PSI - Issue 64

Francesco Bencardino et al. / Procedia Structural Integrity 64 (2024) 932–943 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Many existing structures, whether due to aging, environmental factors, or changes in design codes, exhibit deficiencies that compromise their structural integrity, safety, and performance (Hollaway and Teng 2008; Teng et al. 2002). These deficiencies can manifest in various forms, including reduced load-carrying capacity, deterioration of materials, inadequate seismic resistance, or outdated design configurations. Retrofit interventions aim to address these shortcomings by implementing targeted modifications or improvements with the objective of upgrading the structural system and improving its overall performance. By retrofitting degraded structures, it becomes possible to extend their service life, enhance their behavior when subjected to environmental hazards, and ensure their compliance with modern engineering standards and regulations. However, conventional retrofitting methods often present challenges such as complex installation procedures, high material and labor costs, and potential disruptions to ongoing operations or occupants of the structure (Teng et al. 2002). In this context, Fiber-Reinforced Polymer (FRP) composites, consisting of high-strength fibers embedded in a polymer matrix, offer a range of advantageous properties that make them particularly well-suited for retrofit applications (Bank 2006; Correia 2015). One of the key benefits of FRP retrofitting is its versatility and adaptability to various structural configurations and materials. Indeed, FRP materials can be easily customized and tailored to specific project requirements, allowing for efficient and accurate strengthening of deteriorated structural elements (Nanni 2003). Additionally, FRP materials present a high strength-to-weight ratio, enabling significant improvements in structural behavior without adding excessive dead load to the existing structure. Moreover, FRP composites exhibit excellent resistance to corrosion, chemical degradation, and environmental exposure, making them ideal for reinforcing structures in harsh or corrosive environments (Zaman et al. 2013). Furthermore, FRP retrofit solutions offer rapid installation and minimal disruption compared to traditional retrofit methods, resulting in shorter construction times and less downtime for the structure (Porter and Harries 2007). In general, FRP systems are applied to degraded RC elements to improve their flexural, shear, and torsional behavior (Bencardino et al. 2005; Fyfe 2024; Nanni 2003; S&P Clever Reinforcement 2024). Additionally, it is worth mentioning that in seismic regions, FRP materials can be used to improve the ductility of RC columns by increasing the confinement of the concrete section (S&P Clever Reinforcement 2024; Sika 2024). According to most guidelines available regarding the use of FRPs, the most prevalent failure modes for RC elements strengthened with these composite materials include concrete crushing, FRP rupture, and debonding of the FRP from the surface (Bank 2006; Nanni 2003). All these phenomena can occur both before and after the yielding of the longitudinal steel rebars. In general, concrete crushing after the yielding of the steel rebars while still maintaining the FRP system intact would be the most favorable failure mode. However, this scenario is often challenging to achieve, and more commonly, debonding of the FRP occurs after the yielding of the steel rebars, before the concrete crushing. It is worth mentioning that the debonding phenomenon can occur in various form namely, delamination from the concrete substrate, either at the ends due to high peeling and shear stresses, or within the beam due to flexural and shear cracking (Bank 2006). Due to the complexity of these various failure modes, FRP retrofitting interventions necessitate a reliance on accurate analysis and thorough consideration of the several factors involved. This work presents a real case study of a Carbon-Fiber Reinforced Polymers (C-FRP) retrofitting intervention carried out during the late 1990s on a RC structure exhibiting significant signs of damage. At the time of the intervention, the absence of consensus recommendations for FRP retrofitting required the support of accurate experimental data for the design process. This need mainly stemmed from the relatively new development of FRP materials in structural applications and the lack of universally accepted guidelines and standards regulating their use, particularly during the initial stage of their adoption. This paper aims to contribute to the information available in the literature by performing a comparative assessment of the structural rehabilitation design based on experimental data with the current design procedure outlined in the Italian Guideline (CNR-DT 200 R1/2013). By comparing these methodologies and their respective outcomes, it is possible to highlight the significance of experimental studies for informing design practices and provide comprehensive insights into the long-term durability of FRP-strengthened RC structures.