Interior beam column joints with nominal joint shear reinforcement versus unsymmetrical chamfers

As critical members in moment resisting frames, beam-column-joint (BCJ) is subjected to high shear force during earthquake. In this study, a strengthening method has been proposed by installing unsymmetrical chamfers at the soffit of beam to strengthen BCJ without seismicity consideration. Tests were conducted on four 2/3-scale BCJs under cyclic loading with constant axial force, including two strengthened specimens with and without reinforcement in chamfer, one specimen provided with nominal joint shear reinforcement, and one control specimen. To investigate the joint shear capacity, BCJs are designed to fail within the joint core by providing higher capacities to beams and columns. Performances of specimens are investigated with respect to hysteresis behavior, joint shear force, shear distortion of joint region, energy dissipation, stiffness degradation and strains of chamfers. Performance of strengthened specimens is compatible to the specimen provided with nominal joint shear reinforcement. Unsymmetrical chamfer can effectively increase the joint shear capacity to prevent joint shear failure. A load transfer mechanism for BCJ strengthened by chamfers is proposed. As chamfer provides a strut mechanism under compression, compatible performance can still be achieved by chamfers without U-bars.