Direct versus Indirect Method for Identifying FRP-to-Concrete Interface Relationship

Several proposals have been carried out for modeling a fiber-reinforced-polymer FRP-to-concrete interface whose behavior is not completely described by fracture energy value, which could often be derived in closed form. Although the bilinear formulation is one of the most widely accepted relationships, neither standard testing procedures nor well-established calibration and identification techniques are currently available. The present paper mainly deals with the latter aspect and is basically aimed at examining the differences possibly arising from adopting either direct or indirect techniques for identifying the interface relationship. In particular, after an outline of the analytical formulation of both mentioned identification methods, their application is proposed considering a set of experimental results already utilized by other authors in similar studies. Besides the expected superiority of the indirect procedure in identifying the interface relationship, emphasis is placed on the fact that such a procedure is quite unaffected by the possible reduction in the number of experimental data considered in calibrating the interface relationship.