A low-cycle fatigue approach to predicting shear strength degradation in RC joints subjected to seismic actions

Reinforced concrete (RC) structures realised in earthquake-prone regions are exposed to seismic shakings that may result in significant damage and even lead them to collapse. As well known, high stress concentration occurs at the end of both beams and columns of RC frames, making those members extremely prone to damage. Moreover, beam-to-column joints are particularly sensitive to brittle failure, especially in the cases of unreinforced and unconfined joints. This paper investigates the cyclic response of RC beam-to-column joints. Specifically, it is intended at demonstrating that the decay in shear strength due to cyclic actions can be interpreted in the light of the well-known low-cycle fatigue approach. To do so, cyclic experimental tests on RC joints reported in the scientific literature are collected and analysed. The obtained results show that the parameters governing the shear strength degradation are clearly influenced by both the layout of the RC joints and their actual design criteria. This finding highlights that low-cycle fatigue curves can be considered for describing the decay in shear strength due to cyclic actions; however, further well-documented experimental results are needed to completely identify the relationship between the relevant properties of the RC joint and the resulting low-cycle fatigue curve.