Study of the seismic behaviour of external RC beam-column joints through experimental tests and numerical simulations

The paper is focused on the analysis of some test results obtained in the framework of a wide experimental program on RC beam–column joints carried out at the Laboratory of Structures of the University of Basilicata in Potenza, Italy. Specifically, cyclic tests on full-scale joint specimens having different earthquake resistant design levels were performed, applying different values of axial force. Test results relevant to 4 specimens have been analyzed and compared with the results of numerical simulations based on an accurate finite element modeling using the DIANA code at the Structural Engineering Dept. of the University of Naples. Experimental results show how the value of the axial load acting on the column can change the collapse mode, spreading damage from the beam to the joint panel. Moreover, a collapse mode due to the failure of beam longitudinal rebars, sometimes neglected in structural codes, has been observed. Numerical simulations were used to evaluate the stress distribution in the joint panel as a function of the axial load and to quantify the beam rebar deformations. The reasons for the specimens’ global failure and, specifically, for that of the beam longitudinal rebars were identified and highlighted through a comparison with the experimental results