Shear collapse of reinforced concrete (RC) members is catastrophic and occurs suddenly with no advance warning of distress. In several occasions existing RC beams have been found to be deficient in shear and in need of strengthening. Conventional shear strengthening methods such as external post tensioning, member enlargement along with internal transverse steel, and bonded steel plates are very costly, requiring extensive equipment, time, and significant labor.

Conversely, the relatively new alternative strengthening technique using advanced composite materials, known as fiber reinforced polymer (FRP), offers significant advantages such as flexibility in design, ease of installation, reduced construction time, and improved durability.

The overall objective of this study was to investigate the shear performance and failure modes of RC beams strengthened with externally bonded carbon FRP (CFRP) sheets. The specific goals were to address the factors affecting the shear strength, and to propose a design approach for computing the shear capacity of the strengthened beams. In order to achieve these objectives, an extensive experimental program consisting of testing twenty-seven, full-scale RC beams was carried out. The variables investigated in this experimental study included steel stirrups, shear span-to-depth ratio, and CFRP amount and configurations. As part of the research program, the experimental study examined the effectiveness of CFRP reinforcement in enhancing the shear capacity of RC beams in negative and positive moment regions, and rectangular and T cross-section beams. Furthermore, an innovative proprietary end anchor system to allow a better exploitation of the strengthening system was described and tested.

The experimental results indicated that the contribution of externally bonded CFRP to the shear capacity is significant and depends on the variable investigated. In this thesis, the proposed design approach for computing the shear capacity of the strengthened beams is presented. The design model addresses the CFRP contribution similar to the conventional shear reinforcement, according to the design format of ACI and two other design codes (Egyptian code and Eurocode). Compared with the current test results and all available published in literature up to date, the design approach gives satisfactory and conservative results.