Nonlinear modelling of RC elements built with plain reinforcing bars

The numerical analysis of reinforced concrete structural elements is usually conducted under the assumption of perfect bond conditions, which may lead to predicted lateral deformation significantly smaller than the real element deformation or to predict lateral stiffness larger than the existing element stiffness. Bond-slip effects should therefore be included in the numerical models of structural analysis in order to represent more accurately the elements response. Due to the differences in the interaction mechanisms between concrete and steel in elements with deformed bars (currently used in the RC construction) and elements with plain bars, the models available for simulating the cyclic behaviour of RC structural elements with deformed bars are, in general, not adequate for elements with plain bars. The paper describes the numerical modelling of the cyclic response of two reinforced concrete columns. One column was built with deformed reinforcing bars and the other with plain reinforcing bars. The columns have similar detailing and are representative of structures built up to 1970s. The numerical models were developed using the OpenSees and the SeismoStruct platforms and calibrated with the available experimental tests results. Within each platform, different nonlinear elements were used in the model of the columns. Bond-slip effects were included in the OpenSees models resorting to a simple modelling strategy. The models and the parameters adopted are presented and discussed. Comparisons are established between the most relevant experimental results and the corresponding results provided by the numerical models. It is also present a new tri-linear steel material in order to take into account the slippage of plain reinforcing bars. The parameters of the steel model were obtained empirically. Comparisons with the experimental results are established. INTRODUCTION A significant number of existing reinforced concrete (RC) building structures were constructed before the 70’s, with plain reinforcing bars, prior to the enforcement of the modern seismic-oriented design philosophies. As a consequence of poor reinforcement detailing and of the absence of capacity design principles, a significant lack of ductility, at both the local and global levels, is expected for these structures, resulting in inadequate structural performance even under moderate seismic excitations. Cyclic load reversals (like the ones induced by earthquakes) result in accelerated bond degradation, leading to significant bar slippage. Bond-slip mechanism is reported (Ioannou et al. 2012 and Rossetto et al. 2009) to be one of the most common causes of damage and collapse of existing RC structures subjected to earthquake loading. RC structures with plain reinforcing bars, built prior to the 1 PhD Student, Civil Eng. Department, University of Aveiro, Aveiro; EPICentre, josemelo@ua.pt 2 Associate Professor with Habilitation, Civil Eng. Department, University of Aveiro, Aveiro, hvarum@ua.pt 3 Professor, EPICentre, Department of Civil, Environmental & Geomatic Eng., University College London, London, t.rossetto@ucl.ac.uk