Pier Construction Advice

[ribuck]

Hi all,

I've decided to build my own pier after looking at the prices to buy pier, which seem exceptionally expensive for what they are.

Looking at construction methods, i've seen some people using 8"+ Od pipe filled with sand to suppress vibration whilst other have used thick pvc pipe in similar diameter filled with concrete.

Are there any big merits of using one method over the other ?

I plan to use the pier for Imaging.

Any recommendations for construction, greatly appreciated.

Rich.

[Bizibilder]

The advantage of a bolted down steel pier is that you can move/remove/modify it quite easily. Concrete is pretty much permanent. In terms of "strength" there is not much between the two if properly built.

My own steel pier was made (welded) by the local steel fabricator - I just drilled the holes and shaped the plates (as I have access to machine tools). All the steel (offcuts) and welding came in at around £70 if I remember correctly.

Edited June 24, 2011 by Bizibilder

[George]

I'm pretty much biased as my pier is concrete, its cheap,easily fabricated, easy to maintain and most important vibration free.

The most important thing is with concrete is measure, measure, measure before pouring, you have to get everything right first time. With steel you can pretty much undo any mistakes

So for a permanent pier concrete is a no brainer.

You can trawl thru my build pictures here .

Edited June 24, 2011 by George

[Ags]

My own steel pier was made (welded) by the local steel fabricator - I just drilled the holes and shaped the plates (as I have access to machine tools). All the steel (offcuts) and welding came in at around £70 if I remember correctly.

This is probably a dumb question... What is a steel fabricator? How would you go about locating one?

[Bizibilder]

Steel fabricators are the folk who make fire escape stairs, railings and cut RSJ's etc to size for the building trade - most towns have one - find them in Yellow pages.

[malc-c]

Steel or concrete, they work out about the same price to construct if you shop around. The only thing to remember is that whilst the plastic tube and concrete is cheap, you still need to make (or have made) some form of adapter to take the mount. The pier for my observatory that I'm constructing used 160mm plastic drain pipe, rebar, and approx a barrow and a half load of concrete, cost approx £20 - £22.. The adapter cost me £95 including the anodising.

[ribuck]

Hi Malcolm, i never thought about using drainpipe. I want to use my pier for imaging, so i'm not sure if it would be thick enough for a an imaging platform. i've read a few places that a pier for imaging should be at least about 6"+ diameter but preferably 8" or more diameter.

Would love to know what diameter piers people are using for imaging ?

Also there any people on here that manufacture pier adapter plates ?

Rich.

[Gina]

Well, I'm hoping 7" diameter for a concrete pier will be enough for imaging - it's what I'm planning to do. Though there is still time for me to find something a bit bigger. The weather is holding things up ATM

Just to add... I made up my own pier adapter from a few pieces of plate and simple tools.

Edited June 25, 2011 by Gina

[Helen]

This may be of interest Pier top plate for Skywatcher HEQ5/pro mount & CG5 | eBay UK

Helen

[ribuck]

Hi Gina,

The reason i ask about the diameter is because some boffin placed a post about pier construction and the diameter of the pier vs Angular deflection.

Obviously for imaging i want something super sturdy.

Pier Design: Diameter is your Friend!

The equation for angular pier deflection (given in the appendix) yields a very important relationship regarding the diameter of the pier. The angular deflection is proportional to the inverse (one-over) forth power of the diameter, that is, 1/(D^4). Let's put that into practical table of numbers.

Below we consider a pier that is 6 inches in OD. This purely imaginary pier is constructed of material like PVC pipe - it is not the steel which I recommend. Let's assume that it deflects 10 arc seconds for our 5 pound push - not a very good pier! What happens if we increase the diameter of the steel pipe while maintaining nearly constant wall thickness?

Diameter / Deflection arc seconds

6 / 10.0

8 / 3.2

10 / 1.3

12 / 0.6

Edited June 25, 2011 by ribuck

[ribuck]

Helen,

Thanks for the link, that seems like a decent price as it's about £30 cheaper than the next cheapest altair astro one i've seen.

