Seismic vulnerability

Seismic vulnerability is a building’s potential for a given level of damage due to a seismic event of a given intensity.

One of the main causes of death during an earthquake is building collapse. To reduce the loss of human lives, buildings must be made safe. Laws governing construction in seismic zones today state that buildings must not be damaged by low-intensity earthquakes, must not be structurally damaged by medium-intensity earthquakes and must not collapse in the event of severe earthquakes despite suffering serious damage.

A building may suffer structural damage to its load-bearing parts (pillars, beams) and/or non-structural parts that do not affect its instability (chimneys, cornices, partitions). The kind of damage depends on: the structure of the building, its age, materials, location, vicinity to other buildings and non-structural elements. When an earthquake occurs, the ground moves horizontally and/or vertically, pushing a building backwards and forwards. The building thus starts to sway and deform. If the structure is flexible and therefore able to undergo great deformation, despite suffering great damage it will not collapse. The damage also depends on the duration and intensity of the earthquake.

After an earthquake, to assess a building’s vulnerability, it is enough to inspect the damage caused, associating it with the intensity of the tremor. Whereas assessment of building vulnerability before a seismic event occurs is more complex. This is why statistical and mechanistic methods have been perfected, in conjunction with expert opinions.

Statistical methods classify buildings according to their construction materials and techniques, based on damage observed in previous earthquakes to the same kind of buildings. This technique requires damage data from past earthquakes, which is not always available, and cannot be used to assess the vulnerability of individual buildings, because it is statistical in nature and not specific.

Mechanistic methods, on the other hand, use theory models that reproduce the main characteristics of the buildings being assessed for study of the damage caused by simulated earthquakes.

Finally, some methods use expert opinions to assess the seismic behaviour and vulnerability of predefined structural types or to identify the factors that determine the behaviour of buildings and assess their influence on vulnerability.

In order to assess the vulnerability of buildings throughout Italy, statistical methods must be used that adopt standard data regarding their characteristics. ISTAT census data regarding homes are available for Italy and used in the application of statistical methods.