Seismic vulnerability is the susceptibility of a building to damage and collapse. The more vulnerable a building is (by type, inadequate design, poor quality of materials, mode of construction, and poor maintenance), the greater the consequences on the structure.

In technical terms, the seismic vulnerability of a structure is represented by an indicator that relates the resistance capacity of the structure and the demand in terms of earthquake resistance and/or displacement.

Procedures for assessing the seismic vulnerability of buildings can be conducted with varying degrees of depth and computational complexity: from more qualitative estimates, based on surveying by means of cards of the main characteristics of the building’s constituent elements, to complex numerical analyses using linear and nonlinear computational methods.

The estimation of a building’s seismic vulnerability index follows the design process of ‘Safety Assessment’ in Section 8.5 of the NTC, which can be summarized in the following steps.