Rich.

[Gina]

Hi Gina,

The reason i ask about the diameter is because some boffin placed a post about pier construction and the diameter of the pier vs Angular deflection.

Obviously for imaging i want something super sturdy.

Pier Design: Diameter is your Friend!

The equation for angular pier deflection (given in the appendix) yields a very important relationship regarding the diameter of the pier. The angular deflection is proportional to the inverse (one-over) forth power of the diameter, that is, 1/(D^4). Let's put that into practical table of numbers.

Below we consider a pier that is 6 inches in OD. This purely imaginary pier is constructed of material like PVC pipe - it is not the steel which I recommend. Let's assume that it deflects 10 arc seconds for our 5 pound push - not a very good pier! What happens if we increase the diameter of the steel pipe while maintaining nearly constant wall thickness?

Diameter / Deflection arc seconds

6 / 10.0

8 / 3.2

10 / 1.3

12 / 0.6

I've read this article (if it's the one I think it is) and it applies to tubular steel piers only - concrete was not considered. Obviously a concrete pier will also be stronger/stiffer the wider it is but I've no idea how it compares with steel. Of course, concrete is totally different from steel and it is also extremely variable, depending on the ratios of ingredients and their quality. So I imagine a concrete pier would be virtually impossible to rate theoretically. I guess it's a case of build it and hope! Though users' experiences may still be of benefit.

[ribuck]

Hi Gina,

you make a good point about the concrete. I suppose a decent diameter pipe filled with concrete should give a solid pier.

during the build process, lets assume i used 8" diameter pipe which could be pvc or metal, i have seen people saying that the hole for the concrete in the ground needs to be 2-3ft deep, so firstly is this about the correct depth ?

So lets say i have my hole 3ft deep, and for arguments sake i have a 7ft long piece of pipe for the pier, would i place the pipe all the way to the bottom of the hole or would i only have the pipe inserted in 2ft into the hole leaving 1ft at the bottom for extra concrete ?

I'm assuming that it doesn't make that much difference if i use pvc or metal for the pipe in the ground as it's simply being used as the container to hold the concrete ?

Rich/

[Sp@ce_d]

Confusing isn't it! I'm in the same boat trying to work this one out. The more you read the more harder the decision.. like choosing a scope!

From what I can make out, if using concrete for base and pier it's best to pour in one go so as to have a "one piece" pier. I'm thinking that any other material separating the base from the pier will introduce the chance of flexure/vibration. So I don't think (and I may be wrong here) burying the pipe into the bottom of the base would be a good idea. Rather use rebar/rods for the strength inside the concrete pier.

Another idea I've seen for an adapter is to use an extension tube, something like this.. First Light Optics - Skywatcher EQ6 Extension Tube

I've even wondered about adapting one of these into a concreate base.. First Light Optics - Skywatcher Pillar Mount Support for HEQ5 & EQ6 series mounts

[ribuck]

I originally had the same idea about the skywatcher portable pier being bolted to a concrete base, but the tubing is just not big enough. 4-5" pipe will flex too much from what i have read.

Anyone got any views on placement of the pipe, should it be recessed into the hole or be at ground level just to form the column part of the pier ?

[malc-c]

Hi Malcolm, i never thought about using drainpipe. I want to use my pier for imaging, so i'm not sure if it would be thick enough for a an imaging platform. i've read a few places that a pier for imaging should be at least about 6"+ diameter but preferably 8" or more diameter..

Rich,

You can get 200mm (8") pipe 200mm Ø 3m Single Socket Pipe - P/DL195

Trust me, even the 160mm diameter pipe, once filled with concrete and re-bar is solid enough... if you want larger then others have used stainless steel air-con pipe 12" in diameter... there's lots of options out there, and all make for solid piers

[Gina]

Anyone got any views on placement of the pipe, should it be recessed into the hole or be at ground level just to form the column part of the pier ?

