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How big a anchor for a pier?

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#1 Cfreerksen

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Posted 21 November 2019 - 01:45 AM

I have a small AP enclosure and want to change from the tripod in pavers to a pier. I really don't want to sink a column and mount the mount on it. I may want to change what I have (scope shed) https://www.cloudyni...e-shed-dry-run/ and don't want to have to cut down a concrete column.

 

I have a lifting column at my disposal that is very similar to items I have seen from PeirTech http://piertechinc.c...elescope-piers/ that I would like to mount and be stable.

 

I would like to figure how large a concrete block I should need to get a solid foundation. I live in Utah but the frost line is not very deep. Any ideas or experience you could lend?

 

Chris

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#2 Stevegeo

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Posted 21 November 2019 - 04:57 AM

As many have said in previous posts on pier engineering there is a lot to consider.. a list to consider...not in order..

Scope weight

Desired pier height/ diameter

Soil  conditions and frost  consideration/depth

Pier composition,  steel, concrete,wood.... or????

How much do you want to spend?

Location..... how difficult will it be to build.

Power/ultilities....data?

 

What I'm getting at is you woulldnt want to hang a 100lb scope and mount off a pier that's under rated....

And at the same time I have seen folks put a 20 lbs scope on a 12 in diameter concrete pier.... sure its overkill. But is it really necessary  ? Cost/benefit ratio.

 

How much are you willing to spend,  how much will you use it  ,  will you upgrade your scope anytime?  

I don't believe there are any magical numbers.  Best advice is to READ  , read previous posts on piers, advice, and builds..

Overkill has its benefits. But only as far as your mount, and scope .. poor scope or mount on an over engineered pier.. 


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#3 Stevegeo

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Posted 21 November 2019 - 05:01 AM

Addendum,  anything heavier then what you have now will be an improvement ..

A concrete block (or any real mass) is less likely to move, vibrate ... 

Hope this helps... 



#4 TOMDEY

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Posted 21 November 2019 - 07:18 AM

Going deeper than local code is also prudent. Overbuilt gives you ample margin... underbuilt gives you guaranteed eventual failure.    Tom

 

~click on~ >>>>

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#5 macdonjh

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Posted 21 November 2019 - 08:50 AM

 

I have a lifting column at my disposal that is very similar to items I have seen from PeirTech http://piertechinc.c...elescope-piers/ that I would like to mount and be stable.

 

 

So a permanent pier you'd like to bolt down, rather than a portable pier...?

 

If you don't want to go deep, you can go wide.  If you want to be in the same location your shed is now, move everything out of the way.  Dig out a few inches of the top soil.  This will both get rid of any organic matter/ roots that can rot out from under your concrete and also makes sure the bottom of your slab is below the soil line (so it looks nice).  Construct a simple form and pour a slab as thick as you think you need.  My suggestion would be for a slab just big enough to put your current shed on, and 6" thick.  Even a slab 6' x 6' x 6" thick will weigh just over a ton.  You can either embed anchor bolts directly in the concrete when you pour, or wait until after the concrete is cured and use a hammer drill to set expansion anchors or epoxy some threaded rods to secure your pier. 

 

You could even use the slab with your current tripod while you wait the twenty-eight days for the concrete to fully cure so you can drill for anchors.  Just wait a couple of days and it'll be plenty strong for foot traffic.

 

To me, the only downside of this design is if you walk on the concrete while you're taking data you could induce vibrations and ruin sub frames.  It doesn't look like you stay right by your scope when you're imaging, so that might not be a problem for you.


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#6 John Fitzgerald

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Posted 21 November 2019 - 09:03 AM

The problem with concrete slabs in observatories is that they sweat when a warm moist weather front comes in.  That has been the main problem with mine.  It is 16 inches thick at the edges, 12 inches where the scope sits, and nine inches elsewhere.   Lots of capacity for retaining coldness.  A few days of cold weather followed by warm weather, and there's a stream running out the door.  The building is very well ventilated too.  Best to only pour enough concrete for the pier and supports, and make the rest of the floor from treated or rot resistant wood.


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#7 Arie

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Posted 21 November 2019 - 09:29 AM

How stable is your current set-up?

Satisfactory? Then I see no need for big blocks of concrete.

I have no experience with these lifting columns. How stable and rigid are they?

To be able to move in and out they must have some play in them. (wobble)

If this is true, then you want to increase stability with a concrete mass, while reducing it again with the rising column.

