PSI - Issue 28

Jamal A. Abdalla et al. / Procedia Structural Integrity 28 (2020) 2312–2319 Author name / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction and Background The demand for strengthening of aging reinforced concrete (RC) structures is continuously rising. Over the years, several studies were conducted to explore the effect of using external composite materials in improving both the flexural and shear behavior of strengthened specimens (Bakis et L., 2002, Nani, 2003, Esfahani et al., 2007, Bahn et al., 2008, Akbarzadeh and Maghsoudi, 2010, Hollaway, 2010, Bashandy 2013, Dong et al. 2013, El-Sayed et al., 2014, ACI-440, 2017). Fiber reinforced polymers (FRP) are the most widely used Externally Bonded Reinforcing (EBR) materials for strengthening and retrofitting of RC structural members, both in flexure and in shear (Chaallal et al., 1998, Pendhari et al., 2008, Hollaway, 2010, Siddika et al., 2019, Naser et al., 2019). Carbon Fiber Reinforced Polymers (CFRP) has been developed and used as an EBR material due to many of their desirable characteristics such as high tensile strength, high corrosion resistance, low density, high durability and ease of installation (Khalifa and Nani, 2000, Rabinovitch and Frostig, 2003, Ashour et al., 2004, Toutanji et al., 2006, Esfahani et al., 2007, Naser et al., 2012; Zhou et al., 2013, Ali et al. 2014, De Santis et al., 2016, Hawileh et al., 2017, Salama et al., 2019, Choobbor et al., 2019 ). Toutanji et al., (2006), studied flexural performance of RC beams strengthened externally with different layers of CFRP sheets and bonded with an inorganic resin. They found that by increasing the numbers of CFRP sheet layers there was a 170 % increase in the load carrying capacity compared to the control beam. On the other hand, the ductility of the strengthened beams was significantly reduced. The use of high strength Galvanized Steel Mesh (GSM) strengthening material has recently gained wide acceptance as well (Xing et al., 2010, Borri and Corradi, 2011, Qeshta et al., 2014, Qeshta et al., 2015, Hawileh et al. 2018, Douier et al., 2019, Al-Nuaimi et al., 2020 ). Both CFRP and GSM have many advantages and few shortcomings. One of their major shortcomings is the lack of ductility, low temperature resistance, deboning and degradation due to environmental factors (Naser et al. 2012). Recently developed Aluminum Alloys (AA) has high ductility and some desirable features that may overcome some of the shortcomings of GSM and CFRP (Zhu et al. 2014, Abdalla et al., 2016, Mirghani et al., 2017, Rasheed et al., 2017; Abdalla et al., 2017, Abu-Obeidah et al., 2019). Rasheed et al. (2017) carried out a comprehensive experimental and analytical investigations in the use of AA as externally bonded material for strengthening RC beam in flexure. They studied the effect of using AA plates as externally bonded flexural strengthening material and they observed an increase in strength over the control unstrengthened specimen ranged from 13% to 40% while the ductility significantly surpassed that of beams strengthened with CFRP sheets. Abuodeh et al., 2019 explored the use of AA plates with mechanical anchorage as externally bonded reinforcement material in enhancing the strength, ductility and failure modes of reinforced concrete RC beams. The test results showed an increase in the load carrying capacity by 32% and 24%, whereas deflection capacity increased by 45% and 84% for bonded AA plates and bolted AA plate, respectively compared to control beam. Abdalla et al., 2016 and Abu-Obeidah et al., 2019 studied the use of AA as externally bonded material for shear strengthening of RC beams. They observed that the shear capacity of the strengthened beams has increased in the range of 24%–89% compared to the un-strengthened beam. Hawileh et al. (2018) studied the flexural performance of RC beams that had been strengthened using high density and low density cord of hardwire galvanized steel mesh (GSM). The test results showed an increase in the load carrying capacity by Experimental results showed an increase in the load-carrying capacity of the strengthened specimens ranging from 29% to 62% over the control unstrengthened specimen. The ductility of the strengthened specimens was less than that of the control specimen and all strengthened specimens failed in flexure by delamination of the concrete cover. Hawileh et al. (2014) used hybrid Carbon and Glass sheets to strengthen RC beams in flexure. They observed that the increase in the load capacity of the strengthened beams ranged from 30% to 98% over the un-strengthened control RC beam and the ductility at failure loads of the beams strengthened with glass and hybrid sheets is higher than that with a single carbon sheet. To the authors’ top knowledge, the literature is lacking adequate information on strengthening RC beams with hybrid AA, CFRP, and GSM laminates to enhance the strength and ductility of beams. Thus, this study explores the use of a new set of hybrid combinations of AA, CFRP and GSM where the ductility of AA can be utilized. The use of AA together with CFRP and GSM as hybrid materials for externally bonded reinforcement seem to be very promising in enhancing both the ductility and the strength of RC beams. Few researchers had found that strengthened specimens with hybrid materials have shown an improvement on both strength and ductility under flexure (Zhou et al. 2013, Hawileh et al. 2014, Abdalla et al., 2018; Choobbor et al., 2019).