Experimental research on seismic behaviors of RC columns considering buckling of HRB600 longitudinal steel bars

Abstract

The inelastic buckling of longitudinal bars and premature fracture that followed can always be observed in laboratory research and earthquake damage of reinforced concrete (RC) columns. The buckling deformation and accompanied fracture of HRB600 high-strength steel bars are more significant than those of conventional reinforcing bars, but the buckling properties of HRB600 reinforcement and the influence of premature fracture on the seismic performance of RC columns are far from clear. In this paper, low cyclic loading tests were conducted on six full-scale RC columns reinforced with HRB600 reinforcement by changing the slenderness ratios of longitudinal bars and the axial compression ratios of columns, and the lateral buckling displacements of longitudinal bars were measured by an identified method. Based on the lateral buckling displacements, the buckling behaviors of longitudinal bars were analyzed. It shows that cover concrete has a significant constraint effect on preventing buckling of HRB600 reinforcement. The inelastic buckling behaviors and premature fracture of HRB600 bars on the ultimate deformation capacity and ductility of RC columns were investigated according to the lateral buckling displacements and ductility coefficient. It is found that the increase of the slenderness ratio would cause larger buckling displacements making the local plastic deformation concentration and low-cycle fatigue damage of HRB600 reinforcement more serious, resulting in the premature fracture of longitudinal bars and decrease of ductility of RC columns. Furthermore, a series of individual bars accompanied by the RC columns were tested. Based on the average stress–strain curves, the effects of yield strength and slenderness ratio were discussed. Former researches of conventional longitudinal bars were involved to form a comparison group with HRB600 bars. The results indicate that the deformation capacity reserves of HRB600 reinforcement after 85% peak load were significantly lower compared with conventional bars. It is suggested to limit the application of RC columns reinforced with HRB600 longitudinal bars in high seismic intensity areas and improve the limitation on the slenderness ratio of high-strength steel bars.