Influence of low-cycle fatigue and corrosion phenomena on the ductile behaviour of steel reinforcing bars

Actual standards for constructions prescribe the realization of r.c. structures able to dissipate the energy stored during the earthquake through the development of global collapse mechanisms; the capacity design procedure is generally adopted, individuating specific “plastic hinges” in which the plasticization shall be located and using specific shear design actions opportunely over-dimensioned in order to avoid local brittle failures. The dissipative capacity of the structure is directly related to the rotational capacity of the elements in which plastic hinges are located and strictly depends on the geometrical and mechanical characteristics of the section itself and on the ductile capacity of steel reinforcing bars. The evaluation of the low-cycle fatigue behaviour of the rebars is obviously of relevant importance for the analysis of the structural behaviour of seismic r.c. buildings; two aspects shall be widely discussed, mainly related to the definition of the effective seismic demand on the rebars due to earthquakes and to the effective cyclic capacity of reinforcements. In the present work, developed inside the framework of a European research project called Rusteel (2009) the results coming from an accurate analysis of the seismic behaviour of r.c. structures is presented, evaluating, in particular, the effective level of strain and dissipated energy due to earthquake events on rebars. The mechanical characterization of the low-cycle fatigue behaviour of bars commonly used in r.c. buildings was also executed, leading to the comparison with the data coming from numerical analyses.