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MMD > Archives > November 2001 > 2001.11.17 > 01Prev  Next

Minimizing Earthquake Damage to a Carousel
By Al Sefl

I don't have my USGS map at the moment to tell me whether the fault is
a vertical thrust fault or a slip fault, etc., so the following
information will have to be general.  I am assuming that the entire
weight of the carousel is placed on the center pole bearing.  As I
understand the posting the center pole has shifted so that it is not
truly vertical and this is causing damage.  There is not much that can
be done without removing the carousel and shimming the base but you
can avoid further damage by mounting eight heavy duty pneumatic tires
underneath around the perimeter (not OSHA safe) to run on what is
hopefully a flat concrete surface.  If the seismic event is vertical
then the tires will take up the load all the way around while a
horizontal movement will go to the side that is being pressed down by
the acceleration of the platform in one direction.  Either way the
tires reduce the stress on the center pole.  It is not a good solution
nor should it be a permanent one.  Ideally you would want seismic
isolators on a new cement pad which can be expen$ive.  The isolator
idea is to let the earth move while the carousel stays relatively still.

For the time being, when the carousel is not in operation it might be
a good idea to use hydraulic jacks to support the platform around the
perimeter in the event of another quake (the ones you have had may only
be foreshocks to something larger).  Again, I like the number 8 for
how many points I would suggest.  Wood blocks as double wedges will
also work to remove the load and support the carousel when not in use.
Any quake occurring then would have no effect on bending the pole as
the carousel would be supported uniformly and not tend to bend the
pole in the direction of the quake.

BTW - a quake in the region of 3-4 on the Richter Scale is so minor
that no damage should have been done.  I would check the cement
foundation for liquefaction and the resulting tilt before I would
blame the support pole.  Of the six operating carousels in the San
Francisco Bay Area I know of none that have been damaged by our usual
little tumblers or even our larger ones along the San Andreas, a right
lateral slip fault.  A soils engineer would be good for advice.

Al Sefl
Guaranteed to be correct 50% of the time...
(Minored in Geophysics at Berkeley despite the Rent-A-Mob there.)

(Message sent Fri 16 Nov 2001, 09:47:24 GMT, from time zone GMT-0500.)

Key Words in Subject:  Carousel, Damage, Earthquake, Minimizing

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