Pier design and sand


r1300rs
 

Just a comment about the sand issue.

I tend to disagree about the sand in the tube; although I believe both wood and sand
accomplish similar things-they both absorb energy and act as a dampeng agent to the
system to resist resonance and its inherent fundamental frequency and thus will cease any
oscillations quicker-sort of like applying electrical or viscous resistance to the system.

Generally, sand is a very good vibration control material since it has the ability to absorb a
huge amount of energy without saturating and is able to provide high mass which will lower
the resonant frequency of a decoupled vibration control system. Additionally, it can help
create substantial resistive mass which will address horizontal displacement. Sand is quite
efficient in converting mechanical energy (vibration) into thermal energy (heat). It can be
viewed as a reservoir to absorb and dissipate the unwanted stored energy trapped in the
component.

This is just my opinion to interject.


Woodwind
 

Having been following this thread, I could say with any confidence which side has won the day.

How about a very simple experiment. Does someone have the equipment/instrumentation to monitor vibrational energy, damping etc in a simple steel tube and measure it with and without a dry sand or a sand/oil mix ?

MPH



r1300rs <cardiofuse@...> wrote: Just a comment about the sand issue.

I tend to disagree about the sand in the tube; although I believe both wood and sand
accomplish similar things-they both absorb energy and act as a dampeng agent to the
system to resist resonance and its inherent fundamental frequency and thus will cease any
oscillations quicker-sort of like applying electrical or viscous resistance to the system.

Generally, sand is a very good vibration control material since it has the ability to absorb a
huge amount of energy without saturating and is able to provide high mass which will lower
the resonant frequency of a decoupled vibration control system. Additionally, it can help
create substantial resistive mass which will address horizontal displacement. Sand is quite
efficient in converting mechanical energy (vibration) into thermal energy (heat). It can be
viewed as a reservoir to absorb and dissipate the unwanted stored energy trapped in the
component.

This is just my opinion to interject.


Woodwind
 

Having been following this thread, I could not say with any confidence which side has won the day.

How about a very simple experiment. Does someone have the equipment/instrumentation to monitor vibrational energy, damping etc in a simple steel tube and measure it with and without a dry sand or a sand/oil mix ?

MPH



r1300rs <cardiofuse@...> wrote: Just a comment about the sand issue.

I tend to disagree about the sand in the tube; although I believe both wood and sand
accomplish similar things-they both absorb energy and act as a dampeng agent to the
system to resist resonance and its inherent fundamental frequency and thus will cease any
oscillations quicker-sort of like applying electrical or viscous resistance to the system.

Generally, sand is a very good vibration control material since it has the ability to absorb a
huge amount of energy without saturating and is able to provide high mass which will lower
the resonant frequency of a decoupled vibration control system. Additionally, it can help
create substantial resistive mass which will address horizontal displacement. Sand is quite
efficient in converting mechanical energy (vibration) into thermal energy (heat). It can be
viewed as a reservoir to absorb and dissipate the unwanted stored energy trapped in the
component.

This is just my opinion to interject.


William R. Mattil <wrmattil@...>
 

Murray Hammick wrote:
Having been following this thread, I could say with any confidence which side has won the day.

How about a very simple experiment. Does someone have the equipment/instrumentation to monitor vibrational energy, damping etc in a simple steel tube and measure it with and without a dry sand or a sand/oil mix ?



A few years ago I was in New Mexico visiting Andy Homeyer and he described how he dampened his piers and it made sense. He drilled a hole near the top and mounted the mount, OTA and what not. Additionally he then mounted a small petri dish to the side of the pier and filled with water. Striking the side of the pier would then cause ripples in the water in said petri dish that could be easily observed. He then timed the duration of the ripples and started adding sand and retesting until he reached a minimum. What he did was essentially "tune" the system for maximum damping. You can all decide for yourselves if it makes any real difference. But I thought that it was a very well thought out approach and makes sense.


Regards

Bill

--

William R. Mattil : http://www.celestial-images.com


Jeff Young <jey@...>
 

Murray --

I went through all these arguments when I built my pier. Each side
seemed to have logic (and expertise) in their favor. Finally, I just
experimented.

I have a 10" diameter, 50" tall steel pier. Empty, a solid kick to the
pier would produce 20 arc-second vibrations in the eyepiece that damped
in about 1 second. Filled with oiled sand, the amplitude dropped to
about 15 arc-seconds while the dampening time stayed the same. The
results were hardly scientific, but they were fairly well repeatable.