Anyway.

Alternative, dig a hole 3 ft square and a foot deep.

Construct a square metal base plate to your column or pier.

Put it in the hole and fill it up with fine gravel.

Tap the column to make the gravel settle.

Your column isn't going anywhere and if needed, it can be removed easily.


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#8 Dynan

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Posted 21 November 2019 - 10:14 AM

Winter in Utah can be a problematic time to pour concrete. Don't risk failure by being impatient.

 

Some of the best advice I've seen on pier (or any) construction is to disturb as little soil as possible. It has compacted for years, possibly decades or centuries...and you'll never be able to re-compact it as well.

 

As you followed my pier construction (on a friend's property) I sunk the 7" pipe (just happened to be the diameter I needed, yours may differ of course). The hole was only 12" diameter by 48" deep, then filled with concrete. I see very little movement, as told by my SharpCap polar alignment. Take but a few minutes to reset it, after a month away. As far as future removal, we plan to just cut the pipe with a grinder at ground level...or make a flagpole out of it, so my Aussie Mate can fly a 'Man United' flag.lol.gif


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#9 Cfreerksen

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Posted 21 November 2019 - 10:32 AM

Winter in Utah can be a problematic time to pour concrete. Don't risk failure by being impatient.

 

Some of the best advice I've seen on pier (or any) construction is to disturb as little soil as possible. It has compacted for years, possibly decades or centuries...and you'll never be able to re-compact it as well.

 

As you followed my pier construction (on a friend's property) I sunk the 7" pipe (just happened to be the diameter I needed, yours may differ of course). The hole was only 12" diameter by 48" deep, then filled with concrete. I see very little movement, as told by my SharpCap polar alignment. Take but a few minutes to reset it, after a month away. As far as future removal, we plan to just cut the pipe with a grinder at ground level...or make a flagpole out of it, so my Aussie Mate can fly a 'Man United' flag.lol.gif

Yeah, this plan is for spring at best. I am pretty much locked in for winter. I don't like fumbling with the scope when it's cold outside.

 

I don't get people and "I would rather it be cold, you can always put more layers on" Bull...hot is on the outside...cold is to the bone.

Chris


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#10 Dynan

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Posted 21 November 2019 - 11:48 AM

Yeah, this plan is for spring at best. I am pretty much locked in for winter. I don't like fumbling with the scope when it's cold outside.

 

I don't get people and "I would rather it be cold, you can always put more layers on" Bull...hot is on the outside...cold is to the bone.

Chris

We have polar opposite problems. Remember, I spent most of my life just up I-80, in Wyoming, and worked drilling derricks 110 feet in the air, -20°F, blowing 40 MPH...UPHILL BOTH WAYS! lol.gif

 

You come and stand next to me on Canal St. and Bourbon on August 'Anything-th' and tell me your core isn't cooked! And the joy lasted through October this year. And add the luxuries of the tiniest skeeters you can imaging that leave welts the size of healthy grapes, and 400% humidity...ok...ok...I lied...humidity only hits 250% doah.gif Makes for interesting nighttime astronomy, at 88°F at midnight.

 

There is no 'Best Place'...or EVERYBODY'D BE THERE.



#11 telesonic

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Posted 22 November 2019 - 01:20 AM

Hi Chris

A solid mounted pier is very nice, and hard to go wrong there.

 

If you can plan it right... at best, it's a day or two of work. Mine took a week or two of digging with my hands- tools and the another week of machinist work to get it all together. Well worth it though.

 

I have a 4" diameter steel shedcule 40 (irrigation pipe) pier mounted to a 12" concrete stub base that extends some 40 or 50" below grade, the main hole was around 18" and widened IIRC... plently of concrete for mass. It's a rat-cage design..... but it works fine for me so far.

 

 

 

Backyard pier stub

Pier test B
Pier is done!

 

 

 

 

C8 pier test
 
 
T

 


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#12 John Fitzgerald

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Posted 22 November 2019 - 01:25 PM

That is almost exactly like my pier, 12" stub, 4" sch 40 pipe, flange at bottom, rat cage and all, except mine's not quite as deep, since our frost line is only a few inches.

 

Telesonic, if you saw my posts on my pier a few years ago and copied it, I'm flattered.  It works very well for me also.

 

I used to have an Atlas on it, now have a G11, and it's now in an Exploradome.


