Influence of bond property of longitudinal bars on seismic behaviour of reinforced-concrete columns

Four circular fly-ash concrete columns reinforced by steel rebars with different bond levels were tested to investigate the influence of bond strength of longitudinal steel rebar on the seismic behaviours of reinforced-concrete (RC) members. Furthermore, a fibre-element method considering steel bond slip was used to investigate the influence of bond properties of steel rebar on seismic responses of circular RC columns, with the test results used to validate reasonability. The comparison of results shows that the anchorage of the steel rebar has a significant influence on, and the plastic hinge length no effect on, the seismic behaviours of the columns. The analytical and test results show that low bond strength delays the yielding process of steel rebars adjacent to the beam–column interface, which can improve the deformability of RC columns, but does not obviously influence the moment resistance. However, the stiffness of the cross-section is reduced from a certain drift level. Six equations are proposed to predict with very good accuracy the reduced ratio of the stiffness of the cross-section, the enhanced ratios of the drift at the ultimate moment and the drift at the maximum lateral load of the column models reinforced by bonded or unbonded steel rebars.