Recovery and residual stress of SMA wires and applications for concrete structures

Abstract

In general, NiTi shape memory alloys are used for applications in civil structures. NiTiSMAs show good superelasticity and shape memory effect properties. However, forapplication of the shape memory effect, it is desirable for SMAs to show a widetemperature hysteresis, especially for civil structures which are exposed to severeenvironmental conditions. NiTiNb SMAs, in general, show a wider temperature hysteresisthan NiTi SMAs and are more applicable for civil structures. This study examines thetemperature hysteresis of NiTiNb and NiTi SMAs, and their recovery and residual stressare investigated. In addition, the tensile behaviors of SMA wires under residual stress areevaluated. This study explains the possible applications for concrete structureswith the shape memory effect and illustrates two experimental results of concretecylinders and reinforced concrete columns. For both tests, SMA wires of NiTiNb andNiTi are used to confine concrete using residual stress. The SMA wire jackets onthe concrete cylinders increase the peak strength and the ductility compared tothe plain concrete cylinders. In addition, the SMA wire jackets on reinforcedconcrete columns increase the ductility greatly without flexural strength degradation.