Seismic Assessment of a Reinforced Concrete Frame Beam Column Connection Extracted from an Earthquake-Damaged Building

In seismic assessment of existing reinforced concrete buildings, the plastic behavior of beams and columns are typically represented by concentrated plastic hinges at the end of the members and the beam-column joint is considered rigid or partially rigid. This approach; however, does not account for the joint deterioration caused by cyclic seismic loading as observed during past earthquakes and also in experimental tests. The observations indicate that the potential for joint deterioration is higher in older concrete buildings. In this paper, the seismic behavior of a full-scale reinforced concrete beam-column connection extracted from an earthquake-damaged building is evaluated using structural testing and also numerical analysis. Cyclic testing is performed up to a column drift of 3%. Two analytical models of the connection are developed considering the joint flexibility; one model considers the rigid end offset approach recommended by ASCE/SEI 41, and the other model uses a lumped-plasticity joint spring model which is calibrated using the experimental test results. The test results show that the plastic mechanism of the connection is controlled by the joint flexibility in shear and that slippage of the beam bottom bars occurred after plastic hinges developed at the beam ends. These results are validated using the analytical model with joint lumped-plasticity. The model with end offsets, on the other hand, fails to adequately represent the specimen behavior. These findings indicate that nonlinear modeling of beam-column joints is critical in seismic assessments of older reinforced concrete buildings.