Seismic risk management for water pipeline networks - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 634

natural hazards, including earthquakes. Many structures constructed prior
to 1980 in Japan were designed for a particular seismic load level, i.e. Level
1 ground motion caused by the maximum operational earthquake (MOE).
After the 1995 Kobe Earthquake, revised guidelines for defi ning Level 1
and Level 2 (MCE) ground motions as the designed earthquake load
were introduced. This means that many old infrastructure designs fell
below the acceptable limits according to the current seismic design proce-
dures and practices. Thus, these structures are deemed vulnerable to strong
earthquakes.
23.3.1 Defi nitions of seismic performance
In this section, the defi nition of seismic performance of the lifeline networks
in Japan is described, in which seismic performance for the important
network systems should be selected to fulfi ll the short restoration/recovery
requirement for the severest seismic load in the past earthquakes. The
seismic performance for the ordinary network systems, on the other hand,
must meet the minimum requirement for saving human lives. In addition,
for the frequent earthquakes during the service period, the seismic perfor-
mance for both systems also needs to be operated without any water supply
disruption.
The seismic performance of the lifeline network system can be specifi ed
in relation to the limit states of the system, such as the serviceability limit
state, repairable limit state, and ultimate limit state for the corresponding
seismic disasters. Table 23.5 shows typical defi nitions of the required seismic
performance of a lifeline system. In these defi nitions, both the seismic-
performance damage mode and the component damage mode are also
defi ned quantitatively for seismic disasters of Level 1 (denoted by EQ 1 ) and
Level 2 (denoted by EQ 2 ) ground motions, respectively. The most important
facilities and transmission pipelines are required to have higher safety in
seismic performance 2 than in seismic performance 3, because those struc-
tural components are always necessary for immediate recovery. The distri-
bution pipelines and their facilities should have the capacity to recover from
seismic performance 3 in due course.
In Table 23.5, the limit state function of Z for the component damage
mode specifi es the critical condition that the structural damage mode occurs
when a seismic load exceeds the critical value. The limit state function of D
for the performance damage mode provides the critical condition that the
functional damage mode occurs in terms of the seismic load level. Once
these limit state functions are defi ned, the probability of exceeding the limit
state for the seismic performances can be formulated and developed in
terms of seismic design information.