Pilot Study of Behavior of Concrete Beams Reinforced with Shape Memory Alloys

This paper discusses the superelastic behavior of shape memory alloy, Nitinol $\left(\mathrm{NiTi}\right)$ , when used as reinforcement in concrete beams. The ability of $\mathrm{NiTi}$ to recover and reduce permanent deformations of concrete beams was investigated. Small-scale concrete beams, with $\mathrm{NiTi}$ reinforcement were tested under half-cycle loads. The reinforcement ratio varied from 0.1 to about 0.9%. The experimental results showed that the average residual displacement in the $\mathrm{NiTi}$ reinforced beams was less than one-fifth of that of the steel reinforced test beams. The stiffness of $\mathrm{NiTi}$ reinforced test beams however was lower than those of the steel reinforced test beams. An analytical study of load–deflection relationship for a series of hybrid beams was undertaken. It was found that a hybrid system that incorporated $\mathrm{NiTi}$ combined with high strength steel or carbon fiber reinforced plastic bars was a better choice for design because of their relatively high stiffness.