GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 2.2 363 identification of the areas with the largest seismic risk for industrial buildings in Italy. Firstly, the input models of hazard, vulnerability and exposure are introduced. The validated framework is used to predict he unconditional risk in terms of economic losses expressed in terms of Expected Annual Losses (EAL) and used to rank areas in Italy in terms of seismic risk for industrial buildings. As expected, the area hit by the Emilia-Romagna earthquakes in 2012 is included among those with highest seismic risk, indicating the predictability of large damage occurred on industrial buildings during the seismic event. Description of the input models. In broad terms, seismic risk can be expressed by a convolution integral of three quantities: Hazard (a probabilistic measure of ground shaking intensity), Vulnerability (a probabilistic measure of the susceptibility to damage of a building), and Exposure (containing the socio-economic evaluation of the potential losses, i.e. , characteristics of the population of items at risk). Seismic risk has been defined, mostly for management purposes, as the potential economic, social and environmental consequences of hazardous events that may occur in a specified time window. Seismic risk, determined by the combination of hazard, vulnerability and exposure, is the measurement of the damage expected in a given interval of time, based on the type of seismicity, the capacity of buildings and anthropization (nature, quality and quantity of assets exposed). The hazard model is defined in terms of the Probability Density Function (PDF) of the peak ground accelerations, pga , as: (1) where k 0 and k 1 are two regional empirical constants estimated using the pga corresponding to different return periods (30, 50, 72, 101, 140, 201, 475, 975, 2475 years) provided by the model of the Italian Building Code (MIT, 2018), including soil amplification effects. These latter are estimated by the amplification model of the Italian Building Code (MIT, 2018), which is based on the average shear wave velocity in the substrate up to 30 m from the surface V s,eq . The Italian subsoil classification has been estimated based on the shear wave velocity estimation reported in Michelini et al. (2008). The exposure model is taken from the number of industrial buildings and cadastral value for each municipality from Italian Agenzia delle Entrate ( Tax Revenue Agency ). In the following, the Italian industrial building stock is defined with reference to two specific cadastral categories, labeled D/1 (Factories) and D/7 (Buildings constructed for or adjusted to meet special industrial needs and not liable to be destined for a different use without radical transformations). The exposure is defined in terms of the cadastral value for each municipality of the Italian territory. The vulnerability model is taken from the observational fragility curves (Buratti et al. , 2017) using the data obtained from the 2012 Emilia-Romagna earthquakes based on a Bayesian regression on a log-logit model (notice that: logit ( p ) = ln ( p /(1 – p )) is the so-called logarithm of odds): (2) where D is the damage level DS i is the threshold corresponding to the i -th damage state, and β 0, i = {3.902; 5.268; 4.329; 3.360; 3.001} and β 1, i = {2.247; 3.987; 3.839; 3.467; 3.527} are the model parameters for each limit state. Description of the input models. The unconditional seismic risk assessment requires the calculation of the annual exceedance probability, P f , i , of a specified performance level (damage state DS i ) under a certain hazard, as: (3) where logit –1 is the inverse of the logit function.