Bond Behavior of FRP--Concrete in Presence of Intermediate Crack Debonding Failure.

An experimental and numerical program to investigate the behavior of intermediate crack (IC) debonding failure and the bond-slip relationship between the fiber-reinforced polymer (FRP) plates and concrete in FRP-strengthened concrete beams is presented. Simple notched-beam specimens were used to represent an existing flexural-shear crack that triggers IC debonding. In all experimental cases, it was observed that the IC debonding initiated at the tip of a diagonal crack close to the notch or a flexural crack at the beam midspan. To study the sensitivity of the debonding behavior to the location of the cracks along the beam span, the notch position was placed at different locations along the shear span. The combination of the concrete damaged plasticity model and the extended finite-element method (XFEM) based cohesive method is proposed in this paper to model the complete concrete response, and to examine the stress state of the FRP-concrete interface in the presence of IC debonding failure. The numerical results show that the diagonal crack close to the notch results from a mixed-mode stress state prior to FRP debonding. Once the diagonal crack is initiated close to the flexure-shear crack, IC debonding propagates in pure shear stress condition at the FRP-concrete interface regardless of the moment shear ratio at the location of the flexureshear crack. [ABSTRACT FROM AUTHOR]