Experimental studies on reinforced concrete interior beam-column joints strengthened by unsymmetrical chamfers

Beam-column joints (“BCJ”) are critical members in low-rise to mid-rise buildings. Failure of BCJ may lead to collapse of building. To strengthen non-seismically designed BCJ, a comprehensive study has been commissioned to develop a strengthening strategy for BCJ using unsymmetrical chamfers. Specifically, chamfers are proposed to be installed at beam-column corners and under the soffit only to alleviate the undesirable joint-shear failure. Tests were carried out on four 2/3-scale BCJ, comprising one control specimen and three strengthened specimens including 300 mm chamfers with and without U-bars and 150 mm chamfers with U-bars. The specimens were subjected to moderate level of axial load and loaded to failure under quasi-static cyclic loading. It has been shown that unsymmetrical chamfers are effective to protect a non-seismically designed BCJ against failure at joint core. Mode of failure is shifted from joint-shear in the control specimen to column-flexure in the strengthened specimens. To enhance the performance of BCJ, size of chamfer is more crucial in comparison with providing reinforcements inside the chamfers.