The paper discusses how joint damage and deterioration affect the seismic response of existing reinforced concrete frames with sub-standard beam-column joints. The available simplified modeling techniques are critically reviewed to propose a robust, yet computationally efficient technique for simulating the nonlinear behavior of substandard beam-column joints. Improvements over the existing models include simulation of the cyclic deterioration of joint stiffness and strength as well as pinching in the hysteretic response, implemented considering a deteriorating hysteretic rule. A fibre-section forced-based inelastic beam-column element is developed; considering improved material models and fixed-end rotation due to bond failure, rebars-slip and inelastic extension, to simulate the deteriorating cyclic behavior of existing pre-cracked beam-column members. For the assessment of frames with substandard exterior beam-column joints, a nonlinear model for the exterior joint is developed and validated through a full-scale quasi-static cyclic test performed on a substandard T-joint connection. The proposed model allows considering structural performance in risk assessment while accounting for true inelastic mechanisms at the joints.

Multi-level shaking table tests were performed on 1:3 reduced scale two-story RC IMRF frames conforming to ACI-318-19. The exterior joints lacked shear reinforcement to assess the viability of the ACI model recommended for determining the design shear strength of the beam-column joint panel. The Northridge-1994 earthquake accelerogram was input to the frame for multi-level shaking table testing. Plastic hinges developed in beams under base input motion with a maximum acceleration equal to 0.40g. The exterior joints incurred extensive damage under base input motion with a maximum acceleration equal to 0.70g. The frame achieved displacement ductility and overstrength factors equal to 2.40 and 2.50 respectively. This gives a response modification factor equal to 6. The satisfactory performance of the frame is attributed to the high efficiency of the beam-column joint, which was confined by spandrel beams on two faces, and the high strength of the concrete. The inherent minimal confinement is sufficient to ensure good seismic behavior. The analysis confirmed overstrength equal to 1.58 for joint shear strength in comparison to the design strength determined using the ACI model. The data might serve as a reference for calibrating and validating numerical modeling techniques for performance evaluation, which are crucial in the context of performance-based engineering.