On the Strength of Columns That Fail by Twisting

A F E W of the basic considerations in twisting failure of columns are presented and illustrated without recourse to detailed mathemat ics . I t is s ta ted t h a t the Wagner theory for twisting failure applies when the cross sections rota te about any axis parallel to the column. The axis of rotat ion will then take such a position consistent with the conditions of support as will cause the critical stress to be a minimum. This general case of twisting failure is designated "pr imary failure." The theory is il lustrated with charts giving the s t rength of an angleand of a channel-section column for different locations of the axis of rotat ion. When the column is loaded above the proportional limit, effective moduli must be introduced into the equation for the critical stress. For a free column, the critical stress is given by the sum of two te rms : a bending te rm and a twisting term. When the bending term constitutes an appreciable par t of the critical stress, the principal action of twisting failure is very similar to t h a t of bending failure in an ordinary column. In such cases the allowable stress is very near, if not equal to the critical stress a t which twisting begins.