Lateral reinforcement of welded SMA rings for reinforced concrete columns

Abstract

This study conducts a series of compressive tests of concrete cylinders confined by shape-memory alloy (SMA) rings to provide lateral confinement for reinforced concrete columns. Ni50Ti41Nb9 (at. %) SMA bars with a diameter of 3 mm and a length of 446 mm were prepared and strained to 7% before welding. Three of the six confined cylinders were heated to 200 ◦ C to introduce recovery stress in the SMA rings, which was predicted to provide active confinement of concrete. The behavior of two welded bars with a resulting diameter of 6 mm were tested and compared with that of the continuous SMA bars without welding. The continuous SMA bars showed the typical behavior of martensitic SMAs, such as an elastic range, a transformed state, and hardening behavior due to austenite. However, the welded bars were fractured at the welding point at or just after elastic range. The concrete cylinders confined by the SMA rings showed greater peak strength and larger failure strain compared to the plain concrete cylinders. However, the stress-strain curves of the confined cylinders showed stepping behavior due to the sequential fracturing of the SMA rings. The heated SMA ring cylinders did not show greater peak strength than the unheated SMA ring cylinders, indicating that active confining was not effective. © 2012 Elsevier B.V. All rights reserved.