The results were enough on the plus side of the ledger that I left the
sand in, but I'd be hard pressed to say it makes much of a difference.

-- Jeff.


________________________________

From: ap-gto@... [mailto:ap-gto@...] On
Behalf Of Murray Hammick
Sent: Wednesday, October 31, 2007 1:47 PM
To: ap-gto@...
Subject: Re: [ap-gto] Re: Pier design and sand



Having been following this thread, I could say with any
confidence which side has won the day.

How about a very simple experiment. Does someone have the
equipment/instrumentation to monitor vibrational energy, damping etc in
a simple steel tube and measure it with and without a dry sand or a
sand/oil mix ?

MPH

r1300rs <cardiofuse@... <mailto:cardiofuse%40mac.com> >
wrote: Just a comment about the sand issue.

I tend to disagree about the sand in the tube; although I
believe both wood and sand
accomplish similar things-they both absorb energy and act as a
dampeng agent to the
system to resist resonance and its inherent fundamental
frequency and thus will cease any
oscillations quicker-sort of like applying electrical or viscous
resistance to the system.

Generally, sand is a very good vibration control material since
it has the ability to absorb a
huge amount of energy without saturating and is able to provide
high mass which will lower
the resonant frequency of a decoupled vibration control system.
Additionally, it can help
create substantial resistive mass which will address horizontal
displacement. Sand is quite
efficient in converting mechanical energy (vibration) into
thermal energy (heat). It can be
viewed as a reservoir to absorb and dissipate the unwanted
stored energy trapped in the
component.

This is just my opinion to interject.


Joe Zeglinski
 

Hi,

If the Petrie dish has value, then it is far simpler to attach a mic to
the side of a pier, and plug the mic output into your laptop audio port. The
waveform can be captured and displayed, and displayed at greater convenience
in better detail, in any music editing program - even the rink dink Sound
tools in the Windoze Accessories folder. Using better sound recording
programs, you can measure the amplitudes and frequencies, and even get the
Fourier Transform to identify the dominant frequencies and power. Then one can
apply dampening techniques like sand, or perhaps bolting on step rings at
sections of the pier to change the modes, and perhaps cancel them.

One other side benefit might be to discover if there are any other sources
(traffic, walking on observatory floor, etc) ground vibrations, or stepper
motor frequencies being coupled from an operating mount into the pier, and
being amplified by the steel pier.

The nice thing about the above approach is that these WAV files can be
graphed and saved, to be shared with others in the group in perhaps the FILES
section. Then, any visitor can get the geometries of the pier used, with the
resulting recorded waveform, for download, or even live online playback using
RealPlayer etc., to compare everyone's pier dampening technique.

If you like the Petrie dish approach, capture the mic output and simply
play it back using the RealPlayer or any PC CD playback program - it will show
the same waves as the water in the Petrie dish.

Joe

----- Original Message -----
From: "William R. Mattil" <wrmattil@...>
To: <ap-gto@...>
Sent: Wednesday, October 31, 2007 10:49 AM
Subject: Re: [ap-gto] Re: Pier design and sand


Murray Hammick wrote:
Having been following this thread, I could say with any confidence which
side has won the day.

How about a very simple experiment. Does someone have the
equipment/instrumentation to monitor vibrational energy, damping etc in a
simple steel tube and measure it with and without a dry sand or a sand/oil
mix ?



A few years ago I was in New Mexico visiting Andy Homeyer and he
described how he dampened his piers and it made sense. He drilled a hole
near the top and mounted the mount, OTA and what not. Additionally he
then mounted a small petri dish to the side of the pier and filled with
water. Striking the side of the pier would then cause ripples in the
water in said petri dish that could be easily observed. He then timed
the duration of the ripples and started adding sand and retesting until
he reached a minimum. What he did was essentially "tune" the system for
maximum damping. You can all decide for yourselves if it makes any real
difference. But I thought that it was a very well thought out approach
and makes sense.


Regards

Bill

--

William R. Mattil : http://www.celestial-images.com



To UNSUBSCRIBE, or for general information on the ap-gto list
see http://groups.yahoo.com/group/ap-gto
Yahoo! Groups Links




Joe Zeglinski
 

Hi,

I have been thinking about putting a temporary pier in the ground, to see
how the back yard observing spot works out. I don't want to commit to heavy
steel posts and concrete bunker footing.

