| Shear failure 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 and repairing. RC beams can be deficient in shear capacity due to a variety of factors: error in design calculation and improper detailing of shear reinforcement; construction faults or poor construction practices; changing the function of a structure from a lower service load to a higher service load; and reduction in or total loss of shear reinforcement steel area due to corrosion in severe environments characterized by high temperature and high humidity, and severe ambient and ground salinity. The deficient beams are not acceptable from the points of view of safety and public acceptance, therefore, they require immediate repair to prevent further degradation and to restore their structural integrity. 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 first goal of this study was to investigate the shear performance and failure modes of pre-damaged RC beams, which are deficiencies in shear and have different degrees of damage, and strengthened with externally bonded carbon fiber reinforcement polymer (CFRP) sheets strips. The second goal of this study was on the behavior and effectiveness of CFRP sheets strips (sides-boded) for shear strengthening of pre-cracked RC beams, at a high degree of damage, with epoxy repairing. Whereas epoxy resins usually are used as a treatment in a cracked structure. In order to fulfill these goals, an experimental program consisting of testing a five, rectangular simply supported RC beams, 1700 mm in length with supports of 1500 mm apart, was carried out. The variables investigated in this experimental study included degree of damage before shear strengthening and repair the main shear crack by injection epoxy. The beams were pre-cracked to a predetermined level defined subsequent to testing of the control beam, which was unrepaired. They were pre-cracked by preloading under two symmetrical points load with a 600 mm shear span. The load was then released and beams were prepared for strengthen by CFRP or strengthen by CFRP and repair previous shear cracks by epoxy, then they tested until fail in shear.Results of the tests demonstrated the feasibility of using CFRP sheet bonded side strips to restore or increase the load capacity in shear of damaged RC beams, without considered in their degrees of damage before strengthening. The experimental results indicated that the shear repair of the pre-cracked RC beam by used the epoxy should be carried out prior to development cracks whenever it is applicable. In this dissertation, the available designs proposal in literature were compared with experimental results, and the proposed design approach for computing the shear capacity of the strengthened RC beams by sides- bonded CFRP strips is presented. The design approach gives satisfactory and conservative results.
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