Title: Simplified Design Equation of Minimum Interior Joint Depth for Special Moment Frames with High-Strength Reinforcement
Author(s): Hung-Jen Lee,Hsi-Ching Chen,Tsung-Chieh Tsai,
Appears on pages(s):
Keywords: beam-column joint, bond, cyclic testing, high-strength reinforcement, slip
To avoid excessive slip of beam longitudinal bars at the joints of an earthquake-resisting moment frame, ACI 318 Building Code set a minimum joint depth of 20 times the diameter of the largest longitudinal beam bars passing through the joint, which is based on prior experimental veriﬁcation of beam-column joints with Grade 420 MPa reinforcement. In view of that the 20-bar-diameter criterion cannot be simply extended for concrete frame joints with higher grade reinforcement, this paper summarizes international existing design criteria and proposes a simpliﬁed equation for the minimum joint depth. The equation applicability is assessed by evaluating the cyclic testing results of beam-column joints conducted in East Asian and Paciﬁc Countries, where Grade 490, 590, and 690 MPa reinforcement have been used for earthquake-resistant concrete structures. Beam-column joints that satisfy the proposed equation can demonstrate satisfactory hysteresis behavior at an interstory drift of 4%.