This study is dedicated to the preservation of the heritage of the Modern Movement, particularly through improving the structural response to seismic solicitations, which are common in some of the areas where significant works in this style can be found, including Bucharest, Romania. The focus is on developing and validating methodology according to which the vulnerability of 'interwar' buildings, which is the other name given to the blocks of flats which witnessing the Modern Movement in the Romanian capital. To complement this study with a geographical generalisation, the models proposed have been also tested for selected earthquakes, taking into account that the Modern Movement left its traces in form of that very characteristic blocks of flats there as well. Residences in form of blocks of flats of the Modern Movement have been built in Bucharest in the 1930s. They present a reinforced concrete frame structure, which infill walls of masonry bricks, although the later could only be limitedly taken into account in this study. However, the method used remains perfectly valid. To determine the impacts of strong ground motion on a certain type of buildings, several approaches have been - the static pushover curve analysis - displacement based dynamic time-history analysis - stress-strain approach based on the dynamic time-history analysis These simulation types have been applied first to simple models, reproducing what in an experimentallaboratory might be tested, then to models of progressivelly more complicated buildings, from regular frame structures, to real building models, which all the irregularities usual in the building practice in that time. The methodology adopted included use of several computer support tools, beginning with software for converting accelerograms, fibre based finite elements, spread shet and database programs. A further step in testing the general validity has been the use of the same methodology for simplified models of real buildings which have been found to be of the same typology as the models studied more extenisivelly. This examination has shown that the methodology proposed is perfectly valid for them. The integration within the general frame of assessment of structural performance has been made comparing the computed damages with real damage types. For this purpose a matrix of damages suffered by 'interwar' buildings, previously developed by the author, has been used. It proved again, that the predictions for the buildings with the same geometrical characteristics as those which have been object of this study were close to the reality. The innovative part of this study relies in the stress-strain based approach applied to building models of this size. Such an analysis allows not only description of failure mode and determination of limit states eventually reached by the building, but also the specific determination of the number and, if necessary, position of structural members suffering different types of damage. This kind of output can build the input for other interdisciplinary studies. Of interest for the author is the economic study regarding the retrofit/repair needs of damaged elements as opposed to preventive retrofit. In this sense, an issue for further research, which has been only marginally handled within this work is the retrofit of previously damaged structures, an issue, which perfectly suits into the methodology already proposed and validated.