Wrapping of R.C. column by means of Fiber Reinforced Polymer (FRP) reinforcement can significantly improves its structural behavior. The efficiency of this strengthening technique depends mainly upon the encountered parameters related to the original conditions of the element to be strengthened as well as upon both the volume and configuration of the wrapped reinforcement. Such parameters include concrete strength, percentage of longitudinal reinforcement, volume of internal stirrups, shape of cross-section, volume of wrapped reinforcement and arrangements of wrapped sheets. Therefore, an experimental program including seven circular columns is set-up and tested under axial compression load to evaluate the suggested strengthening technique applied to strengthen R.C. columns by means of wrapping Carbon Fiber Reinforced Polymer (CFRP) sheets. The parameters studied through this paper are the arrangements and volume of wrapped CFRP sheets as well as the volume of internal stirrups along these columns. The obtained results are used to evaluate some specific problems in the modeling of CFRP confined concrete, i.e. effective circumferential strain induced in the wrapped CFRP sheets at failure and effect of confining action. Also, the obtained experimental results together with a proposed modified mathematical model are organized in order to investigate the contribution of the externally bonded wrapped CFRP sheets to the load carrying capacity and structural ductility of the strengthened columns. The proposed modified model is based on the expression suggested by the authors to predict the effective circumferential strain induced in the wrapped CFRP sheets at failure. Moreover, an analytical verification of the obtained test results was performed according to the modified proposed model. Both load carrying capacity and structural ductility of R.C. columns improved considerably when applying the proposed strengthening technique. Also, the proposed modified mathematical models suggested to predict the strength of R.C. columns strengthened with wrapped CFRP sheets showed a considerable approach to the results obtained experimentally.
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