Behavior of Circularized Hollow RC Columns under Different 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.

Performance evaluation of intermittently CFRP wrapped square and circularised square reinforced concrete columns under different loading conditions

“…The ascending response after the first peak flexural load of the flexural load-midpsan deflection responses of Specimens CI-F and SI-F could be due to the confinement effect of CFRP in the compressive concrete of the specimens. A similar ascending flexural load-midspan deflection response after the first peak of CFRP wrapped circularized square RC specimen was also observed in previous studies (Hadi, et al, 2017;Hadi, et al, 2013).…”

“…The ductility ( ) of the test specimens was calculated as the ratio of the ultimate deformation to the yield deformation (Hadi, et al, 2017). The ultimate deformation of the specimens was considered the deformation in the descending part of the load-deformation response, which corresponded to 85% of the ultimate load (Hadi, et al, 2017).…”

“…The ductility ( ) of the test specimens was calculated as the ratio of the ultimate deformation to the yield deformation (Hadi, et al, 2017). The ultimate deformation of the specimens was considered the deformation in the descending part of the load-deformation response, which corresponded to 85% of the ultimate load (Hadi, et al, 2017). The yield deformation of the specimens was considered the deformation corresponding to the intersection point between two straight lines (Foster and Attard, 1997;Hadi, et al, 2017).…”

“…The ultimate deformation of the specimens was considered the deformation in the descending part of the load-deformation response, which corresponded to 85% of the ultimate load (Hadi, et al, 2017). The yield deformation of the specimens was considered the deformation corresponding to the intersection point between two straight lines (Foster and Attard, 1997;Hadi, et al, 2017). The first straight line was drawn from the origin to the point in the linear ascending part of the load-deformation response presenting 0.75 times the first peak load.…”

“…It was reported that the circularization led to a substantial improvement in the strength and ductility of the columns due to the elimination of the stress-concentration at the corners. However, most of the available studies investigated the performance of circularized square concrete cylinders (Jameel, et al, 2017;Kim, et al, 2003;Youssf, et al, 2017), circularized square columns (columns without steel reinforcement) (Zeng, et al, 2017) or circularized square RC columns (Hadi, et al, 2017;Hadi, et al, 2013; with full wrapping. Only one study investigated the performance of circularized square columns (columns without steel reinforcement) (Zeng, et al, 2017) with intermittent wrapping in which the columns were subjected to only concentric axial loads.…”