Issue 48

V. P. Berardi et alii, Frattura ed Integrità Strutturale, 48 (2019) 222-229; DOI: 10.3221/IGF-ESIS.48.23 223 flexural cracks (intermediate debonding). According to the capacity design criteria, failure due to brittle debonding phenomena shall not forego flexural or shear failure of the strengthened member. In common applications, the end debonding generally represents the design condition and a maximum value of composite stress (lower than composite strength) is associated with it. No specific standards are available to experimentally evaluate the FRP maximum stress corresponding to end debonding. Some technical recommendations are provided in the American ACI 440.2R-08 [13], the European fib T.G. 9.3 [14] and the Italian CNR-DT 200 R1/2013 [15] guidelines to predict such design FRP stress by means of semi-empirical formulae. Within this context, some specific aspects of this technique have yet to be studied in deeper detail. With reference to FRP-concrete end debonding, it is well-known that the corresponding mechanical behavior can be modeled via a cohesive law, that allows also the prediction of the mode II fracture mechanism experimentally observed in failure of strengthened systems [16-20]. Several researchers are being studied this local failure mechanism by proposing different test setups, generally based on either linear variable displacement transducers (LVDTs) or laser meter devices installed on composite plate and located at the beginning of bonded area, as well as on strain gauges, positioned along longitudinal direction [21-23]. Some recent studies have introduced a non-contact optical technique, digital image correlation (DIC), to obtain the FRP- concrete slip on extended areas of tested specimen rather than only on the beginning of bonded area [24-32]. This promising method also allows for an estimation, with a good accuracy, of the strain field on FRP and concrete core external surfaces. Within this context, a new experimental setup for the identification of cohesive law at the adhesive interface of strengthened systems is presented. It is based on a mechanical anchorage system of specimen and DIC outcomes, without requiring any strain gauges and LVDTs/laser meter records. An optimized DIC procedure is proposed, consisting of a data processing limited to selected regions of interest (ROI), in order to drastically reduce the computational burden and point out experimental displacements in a more accurate way and overcoming the boundary effects of inhomogeneous zones. Several experimental debonding tests on a concrete block externally plated with GFRP pultruded laminate have been performed for validation purposes at the Design Machine Laboratory of the University of Salerno. Figure 1 : Anchoring device – lateral and top views (dimensions in mm). MATERIALS AND METHODS he experimental setup was designed with the aim to achieve an effective anchoring of strengthened specimen and an optimal placement of camera. It consists of: T