On the definition of seismic vulnerability maps in cross-border Mediterranean areas

The chance to locate and quantify the major risks associated to natural catastrophic events on a territory allows to plan adequate strategies and interventions by civil protection bodies involved in local and international emergencies. The seismic risk depends most of all by the vulnerability of buildings belonging to the urban areas. For this reason the definition, by a deep analysis of the territory, of instruments identifying and locating vulnerability, largely favours the activities of institutions appointed to safeguard the safety of citizens. Seismic and hydro-geological risks constitute the major component of the activities involving assistance actions carried out by civil protection bodies because of their repetitiveness and the amount of human resources needed to face the emergencies. The possible coordinate action and cooperation between different countries is fundamental importance, especially if the procedures are based on standardized rules and civil protection plans are characterized by consciousness of the territory and the associated risks. The promptness of the response is basic for the success of the operations. This feature is however not only achievable by practice exercises aimed to implement a responsiveness system to emergencies, but also through a deep understanding of the existing risks and the major exposure recognized for the urbanized contexts. The challenge for the assessment of seismic vulnerability of buildings is not easy because it involves a large amount on constructions to investigate in a reasonable time. Several researchers, based on the post processing of data coming from the observation of damaged buildings, proposed simplified relationship linking a vulnerability index with the intensity of a seismic event (Benedettini and Petrini (1984), Braga et al. (1984), Angeletti et al. (1988), Casolo et al. (1993). In other studies the interest has been addressed to the definition of fast assessment methods for the vulnerability index and the relative large scale application (Martinelli et al. (1999), Dolce et al. (2004), Dolce and Moroni (2005), Dolce and Martinelli (2005). In this summary the outputs of the activity carried out within the research project “SIMITDevelopment of an integrated cross-border Italian-Maltese civil protection network” are presented with specific reference to the assessment of the seismic vulnerability of buildings and definition of vulnerability maps in terms of vulnerability index and peak ground acceleration limit values. In agreement with the scope of the paper, the criteria adopted for the assessment of vulnerability and definition of the vulnerability maps were calibrated to provide reliable predictions for typically small urban contexts, which are largely widespread in Mediterranean area. The representative test site selected for the activities was the city centre of the island of Lampedusa. The choice was particularly suitable for the prefixed purposes because of the opportunity to operate on a large quantity of buildings concentrated in a small area with and characterized by a repetitiveness of the constructive typology. The final gaol was to develop a standard procedure for the assessment of seismic vulnerability of small urban contexts widespread in the Mediterranean. The specific research activity carried out on the island has been divided in 4 phases, characterized by a progressive level of depth of the analysis, listed below: • Historical, critical, and typological analysis of the urban centre and typical buildings; • Simplified assessment of seismic vulnerability of buildings by standard vulnerability forms; • Choice and validation of a vulnerability model; Definition of fragility functions and vulnerability maps. The historical-critical study was aimed at the recognition of the urban evolution of the city centre of Lampedusa over the time and of the regulations succeeded which have changed the constructive and typological framework of buildings. The subsequent typological analysis of the buildings, performed through several surveys, made it possible to categorize the recurring structural types within the city centre of the island and their similarities and differences in relation to periods of construction. Such preliminary activities permitted to collect fundamental information, necessary for a fast and effective assessment of the buildings vulnerability, carried out by the use of evaluation forms already known in the literature and commonly used in Italy (GNDT (1994)) for the fast assessment of the vulnerability single buildings and building aggregates. The major output coming from the use of such kinds of vulnerability evaluation forms is constituted by possibility to determine a numerical vulnerability index, suitable to be adopted for the definition of the vulnerability maps. The definition of the fragility curves, which provide a relationship between the intensity of the seismic event (synthetically represented by the Peak Ground Acceleration) and the structural damage, passes through a preliminary calibration, necessary to adapt the vulnerability model (index of vulnerability vs. PGA) to the characteristic building context. In the current study, the calibration operations were performed by an experimental dynamic monitoring campaign on two prototype buildings, followed by the realization of the numerical structural models consistent with the experimental results. The seismic assessment of the prototype buildings by static pushover analysis made it possible the determination of the critical PGA values to be linked with indexes of vulnerability previously evaluated, in order to adapt the vulnerability model to the urban context of the island of Lampedusa. The final outputs are the fragility curves and the associated vulnerability maps for the urban area of Lampedusa, presented in terms of index of vulnerability and critical peak ground accelerations.