Re: AP900 sensitivity to wind


Joe Zeglinski
 

Hi Steve,

Let me chime in with yet another anti vibration idea. In recent months,
there have been posts about how to deaden the vibration of a pier - usually
about a fixed pier. The common idea is to fill the tube with "coarse sand".
Problem is that the sand makes the pier, "top heavy". Also, when the sand
picks up moisture, it not only becomes heavier, but also the vibration
dampening is eliminated by the "moisture clumped sand". The National Research
Council of Canada maintains a series of mountain top GPS piers to monitor
quakes, gradual earth movement, etc., and they fill their GPS piers with a mix
of coarse sand and "kitty litter", which absorbs any moisture. Problem is how
to dry out the kitty litter - I assume they vacuum out the sand fill
periodically, and refill the pier.

Another very effective idea mentioned was to insert a round plug of wood
into the top of the pier. The wood kills any vibration quite effectively. A
possible problem here, is that the pier will expand somewhat, as temperature
changes, and the dampening may be lessened, or the plug could slip own, if not
tarred to the insides.

I wonder if another approach might work better than the two above.

I suggest buying a few of those closed foam solid tubes (snakes ?) that
kids use in a swimming pool. They are about 6 feet long by about 4 inch
diameter, and can be purchased at Toys-R-Us, or any kids pool party supply
store. Bundle two or three, depending on the pier diameter, together, and
stuff them down the pier. You might find it easier to slide the bundle down,
if you first spray it with a cooking oil like "PAM". You still might have to
hand compress the bundle from the side, as you inch it down the pier. These
tube bundles will stay tight compressed against the inside of the pier, at all
temperatures, and will not pick up any moisture. They will also leave channels
between them to allow any condensation inside the pier to drift away. Finally,
these tightly fitted tubes of etha foam, mechanically model as "parallel
springs" radiating from the centre, all the way down, so the sectional spring
coefficients "add up".
In effect, you get a lattice of parallel springs, equally balanced down the
tube, dampening all vibration modes - and they are unaffected by temperature
and moisture, or stiffening of the material with age.

Joe

----- Original Message -----
From: "Steve Peters" <capitoladude@...>
To: <ap-gto@...>
Sent: Thursday, January 17, 2008 4:55 PM
Subject: [ap-gto] Re: AP900 sensitivity to wind


That's a good sugggestion, Bob. My AP900 is supported on an ATS
portable pier (which AP also sells), which is very stable, as far as
I can tell. However, I'll try and anti-vibration pads to see if they
have any effect.

Thanks,

Steve

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