Repairing of RC structures has become increasingly important, especially in the last decade. Many RC structures are damaged mostly due to various forms of deterioration, such as cracks or large deflections. These are affected by different factors, like earthquakes, vibrations, corrosion of reinforced bars, and environmental changes. Externally Carbon Fiber Reinforced Polymer (CFRP) is one of the new materials used to strengthen or repair RC structures. Research on use of FRP began in Europe in the 1960s [1], and the first investigation on the use of FRP plate bonding was at the Swiss Federal Laboratory for Materials Testing and Research (EMPA) in 1984[2]. FRP materials have the advantage of high tensile strength fibers and excellent corrosion resistance, fatigue resistance, good performance at elevated temperatures, low density, and high specific stiffness and strength [3,4]. Most of the research on using FRP plate bonding for flexural strengthening has been carried out over the last decade [5][6][7]. Indeed, there has been a tremendous growth in recent years as result of worldwide need for structural performance improvement and retrofitting works. The use of the bonded prefabricated FRP plate has been found to ensure the highest degree of material uniformity and quality control [6,8,9]. An increase in the ultimate capacity is observed after adding the externally bonded CFRP sheets [10], and the ultimate capacity of strengthened beams increases by up to 230%. Even for the preloaded beam before strengthening, the ultimate capacity is significantly increased which indicates good performance for repair application [11]. Strengthening of corroded RC beams with externally bonded CFRP plates was found to increase the ultimate capacity by 37-87%[12]. CFRP laminate for strengthening of RC beams shows the ability for doubling the load capacity with deflection close to that of found that the hybrid laminate of Kevlar/epoxy-graphite/epoxy is more flexible than the graphite/epoxy one. Repairing of corroded RC beams with bonded CFRP sheets restores the undamaged state stiffness and reduces the ultimate deflection in comparison to the un-strengthened beams [16]. Bouchikhi et al. [17] concluded that the interfacial shear stress is affected by the FRP plate thickness and the adhesive layer, where the interfacial stress obviously increases with the increase in the FRP thickness. Experimental work carried out by proved the effect of the
This paper presents the results of both analytical and experimental study on the repair effectiveness of Carbon Fibre Reinforced Polymer (CFRP) sheets for RC beams with different levels of pre-repair damage severity. It highlights the effect of fixing CFRP sheets to damaged beams on the load capacity, mid-span deflection, the steel strain and the CFRP strain and failure modes. The analytical study was based on a Finite Element (FE) model of the beam using brick and embedded bar elements for the concrete and steel reinforcement, respectively. The CFRP sheets and adhesive interface were modelled using shell elements with orthotropic material properties and incorporating the ultimate adhesive strain obtained experimentally to define the limit for debonding. In order to validate the analytical model, the FE results were compared with the results obtained from laboratory tests conducted on a control beam and three other beams subjected to different damage loads prior to repair with CFRP sheets. The results obtained showed good agreement, and this study verified the adopted approach of modelling the adhesive interface between the RC beam and the CFRP sheets using the ultimate adhesive strains obtained experimentally.
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