Seismic risk management for water pipeline networks - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 624

should not exceed the capacity of the joint, so the seismic safety is assessed
as follows:

ΔΔ
joint

≥ [23.2]

design

where

joint is the capacity against joint pull-out at the time of the earth-
quake, and

Δ

Δ design is the design displacement which is given by

Δ = Δ + Δ + 635 . mm [23.3]

design seismic operational

in which Δ operational are predicted seismic joint displacement and

daily operational joint displacement, respectively, and 6.35 mm is factor
used to provide a margin measure of safety.
Furthermore, the ALA prepared a seismic design procedure for restrained
and segmented pipes, which can absorb a large earthquake ground displace-
ment and have a locking ring to prevent pull-out failure from the joint.
When one locking ring is insuffi cient to resist the applied force, the neigh-
boring joints can support the residual force. If n joints are necessary to resist
the applied force, the total axial tensile force F stop is given by

Δ seismic and

( )

F = πτ Dl n + 1 [23.4]

stop G d

where D is the pipe diameter,

G is the shear stress acting between the pipe
surface and surrounding soil, and n is the number of joints necessary to
resist the applied force. The ALA recommends that n should have a value
of 3. So for restrained and segmented pipes, the seismic safety is assessed
as follows:

τ

RF
y

≥

stop

[23.5]

where R y is the critical strength for the pull-out force.

Seismic performance design procedure of existing segmented
pipelines in Japan

The JWWA (1997) published the Seismic Guidelines for Water Pipelines , in
which it developed a design procedure for unrestrained and segmented
joint pipes, that is different from the one suggested by the ALA. Note that
the JWWA procedure is applicable to unrestrained and segmented pipes
only, whereas the ALA method can be used for both unrestrained and
restrained pipes.
In a very strong earthquake, which is defi ned as a Level 2 earthquake in
Japan, or a maximum considered earthquake (MCE), the following analyti-
cal procedure can be used to estimate the joint displacement Δ u J :

Δ u =⋅ ⋅ λα 1 Δ u [23.6]

J G