Geoscience Reference
In-Depth Information
1.5
(1)
(2)
(3)
(4)
1
0.5
0
10
−
2
10
−
1
10
0
10
1
Period (s)
30km:
50-percentile(thicksolidline),16-and84-percentile(thickdottedlines),comparedwith
the values deduced fromthe attenuation relationships (1) Bozorgnia and Campbell
(2004), (2) Ambraseys and Douglas (2003), (3) Ambraseys and Simpson (1996) and
(4)Sabetta and Pugliese (1996), with
M
Fig. 2.7. Response spectral ratios
V
/
H
for 6
.
0
≤
M
≤
6
.
3 and 10km
≤
R
≤
15km. Note that (2) is
independent of magnitude and distance
=
6
.
15 and
R
=
Althoughnotreportedhereforbrevity,itwasverifiedthatthedependenceof
V
H
onthe
site class is relatively modest with median values typically varying between 0.4 and 0.7
both for classBand for class C sites.
/
2.5. ASIMPLIFIED SPECTRAL DISPLACEMENT MODEL
In Figure 2.8 the median 5% damped displacement response spectra for different mag-
nitude ranges, without distinction of ground type, are compared with the normalised
spectrum obtained by multiplying the code (CEN, 2004) elastic acceleration spectrum
for class A ground by
2
. The observed median curves suggest that the design
spectral shape of CEN (2004), consisting, for periods larger than 0.4-0.5s, of a bi-linear
curve with a constant plateau at long periods, provides a reasonable approximation,
while the “bell-shaped” displacement spectrum defined in the Annex A of Eurocode8
(CEN, 2004) for
T
(
T
/
2
π)
4s is not strongly supported by the observations. In the sequel,
wewillsetthevalueofthelongperiodplateauat
D
10
,alreadyintroducedinSection2.2.
>
