Determination of Desirable Lengths of Z- and Channel-section Columns for Local-instability Tests

George J. Heimerl · J. Albert Roy

Jan 1944 · National Advisory Committee for Aeronautics

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Summary: Local-instability tests of 24S-T aluminum-alloy formed Z- and channel-section columns were made in order to determine a length of test specimen that would avoid the increased strength associated with short lengths and also permit the occurrence of a convenient buckling pattern. The effect of column length on the critical compressive stress, on the average stress at maximum load, and on the number of half-waves of the buckling pattern is shown. A buckling pattern of three half-waves is indicated as desirable for test purposes. A curve is presented from which may be determined the lengths of Z- or channel-section columns that give a buckling pattern of three half-waves. When the strength for local instability is very high, a reduction in the length indicated by the curve may be necessary to prevent column failure. In order to avoid the increased strength associated with short lengths, a ratio of length to web width above 3.5 should be used.