Seismic risk management for water pipeline networks - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 619

parts of the network are replaced by new-type joints, while leaving the
remaining portions intact.
Retrofi tting activities allow effi cient management and operation of a
deteriorating system by maintaining a favorable seismic performance level
(Imai and Koike, 2009). In planning retrofi tting of a system to mitigate
seismic damage effectively, it is necessary to develop a procedure to quan-
titatively evaluate the effect of partial retrofi tting on the fragility of the
lifeline network system (FEMA, 1999). Some indicators, such as structural
failure, performance failure, and economic loss, facilitate the evaluation of
the seismic performance of the lifeline system (Imai and Koike, 2009), and
are closely interrelated (Hernandez-Fajardo and Duenas-Osorio, 2011). In
particular, the supply damage rate (ratio of unserviceable users to all users
of a water supply system) after an earthquake is one of the most appropri-
ate indicators for evaluating the seismic performance of a lifeline network
system from the users' viewpoint. However, since a network system nor-
mally has a hierarchical structure, with a considerable number of links and
nodes, it is not simple to estimate the effect of partial retrofi tting on the
seismic performance.
In this chapter, a simple model is used to estimate the relationship
between the probability of structural failure and loss of service without
using the topological characteristics of a network system (Hernandez-
Fajardo and Duenas-Osorio, 2011; Kang and Song, 2011). A seismic-
assessment procedure for a lifeline network system is proposed, using the
probability of system-performance failure based on the supply damage rate
as the index for evaluation, and an example seismic assessment is carried
out for an actual water distribution network model by taking into account
the pipeline deterioration.
23.2 Seismic failure of a lifeline system
23.2.1 Seismic damage to a lifeline system
A water supply lifeline network system located in a metropolitan area of
Japan is shown in Fig. 23.1. The water lifeline network system has a hierar-
chical structure, composed of transmission lines, distribution, and service
network systems. The whole area is divided into several subzones, as
depicted in Fig. 23.2, which are the distribution districts designated by the
city's waterworks bureau. The shaded area in Fig. 23.2 is one of the water
supply service areas in this model. The detailed distribution network of this
area is shown on the right-hand side. Table 23.1 lists the pipe materials and
their total lengths for different diameter classes within the sample pipeline
network presented in Fig. 23.2.