1 New Method of Strengthening Reinforced Concrete Square

5 Abstract: This study investigates three methods of strengthening existing reinforced square concrete columns under different loading 6 conditions. Four groups of sixteen reinforced concrete square columns were made from normal-strength concrete. Reinforcement was kept 7 at minimum ratio, simulating columns that need retrofitting. Columns of the first group were reference columns (Group N), while the corners 8 of the second group columns (Group RF) were rounded and wrapped with three layers of carbon-fiber-reinforced polymers (CFRPs). The 9 sides of the columns of the third group (Group CF) were bonded with four pieces of concrete with a segmental circular shape, thus changing 10 the cross section of the column from a square to a circle before each column was wrapped with three layers of CFRP. The columns of the 11 last group (Group CS) were modified as the 2 third group to result in a circular cross section, but were confined with steel straps. Results 12 from the study showed that all confinement methods increased the capacity and ductility of columns. In particular, segmental circular con13 crete covers dramatically reduced the stress concentration at the corners and increased confinement efficacy. The interaction (P–M) 14 diagrams of experimental results and theoretical analysis all confirmed high performance of groups RF and CF. DOI: 10.1061/(ASCE) 15 CC.1943-5614.0000335. © 2013 American Society of Civil Engineers. 16 CE Database subject headings: Fiber reinforced polymer; Eccentric loads; Reinforced concrete; Concrete columns; Experimentation. 17 Author keywords: Square columns; Steel straps; P–M interaction diagram.