In various countries, the shear-strength design formulas for reinforced concrete beam–column joints are primarily constructed based on concrete strength, and the influence of the main bars of the beam is not explicitly reflected in these expressions. To address this limitation, this study examines the shear behavior of the joint, focusing particularly on the amount and arrangement of the main bars of the beam passing through the joint. Four beam–column joint specimens were tested under cyclic loading. The main variables of the specimens were the amount and arrangement of the main bars of the beam. The detailed strain measurements were conducted to clarify the development of bond deterioration along the main bars and the associated internal force transfer mechanisms. The experimental observations revealed significant tension-shift phenomena and progressive bond deterioration in the compression-side main bars. Within the scope of the present test series, variations in the amount and arrangement of the main bars of the beam did not significantly affect the maximum applied load. However, the indirectly evaluated joint shear force was higher in specimens with two layers in the main beam bars. Force equilibrium using force components obtained by measured strain produced even larger values at greater drift angles, indicating that joint shear assessment depends strongly on the evaluation basis. A mechanics-based diagonal strut model incorporating the internal compression field provided improved agreement with experimental results, confirming its applicability for practical design.
Dong et al. (Wed,) studied this question.