Seismic assessment of gravity load designed RC frames: Critical issues in structural modelling

Reinforced concrete frames designed according to early seismic provisions or, sometimes, without any seismic provision, have usually low strength and, in most cases, show limited ductility. Very often details are poor and, consequently, the critical zones do not behave in a ductile way, showing brittle mechanisms of failure. Because of these problems, the assessment of existing reinforced concrete (RC) structures requires a refined procedure. A summary of models that permit the analysis of the non-linear behaviour of RC structures is discussed. An innovative numerical model is presented which takes into account the most important mechanical phenomena affecting the non-linear behaviour of the RC frames. In conclusion, the influence of different strength and deformation sources on the global behaviour of existing buildings is studied and the needed capabilities of the numerical models are underlined.