EXPERIMENTAL INVESTIGATION ON REINFORCED CONCRETE INTERIOR BEAM-COLUMN JOINTS WITH HEADED DIAGONAL BARS

Beam-column joints (BCJs) have been recognized as the critical elements in reinforced concrete (RC) frame structures as their failure may cause catastrophic collapse of buildings. BCJs are subjected to large shear force during seismic attack and they are normally reinforced with a large number of transverse reinforcements, in accordance with conventional design standards. This brings the problem of reinforcement congestion, construction difficulty, insufficient concrete compaction, and consequently poor seismic performance of BCJs. Although there are attempts to solve the above problems, there is still in lack of practical solution applicable to the construction industry. In this paper, a novel reinforcement method composing headed diagonal bars anchored at beams is proposed. It aims at ameliorating the reinforcement congestion and improving the seismic performance of BCJs. The method involves two mechanisms to enhance the performance of BCJs, namely plastic hinge relocation and shear force reduction. To validate its effectiveness, two 2/3-scale RC interior BCJ specimens were fabricated and tested under quasi-static cyclic loading. The two specimens are identical except the reinforcement at joint region, with one reinforced conventionally and the other adopting the proposed reinforcement method. It is found that the construction of the proposed reinforcement cage is easier than that of its conventional counterpart, as fewer transverse reinforcements were used in the joint core. Test results have shown that the proposed reinforcement method is able to relocate the plastic hinge away from the beam-joint interface and consequently prevents the shear failure of joint core. The BCJ specimen adopting the proposed reinforcement method shows 7.6% increase in loading capacity. Moreover, the proposed reinforcement method enhances energy dissipation and stiffness of BCJs as well as reduces joint deformation. It is generally validated that the proposed reinforcement method can improve both constructability and seismic performance of RC interior BCJs.