Flexural Response of Reinforced Concrete Beams Strengthened with Near-Surface-Mounted Fe-Based Shape-Memory Alloy Strips

This paper proposes an advanced near-surface-mounted (NSM) technique with an Fe-based shape-memory alloy (Fe-SMA) strip which can solve issues of low workability and reduced ductility of reinforced concrete (RC) beams strengthened with an NSM technique using prestressed fiber-reinforced polymer (FRP) strips in the concrete tension section. The flexural behavior of the RC beam strengthened by the NSM technique with the Fe-SMA strip was investigated. A total of seven RC beams were tested by four-point bending tests under displacement control. The type of reinforcements, the quantity of Fe-SMA strips, and the pre-straining level of the Fe-SMA strips were considered as experimental variables. Cracking load, yielding load, and ultimate load increased, respectively, with larger quantities of Fe-SMA strip. In addition, activation of embedded Fe-SMA in the concrete by electrical resistance heating effectively induces a prestressing force on the concrete beam, resulting in a cambering effect. The introduced prestressing force to the RC beam by activation of the Fe-SMA increased the crack and yielding loads, and did not decrease the ductility of the RC beam compared to the RC beam with non-activated Fe-SMA. It can be concluded from the test results that the strengthening technique using the recovery stress of the Fe-SMA strip as the prestressing force solves the various problems of the existing prestressing strengthening systems, meaning that Fe-SMA can be used as a substitute for conventional prestressing strengthening systems.