Geometric Scaling and Instability in FRP-Concrete Debonding

The debonding mode of failure, which is observed in concrete beams strengthened using externally attached FRP sheets, is analyzed. A numerical analysis of the direct-shear response of FRP attached to a concrete substrate is performed to study the initiation, formation and propagation of an interfacial crack between the two adherents. The material response of the bi-material interface, which includes post-peak softening, is considered in the numerical model. An instability in the load response associated with snap-back is predicted close to failure and the arc-length method is used to obtain the entire load response. It is shown that there is a scaling in the load capacity when the bonded length does not allow for the establishment of the full stress-transfer zone associated with interface crack growth.