PSI - Issue 39

Umberto De Maio et al. / Procedia Structural Integrity 39 (2022) 677–687 Author name / Structural Integrity Procedia 00 (2019) 000–000

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valid for ribbed bars and good bond conditions taken from the CEB-FIP Model Code Fib (2013) and illustrated in Figure 2b. The truss elements are constrained in the perpendicular direction to the rebar meaning that only the displacement jump in the rebar direction (i.e. the slip) is considered as an active degree of freedom of the zero thickness steel/concrete interface element.

Fig. 2. Schematic representation of the steel/concrete interaction: (a) bond-layer model; (b) adopted bond-slip relation (taken from the CEB-FIP Model Code Fib (2013).

Moreover, the proposed modeling approach employs a single interface model to predict the debonding phenomena of the FRP reinforcement system. In particular, the detachment of the FRP plate from the tension-side surface of the strengthened RC beam is simulated by means of additional cohesive elements, equipped with a traction-separation law, along the FRP/concrete interface (Figure 3).

Fig. 3. Schematic representation of the single interface model to capture potential debonding phenomena.

3. Numerical results In this section the numerical results obtained by the proposed model are illustrated and discussed involving a plain concrete specimen to predict the Mode-I fracture and an FRP-plated reinforced concrete beam to simulate the mixed mode fracture and debonding mechanisms. Finally, a comparison with experimental outcomes is reported to highlight the effectiveness of the proposed fracture model. 3.1. Mode-I fracture test of a plain concrete specimen In order to validate the prosed model for the mode-I fracture condition, a preliminary numerical simulation of the three-point bending test analyzed in Carpinteri and Colombo (1989) is performed, involving a plain concrete specimen. Both geometry and boundary conditions of the concrete specimen are depicted in Figure 4a and expressed in terms of the specimen thickness 0.15 m b = . The Young’s modulus and the Poisson’s ratio of the bulk material are