PSI - Issue 54

Ahmed Selim et al. / Procedia Structural Integrity 54 (2024) 601–608 Selim et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Introduction One of the greatest challenges that civil engineers face nowadays is the deterioration of existing reinforced concrete (RC) structures (Nayak et al., (2018)). As time progresses, the mechanical properties of RC are subjected to severe degradation. This happens due to several factors, such as corrosion of the reinforcing steel, poor design, excessive loading, change in applied loads, age factors, etc. (Babaeidarabad et al., (2014), Gonzalez-Libreros et al., 2017)). Consequently, there has been an ongoing demand to investigate several strengthening techniques to rehabilitate existing RC structures and increase their life span. Some of the traditional strengthening techniques that have been implemented include enlarging structural members through concrete jacketing or externally bonding a steel plate to the structural member (Yang et al., (2018)). While these traditional techniques are still used worldwide, they are not an optimum solution due to several disadvantages, such as an incr ease in the structure’s self -weight, undesired change in stiffness, and difficulty in workmanship (Gonzalez-Libreros et al., (2017)). One of the innovative strengthening techniques that have received growing interest over the past decade is fiber reinforced polymers (FRP) (Bournas et al., (2015), Tetta et al., (2016)). Studies have shown that FRP composites have excellent corrosion resistance, high strength, lightweight, ease of application, and fatigue resistance (Nayak et al., (2018), Babaeidarabad et al., (2014), Guo et al., (2020)). Nonetheless, one of the major drawbacks of FRP is the associated debonding failure mode, which happens due to the loss of composite action between epoxy and fibers. For that reason, the full capacity is not utilized (Wu et al., (2011), Aram et al., (2008)). This proposed the use of near surface-mounted laminates to enhance the flexural performance of the FRP system by increasing the surface of contact between the concrete surface and epoxy resin; thus, delaying debonding. In this paper, the behavior of concrete prisms was analytically investigated using finite element modeling (FEM). The study employed the commercial product ABAQUS to model and analyze the behavior of externally strengthened concrete prisms under a four-point load bending test. Two models were developed and analyzed. The first model was for a typical concrete prism externally strengthened with FRP laminate bonded to the bottom of the substrate. The second model had the FRP laminate grooved into the substrate of the concrete prism. The Concrete Damage Plasticity model was used to model the concrete prisms and a linearly elastic isotropic model was used to model the FRP laminate. 1. Literature review The utilization of composite materials, such as fiber-reinforced polymers (FRP), for the strengthening and repair of structural elements, particularly in the context of reinforced concrete structures, has been increasingly adopted. For instance, a study conducted by Attari et al. (2012), the effectiveness of FRP materials in externally strengthening reinforced concrete beams was investigated. This research involved seven simply supported beams, all sharing the same dimensions and having identical flexural and shear reinforcements. However, the beams differed in terms of the layout and type of FRP strengthening materials employed. Hawileh et al. (2022) investigated the effects of externally strengthening reinforced concrete (RC) beams using polyethylene terephthalate (PET) fiber-reinforced polymer. PET-FRP possesses a notably large rupture strain and a lower modulus of elasticity when compared to other available FRPs. The experimental program encompassed four beams, each with a width of 125 mm, a depth of 240 mm, and a total length of 1840 mm. All specimens shared the same flexural and shear reinforcement, with a concrete compressive strength of 36.8 MPa. Among these beams, two were strengthened with one and two layers of PET-FRP, one featured a single layer of carbon FRP (CFRP), and the final beam served as an unstrengthened control specimen. The results demonstrated that employing two layers of PET-FRP resulted in a remarkable 47% increase in strength compared to the conventional unstrengthened beam. This substantial percentage increase was also observed in the beam with one CFRP layer. Additionally, the findings revealed a 33% increase in ductility for the former beam compared to the latter. However, the beam with a single layer of PET-FRP exhibited a more modest enhancement in strength. Notably, all strengthened beams experienced flexural failure, particularly through the debonding of the laminate from the concrete cover. It was also observed that in the specimen strengthened with a single layer of PET-FRP, crushing of the concrete in the compression zone was followed by debonding of the laminate.