Another hollow concrete block pier

[malc-c]

I was a "traditionalist" when I built my observatory, and went with the concrete filled pipe set into a large concrete block foundation.  That's not to say that bolting several cinder blocks together to is less suited, or under-enginered for the job.  But, IMO the foundation to which they attach should be of suitable depth and size to give the blocks a good standing. 

It's interesting to see two extremes to pier construction on the forum.  From concrete slab and a couple of cinder blocks bolted together, to a rather substantial installation in this thread http://stargazerslounge.com/topic/247778-windy-knoll-observatory-my-build-thread/

These cinder block piers seem to have the advantage of being cheap to construct, but in reality (based on my costs when constructing my own) the costs compared to the traditional pipe and concrete block, the costs come out about the same.  You could argue that the traditional way is more labour intesive, but that depends if you mix the concrete by hand or use a mixer.  For me apearance plays a major factor in the things I make, and for me I would need to dress the blocks in some way, which is additional costs.  The plastic pipe I used was simply sparyed mat black as the orange wasn't that appealing.

[pete_l]

From my point of view having a base for a pier that is more substantial than the foundations of a house (bulding regs. say 1m deep by 60cm - but depends on the soil) seems to be going to extremes. The internet is full of people making "one-upmanship" recommendations: one person says X, the next says "not that's not enough, it should be 2*X" and the next says something even bigger / better / faster / more (hmmm, good name for an album, that! )

Here in Spain there are many houses, some still standing, that have little or no foundations at all.

Now I appreciate that a pier's foundation is mainly about damping out vibrations, not carrying a load. However most home-owners also need to consider the consequences of trying to sell-on a house when there's a cubic metre (yard: in old money) of concrete sunk into what the next buyer may want to call a lawn.

But on the topic of vibration damping, mass is not always your friend. To do the job properly, you don't just pour more goop down a hole: you need to know what resonances the base+pier will have - heavier == lower frequency, and whether damping out high frequency vibrations (which are usually of low amplitude) leaves you exposed to lower frequencies - such as from a passing vehicle that could have a much higher amplitude and therefore cause a larger magnitude movement to be induced into the mount, even if they aren't resonant.

Oh, and if anyone even attempts to analyse the Eigenvalues for their pier design, I promise to be seriously impressed.

Edited August 28, 2015 by pete_l

[Mr Spock]

I'm going to use four 610x610x50mm paving stones for the base of my pier. This will be sitting on a clay and gravel 'soil' which is rock solid (I have to hack it with a pick). I find one of these paving stones difficult to lift - four are going nowhere and my scope will not be toppling!

[ChrisLX200]

For my pier I had given to me some 9" dia steel steam pipe x 3/8" thick wall. It was being used to put in a high-pressure water pipe system at work and they had an 'offcut'. I didn't know what to expect until a lorry turned up and workmen dumped it on my driveway. Shock: it was about 10ft long! OMG, there was no way I was going to cut that with a hacksaw - I couldn't even move the thing on my own, so consequently the hole ended up being about 5-1/2 feet deep and 5 feet diameter. Believe me when I say that was a lot of concrete to mix (with a shovel!). My pier is going nowhere I can assure you :-)

ChrisH

[Alienfox]

Pete_l made a valid point about selling on the house, I have been considering a pier for my garden but I do not intend to be here for ever, so I would probably have to dig up the pier at some point (not easy if you have a concrete block 1m down and a steel pier to boot) so the easy to remove cinder blocks look promising, I am on clay that moves a fair bit.

So I will watch this forum closely over the next few weeks.

Den

[Scorpius]

From my point of view having a base for a pier that is more substantial than the foundations of a house (bulding regs. say 1m deep by 60cm - but depends on the soil) seems to be going to extremes. The internet is full of people making "one-upmanship" recommendations: one person says X, the next says "not that's not enough, it should be 2*X" and the next says something even bigger / better / faster / more (hmmm, good name for an album, that! )

Here in Spain there are many houses, some still standing, that have little or no foundations at all.

