Post-Buckling of Redundant I-Beams

It is shown that while redundant I-beams have similar potential post-buckling reserves of strength to those possessed by redundant rectangular beams, their decreased section slendernesses require great post-buckling deformations to take place before these reserves of strength can be realized. It is concluded that redundant I-beams are less likely to achieve their potential post-buckling strengths than narrow rectangular beams because of premature yielding, and that the elastic post-buckling behavior of steel I-beams will rarely be important, except when the member and section slendernesses and the yield strength are high and large deformations are acceptable. The reliability of Southwell Plot methods of predicting the experimental critical loads of redundant I-beams is investigated and the methods are shown to be adequate provided that the deflections are only small to moderate.