DIRECT DERIVATION OF FRAGILITY CURVES FROM ITALIAN POST-EARTHQUAKE SURVEY DATA

摘要

A very complete and homogeneous database of post-earthquake building inspections, carried out after the main Italian events of the last 30 years, has been processed to derive fragility curves for 23 building typologies. The records (more than 91000) have been converted into a single damage scale with 5 levels of damage, plus the case of no damage. For each affected municipality a value of PGA and Housner Intensity (IH) has been evaluated using attenuation laws. Experimental data have been converted in damage probability matrices and then fitted through lognormal fragility curves, with an advanced nonlinear regression algorithm. The relative reliability of each point has been taken into account by applying the bootstrap technique. The significant concentration of experimental data at low levels of ground motion and the selected analytical expression determine the peculiar shape of some of the curves, with a very steep initial branch followed by an almost horizontal curve for increasing values of ground motion. Explanations and possible solutions are discussed.