In the urban areas of Central Europe a notable amount of residential buildings are older than 90 years. For instance in the city center of the Austrian capital Vienna approximately 32.000 houses were erected between 1850 and 1918, which is about one third of the present-day stock of buildings. Mostly, these structures have been retained unchanged, without considerable structural improvement since decades. Many of these objects are landmarked, space is limited for the construction of new houses, and so in the last twenty years unused attics of these historic buildings have been converted into new apartments in order to create additional living space.

The reconstruction and development of attics in historic buildings is regulated by national standards. Since recent investigations have revealed that in Central Europe the earthquake hazard was considerably underestimated, these regulations were tightened in the spring of 2006 by increasing the effective earthquake loads. In the national code for the assessment of sufficient seismic resistance of existing buildings the following cases are distinguished:

• up to an additional vertical load of 7.2 kN/m² a simplified seismic analysis is permitted,
   
• for larger additional loads sophisticated seismic analysis procedures must be applied.

The simplified analysis is applicable only for lightweight constructions with a small increase of vertical loads. However, in the vast majority of cases the earthquake resistance of the structure to be remodeled must be verified by means of complex numerical methods considering large uncertainties, and thus the expenses for most reconstructions increase dramatically. The actual condition of the masonry of old buildings is in general hardly known, and the structural system and parameters are in general not well documented. There is also a lack of information on parameters of construction material utilized in old houses. It is a matter of fact that the new regulations led to a major decline in reconstruction of historic buildings and thus to economic setback for the real estate market.

Hence, there exists a high demand for an economical and sufficiently accurate seismic analysis, which is relatively easy to implement.