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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material constituents, also predicting crack patterns very similar to that provided by the experimental tests. The most common fracture models rely on cohesive zone approaches to predict the debonding processes of the FRP reinforcement system, assuming a nonlinear mechanical behavior of the concrete/FRP interface via cohesive elements equipped by a traction-separation law (Rabinovitch (2008); Houachine et al. (2013); Pascuzzo et al. (2020)). An innovative inter-element cohesive fracture model has been developed by some of the authors to simulate the concrete cover separation failure of an FRP-plated reinforced concrete (RC) beam, taking into account also the nonlinear behavior of the concrete phase through cohesive elements inserted along all boundaries of the computational discretization (De Maio et al. (2019a), (2020b)). However, such an inter-element fracture approach suffers of mesh dependency issues and artificial toughening effects induced by the mesh, partially solved by using the recently introduced moving mesh techniques (Ammendolea et al. (2021); Greco et al. (2021a)). Moreover, the cohesive extended finite element models (XFEM) are judged very effective to correctly simulate crack patterns in strengthened structural elements without requiring mesh update procedures (Benvenuti and Orlando (2017); Esna Ashari and Mohammadi (2012)). In the present work, an innovative finite element model to simulate the debonding failure of RC beams externally strengthened with FRP plate is proposed, based on an inter-element cohesive fracture approach recently introduced by some of the authors in De Maio et al. (2019b), (2020c). Such a model allows the multiple crack nucleation and propagation in the concrete phase and along the physical interface between concrete and FRP system by using cohesive elements inserted along all mesh boundaries. The model is used in combination with truss elements, equipped with a bond-slip relation in order to capture the interaction between rebars and the surrounding concrete. The paper is organized as follows: a brief description of the adopted fracture model together with computational details is reported in Section 2; in Section 3 the numerical results obtained by a failure analysis of an FRP-plated RC beam are illustrated. Finally, section 4 provides concluding remarks. 2. Description of the adopted cohesive FE fracture model In this section the adopted FE model, based on a cohesive fracture approach, is briefly described together with some computational details. In particular, the modelling of the concrete phase by means of a diffuse interface model is explained in Section 2.1, whereas the steel and FRP reinforcement modelling, which involves an embedded truss model and a single interface model, is described in Section 2.2. 2.1. Concrete modeling A diffuse interface model, recently introduced by some of the authors for plain and fiber-reinforced concrete in De Maio et al. (2021), (2020a), able to simulate the multiple crack nucleation and propagation in quasi-brittle materials is employed. Such a model is based on the insertion of cohesive elements, equipped with a traction separation law, between the bulk elements of a computational mesh, thus allowing crack branching and coalescence to be easily simulated (Figure 1).

Fig. 1. Schematic representation of the diffuse interface model.