Seismic retrofit of exterior beam-column joints using steel angles connected by PT bars

A review of past earthquakes has shown that due to the lack of specific seismic details for beam-column joints, the brittle mechanisms of the structure caused by the joint behavior often lead to severe damage or even collapse of the building. Fracture of the beam-column connection is common in these mechanisms due to shear failure of connection core or reinforcement slip. The aim of this paper is to seismically retrofit the external beam-column connections without specific seismic details in existing reinforced concrete structures, considering the effect of the slab and transverse beam. For this purpose, the beam-column connections have been retrofitted using prestressed angles and bars based on the enlargement of the beam-column connection core. In this regard, seven half scale exterior beam-column connections were subjected to lateral cyclic loading with increasing amplitude. The tested specimens consist of four control specimens, one of which has special seismic details and the other three control specimens do not have special seismic details and have shortcomings such as lack of cross-sectional reinforcement of the connection core, increase of intervals for cross-sectional reinforcement of beams and columns and lack of sufficient anchorage length (with no end hook) for bottom longitudinal beam reinforcements below the beam in the connection core. The other three retrofitted specimens, like the control specimens, do not have the seismic details. Experimental results show that the use of this retrofit system has shifted the plastic hinges to the outside of the joint core and improved the bond between the concrete and the longitudinal tensile reinforcement in the joints. Moreover, the retrofit method increases loading capacity, energy dissipation, damping percentage, stiffness and ductility capacity of the members.