Abstract
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.
Highlights
Shape memory alloys (SMAs) are active materials that have the ability to cancel apparent “plastic” strain by heating, a phenomenon known as the memory effect [1,2,3,4,5]
The present paper focuses on the creation of prestressing forces in SMA wires placed externally on concrete prismatic beams, prior to any external loading
The present study focused on the development of the prestressing forces during the thermal cycle required in the procedure for the activation of the memory effect in the SMA
Summary
Shape memory alloys (SMAs) are active materials that have the ability to cancel apparent “plastic” strain by heating, a phenomenon known as the memory effect [1,2,3,4,5]. When the latter is mechanically hindered, the SMA component develops forces, a mechanism that has found many applications in engineering. The underlying physical phenomenon is a solid–solid transition between two phases, namely austenite (A) and martensite (M), triggered by temperature and stress. Austenite and martensite are present at “high” and “low” temperatures respectively.
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