Design-Oriented Strength Model for FRP-Confined Concrete Members

AbstractThis study concerns assessing 20 existing models for predicting the compressive strength of concrete uniformly confined externally with composite materials. An extended database of 471 experiments on cylindrical concrete columns is utilized for the comparisons. The research classifies the experimental data in three distinguished subcategories according to the information available for the mechanical properties of the FRPs to investigate their effect on the divergences of the models. Apart from the use of the tensile strength obtained from coupon tests, the use of properties from the manufacturer data on FRP fibers can lead to minimum error of predicted strength of concrete externally wrapped or encased in FRP tubes. The study results in the proposal of an upgraded empirical model that indirectly encompasses the unique deformational characteristics of different Young’s moduli of FRP sheets and tubes. The model utilizes the strong linear dependence of the product of the varying effective strain at failure of the confining material (εje) times the varying confinement effectiveness coefficient (k1) on the Young’s modulus of the reinforcing fibers (Ef). Thus, there is no need to estimate average empirical constant values for the εje or k1, and a more rational approach comes up that further restricts errors in strength modeling. The proposed model provides a prediction with absolute average error of 8.6% for wrapped columns and 6.3% for FRP-tube encased columns.