Civil Engineering Reference
In-Depth Information
1
IM
j
:
SA
(3.0 s) = 0.0827
Prob = 0.1
GM selection weight = 0
84th percentile
of selected motions
10
0
0.8
0.6
10
-1
16th percentile
of selected motion
s
0.4
GCIM distribution
Realized GCIM values
Selected ground motions
Single realization
Single ground motion
K
S bo
u
nds,
10
-2
Selected ground motions
Single ground motion
GCIM median
0.2
GCIM 16th, 84th percentiles
a
=
0.
1
0
10
-1
10
0
10
1
5
10
20
50
100
Period,
T
(s)
Peak ground velocity,
PGV
(cm/s)
(a)
(b)
1
1
GCIM distribution
Realized GCIM values
Selected ground motions
Single realization
Single ground motion
KS bounds,
IM
j
:
SA
(3.0 s) = 0.0827
Prob = 0.1
GM selection
weight = 0
0.8
0.8
= 0.1
a
0.6
0.6
0.4
0.4
GCIM distribution
Realized GCIM values
Selected ground motions
Single realization
Single ground motion
KS bounds,
0.2
0.2
IM
j
:
SA
(3.0 s) = 0.0827
Prob =0.1
GM
se
lection wei
g
ht = 0
a
= 0.1
0
0
10
-1
10
2
10
3
0.1
0.2
0.5
1.0
2.0
Cumulative absolute velocity,
CAV
(g s)
5-95% Significant duration,
Ds
595 (s)
(c)
(d)
4.4
Semi-automated ground motion selection based on the
realizations in Fig. 4.3 using a weight vector with uniform weights
for nine
SA
ordinates: (a) pseudo-acceleration response spectra,
SA
;
(b) peak ground velocity,
PGV
; (c) cumulative absolute velocity,
CAV
;
and (d) 5-95% signifi cant duration,
Ds
595 (after Bradley. 2012b).
are discussed subsequently; however, at present it is important to emphasize
that if this ground motion set was used for seismic response analyses in
which the cumulative effects and duration of strong ground motion are
important, then they will lead to biased results (see Bradley, 2010a, p. 1337,
for further details).
From the observation in Fig. 4.4, that ground motion selection based on
only
SA
ordinates lead to selected ground motions with biased distributions
of
CAV
,
Ds
575 and
Ds
595, an alternative weight vector was considered in
the ground motion selection algorithm by including these three additional
IM
i
s. In assigning the weight vector values, it was decided to give 70% of
the total weight uniformly for
SA
ordinates, and 10% weight to each of
CAV
,
Ds
575 and
Ds
595.
This decision to associate 70% weight to ampli-
tude-based
IM
i
s (at various frequencies) and 30% weight to
IM
i
s which
account for cumulative and duration effects is done so for the purposes of
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