Vulnerability Methods and Damage Scenario for Seismic Risk Analysis as Support to Retrofit Strategies: an European Perspective
The inherent seismic vulnerability of existing R.C. buildings, designed prior to the introduction of adequate seismic code provisions in the early/mid-1970s, has been dramatically confirmed by the catastrophic socio-economical consequences of earthquake events that have occurred worldwide in the past decade. The urgent need for the development of feasible and efficient structural mitigation strategies, and the implementation of “standardized” retrofit solutions for intervention at urban or territorial scale, has received increasing recognition and attention. Damage scenario and seismic risk analysis, along with the use of a GIS-environment to represent the results, are considered as a helpful tool to support the decision making for planning and prioritizing seismic retrofit intervention programs at large scale. In this paper, after an overview of current vulnerability methods for seismic risk or damage scenario analysis at a territorial scale, tentative suggestions for possible refinements will be provided with particular focus on the vulnerability models for pre-1970 reinforced concrete buildings. Improvements should include the possibility to account for the peculiar alternative damage limit states and collapse mechanisms observed in real earthquakes and further confirmed by recent numerical and experimental investigations. Comparative evaluation of the reduced level of expected damage after alternative retrofit solutions will be carried out and described in terms of fragility curves. A damage scenario analysis, referred to a case study area in Italy, will be provided as further exemplification of the effects of implementing a multi-level retrofit strategy approach at territorial scale.