Shape memory alloys (SMAs) are metallic materials with great potential to enhance civil engineering structures. They are often referred to as smart materials. A basic description of their highly non-linear material behaviour in terms of shape memory effect, superelasticity, martensite damping and variable stiffness is given in this aiticle. It is followed by a brief introduction to Ni-Ti and Fe-Mn-Si SMAs. Preexisting and new applications in the fields of damping, active vibration control and prestressing or posttensioning of struchues with fibres and tendons are being reviewed with regard to civil engineering. Furthermore, the relatively high costs ai1d the problem of retaining posttensioning forces when using some types of SMAs are nained. In this regard is Fe-Mn-Si-Cr discussed as potential low cost SMA. A simple model for calculating the activation times of resistive heated SMA actuators or springs is presented. The results and measured data lead to fmther constrictions. Finally, new ideas for using SMAs in civil engineering structures are proposed in this aiticle such as an improved concept for the active confinement of concrete members. This article is to introduce civil engineers to the world of shape memory alloys and invite them to contribute to their wider use in civil engineering structures.

No abstract

Shape memory alloys (SMAs), in the form of bars and strips, can be used as prestressing elements in new reinforced concrete (RC) members or for strengthening existing RC structures, owing to their special characteristic known as the shape memory effect (SME). When the SME comes into play, the material returns to its initial shape upon heating after having been deformed at ambient temperatures. If a return to the initial shape is prevented by mechanical fixation, stress develops in the SMA. A cost-effective iron-based SMA (Fe-SMA) has been developed for application in civil engineering structures. The composition of the developed alloy is Fe-17Mn-5Si-10Cr-4Ni-1(V,C) (mass%). This Fe-SMA exhibits high tensile strength, excellent shape recovery stress (prestress force), and high elastic stiffness. Moreover, its material cost is low and it is easier to manufacture than nickel-titanium (NiTi) alloys. Recently, Fe-SMA strip production has been started at an industrial scale. In this study, the experimentally determined properties of such industrially produced Fe-SMA strips are presented, and their recovery stress and recovery strain have been measured. The effects of prestraining and maximum heating temperature on the obtained recovery stress have been studied. These Fe-SMA strips can be used as external end-fixed reinforcements to strengthen RC structures.

No abstract

No abstract