Effect of Main Bars of Beam on Shear Strength of Beam-Column Joint in Reinforced Concrete Frame Structure

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 main bars of beam is not explicitly reflected in these expressions. To address this limi-tation, this study examines the shear behavior of the joint, focusing particularly on the amount and arrangement of main bars of 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 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 ex-perimental observations revealed significant tension-shift phenomena and progressive bond deterioration in the compression-side main bars. Variations in the amount and arrangement of main bars of beam did not significantly affect the maximum applied load. However, the indirectly evaluated joint shear force was higher in specimens with two layers in beam main 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 diag-onal strut model incorporating the internal compression field provided improved agreement with experimental results, confirming its applicability for practical design.