Title: Special Moment Frames with High-Strength Reinforcement—Part 2: Columns
Author(s): Drit Sokoli, Albert Limantono, and Wassim M. Ghannoum
Publication: Structural Journal
Appears on pages(s): 253-265
Keywords: high-strength reinforcement; nominal Grade 100 reinforcement; rotation capacity; special moment frame columns; spread of plasticity
High-strength reinforcing bars (HSRB) with a yield strength of at least 80 ksi (550 MPa) are currently under development in the United States, and are being considered for implementation in the ACI 318 Building Code. The laboratory tests presented in this publication were conducted to support the initiative of introducing these higher-strength bars into ACI 318-19. The primary focus of the testing program was to uncover any major issues in the performance of HSRB in concrete members, and more specifically to assess the influence of the tensile-to-yield strength (T/Y) ratio, fracture elongation, and shape of stress-strain curve of HSRB on the behavior of seismically detailed concrete columns. Four specimens were tested under constant axial load and reverse cyclic lateral loading of increasing amplitudes until fracture of longitudinal bars. Three columns were reinforced with Grade 100 (690 MPa) bars sourced from different manufacturers and therefore having different post-yield mechanical properties. The fourth column was reinforced with conventional Grade 60 (420 MPa) ASTM A706 bars. Concrete columns reinforced with HSRB reached similar lateral drift levels as the specimen reinforced with Grade 60 bars before significant loss in lateral strength. Longitudinal bars with higher T/Y ratios achieved greater plasticity spread and lower strain concentrations compared with those having lower T/Y ratios.