I was thinking of using one of those very thick walled, 10" diameter,
street water main/sanitation pipes, and simply bury it 3 or 4 feet deep (3
feet above ground), and fill the inside back in with earth (perhaps only to
ground level). I am hoping that the perhaps 1/2", (or thicker), PVC walls
won't ring as much as steel, and will be solid enough for an AP900 system. I
think these street pipes should be temperature stable and should not warp or
vibrate, in normal city street use, so it might have advantages as pier
material. Advantages include being easier to construct, (even remove to adjust
for height), and can eventually be moved to a better spot, or removed
entirely.

Opinions please.

Joe


William R. Mattil <wrmattil@...>
 

Joseph Zeglinski wrote:
If you like the Petrie dish approach, capture the mic output and simply play it back using the RealPlayer or any PC CD playback program - it will show the same waves as the water in the Petrie dish.









Joe,

No thanks .... There are too many variables that would skew the results using a microphone not the least of which is the frequency response and how are you going to couple that to the pier. I'll stick to water. You can, however, use any method that you like <g>


Bill

--

William R. Mattil : http://www.celestial-images.com


N. Foldager
 

Jeff:

I have a 10" diameter, 50" tall steel pier. Empty, a solid kick to the
pier would produce 20 arc-second vibrations in the eyepiece that damped
in about 1 second. Filled with oiled sand, the amplitude dropped to
about 15 arc-seconds while the dampening time stayed the same. The
results were hardly scientific, but they were fairly well repeatable.
Of course Don is right, when he argues for as low mass as possible at
the top of the pier. That is also the part of the pier where I would
expect almost no bending to take place.

For that reason I would think that filling the pier *partly* might
give the best result: sand in the lower part where the bending is
maximal, but empty at the upper part to limit the mass at the top.

The results were enough on the plus side of the ledger that I left the
sand in, but I'd be hard pressed to say it makes much of a difference.
The most important is without question the dimensions of the pier;
lower and thicker is better (as long as the OTA can pass).

Best regards,

Niels Foldager


N. Foldager
 

If the Petrie dish has value, then it is far simpler to attach a mic to
the side of a pier, and plug the mic output into your laptop audio port.
I question the "Petri method" as I don't think it for sure can
discriminate between the bell like oscillations (which we don't care
about) and the bending oscillations. (Or can it? The frequency of
latter should be much lower.) I believe that a microphone attached to
the pier will only record the "sound of the bell", not the bending of
the pier.

Best regards,

Niels Foldager


masterson_harold <hfm5022@...>
 

You are trying to measure the motion of the pier. Use an
accelerometer, not a microphone.

--- In ap-gto@..., "N. Foldager" <nf@...> wrote:

If the Petrie dish has value, then it is far simpler to attach
a mic to
the side of a pier, and plug the mic output into your laptop audio
port.

I question the "Petri method" as I don't think it for sure can
discriminate between the bell like oscillations (which we don't care
about) and the bending oscillations. (Or can it? The frequency of
latter should be much lower.) I believe that a microphone attached to
the pier will only record the "sound of the bell", not the bending of
the pier.

Best regards,

Niels Foldager


Woodwind
 

The bending can be captured using strain guages (gages for US speakers)

Would anyone be prepared to give all of this a go ?

I liked the idea of the 10" concrete drain pipe - I cannot see that bending very much. Its a quicker and possibly cheaper alternative to constructing a reinforced concrete pillar.

MPH

"N. Foldager" <nf@...> wrote: > If the Petrie dish has value, then it is far simpler to attach a mic to
> the side of a pier, and plug the mic output into your laptop audio port.

I question the "Petri method" as I don't think it for sure can
discriminate between the bell like oscillations (which we don't care
about) and the bending oscillations. (Or can it? The frequency of
latter should be much lower.) I believe that a microphone attached to
the pier will only record the "sound of the bell", not the bending of
the pier.

Best regards,

Niels Foldager


Joe Zeglinski
 

Hi,

The other benefit, I was considering, is that it can be sawn to length,
with some work. However, you can do a deal with a contractor doing road work,
and he will cut one evenly, to your requirements, using his machinery - you
might even get the pipe cheaper than from the dealer (who might not want to
sell you just one). I think they are standard 10 foot long, too much to bury.
You can also decide if you want the bell-swaged wider end up, for an inlaid
(wooden ?) plug/mounting-plate/pier vibration reducer - or swaged end down, to
have a slightly wider footing 4 feet down.

