Edilizia diffusa e vulnerabilità sismica nei centri storici siciliani. Linee guida per il recupero

Simultaneously to the drafting of a seismic micro-zonation, highlighting the different responses to earthquake that various areas offer in terms of amplification of ground seismic wave, appears essential to predict the effects of an earthquake on urban system. It is also important to carry out an analysis of existing built heritage, in order to know its characteristics, to assess the level of vulnerability and to identify a scale of intervention priorities, investigating on historical centers, that constitute complex contexts, presenting sometimes a potential vulnerability. Starting from these general assumptions, set at a territorial scale, every intervention on the construction scale must therefore be conducted taking into account the results of these analyses: these are the basic principles that define a “Plan of Seismicity”. A research and an experimentation was carried out for the Sicilian historical center of Carini, presenting a medieval origin and a great architectural and urban interest but having criticalities in terms of seismic safety. The first level of investigation has been that on a territorial scale, in which the entire municipal territory was analyzed, in order to define homogeneous zones of seismic vulnerability, based on the knowledge of the existing building heritage and its current conditions. The second level of investigation, conducting on a scale of greater detail, concerned instead the historical center, doing an identification of typological-construction characters of about twenty-two blocks identified as a significant sample of different configurations of urban tissue and buildings. Seismic vulnerability has been evaluate, for these urban blocks, basing on the quickly method devised by Italian professor Giovanni Mochi of University of Bologna, well adapting it to the specific historical-construction context of Western Sicily. This method consists in the evaluation of some un-dimensional indexes, useful for determining the level of vulnerability of building aggregates. The analytical approach related to building aggregate –in fact - is more appropriate than an analysis of a single building, because of the strictly structural interdependence between nearby buildings inside an urban block.