Cyclic Inelastic Buckling of Thin Tubular Columns

Experimental results are described on cyclic inelastic buckling of one-sixth scale thin tubular steel columns typical of braces employed in fixed offshore platforms. Six 4-in.(102-mm) diam tubes were tested. Tube diameter to wall thickness (D/t) and slenderness ratios considered are typical of those used in practice. The D/t ratio was 33 for three specimens and 48 for the other three. In each group of three, two had pinned ends and one had fixed ends. All specimens were annealed, except for one of the pin-ended specimens in each group that was tested in the as received condition. Hysteretic loops for the applied axial force versus axial deformation, as well as versus the maximum lateral deflection, are presented and interpreted. Based on these data, suggestions are made for analytic (computer) representations of such loops for use in seismic response analyses of braced offshore towers.