Numerical Modeling for the Interface Bond of Concrete and FRP Bar

This study presents a numerical modeling procedure for the pullout of FRP bar from concrete cylinder, when the bond failure of concrete/FRP occurs mainly within the bar surface. From the governing equation of bond-slip, the normal force along the bar is defined in terms of a local bond stress-slip law and the relative displacement between concrete and bar surface. A shear stress-slip relationship that was successfully used for interface between concrete and externally bonded FRP sheet is modified and adopted as the local bond stress-slip law for FRP bar in concrete. Then values of parameters in that expression are determined by minimizing the difference between bond-slip (normal force vs. slip at the loaded end of the bar) from the analytical method and experimental result. Finite element analysis is also carried out to model the bond-slip of bar in concrete. The interaction between FRP bar and concrete is defined using a nonlinear spring element. The force-deflection curve of the spring element is determined by the local bond stress-slip law. With the proposed procedure, the local bond stress-slip law can be quickly determined, avoiding tedious computations, and the development length for FRP bar can be easily obtained.