Issue 47

E. Grande et alii, Frattura ed Integrità Strutturale, 47 (2019) 321-333; DOI: 10.3221/IGF-ESIS.47.24 327 the part “3” equal to b=50 mm, a shear strength of the lower mortar equal to 0.9 MPa, a shear strength of the upper mortar equal to 0.45 MPa, a residual value of shear strength equal to zero for both the interfaces and the data reported in Tab. 1. a) b) c) Figure 3 : Approach 2: a) shear stress developing at the interfaces; b) slip of the interfaces; c) normal stresses at the upper mortar layer. Numerical applications for the approach 1 and the approach 2 In order to assess the capability of the proposed model in providing a reliable prediction of the bond behavior of FRCM strengthening systems, some case studies derived from the current literature are considered ([4]). The case studies, here considered, consist of single lap shear tests of concrete blocks strengthened by a bidirectional unbalanced PBO fiber net with two mortar layers. In particular, in the present research the specimens are considered characterized by a bond length equal to 450 mm and two different values of the reinforcement width: b p =60 mm and b p =80 mm. These tests are of particular relevance since the experimental outcomes showed the damage of the upper mortar layer of tested specimens before the slipping at the interface level. Regarding the application of the approach 1, a shear stress-slip law for the lower interface characterized by a shear strength equal to 0.9 MPa and a slip threshold equal to 1.2 mm is considered (see [4]). On the other hand, for the approach 2 a shear strength value of the upper interface corresponding to the attainment of the tensile strength of the upper mortar layer (f ct =3.5 MPa) is considered. For both the approaches, a null value of the residual shear strength is assumed for both the interfaces. The obtained results are shown in Fig. 4 in terms of applied load P versus the slip of the lower interface at the loaded section. In the same figure the envelop of the experimental curves (grey region) and the curve carried out in [4] are also reported. a) b) Figure 4 : Comparison with experimental tests in terms of applied force vs. slip curves. 0 2 4 6 8 10 0 2 4 6 8 10 12 Grande et al. 2018 approach 1 approach 2 slip s i (x=L) [mm] applied load P [kN] D’Antino et al. 2015 – b p =60mm 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Grande et al. 2018 approach 1 approach 2 slip s i (x=L) [mm] applied load P [kN] D’Antino et al. 2015 – b p =80mm