GNGTS 2013 - Atti del 32° Convegno Nazionale

Results of the seismic vulnerability assessment carried out according to the previously illustrated procedure can be reported in terms of mean damage value, obtained by Eq. (1) with a macroseimic intensity value corresponding to a the peak ground acceleration PGA value with a return period of 475 years for the site of construction of the building. The correlation between the macroseismic intensity I EMS−98 and PGA has been set in the form of: (3) where c1 represents the PGA value corresponding to the reference intensity I ( c1 = 0.03) and c2 measures the rate of the PGA increase with intensity I ( c2 = 1.6). Then, stratigraphic effects are taken into account through Intensity Increment ΔI depending on the soil category of the site of interest previously defined. In Fig. 2 the results in terms of mean damage value compared to number of storeys and age of construction are reported, where the central mark is the median value, the edges of the box are the 25th and 75th percentiles, the whiskers extend to the most extreme data points not considered outliers, and outliers are plotted individually A clear trend is observed, showing the higher vulnerability of taller and above all older buildings. As a matter of fact, the major change represented by the introduction of seismic load prescriptions in Avellino city took place in 1981, as reported in (Ricci et al. , 2011). The procedure described in previous Section can also be carried out assuming for the geometric building parameters the LIDAR data instead of the data from the field survey. LIDAR data provide (based also on cartography) global dimensions of buildings, and hence Plan Irregularity in addition to the number of storey. In order to evaluate the latter parameter, interstorey height is calculated as the values providing the least scatter with a value of 3.5m. Hence, the available input data for the application of the seismic vulnerability assessment procedure are: 1. Number of storeys; 2. Plan Irregularity; 3. Soil type. The remaining parameters: 1. Building Typology; 2. Age of construction; are evaluated by means of ISTAT Census data (ISTAT, 2001), which are provided aggregated for census cell. In particular for each census cell a disaggregation process is carried out through the use of reference distribution for Masonry and RC Buildings consisting of a sample of 10% of the surveyed building stock. In this manner distribution of age of construction for both Masonry and RC Buildings for each census cell is evaluated, representing the probability that a generic building in a generic census cell belongs to a specified building typology and age of construction. In the following, results from the application of the procedure based on LIDAR data on the same population of buildings will be compared with the results based on field survey data. Hence, the mean damage value obtained with different data sources (field survey or LIDAR) can be compared, evaluating the difference between the latter and the former; such difference can be considered the error resulting from an application of the procedure based on more poor data: (4) The latter is related with the error in the estimate of the number of storeys as well as with the error in the disaggregation process of ISTAT data. In particular denoting by p ij the probability 56 GNGTS 2013 S essione 2.1