Behavior and modeling of confined concrete cylinders in axial compression using FRP rings

This study suggests a secondary dense lateral reinforcement for reinforced concrete (RC) columns that are located between the primary lateral reinforcement and concrete surface, which are used to delay the buckling of longitudinal reinforcement and increase the ductility of RC columns. 'Dense' means that the spacing of the lateral reinforcement is smaller than the maximum gravel size. This study conducted axial compressive tests on concrete cylinders confined by dense reinforcement in order to improve the effectiveness of the dense lateral reinforcement. FRP (Fiber Reinforced Polymer) rings were used for the reinforcement since they are corrosion resistant. The dense reinforcing method with FRP rings can successfully increase the peak strength of the concrete and the failure strain. The stress-strain curves of the confined concrete became almost bilinear with hardening behavior, which were similar to that of the concrete confined by the jackets of FRP sheets. This study also provides models of stress-strain in an axial direction and lateral strain. Based on the models, this study analyzes the confining effectiveness of the FRP rings on concrete.