Implementazione del fenomeno del bucklig delle armature soggette a carichi ciclici nel modello fessurativo PARC_CL2.0

Collapse mechanisms of existing reinforced concrete members subjected to cyclic loading are often due to buckling phenomena of longitudinal bars. Indeed lacking of detailing in existing structures, like high value of stirrups spacing, is often associated to bar slenderness values that typically may cause second order effects. Furthermore damage induced by environmental actions, like corrosion, can cause breaking of stirrups or transversal area reduction of longitudinal bars which may increase the buckling effects on steel bars. Monti-Nuti model, able to take into account for the softening of steel in compression in case of bar slenderness values higher than 5, has been implements in PARC_CL2.1 for the nonlinear finite elements analysis of RC members subjected to cyclic loading. PARC_CL2.1 crack model is a fixed crack model assuming smeared reinforcement implemented in UMAT.for user subroutine of Abaqus software. The paper present the response prediction of steel bars subjected to cyclic loading and some comparisons between the results obtained using Menegotto and Pinto stress-strain law, implemented in the previous version of the crack model (PAR_CL2.0), with the results obtained using PARC_CL2.1 and Monti - Nuti stress-strain law. Finally NLFEA of a RC column tested at the University of Bergamo is provided to highlight that the actual modelling requires further improvement for the response prediction of bars having slenderness higher than 11.