Hybrid Confinement of Concrete by Fiber-Reinforced Polymer Sheets and Fiber Ropes under Cyclic Axial Compressive Loading

This study looks into the mechanical behavior of concrete lightly confined by fiber-reinforced polymer (FRP) sheets made with glass fibers and by polypropylene fiber ropes (PPFRs). PPFRs have ultrahigh deformation at failure. The hybrid confining technique suggests applying the fiber rope on already cured FRP jackets as external unbonded reinforcement. No impregnation or gluing resins are necessary for the fiber rope (FR) application. The technique uses mechanical anchorage for the ends of the FR. Sixteen confined standard concrete cylinders, in two series and with different concrete qualities, were tested under repeated axial compression cycles of increasing displacement. They included confinement of one layer of glass FRP and FR confinement in different volumetric ratios. The investigation also compares columns confined only by glass fiber-reinforced polymer (GFRP) jackets or only by PPFR wrapping. The elaboration evaluates the axial stress versus axial and lateral strain behavior of the columns. Proper design of the hybrid confinement utilizes further the confining effects of the FRP sheet up to its multiple fracture. Then, FR ensures increased axial strain (higher than 5%) and dissipated energy of concrete. The load presents a temporary yet controlled loss, followed by an increase for further loading.