Page 267 - Numerical Analysis and Modelling in Geomechanics

248 SEISMIC MICROZONING USING NUMERICAL MODELLING
For any value other than 4.5, other values of Fb* can be calculated, keeping the
a constant, as:
(8.16)

where q is the assumed behaviour factor. Therefore the coefficient Fb*(q) is only
a scaling parameter depending on the level of structural ductility which is
adopted. According to the Italian seismic code (Decree of 16 January 1996 of the
Ministry of Public Works) for static analysis, seismic actions are represented by
a set of horizontal forces proportional to the weight, through a seismic
coefficient K:
(8.17)

where C is a coefficient of seismic intensity, which depends on the seismic
category zone (0.07 for second category zones), that is the seismic protection
level assumed by the law in absence of site amplifications; R is a response
coefficient which assumes the value of 1 in the period range 0–0.8s; ε is the
“foundation coefficient”, which assumes the value of 1 for rock or stiff soil and 1.
3 for loose alluvial deposits shallower than 20 metres; β, γ, I are coefficients
depending on the structure typology, geometry and class of importance.
It was proposed to modify the seismic coefficient as follows:

(8.18)
introducing the coefficient Fb*(q) to take into account the seismic hazard given
on a probabilistic basis, for reference site conditions, and substituting the
foundation coefficient e with the amplification coefficient Fa, to account for
geotechnic and topographic effects.

Example of application
Field surveys and numerical computations of the local seismic response of the two
villages of Cesi and Colfiorito, located in the near field area of the seismic
sequence, are shown below, as an example of the adopted methodology. They
show geologic and geomorphologic settings typical of the Umbria-Marche
Apennine framework.

CESI VILLAGE
The village of Cesi, located in the epicentral area of the 26 September 00.33
GMT, Ms 5.5 earthquake, suffered damage up to degree IX on the MCS scale.
The damage distribution was inhomogeneous, having been stronger in the lower
part of the village, where some buildings collapsed and many were seriously