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Graphical Abstract:

The present study deals with crush tests of concrete cylinders confined by shape memory alloy (SMA) wires. Two cases were considered. First, an active confinement was achieved by wrapping a wire previously prestrained in martensitic state and then subjected to the memory effect. Second, a passive confinement was obtained by using the same SMA, but in austenite state. For comparison purpose, an unconfined cylinder was also tested. The influence of the unwrapped zones of the confined cylinders was also investigated, leading to the use of a specially designed device to avoid premature failure in these zones. The comparison between active and passive confinements was investigated. The test results show that stiffness, strength and ductility are significantly improved in the case of the active confinement.

The present study deals with crush tests of concrete cylinders confined by shape memory alloy (SMA) wires. Two cases were considered. First, an active confinement was achieved by wrapping a wire previously prestrained in martensitic state and then subjected to the memory effect. Second, a passive confinement was obtained by using the same SMA, but in austenite state. For comparison purpose, an unconfined cylinder was also tested. The influence of the unwrapped zones of the confined cylinders was also investigated, leading to the use of a specially designed device to avoid premature failure in these zones. The comparison between active and passive confinements was investigated. The test results show that stiffness, strength and ductility are significantly improved in the case of the active confinement.

The present study deals with the creation of so‐called “recovery stresses” in SMA wires. Two approaches are developed. First, experiments are performed on nickel‐titanium wires with suitable transformation temperatures. The wires are stretched in the martensite state at ambient temperature. A thermal cycle at constant strain is applied to transform the martensite to austenite, in order to activate the shape memory effect. During the thermal loading, both the phase transformation and the thermal expansion lead to stresses in the wires. Second, a thermomechanical model is used to analyze the experimental results. The model accounts for the phase transformations caused by combinations of stress and temperature loadings. The results are then discussed in the framework of application to concrete component reinforcement.

The memory effect of shape-memory alloys (SMAs) has opened interesting perspectives to create prestress states in concrete elements. However, the procedure has not been yet fully resolved due to the complex thermomechanical behavior of these alloys, in addition to the practical difficulties of mechanical coupling between SMA and concrete elements. The present study deals with tests on the development of prestressing forces in concrete beams during the thermal cycle required in the procedure. Pre-stretched nickel–titanium wires were externally placed on concrete prismatic beams equipped with strain gauges. As concrete rupture may occur during the heating by the Joule effect, a compromise must be found between the SMA pre-stretch level and the maximum temperature to be applied before returning to ambient temperature. A macroscopic model was developed to analyze this compromise. The complex thermomechanical response of SMAs implies a particular attention in the definition of the ambient temperature and heating conditions for the creation of prestress states in concrete components.