Strengthened reinforced concrete (RC) beams should be designed to have adequate strength and ductility to satisfy the ultimate limit states. In this paper, first, a brief review was performed on the existing ductility and deformability models expressed in terms of deflection, curvature, rotation, energy, and strength, then, three deformability models were modified to be applicable for FRP strengthened RC beams. Afterwards, results of four series of tests on eighteen RC beams were used to evaluate their ductility and deformability. The RC beams were strengthened with prestressed and non-prestressed Near-Surface Mounted (NSM) Carbon Fibre Reinforced Polymer (CFRP) strips and rebars. The considered variables in the experimental program include prestressing level in the CFRP reinforcement (0, 20, 40 and 60% of ultimate tensile strength of the CFRP material), the geometry of the CFRP reinforcement (rebar versus strip), and the environmental exposure (room temperature versus freeze-thaw). In addition, two control un-strengthened beams were considered: one exposed to freeze-thaw and one without exposure. The freeze-thaw exposure consisted of 500 cycles, each one from temperature -34°C to +34°C within 8 hrs with a relative humidity of 75% for temperature above +20°C. Analysis of deformability was performed based on the modified models and conventional models applied to the beams. Furthermore, the design Codes' limits for ductility and deformability of the beams are checked and new limits were proposed and validated for different models to be used in practice.
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