Multi-physical Simulation of Reinforced Concrete Bars Strengthened with Iron-Based Shape Memory Alloys

Extensive research has shown that iron-based shape memory alloys (Fe-SMA) can be used as prestressing materials in new reinforced concrete (RC) structures or existing RC structures. Currently, the Fe-SMA is thermally activated using various methods, including resistive heating, infrared, fire torch, propane torch, and heating jacket. Among them, resistive heating is a relatively better method with a wide range of applications and a short activation time. However, for the resistive heating method, the influences of the current magnitude and the activation time on the temperature distribution and the generated recovery stress in the Fe-SMA are still unclear, which restricts the field application of the Fe-SMA. The self-prestressing behavior of the Fe-SMA involves multiple physical fields such as electric currents, temperatures, and mechanics. This paper developed a multi-physical finite element model to simulate the self-prestressing behavior of the Fe-SMA when it is used as a strengthening material. The model is verified by the experimental results reported in literatures. The results show that the model can accurately predict the temperature distribution and the recovery stress of Fe-SMA strengthened RC beams. Furthermore, the model helps choose the appropriate activation current magnitude and activation time needed to achieve the design prestressing value in the Fe-SMA, reducing the risk of thermal damage to concrete caused by constant high temperatures. This study provides a constructive guideline for the field application of the Fe-SMA.