Seismic risk management for water pipeline networks - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 646

water-supply service after the retrofi tting, because the deterioration effect
due to old joints rapidly decreases. Scheme 3, on the other hand, cannot
achieve higher performance of the water-supply service, because the dete-
rioration effect due to old joints is maintained over the whole residual
period.
It is noteworthy that the investments required for schemes 1-3 are same,
i.e. scheme 1 rapidly can improve the seismic performance, but in the
remaining longer period, the deterioration process for DCIP (new-type
joint) will start again. On the other hand, scheme 3 can gradually improve
the seismic performance during the whole service period, but potentially
vulnerable old-type joints of CIP/DCIP cannot be replaced during the
whole service period.

Simulation results

Figure 23.18 shows the probability of system-performance failure for various
retrofi tting periods under the seismic investment ratio C S /C 0

0.5, in which
C S and C 0 are the seismic investment cost and initial cost, respectively. As
shown in Fig. 23.19, all existing old pipes are replaced when C S /C 0 exceeds
0.4. Therefore, this is the case when suffi cient seismic investment has been
achieved.
Rapid retrofi tting cases indicate that the improvement in seismic perfor-
mance is remarkable in the minor damage mode (Fig. 23.18). This result
indicates that the intensive retrofi tting plan is effective in reducing the
seismic risk when suffi cient investment has been made. Figure 23.20 com-
pares the probability of value loss and that of system-performance failure

=

Minor Moderate Major

1.E+00

1.E-01

1.E-02

0 20 40 60 80

Retrofitting period T n
under the same cost, C s / C 0

23.18 Probability of system failure for retrofi tting periods under
C S /C 0 = 0.5.