Bond Slip Behavior of Beam Main Bars within the Reinforced Concrete of Interior Beam–Column Joints

Bond Slip Behavior of Beam Main Bars within the Reinforced Concrete of Interior Beam–Column Joints

The use of high-strength reinforced steel bars in the construction of high-rise buildings reduces the amount of steel bars required and mitigates poor construction quality caused by congested reinforcement configurations. However, in the absence of structural test verifications using bars of grade SD 550W or higher, most current seismic design provisions in concrete structure design codes stipulate that steel bars be limited to grade SD 420W. In a revision of the American Concrete Institute building code requirements (ACI 318-19), a yield strength of 550 MPa is permitted for reinforcement bars in special moment resistant frame systems. In addition, in prescribing dimensions of column members in beam-column joints, the revised code specifies that the development length of the beam reinforcement through the joint is proportional to the yield strength. This means that the minimum depth of column members should not be less than 20 or 26 times the diameter of beam bars of grade SD 420W or SD 550W, respectively. However, this provision does not consider the contribution of concrete strength, which is inconsistent with the design concept of the bond between the reinforcement bar and the concrete. To address this problem, a series of full-scale reinforced concrete (RC) internal beam-column joint seismic tests were conducted to clarify the bond performance of beam reinforcement through joints. Based on the beam-column joint seismic performance, an equation is proposed for the minimum dimensions of column members.