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

Several proposals have been carried out for modeling FRP-to-concrete interface whose behavior is not completely described by fracture energy value which could be often derived in closed-form. Although the bi-linear 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 to examine 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 the 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.