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In the present paper, several well-known existing design-oriented relations for circular and rectangular columns confined with fiber reinforced polymers (FRP) are reviewed and their accuracy are compared using a comprehensive database set up by the experimental results extracted from the previous research works. The main motivation for this study is the fact that despite several performed studies to develop practical models for predicting compressive strength of concrete confined with fiber reinforced polymer wraps in the past two decades, which some of them are reviewed in the present paper, it is not known clearly that which model has the most accuracy and applicability. In addition to the performed review and evaluation, new and more accurate relations are proposed using nonlinear regression techniques and their accuracy verified using same experimental data. Based on the attained results, the new proposed relationships displayed better accuracy than the existing FRP confined concrete strength models. The average values of error for the proposed relations correspond to circular and square cross sections were about 13.0 and 15.5%, respectively.

Application of fiber-reinforced polymer (FRP) for retrofitting and rehabilitation of concrete structures is a common method. The main role of FRP confinement for reinforced concrete (RC) columns is to increase the ultimate strength and strain of confined concrete core and therefore improve in the load carrying capacity of the columns. However, it is possible that a previously short column fails due to buckling after the application of FRP confinement. In other words, the enhanced compressive strength of a retrofitted column may go beyond its buckling load. Therefore, a design criterion to predict this condition is necessary for the designers in the preliminary and final stages of the design. In this paper, a predictive model is proposed to determine the slenderness limit of FRPconfined circular RC columns. The suggested relation was derived using one of the accurate design-oriented strength models for FRP-confined concrete columns as well as analytically derived buckling equations. The effect of hybrid FRP confinement is also incorporated in the suggested slenderness limit. Moreover, a parametric study was performed on the suggested model to specify most influential parameters. The accuracy of the proposed relation was evaluated using a database of experimental results collected from previous studies. The results of the evaluations demonstrated acceptable accuracy of the proposed relation in predicting behavior and failure mode of FRP-confined RC columns.

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