Vulnerability assessment
Seismic safety assessment
Seismic vulnerability assessments of existing buildings are carried out according to the procedures defined by the “Technical Standards for Construction” and the guidelines for “Assessment and Reduction of Seismic Risk of Cultural Heritage”. These procedures establish a systematic path of knowledge aimed at achieving an adequate understanding of the various parameters involved in the model, structured through the following steps:
- Survey of the building and assessment of cracks and deformations;
- Interpretation of the building’s historical evolution;
- Structural identification of the building and its construction details;
- Evaluation of the mechanical properties of materials and their degradation;
- Assessment of the soil-foundation system.
Based on the level of knowledge achieved through this process, a specific confidence factor can be defined, which is used in the assessment as an additional partial safety coefficient. Deepening the understanding of the model parameters is essential both to increase the reliability of the data used and to allow the application of less conservative confidence factors in calculations.
The structural safety assessment is then developed through a structural analysis aimed at translating the verified behavior of the building into mechanical and quantitative terms. This analysis is performed by defining different interpretative models, with varying degrees of accuracy, which can cover the entire structure or individual components (macro-elements). Starting from a model based on minimal knowledge—or a limited amount of information—progressively more refined interpretative models can be defined, calibrated, and validated through the accumulation of knowledge, ultimately iteratively determining the most reliable model for the building.
Mathematical Modeling
The mathematical model of a structure is a tool that forms an integral part of a broader analysis framework aimed at acquiring information on the building’s state of conservation. Since no mathematical theory can fully reproduce the objective reality of physical phenomena, mathematical models serve as aids for understanding these phenomena, rather than providing direct comprehension. It should also be noted that there is never a single model for a given structure.
The complexity of the models created must be closely correlated to the level of knowledge of the mechanical properties of materials and the structure, obtained through the diagnostic investigations carried out.
To determine whether a model correctly fulfills its purpose, the analytical model must, for a given class of problems, provide an accurate description of the phenomenon, and different numerical techniques should yield comparable results when applied to the same data. Moreover, an analytical model that accurately reproduces the behavior of a real structure can only be considered reliable for correct predictions within its field of applicability.
From the perspective of seismic assessments, a masonry building may, depending on its regularity in plan or elevation, be analyzed using a global model with linear static analysis, supplemented by micro-element checks that evaluate the main local damage mechanisms. If the building is irregular, a nonlinear static analysis (push-over) may be performed, which also allows for the assessment of structures composed of mixed load-bearing systems (e.g., masonry-reinforced concrete).
Buildings with reinforced concrete or steel structures, on the other hand, are analyzed using linear dynamic analyses, carefully evaluating the main vibration modes, or through nonlinear static (push-over) analysis.
PROFESSIONAL QUALIFICATIONS
- Alessandro Armanasco – Certified technician for the usability assessment of buildings following seismic events, issued by the Presidency of the Council of Ministers – Department of Civil Protection, since 17/12/2015
