PSI - Issue 28

Kais Douier et al. / Procedia Structural Integrity 28 (2020) 986–993 Douier et al./ Structural Integrity Procedia 00 (2020) 000–000

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1. Introduction Externally strengthening reinforced concrete (RC) structures with fiber reinforced polymers (FRP) have been widely investigated in the past few decades (Choobbor, Hawileh, Abu-Obeidah, & Abdalla, 2019; Firmo, Correia, & França, 2012; Helal, Yehia, Hawileh, & Abdalla, 2020; Maraveas, Miamis, & Vrakas, 2012; Sen & Jagannatha Reddy, 2013). Members such as walls, beams, columns, and slabs could be weakened and weathered over time, instigating a need for externally bonded reinforcement (EBR) systems to emerge. Researchers have found various methods to utilize FRP sheets or plates to enhance RC members’ flexure and shear strengths, as well stiffness and durability (Ekenel & Myers, 2007; El-Hassan, El-Maaddawy, Al-Sallamin, & Al-Saidy, 2018; Rami A. Hawileh, Abdalla, Tanarslan, & Naser, 2011; Rami Hawileh, Nawaz, & Abdalla, 2018; Naser, Hawileh, & Abdalla, 2019; Rasheed, Abdalla, Hawileh, & Al-Tamimi, 2017). One of the most common types of FRP materials used in EBR systems is carbon-FRP (CFRP) sheets, which can only be bonded to concrete surfaces with epoxy adhesives due to the high density of fibers in such sheets. However, galvanized steel mesh (GSM) sheets were also found to be as effective as CFRP in externally strengthening RC structures (Ascione, Lamberti, Napoli, Razaqpur, & Realfonzo, 2017; R Hawileh, Abdalla, Nawaz, Mwafi, & Alzeer, 2014). The GSM sheets have mainly three cord-densities: high (7.09 cord/cm), medium (4.72 cord/cm), and low (3.15 cord/cm). High and medium cord-density GSM sheets can only be bonded to concrete surface with epoxy adhesive, but low cord-density GSM sheet can also be bonded with cement mortar to concrete surfaces (K.A. Douier et al., 2019). The utilization of CFRP and GSM sheets in flexural strengthening can add a great advantage in increasing RC member’s load-bearing capacity. According to De Santis et al., (2016) GSM sheets may be used to increase the load carrying capacity of RC members in flexure and shear. They also stated that it can increase the flexure and shear strength of RC members by 300 and 200%, respectively. A study was conducted by Napoli & Realfonzo, (2015), investigated the performance of 10 RC slabs strengthened with steel reinforced polymer (SRP) and steel reinforced grout (SRG) subjected to four point bending test. Their study concluded that such EBR systems increase the flexural capacity of RC slabs disregarding the type of matrix used as a bonding agent, and flexural strengthening increases the SRG systems efficiency and highly comparable to that of the SRP systems. They also concluded that when compared to control un-strengthened specimens, the flexure strength of strengthened specimens increase by a range of 27 – 106%. Another study was conducted by Hawileh et al., (2018), where they investigated high and medium cord densities of hard-wire steel fiber (HSF). The authors tested 7 RC beams that were strengthened in flexure with high and medium density GSM sheets and bonded with epoxy adhesive under four-point loading. The load-carrying capacity of RC beams strengthened with high and medium cord densities have increased by 29 and 62% when compared to control un-strengthened beams, respectively. The study also concluded that the ductility of strengthened specimens was lower than that of the control un-strengthened specimen. However, these EBR systems create a big disadvantage in decreasing the strengthened RC member’s ductility, due to its brittle failure mode (Abuodeh, Abdalla, & Hawileh, 2019; R. A. Hawileh, Musto, Abdalla, & Naser, 2019; Mohammed, Abdalla, Hawileh, & Nawaz, 2018; Napoli & Realfonzo, 2015; Rasheed et al., 2017). Accordingly, researchers have been studying the effects of anchoring flexure EBR systems in order to delay the laminate’s debonding or concrete cover separation (brittle failure), that will attain higher strain levels in the sheets and thus enhances the member’s flexural strength (Elsanadedy, Almusallam, Alsayed, & Al-Salloum, 2013; Rasheed et al., 2017; Salama, Hawileh, & Abdalla, 2019). Aljaafreh et al., (2017) experimentally investigated the effects of mechanical and U-Wrap end anchors on flexural strengthened RC beams with CFRP sheets. The authors tested a total of 8 RC beams under four-point loading with a ranging rate of 22 to 35 N/sec. The beams were divided into four groups (control un-strengthen, flexural strengthened only, flexural strengthened with mechanical anchorage, and flexural strengthened with U-Wrap anchorage systems), and each group included 2 specimens to average the data. The study concluded that flexural strengthening of all specimens increased the load-bearing capacity up to 12%. Also, the U-wrap end anchors increased the tensile strain of the strengthened specimens up to 81%. Although the U-wrap end anchors were more effective in delaying the brittle debonding failure than the mechanical end anchors, however the mechanical end-anchors were found to be better in increasing the specimens’ elastic stiffness.