عنوان مقاله [English]
Despite extensive field applications of FRP plates, not all behavioral aspects of this construction material have yet been fully understood. One neglected aspect is their rupture and the causes for their debonding off the concrete surface to which they are adjoined under unexpected and premature loads. All plate debonding types in RC beams can be generally considered as a kind of discontinuity. From this viewpoint, plate-end debonding causes discontinuity in the strengthening sheet, and higher thicknesses of the strengthening sheet causes intensified discontinuity in the concrete member thickness. Furthermore, flexural and shear cracks cause discontinuity in the concrete member, causing crack width to intensify discontinuity and, finally, leading to the debonding of the strengthening sheet. Different arrangements of flexural bars in the concrete beam lead to different crack distributions during loading. The difference in distribution involves, not only crack spacing, but, also, crack width; both of which are discontinuities in the beam. On the other hand, cracks and crack propagation also lead to moisture and destructive ions penetration and, thereby, to corrosion of the embedded reinforcement in concrete members.In this study, the effects of different arrangements and layouts of internal steel reinforcement on design de- bonding loads and the cracking pattern of RC beams strengthened with CFRP sheets are experimentally investigated. A total of nine 3-m long beams were tested under 3- point loading. Three different bar sizes were used to reinforce the beams, i.e.$5\Phi$14, 3$\Phi$18 and 2$\Phi$22 while the reinforcement ratios in all beams were almost the same. The first three beams were used as base specimens and just for comparison. The second three specimens were loaded, after strengthening with two layers of CFRP up to failure. Finally, the last three beams were loaded, before strengthening up to 70\% of the maximum load in the linear part of the load-deflection response. Then, the beams were reloaded and strengthened with two layers of CFRP and loaded again up to failure. The results showed that smaller-size steel bars cause more uniform distribution of cracks along the beam, accompanied by lower crack widths. Furthermore, the axial strain distribution in the CFRP strengthening plate had more uniform distribution in beams with fewer tensile steel bars. No significant differences were observed among specimens with various bar sizes, in terms of the peeling load of the CFRP plates.