Research Online Research Online Behavior of circularized hollow RC columns under different Behavior of circularized hollow RC columns under different loading conditions loading conditions

Abstract One of the methods for strengthening square concrete columns is shape modification. The method involves modification of the column cross section from square to circular by bonding concrete segments and then wrapping the column with fiber reinforced polymer (FRP). This paper investigates experimentally the applicability of the shape modification (circularization) for square hollow reinforced concrete (RC) specimens under different loading conditions. Five groups of four hollow RC specimens made from normal strength concrete were cast and tested. The specimens in the first group were RC hollow specimens, which served as reference specimens. The corners of the specimens in the second group were rounded to 20 mm and wrapped with two layers of carbon FRP (CFRP). The specimens in the third group were circularized and wrapped with two layers of CFRP. The specimens in the fourth group were bonded with one CFRP strap longitudinally on each side and then circularized and wrapped with two layers of CFRP. The specimens in the fifth group were wrapped with one layer of CFRP and then circularized and wrapped with two layers of CFRP. The results show that circularization increased the strength and ductility of the hollow specimen. Transverse wrapping with CFRP mainly improved the performance of the specimens under concentric axial loadings, while the longitudinal CFRP straps mainly improved the performance of the specimens under eccentric axial loading. ABSTRACT: One of the methods for strengthening square concrete columns is shape 5 modification. The method involves modification of the column cross-section from square to 6 circular by bonding concrete segments and then wrapping the column with fiber reinforced 7 polymer (FRP). This paper investigates experimentally the applicability of the shape 8 modification (circularization) for square hollow reinforced concrete (RC) specimens under 9 different loading conditions. Five groups of four hollow RC specimens made from normal 10 strength concrete were cast and tested. The specimens in the first group (N) were RC hollow 11 specimens, which served as reference specimens. The corners of the specimens in the second 12 group (RF) were rounded to 20 mm and wrapped with two layers of carbon FRP (CFRP). The 13 specimens in the third group (CF) were circularized and wrapped with two layers of CFRP. 14 The specimens in the fourth group (VCF) were bonded with one CFRP strap longitudinally 15 on each side and then circularized and wrapped with two layers of CFRP. The specimens in 16 the fifth group (HCF) were wrapped with one layer of CFRP and then circularized and 17 wrapped with two layers of CFRP. The results showed that circularization increased the 18 strength and ductility of the hollow specimen. Transverse wrapping with CFRP mainly 19 improved the performance of the specimens under concentric axial loadings, while the 20 longitudinal CFRP straps mainly improved the performance of the specimens under eccentric 21 axial loading. 22