Computer-aided risk assessment at urban scale. Model definition and validation on a case study

Disaster risk reduction has become a global urgent need. Similarly to other natural hazards, earthquakes may cause significant damages on a large scale. In Europe, seismic events mainly affect historical city centers, which are characterized by dense urban structure, usually constituted by ancient masonry and pre-code R.C. buildings, often in aggregate se- quence. Historical city centers are very much part of the European cultural heritage and their preservation is considered a strategic issue for the EC due to their tangible and intangible values. Furthermore, it is an undisputable fact that natural disasters may have severe nega- tive short-term economic impacts on the built environment and adverse longer-term conse- quences for economic growth and development. For this reason, the development of an efficient digital tool for urban seismic risk assessment and resilience enhancement becomes essential. With this aim, an original numerical procedure is proposed in this paper, based on multidisciplinary concepts combined in an innovative way. First of all, the concept of Limit States for the Minimum Urban Structure is introduced and described by means of simple me- chanically based models. Then, elliptically distributed vulnerability indices are worked out by considering multidirectional seismic hazard, and 2D seismic risk assessment computation is performed. The results are implemented within the GIS software, where they are easily shown and discussed thanks to the graphical mapping tool. The proposed approach allows the defi- nition and evaluation of a global intervention plan for resilience enhancement at the urban scale. Finally the proposed numerical procedure is applied for validation to the Italian city- center of Concordia Sulla Secchia (Italy), damaged by the 2012 Pianura Padana Earthquake (PPE). The predicted damage scenarios are compared with the actual post-seismic damage scenarios in order to evaluate the accuracy of the proposed evaluation procedure.