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Photon
sage
Reged: 03/10/06
Posts: 264
Loc: Aurora, Colorado, USA
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When I taught middle-school science, I used to make a "seismograph" in the classroom that would pick up vibrations from traffic a couple of hundred feet from my room.
I guess pier construction has been well thought out, and yes, I'm a newbie, but....
I'm wondering if having such a rigid pier material as concrete or steel might not just transmit vibrations better than something more flexible like wood. Any thoughts?
Pete
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Zack DeMoss
sage
Reged: 03/08/06
Posts: 252
Loc: Roanoke, VA
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Interesting thought. I think though that you would need something more durable than wood, but i do know they use essentially "Rubber boots" in plants that manufacture microchips to avoid vibration.
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Zack DeMoss
Old Dominion University
Information Technology Major
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imjeffp
Senior Space Cadet
Reged: 09/30/03
Posts: 4411
Loc: Cedar Park, Texas
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How about using a railroad tie?
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 11995
Loc: Rockford Illinois
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Wood would (Try that 10 times real fast!) also vibrate. Think about it. Trees sway in the wind. If it didn't have some "Give" to it, it would break.
I think what stops (Or at least slows down/dampens) vibrations through a concrete pier is a combination of Mass, Large Footing, Diameter of Pier, Internal Reinforcement... All that works in sync to help limit vibrations.
If I recall correctly, the rule of thumb for a concrete pier is at LEAST the same diameter of the scope you'll put on it. Going 2" larger is my plan. (10" LX200, 12" pier).
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Neo... (Jeff)
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John Jarosz
I'm being watched...
Reged: 04/25/04
Posts: 2184
Loc: Chicago area, IL
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All materials are compromises.
Wood transmits vibrations worse than steel or aluminum. I am not sure about concrete.
However, wood is more elastic than any of the other common construction materials. So to build a wood pier that is the equivalent stiffness of a steel or concrete pier, a much larger cross section is required. At some point the cross section of the pier will get too large to get close to the scope for observing, so it may not be possible to build a pier with the same stiffness as steel or concrete in the space available.
So a design that commands a certain material be used may impose constraints that will still allow you to solve the problem, but not make something that can be used efficiently.
The difference in vibration damping between wood and concrete may not be enough that entices people to spend time trying to use wood for a pier. Concrete is a pretty dead material, and it is much stiffer than wood which permits a more compact design..
A design effort using either material may well prove sucessful, but to optimize a solution the analysis needs to be done numerically.
Once you start numerical analysis, you need answers to all sorts of questions:
Frequency, magnitude and direction of expected vibrations that are required to be damped?
Time permitted to reduce same vibrations?
Magnitude, etc of acceptable levels of vibrations after damping?
At this point most people start to think about seat-of-the-pants judgements instead of measuring everything. So the question never really gets answered empirically, but rather on a case-by-case basis, where everything is analyzed after the fact, but again not using instrumentation that gives measurements, but by observational subjective data.
Will wood work? Yes. Is it better? That depends...........
John
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6" F4.6(w/Paracorr) GEM reflector, 8" F11 Dall Relay Scope
6" F5 RFT Refractor, Garrett Gemini 20x80 LW
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