Influence of the modelling approach on the seismic assessment of RC structures by nonlinear static analyses

Different modelling approaches are available for the evaluation of the nonlinear response of structures. The goals of this paper are to determine the implications of two frame modelling strategies, one based on lumped plasticity and the other on distributed plasticity combined with a fibre section modelling, to assess the differences in predicting the structural response of existing RC framed buildings, and to provide guidelines on the range of applicability of the two different modelling approaches. The study is carried out using two RC framed buildings as studies. Both buildings are characterized by seismic deficiencies typical of existing buildings belonging to the Mediterranean building stocks, but with different ductility capacities and collapse mechanisms. For each case study, two 3D numerical models are built in OpenSees, considering the above mentioned models. For each plan direction, two pushover analyses are run on each numerical model with two distributions of forces. The seismic response is assessed at the Damage Limitation (DL), Significant Damage (SD) and Near Collapse (NC) limit states. The seismic responses assessed by the two numerical models showed that the lumped phenomenological plastic hinge model tends to provide more conservative results than the distributed plasticity, fibre-section model, leading to relevant differences especially in case of structures with a low ductile behaviour.