Analysis of the low-cycle fatigue behaviour and corrosion phenomena on reinforcing bars of concrete structures in earthquake prone areas

In the present work, the combined effects of Low-Cycle Fatigue (LCF) action and corrosion phenomena on steel reinforcing bars were accurately investigated, aiming at the definition of the effective seismic mechanical capacity of steel bars in comparison to what required by real earthquake events. The ability of corroded specimens to still sustain the ductile demand (in terms of strain and dissipated energy) of seismic events was accurately investigated. The thesis was developed inside the widest framework of an European Research project, (Effects of Corrosion on Low-Cycle Fatigue (Seismic) Behaviour of High Strength Steel Reinforcing Bars, 2009), funded by the Research Fund for Coal and Steel. The necessity to investigate the ductile behaviour of steel reinforcing bars lies in the absence of detailed studies about the effective behaviour of rebars under seismic action, that is reflected in the lack of codified standards and procedures for the production control of the seismic behaviour of steel bars. In this context in fact, the revision of European standard EN10080 and in particular, Mandate M115 aims at the individuation of common procedures for the harmonization of the standards about reinforcing and pre-stressed steels for concrete. A detailed investigation of the effective mechanical capacity under cyclic-seismic action was carried out on a set of steel reinforcing bars representative of the actual European production: in particular, a preliminary protocol for the execution of LCF tests was elaborated taking into account the information actually provided by scientific literature and standards. The ductile capacity of steel reinforcements so evaluated was then compared to the effective ductility demand required by real earthquake, leading finally to the elaboration of a proposal for the assessment of the LCF behaviour of steel bars during the production process. More in details, the demand in terms of strain and dissipated energy density on steel reinforcing bars was evaluated through an accurate numerical analysis of the structural behaviour of r.c. case studies designed according to actual standards for constructions (Eurocode 8, Italian Standard D.M. 14/01/2008). Moreover, since the current scientific literature (Apostolopoulos 2006, Apostolopoulos and Papadakis 2008) evidenced that, in presence of aggressive environmental conditions, TempCore steel reinforcing bars generally exhibit a progressive damaging and a rapid decrease of the mechanical properties (i.e. strain, strenght and dissipative capacity), the experimental test campaign on rebars was consequently repeated on corroded steel reinforcements. The effects of corrosion on rebars were opportunely reproduced through the execution of accelerated corrosion tests in salt spray chamber following a suitably defined protocol. The analysis of the ductile capacity of corroded steel reinforcing bars allowed the assessment of the ability of corroded bars to still sustain the ductile requirements due to real seismic events.