Seismic fragility for Italian RC buildings based on damage data of the last 50 years

A set of about 25,000 residential reinforced concrete (RC) buildings has been investigated in this study to define fragility curves. The sample originates from a wide database, reported in the online Da.D.O. (Database of Observed Damage) platform, related to about 320,000 buildings inspected in the aftermath of the nine most devastating earthquakes occurred in Italy between 1976 and 2012 (Friuli 1976; Irpinia 1980; Abruzzo 1984; Umbria-Marche 1997; Pollino 1998; Molise 2002; Emilia 2003; L’Aquila 2009; Emilia 2012). The coherence of data has been guaranteed by a thorough critical analysis among all databases. Then a refined procedure dealing with the completeness of survey campaigns at Municipality level has been applied to avoid biases in fragility fitting. The final sample is then subdivided in different structural design types, determined as a function of the evolution of seismic classification for investigated areas and the sequence of technical codes enforced through the years. The available shakemaps in terms of PGA values, derived by National Institute of Geophysics and Volcanology, are used to characterize seismic ground motion at buildings’ site. The opportunity of enriching the sample of data with undamaged supplementary buildings, located in areas very far from epicenter but missing in the database (only because survey inspections were not required) is deeply discussed and investigated. Finally, according to such a set of data, different classes of buildings representative of existing RC building portfolio in Italy are defined and relevant vulnerability and fragility curves are determined.