Experimental and theoretical investigation of the seismic behaviour of RC beam-column joints

Beam-column joint behaviour plays a crucial role in the seismic performance of framed Reinforced Concrete (RC) structures. Whereas several studies are available in literature about the behaviour of RC joints, a wide consensus design approach is not yet available. Hence further studies on joint behaviour represent an interesting topic through the seismic and structural engineering. Main aim of this paper is to improve the knowledge on the behaviour of RC beam-column joints and rationale Fibre-Reinforced Polymer (FRP) retrofit design according to capacity design. To this purpose, experimental cyclic tests have been carried out on full-scale beam-column joints designed according to different earthquake levels. Numerical simulations, based on an accurate finite element modelling, were performed by means of the TNO DIANA code. The analyses allowed to evaluate the stress distribution in the joint panels as well as to quantify the strains in the reinforcement bars in the beam. The main results of the experimental tests have been discussed through a comparison between experimental and numerical outcomes. Moreover, a simple analytical model is applied to simulate theoretically the seismic performance and the failure modes of beam-column joints in RC structures. The rationale of the simplified model is to identify the strength hierarchy, evaluating the available capacity for any different potential failure mode (namely failure of the cracked joint, bond failure of the bars passing through it, flexural/shear failures of beams or columns). Based on the validated simplified model, retrofit design possibilities with FRP have been discussed according to modern capacity seismic design principles.