Shear Strength of Reinforced Concrete Interior Beam–Column Joints with Different Aspect Ratios

Abstract In reinforced concrete moment-resisting frames, beam–column joints are critical structural members that are subjected to very large shear forces when lateral loads, such as those caused by earthquakes, act on the structure. These joints play a vital role in transferring loads from the upper column to the lower column, anchoring the main reinforcement of the beam, and distributing the stiffness of the entire frame. Since failure of these joints can lead to the collapse of the entire building, their performance is of critical importance in seismic design. Current seismic design codes estimate the shear strength of beam–column joints based on a limited set of parameters, including concrete compressive strength, confinement effects, and effective joint area, but they do not consider the influence of the aspect ratio (column depth relative to beam depth). In this study, four reinforced concrete interior beam–column joint specimens were fabricated, with aspect ratio as the primary variable, and subjected to cyclic loading tests. The experimental and analytical results showed that the maximum load-bearing capacity tended to increase as the aspect ratio of the joint increased; however, the shear strength of specimens J1.5 and J2.0 was approximately 14–20% lower than the values specified in current design codes. Furthermore, the angle of the compression strut calculated through strain-based analysis increased proportionally with the aspect ratio, while the width of the compression strut remained nearly constant. In specimens with large aspect ratios, shear cracks were observed on the outer surface of the compression strut, indicating an increased influence of the truss mechanism. Consequently, the shear strength due to arch action decreased with increasing aspect ratio and was estimated to account for approximately 23–30% of the experimental values. These findings highlight the need to consider the contribution of the truss mechanism when evaluating the shear strength of beam–column joints.