PSI - Issue 64

Mohamed Elkafrawy et al. / Procedia Structural Integrity 64 (2024) 436–444 Author name / Structural Integrity Procedia 00 (2024) 000–000

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1. Introduction Web openings are commonly found in reinforced concrete beams to permit air conditioning, power, and network services via utility ducts and pipes. While openings can eliminate the need for dropped ceilings and minimize building height, they lead to structural deficiencies by disrupting the natural flow of stresses, causing stress accumulation and early cracking around the opening. Numerous studies investigated the effects of openings in RC beams (Ahmed et al. , 2012). Opening size plays a predominant role in determining the failure mechanism of RC beams. As the opening size increases above 250 mm, failure occurs gradually rather than suddenly due to the relative rotation of three separate beam segments in the shear span (El Maaddawy and Sherif, 2009). According to El Ame et al. (El Ame, Mwero and Kabubo, 2020) small circular openings having a diameter less than 40% of the beam’s effective depth (d) placed in the bottom chords have no significant influence on ultimate load capacity or first crack instant, and the beam preserves both elastic and plastic deflections, allowing for some ductility. Opposingly, wide openings weaken the beam and cause early cracking. They also restrict the beam’s behavior at the elastic range, resulting in a lesser deflection. Osman et al. concluded through experiments and 3D nonlinear finite element (FE) models that openings reduce stiffness, failure load, and shear strength while increasing deflection (Osman et al. , 2017). El Maaddawy and Sherif also determined that increasing the opening size by nearly 33% with height-to-depth values of 0.3 and 0.4 causes the beam’s average shear strength to decrease by around 20% (El Maaddawy and Sherif, 2009). Few research articles focused on the behavior of beams with web openings under hogging moment. For instance, Chen et al. investigated the effect of web openings on composite cantilever beams under negative moments using experiments and nonlinear FE analysis (Chen, Gu and Li, 2011). They concluded that composite beams with web openings have lower initial cracking loads than those without web openings and collapse due to shear failure of the concrete slab at the opening. The beam’s load-bearing capacity decreases with a reduction in the web area and when the moment-to-shear ratio at the center line of the opening is increased. However, strengthening steel plates surrounding the opening can significantly enhance its mechanical behavior (Chen, Gu and Li, 2011). Enclosing or special reinforcing of the opening along its periphery is necessary to limit fracture widths and prevent early beam failure (Ahmed et al. , 2012). Many researchers have studied several different techniques to strengthen RC beams with openings. In many cases, Fiber Reinforced Polymers (FRP) are reinforced in beams with openings to improve the beam’s shear capacity and strength. Rahim et al. (Rahim et al. , 2020) investigated the structural behavior of deep RC beams with web openings reinforced with carbon fiber-reinforced polymer (CFRP) composite in the shear zone. Experimental results demonstrated that CFRP enhances the strength of deep beams. The most effective number of CFRP layers for the deep beam with 150 mm and 200 mm opening diameters was determined to be two and three, respectively. A single layer of CFRP proved insufficient for a 150 mm opening, causing shear failure. For a 200 mm opening, single and double layers of CFRP were insufficient to prevent load passage, resulting in shear failure (Rahim et al. , 2020). El Maaddawy ans Sherif also investigated reinforcing RC beams with CFRP openings (El Maaddawy and Sherif, 2009). They observed that CFRP shear strengthening around the opening significantly increased beam strength, particularly when the opening was positioned near the top of the beam; CFRP around the opening resulted in a shear strength gain of around 72%. CFRP shear strengthening increased stiffness significantly when the opening was positioned in the middle of the shear span (El Maaddawy and Sherif, 2009). Another study by Elkafrawy et al. numerically analyzed the effectiveness of employing Fe-SMA bars to reinforce the opening in the shear zone of RC beams with varying opening lengths, pre-stressing levels, and reinforcement diameters of Fe-SMA bars (Elkafrawy et al. , 2023). The study concluded that Fe-SMA bars can help the beam with openings regain its shear capacity and function similarly to solid beams. Fe-SMA bars with varying diameters to strengthen small openings can improve a beam’s shear capacity and stiffness. Increasing the pre-stressing level or the Fe-SMA reinforcement amount in RC beams with openings can reduce fracture concentration while increasing overall structural strength. Activated Fe-SMA bars were discovered to be most efficient in beams with small to medium web openings, restoring both shear strength and stiffness. However, while reinforcing beams with Fe-SMA bars improves capacity and stiffness for larger openings, it does not fully restore the original beam strength (Elkafrawy et al. , 2023). Although there is a significant amount of literature on strengthening RC beams with openings, little exploration has been done on using Fe-SMA bars as a strengthening technique. This study investigates using Fe-SMA reinforcement to strengthen RC beams with openings. This paper introduces the novel application of Fe-SMA reinforcement in RC beams with square openings of varying sizes, expanding upon the authors' previous work which focused on rectangular openings. By assessing the impact of different square opening sizes, the study provides new insights into optimizing RC beam designs for enhanced stiffness, reduced crack propagation, and improved ductility and load-carrying