GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 2.2 387 As far as RC buildings are concerned, the great part of the buildings of Irpinia 1980 event, for which the information on the age of construction was available, was built after 1962, while for L’Aquila dataset about 35% of the buildings was built before 1981 and 65% after 1981. With regard to the number of stories, 65% of Irpinia dataset is between 1 and 2, 30% between 3 and 4, and 5% greater than 4, with a modal value of 2, whereas 28% of L’Aquila dataset is between 1 and 2, 61% between 3 and 4, and 10% greater than 4, with a modal value of 3. Damage analysis. The definition of the damage scale represents a key issue of seismic fragility assessment (e.g. Rosti et al. 2018). In this work, damage states were defined consistently with the European Macroseismic Scale EMS-98 (Grünthal 1998). A global damage level was assigned to each inspected building, in accordance with the damage conversion rules proposed by Rota et al. (2008) and Del Gaudio et al. (2017), considering the maximum level of damage observed on preselected building components. Derivation of typological fragility curves. The PGA was the selected ground motion intensity measure, estimated at the building locations by the INGV ShakeMaps (Michelini et al. 2008). The ground motion range was subdivided into equally-spaced bins of 0.05g width. Empirical damage data were approximated by fitting a lognormal cumulative distribution through the Maximum Likelihood Estimation (MLE) method. To ensure the ordinal nature of damage, a constant dispersion value for all damage states of a given building typology was assumed. The random component was described by the multinomial distribution (Charvet et al. 2014). In order to derive empirical fragility curves, building typologies were defined first, based on the selection of main building parameters influencing seismic fragility. Typological fragility curves for masonry buildings. Fragility curves were derived for eight masonry building typologies, identified based on the layout and quality of the masonry fabric, in-plane flexibility of diaphragms and presence of connecting devices (e.g. tie-rods and tie-beams), consistently with the information reported in the damage survey forms. Typological fragility curves for RC buildings. Fragility curves were derived for RC buildings by defining building typologies based on two parameters, namely the number of stories (from 1 to 5, including the vast majority of the buildings in the selected database) and the type of design (for gravity loads only, for seismic loads pre-1981 – deemed as “obsolete”, and for seismic loads post-1981). Roughly speaking, data on buildings designed for gravity loads only or for seismic loads came from the Irpinia 1980 and L’Aquila 2009 event, respectively, because the vast majority of Municipalities hit by the Irpinia event were not yet classified as seismic in 1980, whereas most of the Municipalities hit by the L’Aquila event were classified as seismic since 1915 (R.D.L. 29/04/1915). The choice of a distinction between pre- and post-1981 buildings designed for seismic loads was based on a side on the evolution of technical codes (D.M. 03/03/1975) and, on the other side, on the need of consistency between the databases of the two events. The analysis of the damage suffered by these RC building typologies through vulnerability curves showed a clear hierarchy with increasing damage for buildings designed for gravity loads only, for seismic loads pre-1981 or for seismic loads post-1981, respectively. Then, fragility curves were derived for each one of these 15 (=5×3) typologies. Class fragility curves for damage prediction based on census data. The fragility curves proposed in this study have to be applied starting from information on building characteristics provided by ISTAT census data. Therefore, consistent with this need, further fragility curves had to be derived, starting from the abovementioned typological fragility curves, for specific classes of buildings with characteristics that could be determined based on ISTAT census data. Five fragility curves (i.e. A, B, C1, C2, D) were derived, three for masonry buildings and two for RC buildings, based on the procedure described below. Class fragility curves for masonry buildings. Masonry building typologies were associated to vulnerability classes A, B and C1, of decreasing vulnerability. To this aim, the attribution of masonry building typologies to vulnerability classes was carried out through an agglomerative hierarchical clustering, up to the identification of the three classes, which were