Geoscience Reference
In-Depth Information
Fig. 4.6. PGA Histograms on theground surface for PGA scaled acceleration
records forfour soil profiles
from related attenuation relationships as PGA
=
0
.
25g
,
PGV
=
30cm
/
s, and AI
=
55cm
/
s (Joyner and Boore, 1988; Ambraseys, 1995; Travasarou et al., 2003).
The peak ground acceleration histograms calculated for four soil profiles shown sepa-
rately in Figure 4.6, indicate the importance of the variations in the soil profiles. Thus
one option to account for these differences in the soil profile at the site is to consider the
site response results obtained for four soil profiles together and to determine the varia-
tion of peak ground acceleration with respect to different scaling procedures adopted as
shown in Figure 4.7 for 80 site response analyses. The distribution of calculated PGA
is assumed to fit normal distribution and PGA values corresponding to probability of
exceedance level of 10%were calculated as shown inFigure 4.7.
Theadoptedprocedureaccountsforthestatisticalvariabilityinthesiteconditions,there-
foremoreconsistentresultswouldbeobtainedwithrespecttotheinitiallyselectedhazard
level. However, the limited number of soil borings and in-situ tests can be a problem for
evaluating the statistical variability of the site conditions. In such cases, the site varia-
bility may be taken into account by assuming that this variability can be modelled by
normaldistributionwithanassumedstandarddeviation.Andthusthesiteresponsechar-
acteristicsintermsofPGAorelasticaccelerationresponsespectracanbecalculatedwith
respect to selected exceedance levels.
BasedonthehistogramsforthecalculatedPGAsforallfourboringsandtakingintocon-
siderationallthreeparameterscalculatedtodeterminethevariabilityineachset(kurtosis
andnormalizedstandarddeviationbeingminimum,andrangebeingthesmallest),among
thethreescalingoptionsevaluated, thescalingwithrespect topeak ground accelerations
yielded the most appropriate results for site response analyses and should be preferred
for microzonation and vulnerability assessment of thebuilding stock.
