After years in service, strengthening or retrofitting of structural reinforced concrete (RC) elements may be needed. To do so, externally bonding Fiber Reinforced Polymer (FRP) sheets to the tension face of beams and slabs has been used as an appropriate solution to flexural strengthening of structures for years. Superior benefits of this technique that lead to increasing application in structural strengthening include high strength to weight ratio, high resistance to corrosion, ease of application and low creep. In FRP strengthened beams, when composite action between FRP and concrete is not maintained until the ultimate load is reached, premature failure results from debonding of FRP laminate. One of the debonding failure modes is intermediate crack induced debonding that can be resulted from a relative vertical displacement of the FRP across the crack opening. The relative vertical displacement, by inducing positive angle, puts the FRP plate in normal tension stress and speeds up debonding. Also at the other face of crack opening, the FRP-concrete interface is subjected to normal compressive stress and certainly the debonding is postponed. Considering the limited investigation in this field, the current study will evaluate the effect of FRP plate angle on bond behavior of FRP-to-concrete. To attain the purposes of this study, concrete prism specimens with dimensions of 150 × 150 × 330 mm were cast. CFRP plates with constant width of 50 mm were adhered to 31 specimens by using EBR method, and the other 31 specimens were strengthened by using grooving method (GM). Furthermore, to investigate the effect of FRP bond length on the bond behavior of FRP-to-concrete under normal stress, FRP sheets having bond length of 100 and 150 mm were used. In addition, to evaluate the FRP displacement field by Particle Image Velocimetry (PIV), successive images were taken until the specimen failure in single lap-shear test. Investigation of the results in the range of -4.7 up to +6.0 degree angle shows that positive angles make a sever reduction in EBR specimen ultimate load. So that in specimens with the bond length of 100 mm, the debonding load were reduced up to 41.2% in comparison with zero-angle specimen. However, introducing negative angle so that the interface undergoes compressive normal stresses, increases the stiffness and consequently the ultimate load; So that in specimens having bond length of 150 mm, the ultimate load increased up to 37.3% in comparison with zero-angle specimen. Furthermore, experimental results proved the capability of grooving method proportional to EBR method in such a situation that interface undergoes normal stresses. For instances, the ultimate load increased up to 75.9% in GM specimens undergoing negative angle in comparison with similar EBR specimen. Also, in specimens undergoing positive angle, grooving method increased the ultimate load up to 47.1% in comparison to EBR specimens. Key Words Externally bonded reinforcement (EBR), Fiber Reinforced Polymer (FRP), composite action, intermediate crack induced debonding, grooving method (GM), Particle Image Velocimetry (PIV), single lap-shear test.