Behavior and modeling of partially CFRP confined reinforced concrete columns under axial compression

This study presents an experimental investigation on the compressive performance of reinforced concrete (RC) columns wrapped with CFRP strips. The main test variables included the wrapping strategies, the clear spacing ratio of CFRP strips, and the number of CFRP layers. The experimental results indicate that the application of CFRP strips located in between the internal steel hoops exhibits superior compressive behavior of columns due to the more uniform confinement along the height of columns, especially for the deformation capability. Besides, the hoop strains of both external CFRP strips and internal steel stirrups at a given axial strain under the above wrapping layout are found to be smaller than those in the columns with the CFRP strips and steel hoops located at the same height. Moreover, the improvement in both strength and deformation capacity is more significant for the specimens with a smaller clear spacing of CFRP strips and thicker CFRP jackets. Based on the existing studies, the accuracy of several selected models is assessed for the predictions of stress and corresponding strain at the ultimate state, and a new confinement coefficient is further proposed to interpret the influence of the relative location between CFRP strips and steel stirrups on the ultimate axial strain. Comparisons between the theoretical predictions and test results reveal that the refined ultimate strain model can provide more accurate and reasonable predictions.