Joe

----- Original Message -----
From: "Murray Hammick" <mphammick@...>
To: <ap-gto@...>
Sent: Wednesday, October 31, 2007 5:29 PM
Subject: Re: [ap-gto] Re: Pier design and sand


The bending can be captured using strain guages (gages for US speakers)

Would anyone be prepared to give all of this a go ?

I liked the idea of the 10" concrete drain pipe - I cannot see that bending
very much. Its a quicker and possibly cheaper alternative to constructing a
reinforced concrete pillar.

MPH

"N. Foldager" <nf@...> wrote: > If
the Petrie dish has value, then it is far simpler to attach a mic to
the side of a pier, and plug the mic output into your laptop audio port.
I question the "Petri method" as I don't think it for sure can
discriminate between the bell like oscillations (which we don't care
about) and the bending oscillations. (Or can it? The frequency of
latter should be much lower.) I believe that a microphone attached to
the pier will only record the "sound of the bell", not the bending of
the pier.

Best regards,

Niels Foldager









To UNSUBSCRIBE, or for general information on the ap-gto list
see http://groups.yahoo.com/group/ap-gto
Yahoo! Groups Links




dmwmpd <westergren@...>
 

Hi Joe,

I really don't think PVC pipe buried in the soil is going to be a
very good pier. The ringing that you mention is a high frequency
tone, that the PVC pipe wouldn't have compared to a metal (steel)
pipe. But the real concern for pier design is how stiff it is
against bumping (not hitting), wind, weight shift (as the mount
moves with any unbalance), pulling cables, etc. These are all long
time effects, like many seconds to hours. The stiffness of the pier
pipe is a function of E (modulus of elasticity of the material) and
the Section Moment of Inertia (depends on diameter and wall
thickness. The stiffness is E*I. It then determines how much
delction of a canteleverd pier has at the top, when one or more of
the steady forces or moments I mentioneed above are applied.

The modulus for steel is 30 million. The modulus for PVC is between
380,000 and 540,000. In other words, the PVC pipe would flex more
than 55 times as far compared to the the same size steel pipe.

The paper on pier design by Dennis Persyk mentioned a few days ago
on this forum is a very good guide to best pier design, although it
doesn't address the dynamics that I mentioned in my posts.

Regards,
Don

--- In ap-gto@..., "Joseph Zeglinski" <J.Zeglinski@...>
wrote:

Hi,

I have been thinking about putting a temporary pier in the
ground, to see
how the back yard observing spot works out. I don't want to commit
to heavy
steel posts and concrete bunker footing.

I was thinking of using one of those very thick walled, 10"
diameter,
street water main/sanitation pipes, and simply bury it 3 or 4 feet
deep (3
feet above ground), and fill the inside back in with earth
(perhaps only to
ground level). I am hoping that the perhaps 1/2", (or thicker),
PVC walls
won't ring as much as steel, and will be solid enough for an AP900
system. I
think these street pipes should be temperature stable and should
not warp or
vibrate, in normal city street use, so it might have advantages as
pier
material. Advantages include being easier to construct, (even
remove to adjust
for height), and can eventually be moved to a better spot, or
removed
entirely.

Opinions please.

Joe


Joe Zeglinski
 

Hi Don,

My engineering background reminds me of these pitfalls as well, and it is
a concern at the back of my mind, but I still wonder how much stiffness in
this application, is really enough. If I were building an "observatory pier",
fully committed to location, I would go for maximum strength of materials, but
this pier is a test system, if I can call it that. If it works sufficiently
well, (and I don't kick it, intentionally out of frustration, or
unintentionally), then I will consider it a viable success. Since this is my
backyard, I don't expect blustery winds (certainly not if I have to be
outside - in which case the seeing will be a deciding factor, not the pier).
There are enough buildings, shrubs, fences, and low trees, etc. to provide
some wind break. Heaving of the ground from year to year, might eventually
require a reset, or redesign with heftier materials, but a 4 foot depth and
packed with yard soil (not necessarily sand). I don't expect much long term
motion, especially since there is no "footing" to push up - it's just a
relatively thin 1/2" cylinder wall rather than a flat bottom. As for short
term stability, I am trusting that the wall thickness will suffice for the
load being carried. But by then I will know if this is the best spot -
certainly can't be worse than using my 6" diameter Losmandy G11 aluminum
tripod supporting my AP900 and Questar-7. If there is any shift caused by
seasonal heaving, I can realign the mount, but hopefully it won't be required,
or at least not often. I like the clean lines of green PVC, no painting
required, no pitting or rusting below ground, and it won't ring like a bell.

