Point of VIEW. A
purely analytical perception...
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Japan
AN EXAMPLE TO FOLLOW | Continued
from pg. 4
A suspension bridge was built between
Kobe and Awaji-shima in Japan that has
so dwarfed what had preceded it, relative to all of the other suspension bridges
ever built, that any serious comparisons are almost nonsensical.
The bridge’s construction cost was $4.3 billion, and it stretches 12,838
feet across the Akashi Strait. To
give you some idea of the magnitude of what this means, it would take four Brooklyn
Bridges to cover the same body of water.
In actual total length, the Brooklyn Bridge is only about 1/6th
the size of the Akashi Kaikyo. It
is easily the longest suspension bridge in the world and is twice the size of
both the Verranzano Narrows Bridge in New York and the Golden
Gate Bridge in California. However,
if you laid the Verranzano and the Golden Gate Bridges end to end, they
would be only a tad longer than the Akashi Kaikyo Bridge by itself. The towers that give the bridge it’s support rise to almost
the equivalent of 100 stories above the their base and are large enough to allow
ships of any size to comfortably pass under it. Because of the fact that the ports
of Kobe and Awaji-shima are so active, the bridge was built particularly high
to accommodate anything that the world’s ship builders could throw at it, now
or in the foreseeable future. Moreover,
that wasn’t the only problem that had to solved: the Kobe area has a history of
having some of the worst weather on the planet, and it was critical that the bridge
be constructed so that gale force winds would not cause it to collapse.
Ultimately, the builder was able to design this bridge to withstand 180
mile an hour winds. In addition,
annual rainfall in this area even in a relatively dry season can equal 57 inches
a year, and if that wasn’t enough, the bridge is located directly on an earthquake
fault line, the region is a magnet for tsunamis and hurricanes that are about
as normal here as sushi. Given all of these challenges, you
might have thought that the engineers would have just plain given up the ghost.
Instead of that, they used some very interesting architectural innovations
in getting the job done: “They
supported their bridge with a truss, or complex network of triangular braces,
beneath the roadway. The open network of triangles makes the bridge very rigid,
but it also allows the wind to blow right through the structure.
In addition, engineers placed 20 tuned mass dampers (TMDs) in each tower.
The TMDs swing in the opposite direction of the wind sway. So, when the wind blows the bridge in on direction, the TMDs
sway in the opposite direction, effectively “balancing” the bridge and canceling
out the sway. With this design, the
Akashi Kaikyo can handle 180-mile-per-hour winds, and it can withstand an earthquake
with a magnitude of 8.5 on the Richter scale!”
Earthquakes with a magnitude of about
2.0 or less are usually called micro- earthquakes; and they are not commonly felt
by people. The only way that we even
know that they exist is by the fact that local seismographs are able to sense
them. Upping the ante, the next level
on the Richter Scale contain those earthquakes in which the magnitudes hover between
4.5 and 8.0. There are thousands
of these every year but anything above the level of 5.5 can be very serious if
it strikes the wrong place at the wrong time.
At the top of the earthquake scale are those over 7.0. Those from 7.0 to
8.0 are considered “Major” and those over 8.0 are considered to be “Great.”
The Los Angeles Earthquake of 1994 only had a magnitude of 6.7, and you
probably can still remember the damage that it caused.
The San Francisco Earthquake of 1906 had a magnitude of 7.9 and The Great
Earthquake of 1964, also known as the Good Friday Earthquake, that hit Alaska
registered about 8.0. Fortunately,
it struck a remote area where there were few people, for if it had hit San Francisco
or New York, we would have had to rebuild those cities literally from scratch.
On the average, one earthquake of such size occurs somewhere in the world
each year. The largest earthquakes ever recorded
run in the 8.8 to 8.9 range. Although
the Richter Scale has no upper limit, the largest known shocks have had magnitudes
in the above range. If an earthquake
of this nature struck under the ocean, there might not be any damage at all, at
least visibly, and if it were not for our highly sensitive scientific instruments,
we would not have known that it even occurred.
Contrarily, an earthquake of this magnitude could well send shockwaves
to the oceans surface that would create enormous tidal waves, which could be devastating
depending upon where they struck land. For
each whole number value of Richter Scale increase, the power of the earthquake
being measured increases by 10 times
and the energy released elevates by 32 times.
Moreover, an earthquake 12measuring 12 on the Richter Scale is estimated
to have the power to split the earth in half. “The
amount of energy released by a magnitude 4.3 earthquake is equivalent to the energy
released by the atomic bomb that destroyed Hiroshima, Japan, and is equivalent
to about 20 kilotons of TNT. The
largest earthquakes recorded to date measured about 9.5 and released as much energy
as 66 million Hiroshima–sized atomic bombs.”
Thus,
we are able to grasp the magnitude of what the engineers that constructed the
bridge were able to accomplish. The
mere thought that they could even attempt to control a force of that magnitude
is beyond my own comprehension, but many people in Japan have bet an awful lot
of money that these guys knew exactly what they were doing.
In this prodigious project, they had to create a monolith whose cables
if strung out in a single line would circle the globe 7½ times.
Amazingly, the Akashi Kaikyo Bridge was originally programmed to be three-feet
shorter than it is today. The reason
for the difference is that during its construction, the bridge was hit by the
Great Hanshin Earthquake, which unbelievably stretched the bridge itself the additional
length. However, that earthquake came nowhere near testing the upper limits of
the bridge’s flexibility. Additional
statistics show that the bridge is also the tallest, the most expensive and as
we had mentioned earlier it is the longest.
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