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Pre-cast Pier ?

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#1 astronut17

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Posted 23 February 2021 - 09:28 AM

Hello,

 

I have been imaging for about a year now and realizing that I would get much more out of the hobby with an observatory..... So I am going to build one in my yard with a tandem warm room to use as an office.  I have built many things before, but never an observatory.  The first step of course is the pier.  I have gone back and forth with a cement pier vs. an expensive steel Pier (i.e. PierTech).  The pier would be isolated from the observatory floor which would be a wooden floor.

 

I ran across these pre-cast stackable footings at a home store : https://www.ez-crete...oducts/ez-tube/

 

It got me to think that I could first build a concrete pad myself 24" x 24" x ~40" deep.  Then I could order the stackable footing, roll the sections into the yard and set them on the pad with concrete adhesive, and stack with adhesive between each layer.  The total weight of the concrete for a 52" high pier (for mostly AP) would be over 300 LBS.  I would then need to drill out and add the steel plates at the top using an epoxy resin.

 

 

My concerns are 1) the base - it weighs ~125LBS. I would need to roll it to set into place. and 2) Drilling into the top section for the plate (making sure the bolts are straight).

 

Thoughts?

 

Thanks!

Clear Skies,

Carl

 

 

 



#2 Couder

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Posted 23 February 2021 - 09:35 AM

I like it. Remember, good things usually don't come easy - look towards the end result. A lot of work now = a lot of enjoyment later.


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#3 Berny

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Posted 23 February 2021 - 09:53 AM

Use a log (wood) instead.


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#4 GoFish

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Posted 23 February 2021 - 10:50 AM

I’ve toyed with the idea of using EZ-TUBE segments for a pier. Lots to like in terms of cost, simplicity, and “removability.”

 

What stops me each time is concern about lateral stiffness, which is everything when it comes to a pier. It’s a product intended to carry vertical loads, and to rely on soil confinement for lateral forces. It’s an open question in my mind whether the adhesive is adequate to make the pier behave like a monolithic 11” concrete pier. Or would it act more like a stack of teetering blocks?

 

The 1/2” steel rod isn’t big enough to prestress (precompress) the concrete pieces to keep them in compression when bumped sideways. So, if used as a free standing pier, we’d be relying more or less solely on the “sticky” of the adhesive to keep the joints from opening up when bumped. 

 

Very roughly, I think you’d need to be able to put around 10 tons of “stretch” in the center rod to squeeze the blocks together. If a person could manage this, then the system would act pretty much like a solid 11” pier, yet still be removable by relaxing the rod tension. Nice!

 

But short of having access to professional concrete posttensioning equipment (DYWIDAG Threadbar, for example), I cant think of a way to put this kind of preload into the rod. So I keep coming back to “no, thanks” on the EZ-TUBE system. 

 

 


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#5 DSOGabe

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Posted 23 February 2021 - 12:50 PM

I don't know how to link it but there is a post on this forum back from May 2020 regarding building a pier with these blocks. It may help you get some insight on it.

 

My EZ-Tube (EZ-Crete) Pier is the title.


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#6 GoFish

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Posted 23 February 2021 - 03:43 PM

I don't know how to link it but there is a post on this forum back from May 2020 regarding building a pier with these blocks. It may help you get some insight on it.

 

My EZ-Tube (EZ-Crete) Pier is the title.

From that thread, and it’s predecessor, seems like the real-world experience with these piers has been good, and that my concerns haven’t been borne out in practice.

 

Success is mainly dependent on the adhesive, plus the clamping force from the 1/2” rod, plus a bit of dead weight, to hold the joints tight. That’s not much to avoid getting a joint crack if bumped, but maybe it’s enough.



#7 macdonjh

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Posted 23 February 2021 - 05:34 PM

Perhaps review the thread "pier engineering".  It seems to me you'd do less digging, have less materials cost and a more stable end result simply using an auger to drill a hole the ground, fill it with concrete.  You could either bring the concrete to grade level and then bolt a metal pier to it, or use Sonotube (or better yet, some PVC drain pipe if you can find it, looks great when you're done) above grade to make the concrete pier as tall as you want it.  

 

My concrete pier.  I took a day to dig and pour.  I stayed over night that night so I could make sure everything remained plumb until the concrete "kicked" and remove the Sonotube early the next morning.  

