The seismic vulnerability is the predisposition of a building to be damaged and collapse. The more a building is vulnerable (by type, inadequate design, poor quality of materials, construction methods and poor maintenance), the greater the consequences on the structure will be.
In technical terms, the seismic vulnerability of a structure is represented by an indicator that relates the resistance capacity of the structure and the request in terms of resistance and / or displacement of the earthquake.
The procedures for the assessment of the seismic vulnerability of buildings can be conducted with different levels of depth and complexity of calculation: from more qualitative estimates, based on the survey of the main features of the building elements, with complex numerical analysis using methods of linear and non-linear calculations.
The estimate of the seismic vulnerability index of a building follows the design process of ‘Evaluation of safety’ referred to in paragraph 8.5 of the NTC which can be summarized in the following steps.
- Cognitive survey: the current state of construction is defined by plano-altimetric, structural surveys, and the state of damage and deformation of the structure.
- Historical-critical analysis: it is the tool that guides the designer in the reconstruction of the current state of stress in light of the changes and events that have affected the building over time.
- Mechanical characterization of materials: assessment of the resistance capacity of materials through surveys carried out on site or in the laboratory.
- Definition of the levels of knowledge and of the consequent factors of confidence: we define reductive coefficients of the mechanical properties of the materials gradually smaller as the degree of in-depth investigation increases; from the level of knowledge 1 (lc1), the minimum allowed, to the level of knowledge 3 (lc3), the maximum allowed.
- Structural analysis and determination of the vulnerability of the existing structural system;
- Proposal for possible adjustments and evaluation of the optimal cost / benefit ratio