A Mechanical Interpretation of Low-Cycle Fatigue in Steel Reinforcing Bars

Some major problems still open to investigation, concerning the behaviour of steel reinforcement subjected to low-cycle alternating fatigue (such as during strong earthquakes) are addressed in the present paper and a possible interpretation of the mechanical behaviour is presented. Even if the failure of a rebar during the development of an alternating "plastic hinge" may markedly impair the expected ductile behaviour of the structure, very few papers have treated this problem and, to the authors'knowledge, a clear phenomenological explanation may hardly be found in the scientific literature. The paper presents some experimental results, gives a mechanical interpretation of the major aspects of steel mechanical behaviour and provides a numerical model. The fitting of the highly nonlinear cyclic tests confirms the soundness of the proposed interpretataion and allows to evaluate certain local quantities (such as stresses, strains and dissipated energy), that cannot be derived from the tests.