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Fiber-wrapping or encasement of concrete in fiber-reinforced plastic (FRP) shells significantly enhances strength and ductility of concrete columns. However, design of such hybrid systems requires an accurate estimate of the performance enhancement due to the confinement mechanism. Current design procedures are simple extensions of the models developed for conventional reinforced concrete columns. Previous studies have demonstrated that such models may not be conservative for FRP-encased concrete. A simple model is presented to predict the complete bilinear stress-strain response of FRP-confined concrete in both axial and lateral directions. The model is based on correlation between the dilation (expansion) rate of concrete and the hoop stiffness of the restraining member. The parameters of the model are directly related to the material properties of the FRP shell and the concrete core. The predicted stress-strain curves compare favorably with the results of the present study, as well as tests by others on both fiber-wrapped and FRP-encased concrete columns.
Samaan et al. (Tue,) studied this question.