A3 • Friday, January 11, 2019 | Cannon Beach Gazette | CannonBeachGazette.com
Building a better bridge to survive tsunamis
By BRENNA VISSER
Cannon Beach Gazette
The way bridges are
assessed for tsunami risk
needs to be rethought, new
research suggests.
In a study published by
Oregon State University and
the University of Nevada,
Reno, researchers found that
previous assumptions about
how force from a tsunami
impacts bridge infrastruc-
ture don’t necessarily hold
true.
Most studies have only
looked at the total force a tsu-
nami puts on a bridge, rather
than how force impacts indi-
vidual components like gird-
ers, the horizontal beam that
supports the deck, and bear-
ings, the part that provides a
resting surface between the
columns and the deck.
Standard girder bridges
are built with the assump-
tion that all of the stresses
from a tsunami are being
transmitted and absorbed
through the foundation.
The study found that dif-
ferent types of force brought
on by a sustained rush-
ing wall of water actually
transfers a large amount of
pressure onto the support-
ing parts of the bridge, like
the girders, deck chambers,
bearings and connections.
These parts are not factored
in when designing for tsu-
nami resilience.
The fi nding is important,
said Pedro Lomonaco and
Solomon Yim, Oregon State
researchers who contrib-
uted to the study, because
it can help engineers under-
stand why bridges fail and
lead to more tsunami-resis-
tant bridges along the Ore-
gon Coast.
“The breaking of the
bearing connections was the
main type of bridge dam-
age seen in recent tsunamis,
showing that it’s critical to
quantify what the tsunami is
doing to these components
Colin Murphey/The Daily Astorian
Colin Murphey/The Daily Astorian
Several bridges and roads in Seaside have been deemed potentially problematic in an
earthquake and tsunami.
A new study could help communities like Seaside determine
how to improve aging bridges.
and decipher the underlying
physics,” Yim said.
Deadly examples
The need to better under-
stand wave impacts on
coastal bridges was largely
motivated by seeing bridges
destroyed during tsunamis
off Japan and Indonesia.
Over the past 15 years, big
earthquakes have caused tsu-
namis that killed more than
250,000 people and caused
more than $200 billion in
damage, the study estimates,
washing away or dislodging
hundreds of bridges.
The research could help
coastal cities like Seaside,
which has several aging
bridges that are expected to
fail in a tsunami.
The topic has been raised
recently by City Councilor
Tom Horning, a geologist
who has long advocated ret-
rofi tting bridges as a top pri-
ority for the city.
With two major rivers to
cross before getting to higher
ground, having bridges
that can last will be crucial
to maintaining evacuation
routes.
“Bridges are one of the
easiest, fastest connection
points to help people after
an emergency,” Lomonaco
said. “If you don’t have the
bridges, there is nothing you
can do.”
To fi nd answers, research-
ers simulated a tsunami on
a model bridge at the O.H.
Hinsdale Wave Research
Laboratory’s Large Wave
Flume in Corvallis.
Part of what researchers
found was that most bridges
are built too rigidly, Yim and
Lomonaco said.
Instead of seeing the con-
crete columns under a bridge
as infl exible blocks, imag-
ine them like springs. When
the tsunami hits the deck of
a bridge it will bend, making
it vibrate both back and forth
and up and down.
The bridge deck and pil-
ings not only feel the static
forces coming from the
earthquake and tsunami, but
the additional pressure from
these vibrations.
“We are changing the par-
adigm ... to the concept of
thinking about how a bridge
is moving, changing,” Yim
said.
The irregular shape of tra-
ditional trusses and girders
also creates unaccounted-for
turbulence, they said. In gen-
eral, the wall of water should
be moving in one direction,
but when it has to go through
trusses, the water weaves
in and out, adding different
hydrodynamic forces that
can compromise the bridge’s
stability.
“The high pressure that
developed under the bridge
played a signifi cant role on
the stability of the bridge,
and different mitigation mea-
sures were tested, from clos-
ing the gaps between girders
to incorporating venting on
the concrete deck,” Lomo-
naco said.
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More research
Given how young the area
of study is, more research is
needed to understand why
certain bridges survive and
why others do not, the team
says.
But researchers hope the
study gives engineers a bet-
ter understanding of the
physics of what happens
when a tsunami slams into a
bridge and opens the door to
designing coastal spans that
are better able to withstand
giant waves.
“Think back 10, 15 years
ago, the tsunami was not
even considered,” Yim said.
“We’ve come a long ways.”
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Ocean changes impact Northwest salmon
Salmon will not
be immune to the
eff ects of ocean
acidifi cation
By JES BURNS
Oregon Public
Broadcasting
A new study suggests
that salmon will not be
immune to the effects of
ocean acidifi cation.
Scientists found that
changes to ocean chemis-
try disrupt a fi sh’s ability to
smell danger in the water.
Researcher Chase Wil-
liams of the University of
Washington exposed young
coho salmon to the elevated
ocean CO2 levels expected
over the next few decades.
He then dropped in an odor
that normally makes the fi sh
react as if a predator is near.
The fi sh ignored it.
“They’re still smelling
odorant, but the way their
brain is processing that sig-
nal is altered … Before, they
would avoid this predator
odor and now they’re more
indifferent to it,” Williams
said.
The results are concern-
ing because salmon rely on
smell to avoid danger, fi nd
food and to fi nd their way
back to spawning grounds
in West Coast rivers.
Co-author Andrew Dit-
tman is a scientist with the
federal Northwest Fisheries
Science Center. He said the
results could apply to other
salmon species.
“The
mechanisms
involved … are very similar.
So the expectation would
be that we would see rela-
tively similar phenomena in
the other species as well,” he
said.
The ocean absorbs about
25 percent of the carbon
dioxide in the atmosphere.
The more CO2 humans
emit, the more saturated the
ocean becomes, thus lower-
ing the pH of the water.
Ocean acidifi cation has
already started to have neg-
ative effects on the Pacifi c
Northwest’s shellfi sh indus-
try. Knowledge about poten-
tial impacts on other ocean
species is still limited.
The study was published
in the journal Global Change
Biology.
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Help eliminate invasive ivy
along the Skipanon River
Cannon Beach Gazette
Invasive English ivy has
a foothold along the Ski-
panon River in Warrenton,
where it climbs into Sitka
spruces and other native
trees, causing them to rot
and ultimately topple.
The North Coast Land
Conservancy is seeking vol-
unteers for a stewardship
day on Saturday, Jan. 26,
from 10 a.m. to 1 p.m. to
tackle ivy in the conservan-
cy’s Skipanon Forest Habi-
tat Reserve.
The spruce forest-and-
swamp habitat type that
characterizes the prop-
erty is considered globally
rare. The land conservancy
scheduled this stewardship
day in the winter, when the
deciduous vegetation has
died back and it’s a little
easier to move around, but
volunteers can still expect
rough walking.
Most of the ivy at Ski-
panon Forest is growing on
large Sitka spruce trees, but
there may be some on the
ground as well. Handsaws,
loppers, and other tools will
be used to remove this inva-
sive vine.
E-mail
stewardship
frector Melissa Reich at
melissar@nclctrust.org
or call 503-738-9126 to
attend.
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