Seismic Assessment of Existing RC Frames: Probabilistic Approach

Recent earthquakes have shown that research in earthquake engineering has to be focused on the assessment of vulnerability of existing constructions lacking appropriate seismic resisting characteristics. In fact, older buildings, designed and constructed until the late 1980s, without considering earthquake provisions, constitute a significant hazard in many cities of southern Europe. Therefore, the retrofit should be made in order to reduce the vulnerability, and, as a consequence, the risk to currently accepted levels. To this scope, the scientific community is developing more accurate methodologies in order to evaluate seismic performances of existing structures. Within this framework, the present paper aims at the evaluation of the mean annual frequency of exceeding a limit state of existing concrete frames by means of the probabilistic approach introduced by the Pacific Earthquake Engineering Research, adopting the application procedure suggested by Jalayer and Cornell and accounting for the uncertainties involved in the seismic response of structures. This procedure properly combines the probabilistic seismic hazard analysis with probabilistic seismic demand analysis and, finally, with the probabilistic seismic capacity analysis. In order to evaluate the seismic reliability of existing structures taking also into account for the model uncertainty, in this paper reference is made to experimental results derived from technical literature. In particular, three full-scale frames (bare frame, frame with brick infilled walls and frame with infilled walls reinforced with shotcrete) tested pseudodynamically at the ELSA Laboratory of Ispra have been considered. The developed analysis allowed to evaluate the seismic reliability of the bare frame, the influence of the infill panels, and, finally, the reliability of the retrofitting solution with shotcrete.