Derivation of Fragility Curves for Italian RC Buildings from Post-Earthquake Damage Data

This paper presents the derivation of empirical fragility curves for the residential reinforced concrete building stock, by taking advantage of post-earthquake damage data collected by the Italian Department of Civil Protection after the major Italian earthquakes occurred in the last 50 years. Reinforced concrete buildings are first classified into fifteen structural typologies, based on the number of stories and type of design. Typological fragility curves are derived, as a function of the peak ground acceleration, by considering five damage states based on the EMS-98 classification and by accounting for damage on both structural and non-structural building components. Observational data are fitted by lognormal cumulative curves through the maximum likelihood estimate approach, using the multinomial distribution to subdivide the number of buildings in the different damage states. To make the proposed fragility model easily usable for territorial seismic vulnerability and risk applications based on poor census data, building typologies are aggregated into two vulnerability classes (i.e. C2 and D), of decreasing vulnerability. Vulnerability class C2 groups buildings designed for gravity loads only and for seismic loads pre-1981, whist vulnerability class D refers to buildings designed for seismic loads post-1981. Empirical fragility curves are derived for predefined vulnerability classes and classes of building height (i.e. low-rise, mid-rise and high-rise), by suitably averaging typological fragility curves. An example of application is also presented, to show the feasibility of the proposed fragility model for large-scale seismic risk evaluations.