| Fiber reinforced plastic reinforcing bars are being considered as potential replacements for conventional steel reinforcing bars for concrete. These bars have composition of advanced synthetic reinforcing fibers embedded in polymer resin matrices or binders, are nonmetallic and have the potential of highly corrosion resistant. It is the resin matrix that plays an important role in transferring forces from the surrounding concrete into reinforcing bars and this resin matrix is potentially susceptible to degradation at the concrete interface. Once this degradation occurs, bond capacity can be reduced or lost completely. Therefore, the main objective of this study was to measure degradation in terms of loss of bond stiffness.; To obtain bond stiffness, it was imperative to model the bond stress-slip curve. This has been done by one dimensional finite element model. Therefore a new finite element for bond stress-slip analysis is presented. A one dimensional finite element model, which is based on equilibrium and local bond stress-slip law, is developed. The relationship between force and slip at the elements nodes is expressed through a stiffness matrix. Bond-slip relationship is idealized as piece-wise linear curve consisting of four zones and closed form solution of the equilibrium differential equation is obtained for each of its zones. The global stiffness matrix is assembled and solution yields slip, strain and stress distributions along the GFRP bar. The nonlinear bond stress-slip relationship leads to an iterative technique, which is found to converge rapidly. The proposed method predictions have been compared with the experimental results and very good correspondence has been established. This analytical model has been used to investigate the degradation in the vinylester and polyester resin matrices and the E-glass fibers of deformed FRP bars. Pullout tests have been used to investigate the bond strength and bond stiffness characteristics of the FRP bars. Under adverse environment GFRP bars embedded in concrete, have shown degradation. That means decrease in bond stiffness and bond strength. Consequent upon, a term ‘Degradation Factor’ has been introduced, which can measure a loss of bond stiffness under a typical environment.; This study has applications in the problems associated with the bond-slip models and the measurement of bond stiffness of FRP bars under a typical environment these are subjected to. With the help of this mathematical model, the degradation of the GFRP bars in terms of the strain and the bond stress can be measured under adverse environmental conditions. |