As for pulling cables, or unbalance - if cables are pulled, I have some
serious soldering repairs ahead of me. The mount should be perfectly
balanced - after all it's one of the best, and if anything, we like our setups
perfectly balanced.

I'm still investigating the feasibility, but appreciate any heads up and
warnings I can get from you and others. For now, I am considering it a
"temporary pier" - with no early plans to require dismantling it (once
planted). I had hoped someone had already tried this approach, but I might
have to be the first to do so.

What I really would like is to turn it into a Greek Column during the day,
as I described - that WOULD be the topper!

Thanks,
Joe

----- Original Message -----
From: "dmwmpd" <westergren@...>
To: <ap-gto@...>
Sent: Wednesday, October 31, 2007 8:51 PM
Subject: [ap-gto] Re: Pier design and sand


Hi Joe,

I really don't think PVC pipe buried in the soil is going to be a
very good pier. The ringing that you mention is a high frequency
tone, that the PVC pipe wouldn't have compared to a metal (steel)
pipe. But the real concern for pier design is how stiff it is
against bumping (not hitting), wind, weight shift (as the mount
moves with any unbalance), pulling cables, etc. These are all long
time effects, like many seconds to hours. The stiffness of the pier
pipe is a function of E (modulus of elasticity of the material) and
the Section Moment of Inertia (depends on diameter and wall
thickness. The stiffness is E*I. It then determines how much
delction of a canteleverd pier has at the top, when one or more of
the steady forces or moments I mentioneed above are applied.

The modulus for steel is 30 million. The modulus for PVC is between
380,000 and 540,000. In other words, the PVC pipe would flex more
than 55 times as far compared to the the same size steel pipe.

The paper on pier design by Dennis Persyk mentioned a few days ago
on this forum is a very good guide to best pier design, although it
doesn't address the dynamics that I mentioned in my posts.

Regards,
Don

--- In ap-gto@..., "Joseph Zeglinski" <J.Zeglinski@...>
wrote:

Hi,

I have been thinking about putting a temporary pier in the
ground, to see
how the back yard observing spot works out. I don't want to commit
to heavy
steel posts and concrete bunker footing.

I was thinking of using one of those very thick walled, 10"
diameter,
street water main/sanitation pipes, and simply bury it 3 or 4 feet
deep (3
feet above ground), and fill the inside back in with earth
(perhaps only to
ground level). I am hoping that the perhaps 1/2", (or thicker),
PVC walls
won't ring as much as steel, and will be solid enough for an AP900
system. I
think these street pipes should be temperature stable and should
not warp or
vibrate, in normal city street use, so it might have advantages as
pier
material. Advantages include being easier to construct, (even
remove to adjust
for height), and can eventually be moved to a better spot, or
removed
entirely.

Opinions please.

Joe



To UNSUBSCRIBE, or for general information on the ap-gto list
see http://groups.yahoo.com/group/ap-gto
Yahoo! Groups Links




dmwmpd <westergren@...>
 

Hi Joe,

I come from the school of thought in astrophotography that there is
no substitude for stiffness, like in auto racing there's no
substitute for cubic inches. A lot of ideas for astro mounts,
cameras, etc can work, but some of them take special care. We are
fortunate now that DSLR's don't need the long term precision guiding
that film required in order to get nice astro photos. I used to
guide film with a piggy back scope that I thought was a very stiff
mount, yet the change in gravity direction in 45 minutes of tracking
caused elongated stars due to the deflection of the structure. Any
imbalance of the scope/mount, or change in the direction of hanging
cables can cause elongated stars over longer exposure times.

Good luck if you decide to try the PVC pier. It's certainly cheaper
and much easier to handle and install than a steel pier. I know, my
steel pier weighed over 450 lbs and took a lot of planning and
manpower to get it into position. It's never going to move now. Let
us know what you try, and how well it works.

