircraft framework it is considerable, if high tensile steel is used. In actual framework, compression members being more or less rigidly joined to nodes which may twist elastically, they represent a case between both forementioned extremes and may best be regarded as elastically encastred. Since according to above statements the load which may be sustained by a strut obviously depends a great deal upon end constraint, it is of great importance for design purposes to determine exactly the effect of elastic encastrement.