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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combination with the above-described bond-slip interface elements, the main cracks nucleated at the tension face of the beam can easily pass through the reinforced steel bars, avoiding their artificial arrest at the steel/concrete interface.

Fig. 9. Deformed configurations of the FRP-plated RC beam predicted by the proposed model.

4. Conclusions In this work, a numerical model for the failure analysis of strengthened structural elements has been proposed, based on the inter-element fracture approach already introduced by some of the authors in De Maio et al. (2019b), (2019a). Such a model is composed by three different sub-models: a diffuse interface model, to predict multiple crack nucleation and propagation in the concrete substrate; an embedded truss model to take into account the mechanical interaction between concrete and steel rebars; and a single interface model to simulate potential debonding mechanisms at the adhesive/concrete interfaces. Moreover, such a model takes advantage of a new path-following methodology able to follow the unstable branches of the equilibrium path, which are typical in brittle failure of the retrofitted structural elements. This model has been preliminarily validated by performing a numerical test involving a plain concrete sample. The numerical predictions, in terms of loading curve and crack path, are in good agreement with the reference results thus ensuring the effectiveness of the proposed methodology. Subsequently, the proposed model has been used to perform a complete failure analysis of an FRP-plated RC beam, with particular attention devoted to the debonding phenomenon. The obtained structural response, in terms of loading curve and crack pattern, has shown the ability of this model to identify with reasonable accuracy the complex nonlinear mechanisms occurring within the strengthened RC elements, such as tensile cracking, compressive crushing, interfacial debonding of the FRP system and yielding of steel rebars. Suitable comparisons with the available experimental results have clearly shown the effectiveness of the proposed approach to investigate in a comprehensive manner all the failure modes in RC elements retrofitted with FRP systems (due to multiple crack initiation, coalescence and propagation), unlike for many models in the scientific literature, generally focused on single failure modes. Moreover, in order to improve the overall computational performances in the case of complex damage analyses which involve building and bridge structural elements (Bruno et al. (2016); Lonetti and Pascuzzo (2020), (2016), (2014)), the proposed numerical model should be integrated within an adaptive concurrent multiscale approach, similarly to that employed in Greco et al. (2020a), (2020c).