ABSTRACT
The applications of Shape Memory Alloys (SMA) in structural engineering field are limited to small-scale projects and not adapted in practical application due to its high cost. 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 more suitable for large-scale structural engineering applications than the most common SMAs (i.e. NiTi) (Awaji, 2014). SMA is mainly characterized by the Shape Memory Effect (SME) phenomenon. The SME represents the ability of the SMA to recover part of the inelastic strain through heating. In the current research project the SME phenomenon is utilized for flexural strengthening of RC beams by using the Fe-SMA as prestressing reinforcement using the NSM technique. The pre-deformed Fe-SMA bar was embedded in a groove cut on the tension side of the beam. Because the bar was restrained through steel anchors at both ends, the application of heat above the activation temperature will result in a permanent prestressing force in the bar that will remain even after the bar cools down. This paper reports on the flexural performance of 150 × 305 × 2000 mm RC beam strengthened with NSM Fe-SMA bar tested under four point bending setup. 6% strain was initially applied to the Fe-SMA bar. The ends of the bar were then anchored inside a groove cut on the tension side of the RC beam. The bar was then heated using flexible heating tapes up to 350°C, at which the transformation from martensite to austenite phase occurred causing a prestressing force developed in the Fe-SMA bar that counteracts the applied loads. The load mid-span deflection curve of the strengthened beam (Beam-SMA) was compared to a control un strengthened beam (Beam-C) tested by Hadiseraji & El-Hacha (2014) as presented in Figure 1. The yielding and ultimate load capacities were increased by 22% and 32% over the control beam, respectively. Furthermore, the ductility of the beam was significantly improved. That is reflected by the 43% increase in the deformability index and 146% increase in the total dissipated energy as presented in Table 1. The deformability index was calculated as the ratio of deflection at ultimate load to the deflection at yield load, and the total dissipated energy was calculated as the total area under the load deflection curve up to the ultimate load.
