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%.

中文翻译：

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高强钢筋特殊弯矩框架最小内部接缝深度的简化设计方程

为避免抗震力矩框架节点处梁纵向钢筋过度滑动，ACI 318 建筑规范将最小接头深度设置为穿过接头的最大纵梁钢筋直径的 20 倍，这是基于先前的实验420 MPa 级钢筋的梁柱节点验证。针对钢筋等级较高的混凝土框架节点不能简单地推广20杆直径标准，本文总结了国际上现有的设计标准，提出了最小节点深度的简化公式。方程的适用性是通过评估东亚和太平洋国家进行的梁柱节点循环试验结果来评估的，其中 490、590、690 MPa 钢筋已用于抗震混凝土结构。满足建议方程的梁柱节点可以在 4% 的层间漂移时表现出令人满意的滞后行为。