Performance of NSM-FRP RC beams in flexure and shear using locally developed CFRP rebars

Abstract

In the present study, an experimental investigation was carried out to evaluate the flexural and shear capacity of near surface mounted (NSM) reinforced concrete (RC) beams using carbon fibre reinforced polymer (CFRP) rebars. A total of 16 half scale beams were tested to study the flexural and shear responses of strengthened RC beams. The CFRP rebars were manufactured at structural testing centre using locally developed twisting equipment to strengthen the RC beams. Also, new anchor system was locally developed to predict the tensile characteristics of CFRP bars using universal testing machine. To examine the flexural and shear behaviour, all beams were tested under two-point loading system. It was observed that the NSM strengthened RC beams have higher load carrying capacity than the corresponding control beam in flexure and shear by 68% and 35.6%, respectively. Typical failure modes of the beams during the experimental investigation were CFRP rupture, CFRP debonding, crushing of concrete and shear failure. Finally, a design example has been presented for better understanding in the analysis and design of NSM FRP strengthened RC beams. Further, the values obtained from the analytical study are in good agreement with the experimental values.Keywords: beam; composite; design example; flexure; NSM-FRP; performance; strengthening; shear; sustainable materials.Reference to this paper should be made as follows: Singh, S.B., Sivasubramanian, M.V.R., Likhith Reddy, A., Chandra Prakash, K., Nagarjuna, K. and Hima Kiran, A. (2012) 'Performance of NSM-FRP RC beams in flexure and shear using locally developed CFRP rebars', Int.

Shear strengthening of RC beams with NSM FRP. I: Review of strength models

“…Figure 3 graphicly shows the interpretation of the variables in those three models (i.e. Islam 2009;Kotynia 2007;Singh et al, 2012). Similar to the previous two models, the assumption on the effective stress of NSM FRP is too simple, and many potential influencing factors (e.g.…”

Shear strengthening of RC beams with NSM FRP. II: Assessment of strength models

“…In terms of the PoE, compared with the combined case, five models (i.e. Parretti and Nanni 2004;Kotynia 2007;Islam 2009;Singh et al, 2012;Dias and Barros 2013) show obvious increases, and two models (Rizzo and De Lorenzis 2009;Mofidi et al, 2016) show obvious decreases, and the other two models (Bianco et al, 2014;Perera et al, 2014) show less difference.…”

“…a certain value was assumed for the effective strain of NSM FRP in Kotynia's (2007) Different from the above models (Kotynia 2007;Islam 2009;Singh et al, 2012), Dias and Barros (2013) proposed a more complex model to calculate the effective strain of NSM FRP, in which various parameters including Ec of FRP and stirrup, the ratio of FRP and stirrup as well as concrete tensile strength were considered. As can be seen in Figure 4, compared with the previous models (Kotynia 2007;Islam 2009;Singh et al, 2012), relatively more accurate predictions were achieved by Dias and Barros's (2013) model, and the difference between the cases of round bars and strips is less obvious, although such difference still exists in Dias and Barros's (2013) model, on the account that the equation for calculating the effective strain was developed based on the database that only included beams with NSM FRP strips. It can be also seen from Figure 4 that the predictions from Dias and Barros's (2013) model with considering the safety factor is closer to the "perfect match line", while those without considering the safety factor are relatively more unconservative.…”

“…As one of the main applications of the NSM technique, the shear strengthening of RC beams by applying the NSM FRPs into the concrete covers on beam sides has attracted a lot of attention from worldwide researchers, and a large number of relevant experimental (e.g. De Lorenzis and Nanni 2001; Nanni et al, 2004; Barros and Dias 2006; Kotynia 2007; Rizzo and De Lorenzis 2007; Rahal and Rumaih 2011; Dias and Barros 2012, 2013, 2017; Jalali et al, 2012; Singh et al, 2012; Wiwatrojanagul et al, 2012; Barros et al, 2016; Mofidi et al, 2016; Kuntal et al, 2017; Al Rjoub et al, 2019; Prabhakaran and Joseph 2019; Abdel-Jaber et al, 2021; Alwash et al, 2021; Saadah et al, 2021) and numerical studies (e.g. De Lorenzis and Nanni 2001; Parretti and Nanni 2004; Kotynia 2007; Islam 2009; Rizzo and De Lorenzis 2009; Singh et al, 2012; Dias and Barros 2013; Bianco et al, 2014; Perera et al, 2014; Mofidi et al, 2016; Chen and Cheng 2019; Bui and Stitmannaithum 2020) have been conducted and presented.…”

Strengthening of RC beams with opening in shear zone using external prestressing technique

“…They also recommended that a higher factor of safety is needed for the design of FRP strengthened beams in view of the potential for brittle failure of such strengthened beams. Singh et al (2012) developed CFRP rebars at the Structural Testing Center of BITS Pilani and used them as near-surface mounted FRP rebars for shear and flexural strengthening of RC and engineered cementitious composite beams.…”