sessione 2.3 - Ogs

GNGTS 2009 SESSIONE 2.3
Fig. 4 - Schematization of the simple FEM
model of the school of Corno di Rosazzo
(UD) and rappresentation of the first and
second eigen-shapes associated to the frequencies
5 Hz and 7.1 Hz respectively (computed
by FEM model).
Possibly, a FEM modeling can confirm or improve how obtained by tremor measurement and in
some case the comparison between the measured natural frequencies and the FEM one may give
information about the material. In this case the FEM model (Fig. 4) has confirmed both, the natural
frequencies and the principal eigen-shapes (Tab. 1 and Fig. 5). The natural frequencies obtained
via FEM model strongly depends from the loads and overall from the elastic characteristic of the
material. Therefore it is possible to find for which type of material the FEM eigen-frequencies tend
to the measured one. In the examined case the best result is obtained with simper stone posed with
a good organization (see Tab. 3 for the elastic and mechanics characteristics).
Tab. 1 - Natural frequencies and natural periods from FEM modeling.
Tab. 2. Mechanical and elastic characteristic of masonry used in the FEM model.
The measured natural frequency can be compared also with the values obtained by empirical
relationship (i.e. Tab. 3). The empirical relationships are really fast to apply but obviously can give
values that are significantly different from the real one, particularly for not regular buildings (see
also Mucciarelli Tuberi, 2007, Mucciarelli et al., 2007).
Tab. 3. Example of empirical relationship to compute the principal periods of some types of structures.
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