letter Flexural behavior of RC beams strengthened by NSM GFRP Bars having different end conditions R.M. Reda a , I.A. Sharaky b,c,⇑ , M. Ghanem d , M.H. Seleem c , H.E.M. Sallam c,e a Civil Engineering Department, Higher Technological Institute, 10th of Ramadan City, Egypt b Civil Engineering Department, Taif University, Taif 888 21974, Saudi Arabia c Materials Engineering Department, Zagazig University, Zagazig 44519, Egypt d Mechanical Department, Faculty of Industrial Education, Suez Canal University, Suez, Egypt e Civil Engineering Department, Jazan University, Jazan 706, Saudi Arabia article info Article history: Received 11 December 2015 Revised 27 February 2016 Accepted 11 March 2016 Available online 23 March 2016 Keywords: RC beam Strengthening GFRP NSM End anchorage abstract Near surface mounted (NSM) fiber reinforced polymer (FRP) bars became more effective in strengthening reinforced concrete (RC) beams. This is because it increases the bond capacity and makes a protection against external damage. Most of previous related researches stated that the failure of the tested RC strengthened beams with NSM FRP is due to debonding or concrete cover separation. In this research the ends of the NSM glass fiber reinforced polymer (GFRP) bars were bent to delay or prevent NSM FRP debond- ing and concrete cover separation and thus increasing the load carrying capacity of the strengthened beams. The inclination angles of GFRP bars with bent ends were 90° and 45°. Straight GFRP bars with variable lengths were also used for comparison. The test results demonstrated that the GFRP bars with bent ends prevented the concrete cover separation and increased the load carrying capacity of the strengthened beams. The load carrying capacity of the strengthened beams by straight NSM bars and those having 45° and 90° inclined ends were 177%, 201%, and 185% of that of their control beam, respectively. Ó 2016 Published by Elsevier Ltd. 1. Introduction Externally Bonded (EB) and near surface mounted (NSM) are the most commonly strengthening methods. In these two methods, Fiber Reinforced Polymer (FRP) reinforcements were used to upgrade reinforced concrete (RC) members. Externally bonded tech- nique using FRP bars had been widely used for strengthening RC members. This is due to many advantages of FRP bars such as high strength to weight ratio, easy installation and high resistance to cor- rosion. Although the use of EB technique increases the load carrying capacity of the RC strengthened members, the NSM FRP strengthen- ing technique offers many advantages over EB. These advantages include increasing bond capacity due to larger bonded surface area and make a protection against external damage results from exter- nal impacts, since the bar is embedded in the concrete cover [1,2]. Although the researches indicated that the EB and NSM techniques are effective techniques for increasing both flexural and shear capac- ity of structural members [3–6], the failure due to debonding of FRP reinforcement is still the most common failure mode [7–10]. Debonding may occur as: a concrete cover separation or end bar debonding [11]. Debonding failure of NSM FRP is interfacial debonding at the FRP–epoxy interface [12]. The failure of NSM FRP structural elements may occur due to splitting of the epoxy cover, cracking of the concrete surrounding the groove and pullout of the FRP bars or combined failure [13–24]. Although debonding failure is less expected to happen in NSM FRP reinforcement com- pared to EB FRP sheets [25], previous researches reported that, NSM FRP reinforcements cannot reach their full tensile strength, due to premature debonding or epoxy and concrete splitting [13–15]. Because of the debonding problem, researches were devoted to find the way by which such type of failure can be pre- vented. Hybrid bonded FRP technique [26] and U-anchor system [27] are suggested to prevent such type of failure. Sallam et al. [2] found that cover separation or debonding failure in EB system can be prevented by concrete cover replacement technique. More- over, external stirrups and U-wraps were used to prevent cover separation or FRP debonding in EB or NSM strengthened beams [28]. It was concluded that [28] the use of external transverse anchoring reinforcement increased the flexural capacity of the strengthened members. http://dx.doi.org/10.1016/j.compstruct.2016.03.018 0263-8223/Ó 2016 Published by Elsevier Ltd. ⇑ Corresponding author at: Materials Engineering Department, Zagazig Univer- sity, Zagazig 44519, Egypt. E-mail addresses: ibrahim.attia@udg.edu, himasharaky@yahoo.com (I.A. Sharaky). Composite Structures 147 (2016) 131–142 Contents lists available at ScienceDirect Composite Structures journal homepage: www.elsevier.com/locate/compstruct