Behavior of concrete columns reinforced with high-strength steel rebars under eccentric loading

In this study, high-strength steel (HSS) reinforcement with a yield stress of about 600 MPa was used in reinforced concrete columns to reduce both the reinforcing bar congestion and the construction costs. For this purpose, 16 square concrete columns reinforced with either the conventional normal-strength steel (NSS) or HSS rebars were subjected to axial and eccentric compression loads. The primary test variables included longitudinal reinforcement with two strength grades, axial load eccentricities, two different concrete compressive strengths, and different longitudinal reinforcement ratios. The structural response of the columns reinforced with reduced HSS rebars (Grade 600) was compared with that of the columns reinforced with grade 420 MPa rebars in terms of their load-carrying capacity, failure mechanism, axial force-bending moment (P-M) interaction, and ductility. Experimental results showed that although the amount of longitudinal steel reinforcement was reduced by about 34% in columns containing grade 600 MPa rebars, their load-carrying capacity and P–M interaction diagrams were comparable to those of the reference columns containing conventional NSS rebars. It was also concluded that simultaneous use of high-strength rebars and high-strength concrete below a balanced point would lead to slightly higher values of ductility index (by up to 4%) than when normal concrete strength and conventional reinforcement steel rebars of Grade 420 MPa are used.