Thermo-Mechanical Training of Iron-Based Shape Memory Alloys Used to Strengthen RC Beams

Abstract

The Shape Memory Alloys (SMAs) are rarely used in structural engineering applications due to the high cost of constitutive materials and production schemes. Recently, the Iron-Based SMA (Fe-SAM) is being developed. The inexpensive constitutive materials of the Fe-SMA and the availability of mass production facilities of steel products makes this material suitable for large structural engineering applications than the most common shape memory alloys (i.e. NiTi). SMAs are mainly characterized by the Shape Memory Effect (SME) phenomenon. The SME represents the ability of the SMA to recover its original shape after being deformed beyond the elastic limits through heating. The SME for some SMAs can be further improved by the thermo-mechanical training. This paper reports on the effect of thermo-mechanical training of Fe-SMA bars used for flexural strengthening of Reinforced Concrete (RC) beam using the Near-Surface Mounted (NSM) strengthening technique. The pre-strained Fe-SMA bar was anchored inside a groove in the tension face of the RC beam and then heated up to 350oC where the activation of the bar occurred causing a prestressing force to be developed in the Fe-SMA bar that counteracts the applied loads. The results were compared with another beam strengthened with Fe-SMA without thermo-mechanical training of the bar. The results revealed a better performance at service loads in the case of the beam strengthened with trained NSM Fe-SMA bar.