Gordiano: an innovative technique for the seismic retrofitting of existing R.C. corner beam-column joints

In the present paper, the results of numerical simulations of corner beam-column joints seismic behaviour before and after retrofitting are discussed. Experimental results on unretrofitted beam-column joints were used for the calibration of the parameters in order to define a suitable model to be adopted for the analyses. The specimens analyzed were characterized by structural deficiencies typical of the Italian construction practice of the 60’s-70’s before the introduction of modern seismic codes, characterized by the absence of any Capacity Design principle: use of smooth bars, inadequate reinforcement detailing, such as absence of stirrups in joint panels and hook-ended anchorage. The purpose of the f.e.m. simulations was the calibration of a model able to reproduce the correct behaviour of corner beam-column joints subjected to seismic loads in order to study the effectiveness of an innovative technique based on the application of a metal insert coupled with a high performance fiber-reinforced concrete jacket in strengthening existing RC structures. The numerical simulations showed the ability of the model to accurately catch both global and local beam-column joint inelastic behaviour and demonstrated that with the proposed technique it is possible to change the joint failure mechanism from a brittle mechanism characterized by joint shear failure into a more ductile one with the formation of a flexural hinge in the beam, according to the principles of Capacity Design.