Groove align="center" Fatemeh Mohammadi fateme.mohamadi@cv.iut.ac.ir September, 2019 Department of Civil Engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: M.Sc Language: Persian Supervisor: Dr. Davood Mostofinejad, Prof. Email address: dmostofi@cc.iut.ac.ir In recent years, owing to their advantageous properties, such as light weight, high tensile strength, and high durability under harsh environmental conditions, using fiber reinforced polymer (FRP) composite have known as an effective way for strengthening concrete structures. Despite certain benefit of externally bonded reinforcement (EBR) technique such as simple and rapid installation, premature debonding of FRP sheet from the concrete substrate is one of its limitation. Grooving method as an effective way to postpone or eliminate FRP debonding has been recently introduced at Isfahan University of Technology. In last studies, number, spacing, and direction of grooves was constant, and only width and depth of groove was changed and evaluated. The main purpose of the current study is evaluation of width, depth, spacing, and direction of grooves and presentation of class of grooves for the first time. In current study, 24 class of grooves were defined. As a result, 48 specimens were strengthened with grooving method (EBROG), and 2 specimens were strengthened with externally bonded reinforcement (EBR) method using CFRP sheet. For this purpose, 36 concrete specimens with dimension of 150×150×350 mm were cast, three side of which could be used in the single-lap shear tests. All specimens were tested through single lap-shear test after strengthening. The PIV technique was exploited to derive the deformation of all the tested specimens in the corresponding digital images. The results were shown that bond resistance in EBROG joints increased by up to 141% relative to that of the EBR joints. For constant groove dimensions, the ultimate load increased with decreasing groove spacing; e.g., for transverse grooves of 2.5×2.5 mm, an increase of about 75% was observed when the groove spacing decreased from 80 to 12 mm. Although groove direction was found to have no significant effect on bond resistance in most groove classes, they had the different stress transfer mechanism. The results show that longitudinal grooves can transfer the stress to profound parts of concrete; however, the transverse grooves propagate the stress along the concrete's surface. In 2.5 and 5 mm grooves, the longitudinal and transverse grooves had approximately similar performance because the height of grooves is small, so the longitudinal grooves cannot penetrate shear stress to profound parts of the concrete. However, because of appropriate dimension of 10 mm grooves, longitudinal grooves can transfer the stress to profound parts of concrete, and transverse grooves can propagate the stress along the concrete's surface. In current study, deonding in concrete were demonstrated in all specimens. In EBROG joints, concrete crushing and cracks in concrete might appear with decreasing groove spacing. Moreover, PIV results reveals that EBROG joints can increase effective bond length up to 250.77%. results show that in Classes LG 2.5×2.5, TG 2.5×2.5, LG 5×5, and TG 5×5 mm, with decreasing the distance of grooves the effective bond length and bond resistance increased. However, in Classes LG 10×10 mm, decreasing the distance of grooves caused to increase the bond strength and decrease the effective bond length. Furthermore, bond-slip curves in EBROG joints exhibited that fracture energies increased by around 5.18 times compared to EBR joints. Comparison of experimental and models shows that these models are not appropriate for predicting bond strength and effective bond length. Keywords: FRP composites, single lap-shear test, externally bonded reinforcement (EBR), grooving method (EBROG), particle