This paper presents the results of experimental and numerical investigations of the retrofitting/strengthening of shear deficient reinforced concrete (RC) beams with externally bonded carbon fiber reinforced polymer (CFRP) sheets. A total of 12 full-scale beams were used in this study. The beams were divided into two series, i.e., A and B, with six beams each. Each series had three groups of beams. There were two identical beam samples in each group with constant depth. The beams in series A were loaded until failure, and failure loads were noted. The beams in series B were loaded to a fraction (70 %) of the failure load. Then, all the beam specimens were retrofitted/strengthened with CFRP sheets and retested until failure. The load at the first crack and at failure, crack pattern and deflections were recorded for all specimens during testing. A nonlinear finite element analysis (FEA) of the control and retrofitted/strengthened beams was also carried out by using ANSYS software. The load-deflection plots, crack patterns, first crack loads and failure loads were predicted from the FEA. The results obtained from the experimental investigation indicated that the load carrying capacity of the retrofitted/ strengthened beams increased remarkably for both series compared with that of the control beams. The loads at the first crack of the series A specimens were lower than those of the control specimens. On the other hand, the loads at the first crack of the series B specimens were greater than those of the control specimens. Compared with those of the corresponding control specimens, the loads of the beams in the SDS, SDM and SDD groups in series A decreased by 27 %, 22 % and 17 %, respectively, at the first crack. Compared with those of the corresponding control specimens, the loads of the beams in the SDS, SDM and SDD groups in series B increased by 9 %, 12.5 % and 15.7 %, respectively, at the first crack. It was further observed that specimens of series B (preload to failure) exhibit significantly higher ultimate load values than those of series A beams. The failure loads of the series B specimens SDS-B, SDM-B and SDD-B were 54 %, 60 % and 62 % greater than those of the corresponding series A beams SDS-A, SDS-A and SDM-A, respectively. The contribution of CFRPs to the load carrying capacity was greater for strengthened beams than for retrofitted beams. All specimens show approximately the same amount of improvement in load carrying capacity regardless of the depth of the specimens after retrofitting/strengthening with CFRP. The general trend of the load-deflection plots at the mid span predicted by the FEA agreed well with the experimental test results. The crack patterns anticipated by FE models at ultimate loads also relate well to the failure modes of the experimental test beams. However, the ultimate loads obtained from the FE models are as high as 15 % of the experimental test results.