 

2021 Observatory pier sm.jpg

 

The magic of the drilled shaft is you pour the wet concrete against undisturbed soil so your finished pier is as stable as can be and there is no back-filling required.


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#8 speedster

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Posted 23 February 2021 - 08:18 PM

Doing it like mcdonjh will have way less deflection than then prefab EZ-Tube.  More deflection may work out fine for you.  You may find the stiffer method is less work as well as a few less dollars.  

 

https://www.cloudyni...ier engineering


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#9 ryanr256

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Posted 23 February 2021 - 08:57 PM

Hello,

 

I have been imaging for about a year now and realizing that I would get much more out of the hobby with an observatory..... So I am going to build one in my yard with a tandem warm room to use as an office.  I have built many things before, but never an observatory.  The first step of course is the pier.  I have gone back and forth with a cement pier vs. an expensive steel Pier (i.e. PierTech).  The pier would be isolated from the observatory floor which would be a wooden floor.

 

I ran across these pre-cast stackable footings at a home store : https://www.ez-crete...oducts/ez-tube/

 

It got me to think that I could first build a concrete pad myself 24" x 24" x ~40" deep.  Then I could order the stackable footing, roll the sections into the yard and set them on the pad with concrete adhesive, and stack with adhesive between each layer.  The total weight of the concrete for a 52" high pier (for mostly AP) would be over 300 LBS.  I would then need to drill out and add the steel plates at the top using an epoxy resin.

 

 

My concerns are 1) the base - it weighs ~125LBS. I would need to roll it to set into place. and 2) Drilling into the top section for the plate (making sure the bolts are straight).

 

Thoughts?

 

Thanks!

Clear Skies,

Carl

 

To address your concerns:

 

1. Yes, the base is over 100lbs. I used a dolly to move it to where it was going to be installed. Once the hole was dug, I used the threaded rod to pick it up and put it in the hole.

 

2. I drilled the holes and, yes, one of them went crooked a bit. It helps to go slow and it also helps to do holes a little bigger than the bolt to give some "wiggle room". I used Sika AnchorFix to secure the bolts, but I don't remember if it was 1 or 2. Thankfully, I was able to enlarge the holes in the mounting plate to accommodate the crookedness of the bolts.

 

I used Sikaflex construction adhesive for the joints between the sections. It's a waterproof, weatherproof adhesive. I've not experienced any movement since I've installed the pier. The soil here is heavy clay and I compacted it every 4 inches as we filled the hole. We did go deeper than planned which made the pier a little shorter than I wanted/needed. I made up the difference by purchasing a pier extension.

 

My goal was to eliminate the setting up of a tripod and mount for each observing session. I wanted to be able to just take the mount out and be polar aligned close enough for visual observing. When I begin taking pictures, I will do a more precise polar alignment.

 

I guess I could have dug a smaller diameter hole and framed some sort of support for the above ground concrete (sonotube, PVC, etc) and then mixed a bunch of bags of concrete, or called a concrete company, and poured concrete.

 

That sounded like a lot of work for me. With the pre-cast pier, I just dug a hole and assembled the pieces, paying attention to plumb and square, and I was done. It was a quick and easy solution for me. But, everyone's needs are different and the pre-cast pier may not work for everyone.

 

About a week or so ago I was walking through the backyard, looking up at Orion. Yes, I walked right into the pier. The mount wasn't on it, just the sundial. I have a nice bruise on my upper thigh now. smile.gif  The next morning I checked the level of the mount plate and it's still between the bubbles.

 

Our plan is to decorate the column this spring to make it more attractive. We have some mosaic tiles we will put on it.

 

-Bob


Edited by ryanr256, 23 February 2021 - 08:58 PM.

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#10 macdonjh

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Posted 23 February 2021 - 11:31 PM

Just to be clear, there is almost no way you can build a permanent pier which will be more hassle to use than a tripod you set up each time you observe.  Wood, poured concrete, precast concrete, steel, back fill, no back fill, it will all be more convenient than a tripod.  

 

I was comfortable using an auger and pouring concrete so that's what I did.  Execution is more important than the pier design, so pick the methods you're confident you can do well.

 

astronut17, oh, and be sure the bottom of your pier is below your frost line.  Frost heave will make any pier unstable year to year.


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