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VALLEJO – A new
bridge over the Carquinez Straits on
westbound Interstate 80 will include
instruments that can help emergency
responders evaluate the safety of the
bridge after a devastating earthquake
and provide engineers the information
they need to design more
earthquake-resistant structures.
Ultimately, there
will be about 103 instruments on the
bridge, which opens November 15, plus
about 27 on the south approach. The
sensors, called accelerometers, are part
of a Caltrans-funded project by the
Department of Conservation’s Strong
Motion Instrumentation Program (SMIP) to
instrument all toll bridges in
California.
Data from such
instruments went into the design of the
new Al Zampa Memorial Bridge -- the
first suspension span built in the
country in nearly four decades - to make
it as resistant as possible to
earthquake shaking. Zampa was an
ironworker who survived a fall from the
Golden Gate Bridge during its
construction.
Northern California
hasn’t experienced a damaging earthquake
since the Loma Prieta temblor, 14 years
ago tomorrow. That 6.9 quake, centered
in the Santa Cruz Mountains, caused part
of the Bay Bridge and the Cypress
Structure on the Nimitz Freeway to
collapse.
“Some scientists
think we’re overdue for a significant
earthquake in the Bay Area, so it’s
important to keep preparing,” DOC
Director Darryl Young said. “This
instrumentation is a key part of being
ready for the next big quake.”
Seismic
instrumentation of Bay Area bridges has
taken place as Caltrans' retrofitting
work has progressed over the last five
years. Instrumentation is complete on
the San Mateo, Benicia-Martinez,
eastbound Carquinez, and Golden Gate
bridges, and is ongoing on the
Richmond-San Rafael Bridge and the Bay
Bridge, among others.
The westbound span
across the Carquinez Straits opened in
1927 and does not meet current seismic
design or traffic safety standards.
Caltrans determined the structure could
not be repaired without closing it for
an extended period to the 109,000 cars
that use it daily. The new bridge, which
will cost about $200 million, will
provide four lanes of traffic --
including a carpool lane -- and a
pedestrian/bicycle path.
“After the 1994
Northridge earthquake, we analyzed the
westbound Carquinez bridge and decided
that replacing it was the best option,”
said Robert Stott, Chief of Structure
Design Services and Earthquake
Engineering for Caltrans. “The seismic
instrumentation on the new bridge is an
important tool our engineers will use to
protect public safety in future
construction projects.”
Part of DOC's
California Geological Survey, SMIP is
the largest program of its kind in the
world. SMIP was established following
the 1971 San Fernando earthquake and has
sensors at more than 900 locations
throughout the state. The SMIP
instruments that will be installed on
the new bridge automatically dial up a
central computer when strong earth
motion -- generally from a magnitude 4.0
or greater temblor -- is recorded.
SMIP data from the
new Carquinez bridge and other sites can
be used in three ways. First, it can be
analyzed in the minutes following a
quake to allow Caltrans engineers to
assess the integrity and safety of the
bridge or structure. Second, it can be
used to guide emergency response
personnel to the hardest-hit areas in
the region. Third, it shows how
structures react to the shaking, and is
applied to engineering principles that
are incorporated into new design codes
for better earthquake-resistant
construction.
The closest major
fault to the Al Zampa Memorial Bridge is
the Concord Fault, approximately 6.5
miles to the east. A magnitude 5.4
earthquake was centered between Walnut
Creek and Concord on or near that fault
on October 23, 1955. There are several
major faults in the greater Bay Area.
The Strong Motion
Instrumentation Program is a member of
the California Integrated Seismic
Network (CISN), along with the U.S.
Geological Survey, the California
Institute of Technology and the
University of California at Berkeley.
SMIP installs seismic monitors on
high-rise buildings, dams, hospitals and
industrial facilities around the state.
The instruments are also placed in open
land to measure the effects of
earthquakes on soils.
Data from SMIP and
other CISN stations produce a ShakeMap
of ground shaking right after an
earthquake. The ShakeMap identifies
areas of the greatest potential damage
and is used by the Office of Emergency
Services and other emergency response
agencies to immediately direct resources
to these areas.
“This information is
critical both immediately after an
earthquake and in the long term because
it can save lives and minimize property
damage,” Young said. “Earthquakes are
inevitable in California, and this SMIP
data fortifies the building codes that
keep us safe.”
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