Regards,
Don

--- In ap-gto@..., "Joseph Zeglinski" <J.Zeglinski@...>
wrote:

Hi Don,

My engineering background reminds me of these pitfalls as well,
and it is
a concern at the back of my mind, but I still wonder how much
stiffness in
this application, is really enough. If I were building
an "observatory pier",
fully committed to location, I would go for maximum strength of
materials, but
this pier is a test system, if I can call it that. If it works
sufficiently
well, (and I don't kick it, intentionally out of frustration, or
unintentionally), then I will consider it a viable success. Since
this is my
backyard, I don't expect blustery winds (certainly not if I have to
be
outside - in which case the seeing will be a deciding factor, not
the pier).
There are enough buildings, shrubs, fences, and low trees, etc. to
provide
some wind break. Heaving of the ground from year to year, might
eventually
require a reset, or redesign with heftier materials, but a 4 foot
depth and
packed with yard soil (not necessarily sand). I don't expect much
long term
motion, especially since there is no "footing" to push up - it's
just a
relatively thin 1/2" cylinder wall rather than a flat bottom. As
for short
term stability, I am trusting that the wall thickness will suffice
for the
load being carried. But by then I will know if this is the best
spot -
certainly can't be worse than using my 6" diameter Losmandy G11
aluminum
tripod supporting my AP900 and Questar-7. If there is any shift
caused by
seasonal heaving, I can realign the mount, but hopefully it won't
be required,
or at least not often. I like the clean lines of green PVC, no
painting
required, no pitting or rusting below ground, and it won't ring
like a bell.

As for pulling cables, or unbalance - if cables are pulled, I
have some
serious soldering repairs ahead of me. The mount should be
perfectly
balanced - after all it's one of the best, and if anything, we like
our setups
perfectly balanced.

I'm still investigating the feasibility, but appreciate any
heads up and
warnings I can get from you and others. For now, I am considering
it a
"temporary pier" - with no early plans to require dismantling it
(once
planted). I had hoped someone had already tried this approach, but
I might
have to be the first to do so.

What I really would like is to turn it into a Greek Column
during the day,
as I described - that WOULD be the topper!

Thanks,
Joe



----- Original Message -----
From: "dmwmpd" <westergren@...>
To: <ap-gto@...>
Sent: Wednesday, October 31, 2007 8:51 PM
Subject: [ap-gto] Re: Pier design and sand


Hi Joe,

I really don't think PVC pipe buried in the soil is going to be a
very good pier. The ringing that you mention is a high frequency
tone, that the PVC pipe wouldn't have compared to a metal (steel)
pipe. But the real concern for pier design is how stiff it is
against bumping (not hitting), wind, weight shift (as the mount
moves with any unbalance), pulling cables, etc. These are all
long
time effects, like many seconds to hours. The stiffness of the
pier
pipe is a function of E (modulus of elasticity of the material)
and
the Section Moment of Inertia (depends on diameter and wall
thickness. The stiffness is E*I. It then determines how much
delction of a canteleverd pier has at the top, when one or more of
the steady forces or moments I mentioneed above are applied.

The modulus for steel is 30 million. The modulus for PVC is
between
380,000 and 540,000. In other words, the PVC pipe would flex more
than 55 times as far compared to the the same size steel pipe.

The paper on pier design by Dennis Persyk mentioned a few days ago
on this forum is a very good guide to best pier design, although
it
doesn't address the dynamics that I mentioned in my posts.

Regards,
Don

--- In ap-gto@..., "Joseph Zeglinski" <J.Zeglinski@>
wrote:

Hi,

I have been thinking about putting a temporary pier in the
ground, to see
how the back yard observing spot works out. I don't want to
commit
to heavy
steel posts and concrete bunker footing.

I was thinking of using one of those very thick walled, 10"
diameter,
street water main/sanitation pipes, and simply bury it 3 or 4
feet
deep (3
feet above ground), and fill the inside back in with earth
(perhaps only to
ground level). I am hoping that the perhaps 1/2", (or thicker),
PVC walls
won't ring as much as steel, and will be solid enough for an
AP900
system. I
think these street pipes should be temperature stable and should
not warp or
vibrate, in normal city street use, so it might have advantages
as
pier
material. Advantages include being easier to construct, (even
remove to adjust
for height), and can eventually be moved to a better spot, or
removed
entirely.

Opinions please.

Joe



To UNSUBSCRIBE, or for general information on the ap-gto list
see http://groups.yahoo.com/group/ap-gto
Yahoo! Groups Links




Joe Zeglinski
 

Hi,

I just ran into another web article on pier construction and sand fill.
This is a Gov. Of Canada design for a remote steel pier - a "GPS Monument" to
hold a GPS in a stable position to measure ground shift.

http://gsc.nrcan.gc.ca/geodyn/wcda/gpsmon_e.php

Notice they pour in "fine grained dry sand" into the pier for thermal
stability. I guess they don't want the GPS unit shifting up or down, or
perhaps sideways, as the pier stretches or shrinks. I suppose this should also
be a consideration for telescope piers as well.

Joe