ETL 1110-2-533
30 Sep 94
to store the water, and a piping system connecting the
system elements and to bring the water into the
facility.
(2) As noted earlier, pumps are seismically rug-
ged; however, wells are vulnerable to sanding of their
intake screens and damage to casings and bindings of
the pump drive due to deformations from soil lique-
faction. Soils around the damsite are likely to be
very vulnerable to soil liquefaction and subsidence.
(3) One of the most common failures observed
in earthquakes is water tank damage, primarily to
unanchored tanks. A problem common to most tanks
is damage to the roof due to sloshing of water in the
tank. This may buckle the roof and tank wall near its
Figure B-37. Large oil storage tank inadequately
top, but usually does not impair the functioning of the
anchored. A large oil storage tank does not have
tank. Unanchored flat-bottom tanks have several
positive restraints for longitudinal motion. Motion
failure modes. Smaller tanks (less than about 30 ft in
of the tank may damage pipe connections and
diameter) may slide. This may break piping connec-
cause a leak
tions, particularly drain pipes that extend below the
bottom of the tank. Unanchored tanks typically rock
back and forth lifting one side and then the other.
Lifting of the tank bottom in excess of 2 ft has been
observed. Pipe connections not provided with suffi-
cient flexibility will fail, allowing the tank to drain.
When one side lifts, the other side often develops a
buckle at the base of the tank, called elephant-foot
buckling. While elephant-foot buckling may not
cause any leaks, if there are poor welds between the
wall and the base plate, or if there is significant cor-
rosion, welds will fail. This allows a rapid emptying
of the tank and usually causes the tank to explode,
causing severe damage to the tank. Well-anchored
tanks have performed very well.
(4) The most vulnerable part of the water system
is the piping that connects the wells, tanks, and user
Figure B-38. Unanchored chiller. In large facilities,
facilities. Water pipes, which usually use bell and
such as a dam, when some equipment was initially
spigot or rubber gasket seals to join pipes, are vulner-
installed, modified, or replaced, it may not have
able to soil liquefaction and subsidence. Key to the
been adequately anchored. A walk-through of
continued functioning of the stem is a carefully
facilities will usually find unanchored equipment
planned series of valves to sectionalize the system so
that damaged parts can be isolated to prevent them
f. Water used for air conditioning needed to
from causing a loss of pressure and water. Large
water systems can drain in a matter of minutes with
just a few failures. One location of particular con-
(1) The water supply system is frequently used
cern is where the water system pipes enter the struc-
ture, as subsidence around the structure may cause
and communication systems. The water system ele-
failures where there is limited redundancy.
ments are pumps (and their power supply and control
system) to draw water from wells or the river, tanks
B-22