Influence of Longitudinal FRP Straps on the Behaviour of Circularised and FRP Wrapped Square Hollow RC Concrete Specimens

This paper investigates the influence of longitudinal CFRP straps on the behaviour of circularised and FRP wrapped square hollow reinforced concrete (RC) columns. Twelve square hollow RC specimens were prepared and tested under concentric axial loads, eccentric axial loads and four-point bending. The specimens were divided into three groups of four specimens. The specimens in the first group were the non-strengthened square hollow RC specimens. The specimens in the second group were circularised by adding concrete segments to the sides of the square hollow RC specimens. Then the circularised specimens were wrapped with two layers of CFRP. The specimens in the third group were strengthened by attaching one longitudinal CFRP strap on each side of the square hollow RC specimens. Then the specimens were circularised with concrete segments and wrapped with two layers of CFRP. The test results showed that circularisation of the square hollow RC specimens enhanced the performance of the specimens in terms of ultimate axial load and ductility. The influence of the longitudinal CFRP straps was insignificant in increasing the ultimate axial load and ductility of concentrically loaded specimens. The presence of the longitudinal CFRP straps enhanced the axial load at yield of concentrically loaded specimens. The presence of the longitudinal CFRP straps enhanced the ultimate axial load and ductility of eccentrically loaded specimens. The contribution of the longitudinal CFRP straps to the ultimate axial load and ductility of the circularised square hollow RC specimens increased with the increase in load eccentricity. Also, the longitudinal CFRP straps increased the bending moment capacity of the circularised and CFRP wrapped square hollow RC specimens