Empirical fragility curves for masonry buildings after the 2009 L’Aquila, Italy, earthquake

This study focuses on the seismic vulnerability of masonry buildings damaged by the 2009 L’Aquila earthquake. A geo-referenced database of 32,520 masonry residential buildings was compiled in the aftermath of the earthquake under the coordination of the Italian Department of Civil Protection through the AeDES survey form. The availability of this enormous amount of data provides an exceptional opportunity to examine in depth damage data and their correlation with the main parameters available from the post-earthquake survey. The original database was grouped into 20 building classes, defined as a function of vertical and horizontal structural types. Damage levels defined according to the European Macroseismic Scale classification are used to derive damage probability matrices and relevant vulnerability curves for these classes. The influences of connection systems, the quality/regularity of the masonry wall layout and the horizontal structural type on the building response are analysed in detail. A vulnerability classification, also supported by the use of statistical post hoc tests, is used to detect a reduced number of independent classes. The parameters of the non-crossing fragility curves are determined via the maximum likelihood estimation method by adopting a lognormal cumulative function to determine the exceedance probabilities of the considered damage levels. The impact of “mixed” classes, characterized by multiple vertical and/or horizontal structural types, on the derivation of the fragility curves is also investigated. Finally, the adaptation of the general version of the fragility curves to large-scale applications based on poor (census) data is also demonstrated, leading to curves that are easily usable in regional/national seismic loss assessments.