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

Kinam Hong,Yeongmo Yeon,Sugyu Lee,Kyusan Jung

doi:10.1186/s40069-018-0279-y

Abstract

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.

Highlights

Various materials and techniques have been developed to strengthen damaged or deteriorated civil structures
Even though researches have not found a way to completely solve the premature failure of the strengthening material in the EBR method, the considerable improvement of the flexural behavior of reinforced concrete (RC) beams strengthened by the NSM method compared to the RC beams strengthened by the EBR method has been demonstrated
Compressive stresses at the bottom of the concrete member and tensile stresses at the top of the concrete member are produced by the prestressing force transmitted from the prestressed strengthening material, which is known as the cambering effect (El-Hacha et al 2001)

Summary

Introduction

Various materials and techniques have been developed to strengthen damaged or deteriorated civil structures. It has been reported that the prestressed FRP NSM technique increases cracking and yielding loads and reduces deflection at mid-span and crack width for the strengthened RC beams. This technique faces the critical problem of reduced ductility of the strengthened RC beam (Badawi and Soudki 2009). The ductility of the strengthened RC beam is reduced with higher prestressing level of the prestressed FRP material, which causes failure at a smaller deflection. The reason for this is that a large part of the strain capacity of the FRP reinforcement is already used during prestressing. This is the reason why the prestressed FRP NSM technique is not widely used in practice

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