Seismic behavior of RC columns internally confined by CFRP strips

During past decades fiber-reinforced polymer (FRP) sheets have been externally bonded to structural elements to increase their axial, shear, or bending capacity. FRP bars also have been widely used to replace the steel reinforcements in columns subjected to a harsh environment. In this study, carbon fiber-reinforced polymer (CFRP) strips were used as the transverse reinforcement for concrete columns. Although FRP bars have already been used as the transverse reinforcement in concrete columns, the efficiency and feasibility of CFRP strips have not been investigated. CFRP strips are flexible; therefore, they can be easily shaped as spirals to confine the concrete core of columns. The efficiency of CFRP strips for the confinement of the concrete core was examined through a series of quasi-static cyclic tests on four full-scale columns that had similar size and longitudinal reinforcements. One of the columns was selected as the reference, and steel spirals transversally reinforced it. CFRP strips transversally reinforced the other three columns with different widths and spacing. The obtained results showed that the number of cracks in the CFRP-confined columns was less than the reference column. The length of cracks in the CFRP-confined columns was also relatively shorter. Besides, the CFRP-confined columns had a larger ultimate load, effective yield strength, and displacement ductility ratio compared with the reference column.