Self-centering capacity of RC columns with smart plastic hinges of martensitic NiTi SMA bars

The objective of this study was to examine the self-centering capacity of reinforced concrete (RC) columns with martensitic shape memory alloy (SMA) bars in the plastic hinge region. To achieve this, three RC columns were prepared: one was conventional and the other two had SMA bars in the plastic hinge zone. The columns had a diameter of 400 mm, height of 1400 mm, and aspect ratio of 3.5. The 400 mm long SMA bars were connected to the steel rebars using specially devised couplers. A cyclic lateral load was applied at the top of the columns, and the lateral displacements along the height of the columns and the corresponding forces were measured during cyclic lateral loading. The strain in the SMA bars was also measured. The RC column with SMA bars exhibited a plastic hinge around the couplers, thus concrete damage from cracking was concentrated at this site. This was completely different from the failure mode of the conventional RC column. The SMA bars in the column were in an elastic state, whereas the steel rebars yielded inside the couplers. The RC column with SMA bars exhibited excellent self-centering capacity, and its displacement recovery ratio was approximately 95% at a drift of 5%. However, its energy-dissipation capacity was lower than that of the conventional RC column. The equivalent damping ratio of the RC column with SMA bars was approximately 3% after 1.75% drift. It is conjectured that the excellent self-centering of the RC column with SMA bars was caused by the elastic behavior of the martensitic SMA bars.