Derivation of Empirical Fragility Functions from the 2009 L'Aquila Earthquake

In the past 30 years, Italy has experienced multiple damaging earthquakes. These have produced a wealth of post-event damage survey data, which can be used for the construction of empirical fragility curves for the Italian building inventory. The present study focuses on the construction of empirical fragility curves using data for 24911 residential buildings collected in the aftermath of the 2009 Aquila Earthquake. A detailed GIS database is developed based on building stock information for the entire municipality territory through data made available by the Special Office for the Reconstruction of L’Aquila (USRA). It includes building usability rating, damage state, building typology and soil information derived from microzonations maps. Using soil type information at each building site, PGA values are derived through different Ground Motion Prediction Equations and compared to the ones estimated through the INGV Shakemap. Adopting an advanced non-linear regression procedure, fragility functions are then constructed in terms of usability rates for different building classes, characterised by their main construction material. The resulting curves exhibit certain anomalies compared to existing fragility functions that is shown to be related to adoption of usability data rather than damage data, for the analysis. Indeed, building safety evaluations may not reflect the sustained structural damage. Moreover it is shown that the conventional assumption that ‘unusable’ corresponds to ‘partial collapse’ or similar damage state is invalid, and the conversion between the two scales should not be adopted for the construction of fragility functions.