Exposure modelling and loss estimation for seismic risk assessment of residential buildings: innovative methods and applications

Defining the seismic hazard, assessing the vulnerability of the main components of the built environment and, consequently, estimating the expected losses are key steps for setting up effective post-event emergency plans as well as medium-long term mitigation strategies. Despite the significant knowledge advancements achieved in the last years, several points need to be further developed. Among them the collection of reliable building inventories, the selection of appropriate measures of seismic intensity and the definition of accurate loss estimation models still propose some challenges for the scientific community. The present PhD thesis aims at providing a contribution in this direction. After a comprehensive state of the art on seismic risk components along with a literature review focused on the main models to estimate the expected seismic losses, some new procedures related to hazard, exposure and loss estimation, have been proposed and applied. Firstly, a model aimed at estimating the direct economic losses (i.e., building repair costs) has been developed by improving the models currently available in the literature. These models generally account for only the severity of damage (i.e., the maximum damage level), while damage extension and distribution, especially along the building height, are implicitly considered in the repair cost values. If on the one side, the assessment of safety condition depends essentially on damage severity, on the other side, damage extension strongly affects the estimation of economic impact. In this regard, the proposed model allows to explicitly consider both damage severity and distribution along the building height. The model is applicable to both Reinforced Concrete (RC) and masonry building types. It requires the determination of the more frequent damage distributions throughout the building height. At the current state, the procedure has been specifically implemented for existing Reinforced Concrete (RC) building types by performing Non-Linear Dynamic Analyses (NLDAs). As for seismic hazard, correlations between macroseismic intensities and ground motion parameters have been derived processing data related to Italian earthquakes occurred in the last 40 years. Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV) and Housner Intensity (IH) as instrumental measures, and European Macroseismic Scale (EMS-98) and Mercalli-Cancani-Sieberg (MCS) as macroseismic measures, have been considered. The correlations can be used both to adopt empirical damage estimation methods (e.g., Damage Probability Matrices) and to convert the macroseismic data of historical earthquakes into instrumental intensity values, more suitable to risk analyses and design practice. Concerning exposure, an innovative methodology has been developed to convert the information on the typological characteristics collected through the AeDES form (currently used in Italy in post-earthquake usability surveys) to recognized international standards such as the taxonomy proposed by the Global Earthquake Model (GEM) and the EMS-98 building types. The methodology allows to fully exploit the exposure and vulnerability data of post-earthquake surveys related to the Italian built environment and to define an exposure model in terms of risk-oriented classes more suitable for large-scale risk assessments. Furthermore, an approach based on the integration of data collected with the CARTIS procedure (i.e., a protocol used in Italy for the typological-structural characterization of buildings at regional scale) and using the RRVS web-based platform (i.e., for a remote visual screening based on satellite images) has been proposed and specifically applied to the village of Calvello (Basilicata region, Southern Italy). This approach represents a useful tool for compiling residential building inventories in a quick and inexpensive way thus being very suitable in data-poor and economically developing countries. To better illustrate the proposed methodological developments, some applications are provided in the last part of the thesis. The first one proposes a comparison among the results obtained applying some casualty estimation models available in the literature using the vulnerability and damage data collected in the L’Aquila urban area after the 2009 earthquake (data available on the Observed Damage Database Da.D.O. platform). After, by using the same data source, an exposure model in terms of EMS-98 types based on the 2009 post-earthquake data has been implemented for the residential buildings of L'Aquila town and the surrounding municipalities involved in the usability assessment surveys. The third - expansive - application deals with the seismic risk assessment of the Val d’Agri area (Basilicata region, Southern Italy). This area has a strategic role for Italy due to the large quantities of oil extracted from local deposits, making available large resources deriving from royalties. Specifically, earthquake damage scenarios for the residential building stock of 19 villages have been prepared. Considering a seismic vulnerability distribution obtained from the integration of a building-by-building inventory and information collected with the CARTIS and RRVS approaches, the expected losses deriving from a seismic event with an exceedance probability of 10% in 50 years (475 years return period) have been determined. Finally, an action plan for the seismic risk mitigation, essentially based on the reduction of vulnerability of the building stock through a structural strengthening program, has been proposed and specifically applied to one of the villages in the area under study.