Existing reinforced concrete (RC) frame structures were often designed for gravitational actions and without adopting the modern seismic design criteria, even in currently recognised seismic area. Therefore, they are generally vulnerable to seismic events due to the poor structural detailing adopted in beams, columns and joints, which are consequently affected by brittle failure modes and, then, characterised by limited displacement capacity. In fact, during their lifetime these frames are likely to be subjected to earthquakes which can unveil the aforementioned vulnerability and result in structural collapses even under moderate seismic actions. Besides the lack in the global conceptual design of the RC frames under consideration, structural failures can also be induced by the local response of their single members which is characterised by a significant degradation under cyclic actions. Nevertheless, the capacity models currently available for beams columns and joints disregard the effect of the actual cyclic response of such components. In this regard, the present paper focuses on the cyclic response of beam-to-column joints in RC frames which are widely recognised as critical components in controlling the seismic response of structures. Particularly, it is intended at unveiling the relationships which describe the strength decay of RC joint under cyclic actions. Starting from a series of monotonic and cyclic tests reported in the scientific literature, a low-cycle fatigue approach is proposed for interpreting the strength decay observed in the tested RC joints as a function of the cyclic displacement history. The proposed elaborations clearly highlight that both strength decay and failure under cyclic actions can actually be described by a low-cycle fatigue relationship which is able to take into account both cycles’ number and amplitudes. Moreover, the fact that the parameters of the resulting low-cycle fatigue curves are clearly influenced by the adopted structural detailing and design criteria is probably the most impacting finding of the proposed research and shed new light on the definition of capacity models and failure criteria for the RC joints under consideration.

Uno studio sulla fatica oligociclica di nodi trave-colonna in c.a.

LIMA, CARMINE;MARTINELLI, Enzo;FAELLA, Ciro
2014

Abstract

Existing reinforced concrete (RC) frame structures were often designed for gravitational actions and without adopting the modern seismic design criteria, even in currently recognised seismic area. Therefore, they are generally vulnerable to seismic events due to the poor structural detailing adopted in beams, columns and joints, which are consequently affected by brittle failure modes and, then, characterised by limited displacement capacity. In fact, during their lifetime these frames are likely to be subjected to earthquakes which can unveil the aforementioned vulnerability and result in structural collapses even under moderate seismic actions. Besides the lack in the global conceptual design of the RC frames under consideration, structural failures can also be induced by the local response of their single members which is characterised by a significant degradation under cyclic actions. Nevertheless, the capacity models currently available for beams columns and joints disregard the effect of the actual cyclic response of such components. In this regard, the present paper focuses on the cyclic response of beam-to-column joints in RC frames which are widely recognised as critical components in controlling the seismic response of structures. Particularly, it is intended at unveiling the relationships which describe the strength decay of RC joint under cyclic actions. Starting from a series of monotonic and cyclic tests reported in the scientific literature, a low-cycle fatigue approach is proposed for interpreting the strength decay observed in the tested RC joints as a function of the cyclic displacement history. The proposed elaborations clearly highlight that both strength decay and failure under cyclic actions can actually be described by a low-cycle fatigue relationship which is able to take into account both cycles’ number and amplitudes. Moreover, the fact that the parameters of the resulting low-cycle fatigue curves are clearly influenced by the adopted structural detailing and design criteria is probably the most impacting finding of the proposed research and shed new light on the definition of capacity models and failure criteria for the RC joints under consideration.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11386/4483062
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