General Analytical Model for the Bond Capacity of NSM FRP-Concrete Joints

Fiber-reinforced polymer (FRP) near-surface mounted (NSM) reinforcement represents an effective solution for strengthening and retrofitting existing concrete structures. As it is embedded into concrete, NSM reinforcement is protected from accidental impact, high temperature, and vandalism and it is less prone to debonding than externally bonded reinforcement. However, debonding of the NSM reinforcement remains the main issue associated with this strengthening technique. Numerous studies have focused on the bond behavior of NSM-concrete joints and in some of them analytical models for the prediction of NSM-concrete joint bond capacity were proposed. However, these models are often based on a few experimental results of a specific strengthening configuration. In this paper, a new analytical model to estimate the effective bond length and the bond capacity of NSM-concrete joints that fail due to cohesive debonding within concrete is proposed. The model is based on a pure fracture mechanics Mode-II loading condition and can be applied to either NSM strips, round bars, or rectangular bars. The accuracy of the model proposed and of existing analytical models was assessed by comparing analytical and experimental results of 117 NSM-concrete joints collated from the literature. The assessment showed that the model proposed provided accurate estimations of the NSM-concrete bond capacity for all types of reinforcement considered.