Embedding NSM FRP Plates for Improved IC Debonding Resistance

The use of near surface mounted (NSM) fiber reinforced polymer (FRP) strips for strengthening reinforced concrete structures shows great promise as the strains at intermediate crack (IC) debonding are generally much greater than for externally bonded FRP strips. In this research, the NSM technique is taken a step further by embedding the NSM strip, i.e., is by providing cover to the strip. It is shown that embedment can increase the IC debonding resistance by up to three times. Importantly, embedment allows: substantially larger strains at IC debonding and, hence, greater ductility; the use of larger cross sections of FRP plate; and, through providing cover to the NSM, may be the first step in enhancing the fire resistance. In this paper, 20 new pull tests are described from which mathematical expressions are developed for the effect of embedment on both the IC debonding resistance and its associated local bond stress-slip (tau-delta) relationship.