Civil Engineering Reference
In-Depth Information
Type 2-EDPs were defi ned using the negative peaks of the moment
demand time histories at the mid-span and at the support to account for
the effects of negative bending due to vertical ground motions as:
=
(
)
Demand
−
DL
min,Stage
1
Type
2
−
EDP
[20.13]
DL
where (
Demand
)
min, Stage1
is the negative extreme of the demand time history
at the base case (Gülerce
et al.
, 2012; Fig. 20.3(b)). To defi ne a possible rela-
tion between the ground motion characteristics and the EDPs, characteris-
tics of the ground motions which produced the largest adverse effects were
studied systematically. As mentioned in the previous sections,
S
a
(
T
1
) at the
fundamental period of the structure along with PGA is the most commonly
preferred IM due to its effi ciency, suffi ciency, and feasibility.
S
a
at the verti-
cal, transverse and longitudinal periods of the bridge were selected as IMs
for this study. The effects of ground motion selection and scaling, defi ned
by the scaling robustness property of an IM, can be checked by evaluating
the dependency of EDP on the scale factor. The ground motions used in
this study were scaled to an example target spectrum (median response
spectrum from Abrahamson and Silva (1997) GMPE for M7, D5km) to
examine this property using two different approaches; in the fi rst approach,
only one scale factor per set (a set is defi ned as two horizontal and vertical
ground motion components) was used, while in the second approach, sepa-
rate scale factors for different components of the ground motion record
sets were used. The distribution of an example Type 2-EDP with respect to
the scale factors is given in Fig. 20.4 for one-scale-factor case and in Fig.
20.5 for separate-scale-factor case, respectively.
Demand
max_Stage 1
Demand
max_Stage 2
4
4
3
3
2
2
1
1
0
0
-1
-1
-2
-2
0
10
20
30
40
0
10
20
30
40
Time (s)
Time (s)
Demand
min_Stage 1
Demand
min_Stage 2
(a)
(b)
20.3
Typical demand-time histories from (a) Stage 1 and (b) Stage 2
of nonlinear dynamic analyses.
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