Structural performance of unreinforced full-scale façade concrete beam-column joint under cyclic load

Post-earthquake observations have shown that poorly reinforced concrete (RC) beam-column joints in existing structures determine premature brittle failures during seismic action. Failure of these critical parts, which transfer stresses and moments between beams and columns, resulted in the catastrophic collapse of structures in low to moderate seismic risk zones. Exterior (i.e. corner or façade) beam-column joints of buildings constructed without or with insufficient transverse reinforcements are commonly involved in the failure. The purpose of this study was to investigate the effective vulnerability of two full-scale exterior façade beam-column joints under transverse cyclic loading. Both the specimen design strategy and the test setup were conceived to emphasize the vulnerability of the joints and, therefore, to achieve shear failure in the joint panel prior to yielding both beam and column reinforcements under the simulated seismic action. In particular: (i) joint was characterized by the absence of any capacity design principle (i.e. total lack of stirrups in the joint panel) to highlight structural deficiencies typical of the 1960s-70s Italian construction practice; (ii) beams and columns were adequately designed to remain in the elastic field during the tests; (iii) the specimen was evaluated in the absence of axial load. In this work, the experimental seismic performance is compared to the one predicted by code/literature models. The test is then simulated using a numerical three-dimensional model for modelling crack propagation and fracture in concrete using the smeared crack technique. The model also allowed for a more comprehensive examination of the effects of certain assumptions on the mechanical performance of the RC joint during the experiment.