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Prestress state evolution during thermal activation of memory effect in concrete beams strengthened with external SMA wires

Debska A., Gwozdziewicz Piotr, Seruga A., Balandraud X., Destrebecq J. F.

Archives of Civil and Mechanical Engineering

2020

Vol. 20, no. 4

659--673

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.

Improvement of the mechanical performances of concrete cylinders confined actively or passively by means of SMA wires

Tran H., Balandraud X., Destrebecq J. F.

Archives of Civil and Mechanical Engineering

2015

Vol. 15, no. 1

292--299

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.