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#13 telesonic

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Posted 22 November 2019 - 10:00 PM

John,

 

It is indeed. I ran across some posts of yours here, regarding yours.... and yep, pretty much did it the same. (aside from the rotating azimuth that you incorporated) This last summer when I was doing this, we'd even exchanged a few PM's here on it. I'll say, the pier gotten me out to observe way more than when I was carting gear in and out.. and it's been great! Mucho thanks for the idea / inspiration John! bow.gif

 

It's been the best thing I've ever done in this hobby. (I'm currently re-greaseing and tuning up a CG-5 ASGT to mount on it, eventually I'll get a higher rated head for it)

 

 

Chris,

Regarding frost line, up here ours is around 18" IIRC so I went really deep with this... probably overkill, but hey. I also went with the steel pier as opposed to a concrete, in case we sell / move, it can be broken off at grade and covered. Sure, concrete is pretty cheap for doing a whole pier.... but I only have maybe $100 into the pipe and flanges / steel plate. (I actually have an extension for it as well.... ) But the main cost was labor from the fab-guy, so that is something to keep in mind as well.

 

Ideas:

Somewhere around here, I've seen folks using these cone shaped concrete forms.... but what they are called is slipping my mind right now. Maybe use one of those to pour your base? There are also pre-cast ones that might work too.

 

Arie's thought in post #7 about a hole 3' sq. would probably work too, heck at 3 foot deep (3 cubic feet) is a pretty big mass of concrete, and I would bet that would hold most things solid just fine.

 

Cheers,

T



#14 John Fitzgerald

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Posted 22 November 2019 - 10:23 PM

Now I remember.  I interact with so many, it's hard to keep it straight.  I am glad it worked out for you.


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#15 Cfreerksen

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Posted 22 November 2019 - 10:35 PM

 

Chris,

Regarding frost line, up here ours is around 18" IIRC so I went really deep with this... probably overkill, but hey. I also went with the steel pier as opposed to a concrete, in case we sell / move, it can be broken off at grade and covered. Sure, concrete is pretty cheap for doing a whole pier.... but I only have maybe $100 into the pipe and flanges / steel plate. (I actually have an extension for it as well.... ) But the main cost was labor from the fab-guy, so that is something to keep in mind as well.

 

Ideas:

Somewhere around here, I've seen folks using these cone shaped concrete forms.... but what they are called is slipping my mind right now. Maybe use one of those to pour your base? There are also pre-cast ones that might work too.

 

Arie's thought in post #7 about a hole 3' sq. would probably work too, heck at 3 foot deep (3 cubic feet) is a pretty big mass of concrete, and I would bet that would hold most things solid just fine.

 

Cheers,

T

OK, if I did a cylinder. What do you do for reinforcement? Re-bar or mesh? Do you set the threaded rod in a jig and just drop it in the concrete? Weld threaded rod to the re-bar? Pour smooth and let cure and drop anchor or epoxy anchor threaded rod?

 

I did look at precast. there are a few places in Salt Lake. I would expect a bit pricey but I'm sure the best/most durable option.

 

Still so many questions.

 

Chris



#16 Cfreerksen

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Posted 22 November 2019 - 10:49 PM

So a permanent pier you'd like to bolt down, rather than a portable pier...?

 

 

Yeah it would be a bolt down column. 

 

Chris

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#17 telesonic

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Posted 23 November 2019 - 05:11 AM

OK, if I did a cylinder. What do you do for reinforcement? Re-bar or mesh? Do you set the threaded rod in a jig and just drop it in the concrete? Weld threaded rod to the re-bar? Pour smooth and let cure and drop anchor or epoxy anchor threaded rod?

 

I did look at precast. there are a few places in Salt Lake. I would expect a bit pricey but I'm sure the best/most durable option.

 

Still so many questions.

 

Chris

Chris,

 

I didn't use any rebar or mesh on my pier base.... so the only thing reinforcing it is the soil around it below ground.

 

The pier is anchored to the concrete stub with four J-Bolts, that I picked up from the local hardware store. Before I mixed and poured the 'crete... I made a rough template or jig from some scrap 3/4" wood, roughly aligned to the NCP or true north and fastened the j-bolts to that.

 

Once the top part  (18" depth) was being poured, I dropped in plywood  jig with the J-bolts, and aligned it as best I could. It worked out pretty good really.




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