Experimental assessment of seismic performance of exterior beam-column joints in existing RC buildings

In the assessment of the performance of typical existing buildings, seismic collapse safety might be significantly affected by the non-linear behavior of the joints that are involved in the failure mechanisms especially if they are characterized by poor structural detailing, such as the lack of an adequate transverse reinforcement in the joint panel. Many retrofit strategies for existing joints are available, but commonly accepted tools to assess existing joint capacity – that is the start point for retrofit – are not available. Few reliable approaches for modeling all sources of nonlinearity are proposed in literature for poorly designed beam-column joints because of relatively poor information from experimental tests. The current study aimed to improve the understanding of exterior joints seismic performance without transverse reinforcement in existing RC buildings through experimental tests. Two full-scale exterior unreinforced beam-column joint sub-assemblages are tested under cyclic loading. Two different kinds of joint failure are expected, with or without the yielding of the adjacent beam, basically depending on the beam longitudinal reinforcement ratio. Strain gauges located on beam bars and LVDT on the joint panel allow the complete definition of the two main deformability contributions (fixed-end-rotation and the shear strain of the panel). Design criteria, adopted setup and main experimental results are described herein.