Civil Engineering Reference
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to medium voltage (60 kV) lines. In this simple application low voltage lines
are not modelled and power demands are aggregated to higher level sub-
stations (the load buses in the fi gure).
The water supply system is made up of three local urban systems inter-
connected by three pipelines. This topology is quite unusual. In order to
highlight interactions, the WSS is made artifi cially weak by providing only
variable-head water sources in the form of tanks served by pumping sta-
tions. Each of these pumping stations can then be out of service as a result
of an EPN failure to provide power at the reference sub-station of the
pump. The well-pump-tank systems are dimensioned to cover the neces-
sary water requirements under normal operational conditions. The network
model comprises a total of 37 nodes, including three source nodes, and 53
edges.
In terms of fragility models, vulnerable components in the EPN are all
the sub-station components, as described in Vanzi (1996). Overhead lines
are not vulnerable. Notably, failure in one sub-station can propagate to
neighbouring stations if circuit-breakers are also damaged. In the WSS, only
pipelines are vulnerable and the fragility model is given in terms of a
Poisson repair-rate per kilometre:
(
)
=
λ
repair
PGV
K
0 0024
.
PGV
km
−
1
[18.16]
⎣
⎦
1
where peak ground velocity (PGV) is in cm/s and
K
1
is a function of the
pipe material, soil and joint type, as well as diameter. The model, described
in ALA (2004), includes a mean rate of repair due to permanent ground
deformation, with the indication that the larger of the two rates should be
used to predict damage. The second rate has not been used in this simple
example where rock/stiff-soil conditions and no susceptibility to liquefac-
tion/landslide phenomena are considered over the entire region.
Regional seismicity model
Seismic activity in the region is caused by the three sources shown in Fig.
18.11. The sources are of the area type, with epicentre location distributed
uniformly within each source. Their activity is described through a trun-
cated Gutenberg-Richter model, and the corresponding parameters are
also reported in the fi gure: sources 1 and 2 have similar activities and the
same lower and upper magnitudes. Source 2 is both more active, with a rate
of events
λ
0
three to four times larger than the other two sources, and char-
acterised by a larger upper magnitude.
For the purpose of predicting local seismic intensity, PGA is taken as the
primary IM, which coincides with the input IM for the buildings' fragility
models at the location of grid cells centroids as well as for EPN sub-station
components (transformers, buses, etc.). At the location of pipe segment
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