Sand filled pier??

[Dealy (Kev)]

Is there any real benefit from filling a steel pier with sand?

Have any of you done it and had noticeable positive results?

If so should the sand be dry or wet?

The reason I'm asking instead of just doing it my pier goes through the floor of my observatory about 400mm and bolts onto its concrete footing. If I fill it with sand I will no longer be able to lift it out if ever I need to make changes to it. (Even if I drilled a drain hole in the bottom and fitted a removable plug I don't think the sand would run out)

Kev

[Merlin66 (Ken)]

Yes,
It makes a great difference in my experience. Dampens the vibration and give a solid result.
I use a mixture of old engine oil and builders sand.

[mswhin63 (Malcolm)]

It made a massive difference to my pier. It was especially beneficial to me as I only have 4 or 5mm thick steel available. By filling it with sand the difference was astounding.

I will be re-fitting my system in the new rental premises I am moving to and will video the results. Still have a heavy block of concrete to move.

EDIT: I only used sand as I knew that it was mean't to move one day so using liquids would have made it difficult to drain.

[leon]

It most certainly dose, I filled my pier with cement, never to be removed, I am sure sand would have the same result.

Leon

[Eratosthenes (Peter)]

the most common corrosion issues with concrete that is contact with steel is chloride ingress. This can be a problem if you use water or sand that has high chlorine levels. In the past the sand that was used to make concrete was sourced from beaches and not cleaned and so had high chlorine content.

If you use sand and water, or concrete, make sure the sand and aggregate as well as the water used is filtered and clean. Even stainless steel is susceptible to Chloride ingress type corrosion.

Its a slow corrosion process but when it takes hold in the steel reinforcement of concrete, structural failure is inevitable. The corrosion products around the steel take up a larger volume and therefore create a pressure within the concrete. This causes the concrete to crack, crumble and lose its structural integrity.

...just for those who are plan to go to their local beach with a bucket or wheel barrow to pick up some sand

[Moon (James)]

I'm clearly out-voted here, but I'm in the no sand camp.
In my case the pier is 10" square section bolted to a cubic meter of concrete.
I can push my pier as hard as I can or hit it with my hand and it has zero impact on the image. But if I so much as touch the end of the scope with my pinky finger - that's a different story - it jumps all over the place.

[ChrisM]

My understanding is that sand is sometimes used to lower the resonant frequency of a pier. Having said that though, if a pier is solid in itself, and solidly fixed to the concrete foundation, I can't see any benefit at all in lowering its resonant frequency. Whether imaging or observing, we want the pier to stop vibrating as quickly as possible, which generally won't happen if it's vibrating slower rather than faster.

If filling a pier with sand makes the pier a lot heavier, then a given force imparted to the pier may produce less movement than it would have if the pier were not sand-filled. In this - I can see a benefit.

I'm not sure if there is any benefit thought to be gained from having a loose filling (like sand), in as much as it can 'slosh' around a bit help the damping.

Chris

[Slawomir (Suavi)]

Taking purely theoretical approach- more mass means more inertia - surely sand will help to make pier more stable. It should also help dampening vibrations, since sand will absorb kinetic energy from vibrating pier more effectively than just air (it takes more energy to move sand than compress air). I would dare to take it even further and propose that sand filled pier will perform better than the one filled with concrete.

[rally]

I think a well designed pier will not benefit from sand - it will already be extremely rigid and this usually means it will also be strong and heavy - since they are most often made from steel or cement.

If its rigid and resists bending (the primary purposes) and if vibration is damped to earth (a secondary purpose and usually by product of the first), then any resonances or intermittent vibrations (caused by movement of other gear, wind, cable movement, fans, stop start slews, gear rotation etc) will be transferred to the ground in a very short period of time.
This will provide a vibration free platform.

Ringing vibrations tend to be dampened by adding sand - that is both a function of adding mass, changing the resonant frequency and some absorbtion. The ringing sound means that the frequency is quite high and therefore the amplitude very small - this isnt generally likely to affect imaging. ie there are plenty of other problems (seeing, tracking, polar alignment, optical aberrations, poor focus) adding to your imaging noise than this !

Greater mass usually means a higher resonant frequency

Will adding sand improve a poorly designed pier's performance ? - If its not adequately attached to the ground - the extra weight will provide a better mechanical transfer of vibration energy.
It will not add anything to the rigidity or strength of the pier.

But if you start with a well designed pier in the first place - and that usualy means simply going to a larger diameter and greater wall thickness steel pipe, you won't need to add anything.
Scrap steel pipe is dirt cheap - I have never understood why anyone would skimp on the part of an imaging system that only costs around $120 in the first place !

[AndrewJ]

I think a well designed pier will not benefit from sand

And who will pay for a "properly designed" pier????
Most just use the biggest chunk of pipe they can find and add some gussets, then add a rat cage at the top.

Greater mass usually means a higher resonant frequency

Make a tuning fork from "tuning fork steel" and another from lead.
The lead one will be heavier ( ie have greater mass ) but i know which one will resonate at a higher frequency.

Design for vibration suppression as well as strength as well as mechanical stability as well as thermal stability ( when talking arcmins or arcsecs ) is a typical engineering tradeoff, and its not a trivial exercise if you want to really do it properly..
Filling a bog std tubular steel pier with some gussets ( not designed, but chucked together with whatever someone can get ) with sand wont hurt, and will likely "help" suppress any higher freq vibrations if they occur. Mixing the sand with heavy used engine oil will also make transmission of any vibrational energy into the slurry more efficient.
Every bit helps ;-)

Andrew

[5ash (Philip)]

My pier is made of 6" pressure pipe and works perfectly for AP not sure what sort of vibrations we are worrying about besides walking around the pier. That can be reduced by suitable floor covering if a problem. Any suggestions of the sort of vibrations we might be discussing?
Regards philip