Yes, referring to the diagram below, the left hand one shows the tube driven into the bottom of the hole. This is bad because there is no concrete connection between pier and base. The base block would do very little to stabilise the pier.

The second, middle, example shows the pier tube part way into the concrete base. This is a bit better but provides a weak point at the bottom of the tube.

Third, right hand, example shows the tube either level or just above the base top. This reduces any weak point and makes best use of the base weight. Further improvement is shown in some reinforcement bars driven into the ground below the base and extending up the pier. You will need to support the tube and provide shuttering to stop the concrete escaping from the pier bottom. Also, it's recommended that all the concrete is poured in one go ie. not allowed to harden part way through.

I have gone a bit further and made the bottom part of the pier wider using a couple of large plant pots with bottoms cut out. Also, the threaded rod used to hold the pier adapter goes way down the inside of the tube and provides further reinforcement.

Edited June 25, 2011 by Gina

[ribuck]

Thanks Gina,

That's a great help and i really appreciate it. Regarding the concrete mix, what are people using ?

Also regarding the concrete mixing, is it ok to mix a batch, pour it, mix the next batch and pour that 10 mins later and repeat the process as i will have to mix mine in a heavy duty plastic box.

Rich.

[ribuck]

oh forgot to ask, on average how many bags of concrete, sand and stone have people used ?

[pritc]

Hi Rich,

For my Concrete/160mm pipe pier build,I used nearly 15 bags of ballast & 3 bags of cement.

For reference my pier build is on the first page:

http://stargazerslounge.com/diy-observatories/103639-wetherview-diy-obsy-build-begins.html

Wayne

[malc-c]

Rich,

You can mix it a wheel barrow. 4 parts ballast to 1 part cement (ie 4 shovels of ballast to one cement). Make up a funnel from some card and use a bucket pour it down the tube. Then use a length of rebar or 2" x 1" ram it up and down in the tube to remove air and to make sure it reaches the bottom of the tube. Mix up the next batch and repeat until it's at the level you want, then having prepared your adapter or template with studded rod sink this into the concrete in the tube, giving it a wiggle to remove air and then line it up so your mount points North. Leave to cure

What you don't want to do is half fill the tube, then leave it and do the rest a few hours later, or worse still the next day. This will cause a weakness where the concrete becomes layered and doesn't bond.

Edited June 25, 2011 by malc-c

[ribuck]

wow, that's a lot of bags of cement and stone to mix......... :-(

[Macavity]

I sense pier flexure and "ringing" might not be quite the same (albeit a related?) thing. Interesting that ringing (the main problem?) might be reduced by more "subtle" methods. Absorbent (rubber!) fillings, damping at vibration maxima. On the other hand, maybe just concrete would suffice.

Telescope Reviews: Filling a metal pier (The debate continues?)

Hardly a solution for imaging (my Skywatcher pillar stands on a patio!) but I sense "not jumping up and down" or accidentally colliding with my stuff, goes a long way. <G> Perhaps juggernauts on a neigbouring road might be the more problematical. But it seems rather "quiet" around here - At least in the "seismic" sense...

[ribuck]

I'm more confused than ever, Gina's post say to have the pipe above ground, yet waynes post of his build clearly has the pipe in the ground ?

Anyone else got any views on this please on pipe in or out of the ground ?

[Bizibilder]

If you are using plastic pipe then the pipe is purely a mould for keeping the concrete in the right place. Therefore you only need the pipe to surround the "above ground" concrete ie the pier. This, however, leads to a practical problem - if you have wet concrete in the pipe and wet concrete in the base then gravity is inclined to take over! The pipe empties its contents! This can be prevented by placing a strong board over the base (with a hole for the pipe to poke through) and putting some substantial weights on the board. This will prevent the problem!

A second way to do things is to put the plastic pipe all the way to the bottom of the hole you have dug BUT after making several large holes in the wall of the pipe below ground level - thus when the concrete is poured the concrete can freely flow between the inside and outside of the pipe and will set "holding" the pipe in place.

Hope this helps.