Description
Shape-memory alloys (SMAs) have attracted considerable interest in structural engineering because of their ability to ‘memorise’ their original form when subjected to thermomechanical variations, a phenomenon termed the shape memory effect. By controlling the heating and cooling (activation) of SMAs under constrained deformation, recovery stresses can be generated, making SMAs suitable for use as prestressing reinforcement in concrete structures. However, recent studies suggest that the benefits of reinforcing with iron-based SMA (Fe-SMA) could be considerably reduced under semi-cyclic loading, due to the decrease on recovery stresses.
This paper focuses on analysing the behaviour of 16 mm diameter Fe-SMA reinforcing bars when subjected to consecutive activations and semi-cyclic tensile tests. Activations at different temperatures (160, 200 and 250 oC) were performed, followed by semi-cyclic load tests until high strain levels were carried out. The results show a correlation between the temperature reached during the activation and the recovery stress achieved. Furthermore, the data reveals that high strain levels induced by semi-cyclic loads can lead to a complete loss of the initially generated recovery stresses. However, by re-activating the Fe-SMA samples, it is possible to restore a similar level of the initial recovery stresses. Moreover, for practical structural engineering applications in RC beams, where strain increments might be modest, only partial stress losses would be produced. These partial losses could be treated, for designing, as a prestressing loss.
