Investigation of the bond behavior of the fiber reinforced composite-concrete interface using the finite difference method (FDM)

Fiber reinforced composite materials, including fiber reinforced polymer (FRP) and fiber reinforced cementitious matrix (FRCM), have been widely used to increase the load-carrying capacity and ductility of concrete structures. The bond-slip relationship of the composite-concrete interface is of pivotal significance to understand the behavior of the strengthened structure. This study presents a generic and versatile finite difference method (FDM) solution that can predict the full-range bond behavior of the composite-concrete interface adopting different (e.g., bilinear, trilinear, exponential, and their combinations) bond-slip relationships. The proposed FDM solution successfully captures the snap-back phenomenon using an arc-length method for iteration. Comparison between FDM and analytical results shows that (i) for some frequently adopted analytical solutions, the assumption of zero slip at the composite free end is not suitable for short bonded lengths and fails to capture the snap-back phenomenon and load descending stage for long bonded lengths; (ii) for bond-slip relationships with different shapes, the load responses are similar but the effective bond lengths can be different when the same fracture energy is enforced; and (iii) for composite-concrete joints with finite bonded length, the peak load may not be the same when adopting different bond-slip relationships with the same fracture energy.