Observatory / pier foundations

On Fri, 07 Jan 2005 11:08:57 -0800, chris.b wrote:

I'm rather surpised to hear about this supposed weakness at the bolted
flange joint John.

If long threaded rods (studding) are used they can be bent where they
are deep into the concrete foundations.

Given sufficient size of flange and diameter of studding I really can't
see the problem.

There are many devices beyond telescope piers bolted down to concrete.
Including some very tall lattice aerial masts *with no guylines* which
have to be totally wind resistant long term. I've seen literally
hundreds of these over here usually held by only 4 bolts onto their
foundations. Their base dimensions are actually rather small in
comparison to their height. As far as I know none of them fell during
the Dec 1999 storm which devastated much of Denmark. Yet masses of
conifers were snapped off half way down the trunk over vast areas of
the country and many deciduous trees were felled. So I think your
information is of rather doubtful value as far as humble telescope
piers are concerned. :-)

One advantage of a flanged pier is that the pier can be increased in
height and girth if necessary. A steel pipe planted permanently in
concrete is not so easily modified.

Something occasionally overlooked is that a wedge is not necessary to
convert an SCT to equatorial use. This can be accomplished by the pier
itself by adding an angled section near the top. Which also increases
the observer's distance from the pier when facing South.
*
Regards
Chris.B
I'll try and find the articles on this and post the link, but from what I
remember I think the issues were not so much about strength per se, but
resonance and vibration.

Your point regarding the difficulty of modifying a steel pier embedded in
concrete is a good one, and one which I ponder occasionally when I
consider upgrading the telescope ;-)

On Sat, 08 Jan 2005 10:45:31 +0000, John Stolz wrote:

On Fri, 07 Jan 2005 11:08:57 -0800, chris.b wrote:

I'm rather surpised to hear about this supposed weakness at the bolted
flange joint John.

If long threaded rods (studding) are used they can be bent where they
are deep into the concrete foundations.

Given sufficient size of flange and diameter of studding I really can't
see the problem.

There are many devices beyond telescope piers bolted down to concrete.
Including some very tall lattice aerial masts *with no guylines* which
have to be totally wind resistant long term. I've seen literally
hundreds of these over here usually held by only 4 bolts onto their
foundations. Their base dimensions are actually rather small in
comparison to their height. As far as I know none of them fell during
the Dec 1999 storm which devastated much of Denmark. Yet masses of
conifers were snapped off half way down the trunk over vast areas of
the country and many deciduous trees were felled. So I think your
information is of rather doubtful value as far as humble telescope
piers are concerned. :-)

One advantage of a flanged pier is that the pier can be increased in
height and girth if necessary. A steel pipe planted permanently in
concrete is not so easily modified.

Something occasionally overlooked is that a wedge is not necessary to
convert an SCT to equatorial use. This can be accomplished by the pier
itself by adding an angled section near the top. Which also increases
the observer's distance from the pier when facing South.
*
Regards
Chris.B
I'll try and find the articles on this and post the link, but from what I
remember I think the issues were not so much about strength per se, but
resonance and vibration.

Your point regarding the difficulty of modifying a steel pier embedded in
concrete is a good one, and one which I ponder occasionally when I
consider upgrading the telescope ;-)
I just found the discussion on MAPUG which is where I found the info about
resonance/vibration in flanged and solif concrete piers:
http://www.mapug.com/AstroDesigns/MA...ermantPier.htm

Thanks John. An interesting read.

The opinion seems to be to use a nut just below the bottom flange and
one on top of the flange to hold the flange/ pier down. This avoids
very high tension loads being placed on the bolts (studs) set into the
concrete. And also allows accurate levelling of the pier flange and
thus the uprightness of the pier.

I must say that I have been delighted with the incredible stability of
my own all-welded pier. Despite it not having underground foundations.

In retrospect I might have made it slightly taller. So that if a floor
was placed over the feet (but not touching them) then I would avoid
tripping over them in the dark. Easy for me to modify thanks to the
facilities and materials available to me. But if I was paying somebody
else to do it I would think very hard indeed before finalising any
design.

Regards
Chris.B