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Faking Earthquakes
By Heather Holliday
I November 22, 2004
The
70-foot-tall, 23,400-pound
wind turbine shuddered
and swayed as it
reacted to the effects
of a simulated magnitude
7.3 earthquake.
The 40-second simulation,
conducted Nov. 15
by the Jacobs School
of Engineering at
Camp Elliott, was
accompanied by an
eerie, low-pitched
whine.
The
fake temblor was
caused by the nation's
largest outdoor
shake table, sized
at 25 feet by 40
feet. The table
is capable of shaking
up to 6 feet per
second – allowing
researchers to reproduce
realistic simulations
of earthquakes.
The facility, which
was designed and
built by UCSD faculty
and students, can
accommodate about
2000 tons, roughly
the size of a five-story
building, said José
Restrepo, a structural
engineering professor
and co-investigator
with the project.
“We’ll
be able to reproduce
accurately the ground
movement that has
been recorded before
in very strong earthquakes,”
said Restrepo. “The
intention with this
facility is to do
landmark experiments
on tall complex
structures that
have never been
able to be performed
before because of
height and capacity
limitations.”
Last
week's experiment
tested how well
large wind turbines
can withstand forces
created during earhquakes.
"Our
demonstration is
a first step towards
understanding how
wind turbines are
impacted by earthquakes,
a question that
will become increasingly
important as California
becomes more reliant
on renewable energy
sources such as
wind energy,"
Restrepo said. "A
significant concern
is the resilience
of wind turbines
to earthquakes because
the main wind energy
producing regions
of California are
within close proximity
to active earthquake
faults."
UCSD
structural engineers
also will use the
shake table to conduct
seismic experiments
on multi-story buildings,
bridge columns and
bents, wharfs and
piers, and lifeline
structures such
as electrical sub-stations
and satellite towers.
The shake table
is adjacent to the
Soil Foundation-Structure
Interaction (SFSI)
facility funded
by the California
Department of Transportation.
Taken together,
the shake table
and SFSI will allow
for one-of-a-kind
testing of structural
systems such as
bridge abutments,
embankments and
foundations.
The
demonstration was
part of a grand
opening for a network
of seismic testing
laboratories at
15 universities
– the National
Science Foundation’s
George E. Brown,
Jr. Network for
Earthquake Engineering
Simulation (NEES).
The network, which
includes University
of Colorado at Boulder,
Cornell University
and Berkeley, Davis
and UCLA from the
UC system, will
implement seismic
experiments on buildings,
bridges, utility
structures and nuclear
containment casks.
The
grand hope, said
Bob Englekirk, chairman
of the board of
directors for Camp
Elliot, is to reduce
the loss of life
during an earthquake
and significantly
reduce the amount
of damage that is
caused. “Wouldn’t
it be nice if after
an earthquake everybody
said, ‘I don’t
have to go to Disneyland
this week, I’ve
had my ride,’”
he said.
“The
significance of
this table from
an engineering standpoint
is that it allows
us to test our analytical
procedures,”
Englekirk added.
“Seventeenth
century thinkers
would say that our
earthquake engineering
procedures today
fall into the realm
of philosophy and
not science. This
table will allow
us to demonstrate
that we do know
what we are doing
when we are predicting
seismic behavior.”
Construction
of the shake table,
located at UCSD's
Elliott campus at
Interstate 15 and
Pomerado Road, was
completed in September.
The $9 million facility
was funded through
a $5.9 million grant
from NSF, as well
as state, university
and private contributions.
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