PSI - Issue 66

Umberto De Maio et al. / Procedia Structural Integrity 66 (2024) 459–470

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Author name / Structural Integrity Procedia 00 (2025) 000–000

© 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of CP 2024 Organizers

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1. Introduction Monitoring of reinforced concrete existing structures has a key priority in the modern civil engineering, especially in contexts where material degradation and progressive deterioration of the structural performance can risk the public safety (Biondini and Frangopol, 2016; Hao et al., 2023). Reinforced concrete structures, widely used in civil infrastructure such as bridges, buildings, and viaducts, are subject to degradation phenomena due to environmental and anthropogenic factors, cyclic loading, and aging. These phenomena include concrete cracking, corrosion of reinforcement, and loss of load-bearing capacity, which can lead to catastrophic failure if not identified promptly. In this context, Structural Health Monitoring (SHM) is an effective tool for detecting and assessing damage evolution, thus ensuring the safety and longevity of existing infrastructure (Katam et al., 2023; Tumrate et al., 2023). Among the various SHM techniques, vibration analysis has gained a significant role due to its ability to provide comprehensive information on the state of structural integrity. The principle behind these techniques is that damage affects the modal parameters of the structure, such as natural frequencies, modal shapes, and damping factors (Fayyadh and Razak, 2013; Katam et al., 2023). Variations in these parameters can indicate the occurrence of cracks or other defects, making modal analysis an effective method for detecting and localizing damage. Previous studies have shown that variations in vibration frequencies can be used to diagnose damage in reinforced concrete structures, and numerous papers in the literature have investigated the effectiveness of such techniques in various engineering applications (Avci et al., 2021; Cao et al., 2017; Gomes et al., 2019; Hou and Xia, 2021). However, the complexity of the nonlinear behavior of reinforced concrete due to the interaction between concrete and steel bars makes accurate modeling of these structures a significant challenge (De Maio et al., 2021; Pranno et al., 2022). In particular, damage modeling in reinforced concrete structures has seen great development in recent years with the introduction of advanced models capable of realistically representing fracture and plasticity phenomena (De Maio et al., 2024b; Rimkus et al., 2020). Among these, the Coupled Damage Plasticity Model has emerged as an effective tool to describe the nonlinear behavior of concrete under load (Hanif et al., 2018; Kenawy et al., 2020; Park et al., 2022). This model combines the effects of plasticity and cracking, allowing the progressive degradation of the material's mechanical properties to be accurately captured. When modeling damage in reinforced concrete structures, it is essential to take into account both mechanisms: on the one hand, the plasticization of the material that occurs prior to crack formation; on the other hand, the progressive loss of stiffness due to the growth of the cracks themselves. The use of finite element based numerical models (FEM) has significantly improved the ability to simulate damage phenomena, such as delamination, instability, and cracking, in complex concrete and composite structures (Bruno et al., 2007; De Maio et al., 2024c; Greco et al., 2007). These models provide a detailed picture of the changes in stiffness and deformation over the life cycle of the structure, allowing the dynamic response to be accurately predicted in the presence of damage. The model-based approach is based on a comparison between the experimental dynamic response, obtained by vibrational monitoring, and that predicted by the numerical model. In this way, damage can be identified and quantified through observed differences in modal parameters (De Maio et al., 2024a; Faizan et al., 2022; Kopsaftopoulos and Fassois, 2013; Zou et al., 2000). The state of the art in this field highlights the effectiveness of vibration analysis for damage detection in existing structures, with emphasis on the combined use of experimental techniques and advanced numerical models. Recent studies have shown how the application of the finite element method to reinforced concrete structures can accurately predict damage evolution under static and dynamic loads (Alkayem et al., 2018; Ereiz et al., 2022; Le Minh et al., 2021). For example, reinforced concrete beam models subjected to monotonic loads have shown that the natural frequencies of vibration progressively decrease with increasing damage, providing a reliable indicator of structural integrity (Hanif et al., 2021; Srinivas et al., 2014). In addition, the literature suggests that the introduction of advanced models, such as the Coupled Damage Plasticity Model, allows for a more accurate description of the overall behavior