Modeling the mechanical interaction between FRP bars and concrete

In recent years there has been an increased interest in applying fiber-reinforced polymer (FRP) reinforcing bars for concrete, as an alternative to steel reinforcing bars. The mechanical interaction between the FRP and the concrete, commonly called the bond behavior, is not well understood and has a significant effect upon the structural behavior of FRP-reinforced concrete. While many experimental bond studies have been conducted for a variety of different bars, modeling efforts to both quantify the underlying bond mechanisms and the resulting behavior have been very limited.; Smaller scale (rib-scale) models explicitly represent the surface structure of the bar and can thus be used to characterize the underlying mechanisms associated with the mechanical interlocking and to help optimize the surface structure of a bar. Existing ribscale models have not addressed the progressive failure of the constituent materials, an issue addressed in this study. There is also a need to model the bond behavior of these bars at a scale amenable to the analysis of structural components. Existing “structural models” do not have sufficient generality to meet this objective since they do not address the dependence of the behavior upon the stress state or allow multiple failure modes (pullout and splitting) to be predicted—the other main issue addressed in this study.; An intermediate scale model (a bar-scale model originally developed for steel bars) is modified and applied to the bond of FRP bars. The model provides a macroscopic characterization of the bond behavior within the mathematical framework of elastoplasticity theory. The model incorporates a non-associated flow rule and elastoplastic coupling. Calibration and validation results for nine pullout specimens and one transfer length specimen demonstrate the model's ability to predict the bond strength and suggest that the model has a measure of generality.; Rib-scale models for several specimens are developed to represent the mechanisms that produce the bond behavior. A micromechanical model using the method of cells is developed for the FRP. An elastoplastic-damage model within the framework of continuum damage mechanics is developed to characterize the plastic and damage behavior of the matrix and fibers. A simple adhesion model is developed to represent the fiber-matrix interaction. The rib-scale models are able to reproduce the bond strengths of three independent experimental studies with acceptable accuracy. The predicted failure modes and surface structure damage are consistent with experimental observations.