Experimental Evaluation of The Ultimate Capacity of External RC Beam-Column Joints

Some results of a wide experimental program carried out on beam-column RC joints are presented. All the experimental tests were performed at the Laboratory of Structures of the University of Basilicata, Italy. Current assessment procedures on existing buildings usually neglect the variations of joint stiffness due to axial load variations. Main objective of the paper is to show how the axial load value on the columns can affect both ultimate capacity and stiffness of joints. To this purpose, the behaviour of three identical specimens tested under different axial load values is analysed and compared in terms of ultimate capacity and deformation behaviour. Results show significant variations of the joint stiffness at increasing drift values and, moreover, that the main source of deformability moves from the beam to the joint panel when the axial load decreases. The increase in joints’ deformability is mainly due to early cracking of the joint panel as a consequence of the stress state determined by low axial load values