Behavior of Circular Reinforced-Concrete Columns Confined with Carbon Fiber–Reinforced Polymers under Cyclic Flexure and Constant Axial Load

Deficient concrete-bridge columns can be effectively upgraded by bonding on the exterior surface fiber-reinforced polymer composite sheets with the fibers oriented in the columns’ circumferential direction, thus providing additional confinement. The efficiency of this rehabilitation method has been proven by the results of a number of cyclic loading tests performed on column specimens. The number of these tests, however, is much less than similar ones performed on reinforced-concrete columns without fiber-reinforced polymer confinement. This paper presents cyclic flexural test on reinforced-concrete columns confined with conventional circular hoops and carbon fiber–reinforced polymer and subjected to different axial-load levels. In addition to enriching the available database, the tests in this research program were programmed such that failure would occur in the composite sheets to validate an innovative stress-strain model that considers the passive confinement provided by both transverse-steel reinforcement and fiber-reinforced polymer wrapping. This experimental program includes eight circular reinforced-concrete columns having a 305 mm diameter and a height of 2 m. The parameters studied in this research program include the spacing of the hoops (75 or 150 mm), the intensity of the constant axial load (10 or 35% of the gross section capacity), and the presence of one or no carbon fiber–reinforced (CFRP) layer. The test results show that the addition of CFRP sheets enhances the behavior of the columns in terms of ductility and energy dissipation. The enhancement is more pronounced for the specimens with larger transverse steel–reinforcement spacing and lower axial-load level. The predictions of the moment-curvature show very good correlation with the measured responses.