PSI - Issue 37

Haya H. Mhanna et al. / Procedia Structural Integrity 37 (2022) 359–366 Mhanna et al./ Structural Integrity Procedia 00 (2021) 000 – 000

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Keywords: Fiber-reinforced polymers; FRP shear predictions; retrofitting

1. Introduction Shear failures of reinforced concrete (RC) structures are generally dangerous as it occurs suddenly without adequate warning signs before failure (Mhanna et al. (2020); Pellegrino and Modena (2008)). Hence, it is very important that RC members have sufficient shear capacity to prevent this type of brittle failure. Over the decades, many RC structures, such as buildings and bridges, have deteriorated mainly because of the corrosion of steel inside the concrete. Other factors that resulted in the accelerated deterioration of RC structures include neglect, overuse, and increased loading (Hawileh et al. (2019); Salama et al. (2019); Zhuang et al. (2019)) . One of the effective methods used in the retrofitting industry is conducted via externally bonding fiber-reinforced polymer (FRP) composites to the concrete surface to enhance the flexural and shear capacity of RC beams and confinement capacity of columns (Helal et al. (2020); Zeng et al. (2018)). The main advantages of FRPs over other retrofitting techniques include noncorrosive nature, high stiffness and tensile strengths, light-weight, low maintenance cost, ease of installation, and versatility (Hawileh et al. (2014); Mahmoud et al. (2021)). In general, to enhance the shear capacity of the member, FRP fibers should be oriented perpendicular to the beam’s longitudinal axis or at an angle orthogonal to the shear cracks, to suppress the formation and widening of the cracks (Bousselham and Chaallal (2008); D’Antino and Triantafillou (2016)) There are three different ways in which FRPs can be bonded to the concrete substrate to enhance its shear capacity. The most effective method is by fully wrapping the beam from all sides. This method provides the maximum shear enhancement and optimum beam confinement. However, it is impractical to implement in many cases where the beams are monolithically cast with the slabs (Mhanna et al. (2019)). Therefore, the most commonly used technique is the U-wrapping scheme, where the FRPs are connected to the beams from three sides (Bae and Belarbi (2013); Nawaz et al. (2016)). Finally, FRPs could be bonded to the two sides of the web using the side-bonded configuration. However, this method is the least effective and has been ruled out from several design guidelines, such as fib bulletin 90 (fib bulletin 90 (2019)). The typical failure mode of U-wrapped strengthened RC beams is the debonding of the FRP laminates prior to utilizing the tensile strain in the laminates. Studies have shown that the effectiveness of the U-wraps can be significantly enhanced using appropriate anchorage systems (Bae and Belarbi (2013); Kalfat et al. (2013)). On the other hand, failure of completely wrapped specimens is dominated by FRP rupture or loss of aggregate interlock which results in concrete failure. In general, most failure modes typically occur at FRP strains lower than the ultimate strain of FRP laminates (Belarbi and Acun (2013)). As a result, all design guidelines limit the strain in the FRP to a fraction of the ultimate strain, known as effective strain. Several factors influence the shear capacity of FRP strengthened members. These include the geometry and mechanical properties of the member (such as width, height, compressive strength of concrete), the geometry and mechanical properties of the transverse steel reinforcement (such as spacing, diameter, yield strength of steel stirrups), and the geometry and mechanical properties of the FRP reinforcement (such as wrapping scheme, FRP type, width, thickness, etc..) (Naser et al. (2019)). Due to the complexity in determining the shear capacity of FRP strengthened members, a conservative approach is adopted by many design guidelines to compute the shear resistance of a section. This approach assumes that all the shear resistant components reach their peak values without one component failing before the other (Abuodeh et al. (2020); Chen et al. (2017)). Hence, the shear capacity is determined by superimposing three shear resisting components: concrete ( V c ), steel ( V s ), and FRP ( V f ). This paper focuses on evaluating and comparing FRP shear strength design models available by the following design guidelines: American Concrete Institute (ACI440.2R-17 (2017)), Canadian Standards Association (CSA-S806.12 (2017)), technical report task group 5.1 (fib bulletin 90 (2019)), and Concrete Society in the UK (TR55 (2000)). The accuracy of the models was assessed against an experimental database collected from the literature. 2. Research Significance and Objectives The behavior of RC beams strengthened in shear is complex. This is because of the interaction between the three components that resist the shear force (concrete, steel, and FRP). As a result, less research has been undertaken for