Seismic risk management for water pipeline networks - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 642

During the time points between T 1 and T 2 , the most important transmission
pipelines and their relevant facilities are preferentially checked and repaired.
If the water purifi cation plants are operational, the water will be supplied
to the nodes connected to the important demands. At the time point of T 3 ,
the water will be supplied to the nodes connected to the distribution net-
works, and the damaged pipelines are replaced by temporary pipelines. At
the time point of T 4 , the whole water supply system, including all kinds of
pipeline networks, control facilities, storage reservoirs, and pumping facili-
ties, is completely recovered.
The performance level of the network system after the seismic event can
be estimated by the supply damage rate. The supply damage rate immedi-
ately after a seismic event strongly depends on the structural damage rate
of the water distribution network system. The water unserviceability over
the distribution ( Γ major ( T p )) areas is quantifi ed as follows:

n
N

⎧

1 − at TT =

⎪

p 1

() =

Γ major T [23.39]

⎨

p

T
T

⎛
⎜

⎞
⎟

⎪
⎪

p

1 − g at TTT ≤≤

T 2 p 4

⎩

4

where n / N is the water supply ratio and g T is a restoration function showing
the recovery ratio at time point T p . Therefore, the supply damage rate in
the damaged network system can be expressed as:

NL

⎡
⎢

⎤
⎥ =

{ }

()

major

∪

major

()

PD Z l Γ T

[23.40]

EQ link i major p

i =1

where D EQ jor is the major damage state in terms of serviceability of water
supply.

23.4 Seismic risk mitigation

23.4.1 Decision making for seismic mitigation

Generally, an insurance company can manage many kinds of risks on the
basis of expected risk evaluations. The public sector managing a water
pipeline system, however, has to take proactive measures to reduce the
seismic risk of the system by seismic retrofi tting activities. Communication
with regard to risk is necessary among stakeholders to obtain a fi nal accep-
tance of the investment in seismic retrofi tting activities; to this end, the
engineer must provide with an appropriate solution in monetary terms that
can be understood by the stakeholders. A viable approach to establishing
decision-making measures is outlined below.