Flexural Behavior of Concrete Beams Strengthened with Near-Surface-Mounted CFRP Strips

Abstract

Engineers have proposed relocating externally bonded strengthening fiber reinforced polymer (FRP) material from the unprotected exterior of the concrete to the protected interior. This technology is known as near-surface mounted (NSM) strengthening. In NSM reinforcement, the FRP is surrounded by concrete on three sides so the bond and damage problems associated with externally bonded FRP strengthening systems are reduced or eliminated. This paper presents experimental results from 12 full-scale concrete beams strengthened with NSM carbon FRP (CFRP) strips. Three companion unstrengthened specimens were also tested to serve as a control. Experimental variables include three different ratios of steel reinforcement and two different ratios of CFRP reinforcement. Yield and ultimate strengths, flexural failure modes, and ductility are discussed based on measured load, deflection, and strain data. Test results show measurable increases in yield and ultimate strengths in all beams strengthened with CFRP as well as predictable nominal strengths and failure modes. Force transfer between the CFRP, epoxy grout, and surrounding concrete was able to develop the full tensile strength of the CFRP strips. Energy and deflection ductilities were reduced for CFRP strengthened beams. Future research needs are addressed.