Iron-based shape memory alloys for prestressed near-surface mounted strengthening of reinforced concrete beams

Abstract

Low-cost Fe-Mn-Si-based shape memory alloys (SMAs) have attracted much attention in the research community and in practice over the past two decades as a cost-effective alternative to the expensive Ni-Ti-based SMAs. The shape memory effect refers to the phenomenon in which SMAs, if they are deformed, return to their former shape upon heating. Near-surface mounted (NSM) strengthening techniques can be used to strengthen concrete beams. The advantages associated with NSM strengthening are its ability to significantly reduce the probability of harm that results from corrosion, fire, acts of vandalism, mechanical damage, and aging effects. Iron-based SMA (Fe-SMA) strips can be used as NSM reinforcements. The NSM Fe-SMAs can more easily be prestressed than NSM fiber reinforced polymers, because the prestressing of SMAs does not require any mechanical jacks and anchorheads.In this study, an experimental program was established to investigate the flexural behavior of reinforced concrete (RC) beams that were strengthened and prestressed with Fe-SMA strips. The specific focus was on the demonstration of the feasibility of this strengthening technique. A total of six RC beams were experimentally examined under deflection control in a four-point bending loading rig. The experiments consisted of one beam strengthened by Fe-SMA strips but not prestressed, three beams strengthened by prestressed Fe-SMA strips, and one beam strengthened by one CFRP strip. Additionally, one beam with no strengthening, which served as the reference beam, was examined. The results showed that the cracking loads and mid-span deflections of prestressed beams compared to other beams were, respectively, higher and lower. Significant strengthening effects were achieved in NSM Fe-SMA-strengthened beams compared to the reference beam. These direct effects showed that the application of near-surface mounted Fe-SMA strips worked well as prestressing elements in concrete beams.