This paper presents the experimental results on the influence of the diameter-to-thickness ratio (D/t ratio) to the response and stability of circular tubes subjected to symmetrical cyclic bending. To highlight the influence of the D/t ratio to the response and stability of circular tubes under symmetrical cyclic bending, the raw tubes were slightly machined on the outside surface to obtain the desired D/t ratio. However, the magnitudes of the inside diameter were intact and the same for all tested specimens. It was observed that if a certain amount of controlled curvature is considered, specimens with smaller outside diameters have a few number of cycles to produce buckling than these with larger outside diameters. In addition, although four groups of tested specimens had four different D/t ratios, four parallel straight lines can be seen from the relationship between the controlled curvature and the number of cycles to produce buckling in log-log scale. Finally, the empirical relationship, proposed by Kyriakides and Shaw (1987), was modified so that it can be used for simulating the relationship between the controlled curvature and the number of cycles to produce buckling for circular tubes with different D/t ratios. The simulation was compared with the experimental test data. Good agreement between the experimental result and modified empirical relationship has been achieved.
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