GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 2.2 461 fragility curves for three vulnerability classes of decreasing vulnerability (i.e. vulnerability class A: high vulnerability, B: medium vulnerability and C1: low vulnerability) and two classes of building height (i.e. low-rise: 1-2 storeys and mid-/high-rise: >2 storeys). Although alternative seismic intensity measures could be used (e.g. Rosti et al., 2020), the peak ground acceleration (PGA), estimated from shakemap, is selected to characterize the ground motion severity at the building locations, consistently with the seismic hazard model implemented in the national seismic risk platform. Appropriate damage conversion rules (i.e. Rota et al. 2008 and Dolce et al., 2019a) are employed to convert the damage description of the survey forms into the five damage levels of the EMS-98. Global damage levels are then defined by the maximum seismic damage detected on preselected building components (e.g. Rosti et al., 2018). Fragility curves are first derived for eight building typologies representative of the Italian building stock, identified based on the quality and layout of the masonry fabric, in-plane stiffness of intermediate diaphragms, presence (or absence) of tie-rods and tie-beams, based on the typological classification system proposed by Rota et al. (2008). The probability of reaching or exceeding a given damage level is described by the cumulative lognormal distribution, whereas, for a given PGA threshold, the multinomial distribution is adopted to approximate the subdivision of buildings in the different damage states. Fragility curves are simultaneously fitted to empirical data points via the maximum likelihood estimation (MLE) approach. A constant value of dispersion is assumed for all damage states to avoid crossing fragility functions. The vulnerability classes are then identified by iteratively merging predefined building typologies into wider clusters, based on the similarity of the observed seismic fragility. To this aim, a specific clustering algorithm is implemented. A procedure for defining the composition of the existing building stock in terms of vulnerability classes is also developed, allowing to associate the proposed fragility curves to building categories consistently defined with the information from the national building census. The presented fragility model was used, together with others, for assessing seismic risk in Italy (Rosti et al., 2019; Dolce et al., 2019b). Acknowledgements. This study was developed under the financial support of the Italian Department of Civil Protection, within the ReLUIS-DPC 2018 project. This support is gratefully acknowledged. References Borzi B., Faravelli M., Onida M., Polli D., Quaroni D., Pagano M. and Di Meo A.; 2018: IRMA Platform (Italian Risk Maps) . 37° National Conference GNGTS, November 19-21, Bologna, Italy. Dolce M., Speranza E., Giordano F., Borzi B., Bocchi F., Conte C., Di Meo A., Faravelli M. and Pascale V.; 2019a: Observed damage database of past Italian earthquakes: the Da.D.O. Webgis . B Geofis Teor Appl, 60(2), 141-164. Dolce M., Borzi B., Da Porto F., Faravelli M., Lagomarsino S., Magenes G., Moroni C., Penna A., Prota A., Speranza E., Zuccaro G. and Verderame G.M.; 2019b: Seismic risk maps for the Italian territory . XVIII National Conference in Earthquake Engineering, September15-19, Ascoli Piceno, Italy. Rosti A., Rota M. and Penna A.; 2018: Damage classification and derivation of damage probability matrices from L’Aquila (2009) post-earthquake survey data . Bull Earthq Eng, 16, 3687-3720. Rosti A., Del Gaudio C., Di Ludovico M., Magenes G., PennaA., Polese M., ProtaA., Ricci P., Rota M. and Verderame G.M.; 2019: Use of empirical fragility curves for assessing seismic risk at the national scale. XVIII National Conference in Earthquake Engineering, September 15-19, Ascoli Piceno, Italy. Rosti A., Rota M. and Penna A.; 2020: Influence of seismic input characterization on empirical damage probability matrices for the 2009 L’Aquila event . Soil Dyn Earthq Eng, 128, doi.org/10.1016/j.soildyn.2019.105870. Rota M., Penna A. and Strobbia C.L.; 2008: Processing Italian damage data to derive typological fragility curves . Soil Dyn Earthq Eng, 28, 933-947.