In the moment in which Italy is crossed by several earthquakes the evaluation of seismic vulnerability for existing buildings assumes a paramount importance. The assessment of an existing building must be preceded by an investigative phase in which geometry, characteristics of structural elements, structural details, reinforcement ratio non-structural element must be known. An important role is also demanded to the modelling of the structures in plastic range, therefore, to perform a realistic seismic analysis of non-seismically detailed RC structures, it is important to have models to capture the hysteretic behaviour of beams, columns and joints. The problems being addressed in this paper regard the development of models for realistic assessment of seismic behaviour of non-seismically detailed R.C. frame structures with reference to beams, columns and joints. To this scope a R.C. frame non-seismically detailed adopted as study case has been properly modelled and analysed by both non-linear static and dynamic analyses. A critical discussion about the optimal modelling of R.C. structures is also reported.
