Building vulnerability

Vulnerability describes the susceptibility to damage of buildings at given earthquake magnitudes. For the earthquake risk model, the vulnerability for different, representative building types was derived based on their characteristics and divided into so-called vulnerability classes. On this basis, the building stock was statistically assigned to these classes based on simple characteristics such as the number of storeys or the construction period. This, combined with information on the people and assets affected, makes it possible to determine the consequences for residents and the financial losses. The latter are expressed as a proportion of the building reinstatement costs. The majority of Swiss buildings were not built in accordance with the currently applicable building standards for earthquake-resistant construction.

Classifying the vulnerability of existing buildings according to construction materials is not helpful. For each type of construction, good and bad examples of earthquake behaviour can be found. The design of the supporting structure is the primary factor determining a building's vulnerability. For example, a building with continuous bracing walls running from the roof to the foundation without interruption has a much lower vulnerability than a similar building where the bracing walls are interrupted at ground-floor level and replaced by columns. This classic weak point, known as the 'soft storey', is an indication of very inadequate earthquake resistance. Older masonry buildings with timber beam ceilings can also be particularly vulnerable if the masonry is of poor quality and the façades are not sufficiently connected to the ceilings and transverse walls.