Now I appreciate that a pier's foundation is mainly about damping out vibrations, not carrying a load. However most home-owners also need to consider the consequences of trying to sell-on a house when there's a cubic metre (yard: in old money) of concrete sunk into what the next buyer may want to call a lawn.

But on the topic of vibration damping, mass is not always your friend. To do the job properly, you don't just pour more goop down a hole: you need to know what resonances the base+pier will have - heavier == lower frequency, and whether damping out high frequency vibrations (which are usually of low amplitude) leaves you exposed to lower frequencies - such as from a passing vehicle that could have a much higher amplitude and therefore cause a larger magnitude movement to be induced into the mount, even if they aren't resonant.

Oh, and if anyone even attempts to analyse the Eigenvalues for their pier design, I promise to be seriously impressed.

I find it intriguing that discussion of pier design generates such strong opinions even more so it seems than choices of equipment like OTA’s, mounts and cameras. First and foremost, I’d like to say - I completely understand the need to forego a substantial pier solution when the proposed site may not be long term - which apparently is the case for many following this thread.

Yes, there are codes which regulate foundations for houses and I happen to be very familiar with those in the US since I work as a building inspector (18 years’ experience) and have about as many years’ experience working construction prior to my current job. Foundations (footings) for structures must be placed on undisturbed soil of suitable bearing capacity and installed below the frost line to prevent a natural phenomenon called frost heave where frozen ground can actually lift tremendous weight and then lower it again as the ground thaws out. In terms of structures, it’s this up and down movement over time that can crack foundations and create other stresses that negatively affect a building’s structural integrity. Obviously, in warmer climates frost heave isn’t much of a concern (hence the more shallow code-defined frost lines in those areas) however, not everyone lives in a warm climate. So it’s a given that frost heave can exert the same type of force on a telescope pier which completely negates any attempt at permanent alignment and that’s the whole point of building an observatory where everything remains in place. However, this may not be a concern for a pier constructed “in the garden out back” since the scope is usually not permanently attached and this would seem to be a great application for the concrete block pier described here and other similar designs – especially when removing it at a later date may become necessary.

But regarding your statement that damping vibration is a pier foundation’s main purpose, I disagree. My understanding is the primary goal of pier construction should be to reduce deflection – meaning the slightest movement at the top caused by the dynamic nature of the equipment supported. This article in particular seems to indicate vibration is of little concern if the pier is constructed to keep deflection to an absolute minimum.

http://www.cloudynights.com/page/articles/cat/articles/how-to/pier-design-fundamentals-r1236

Here’s an excerpt from the link above which specifcally addresses the question of vibration:

“Some astronomers concern themselves with vibrations, damping time and ringing. If you design your pier using my guidelines you can forget about these considerations completely. You will not worry about the period of oscillation (damping time) because your pier will not deflect enough to disturb imaging or observing, whatever the fundamental frequency may be. Similarly, your steel pier will ring with a crisp high C bell tone if you strike it forcefully with a hammer. Just don't do that while you are imaging or observing and the ringing will be of no consequence. There are no natural forces that can excite the ringing mode as long as you keep your hammer away.”

At the end of the day, how one builds their pier is a personal choice which should not invoke cries of protest from others. If I choose to sink my pier deep in the ground and surround it with copious amounts of rebar and concrete that’s certainly up to me and by the same token if someone else chooses to connect some concrete blocks together - and this suits their purposes and circumstances - they will hear no further negative comments from me. It’s not about one-upmanship – it’s about what works for the individual and what will hopefully meet their expectations...

[dtastro]

On 04/07/2015 at 10:10, Tinker1947 said:

My choice of glue would be this stuff......

http://stickwithusltd.co.uk/index.php?_a=product&product_id=8

What glue...link doesn't go anywhere?

 

[JamesF]

Looks like the shop has disappeared.  I used Gorilla Glue for mine, with 10mm studding for good measure.  The Gorilla Glue foams up as it cures, filling the holes in the blocks.

James

[Oldfort]

17 hours ago, dtastro said:

What glue...link doesn't go anywhere?

 

Stick a www.  in front of stickwithusltd, and it seems to work, although it doesn't link to a specific product.