Implementation of Steel Constitutive Model Including Buckling in Parc_CL 2.1 Crack Model

Lacking of details in existing structures, like high value of stirrups spacing, causes a bad confinement of concrete and consequently high lateral deformations of longitudinal bars after the spalling of the concrete in case of cyclic loading induced by seismic actions. Longitudinal reinforcing steel in reinforced concrete (RC) elements may undergo large tension and compression strain reversal that lead to buckling of steel bars. The buckling is a phenomena associated to bar slenderness values that typically may cause second order effects. In non-linear finite element analysis (NLFEA) rebar can be modelled using beam elements with geometrical and mechanical non linearity or using different approaches like fibre models or smeared models in which the steel behaviour is represented by constitutive model derived on the average behaviour of bare bar experimentally calibrated. In this field it is located the PARC_CL 2.1 smeared crack model implemented at the University of Parma in UMAT.for user subroutine of Abaqus software. Two different models for the buckling effect have been implemented. The first one is the Monti-Nuti model, able to take into account the softening of steel in compression in case of bar slenderness values ranging from 5 to 11. The second one is the Kashani model, for slenderness values up to 30. In this paper, NLFEA of a RC column is provided to highlight the differences of the response prediction between the two models.