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#1 PeteM

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Posted 07 September 2020 - 02:59 PM

I am trying to figure how best to form the top few inches or so of a pier footing I am planning to put in to hold a 10" dia steel pier (SB ME/MX pier). I am planning on a 18" diameter concrete footing 48" deep from ground level. I do want the top few inches to be formed to look decent and be level. So I trying to figure out how best to do that. Or is it as simple as cutting the desired length of sonotube and suspending it at the top of the hole? Guess I am thinking that as I pour the concrete in it would go around the sonotube. I also plan on using a plywood template to set the J-bolts into the top. So I hope to be able to keep it pretty center, with a smooth concrete surface at the top also for the pier to sit on.

 

Thanks for any tips on this!
 



#2 macdonjh

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Posted 08 September 2020 - 08:35 AM

It's as simple as cutting your Sonotube to length.  When I poured my pier, I pushed the Sonotube 3"-4" into the ground just to be sure I had a finished surface visible above the ground.  When the concrete was a couple days old, I dug the soil out from around the Sonotube, removed the Sonotube, and put the soil back.  Then I had formed concrete all the way to the soil line.

 

If you are using 18" Sonotube, don't dig a hole bigger than 18" diameter.  Look at the thread "Pier Engineering" for a comprehensive discussion about that.  You'll have a better foundation and you won't have to worry about concrete going around your form, either (it wouldn't anyway).

 

In order to have a level top, you'll have to have at least one of the Sonotube ends cut square.  It the other end isn't quite square, put that end into the soil.

 

As for your anchor bolt template, the simplest thing to do is make an 18" diameter circle template out of plywood and install your bolts on that.  You can also make a smaller template and support it from a cross made from 2"x2" or 2"x4".  If you also add some blocks 18" apart on the cross' "legs" the template will be self-centering.

 

Good luck.



#3 PeteM

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Posted 08 September 2020 - 08:50 AM

Thanks, I have been studying that exact thread and based off you input here, am confident in getting this done correctly. Appreciate it!



#4 Peterson Engineering

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Posted 08 September 2020 - 01:49 PM

Believe 18" to be overkill.  It's what I did shocked.gif   You don't mention what's to be mounted but for anything under 100#  I'd suggest digging a 48" hole and using a 12 sonotube in sort of an inverted mushroom.  Leave the top of the concrete about 2" below ground level as that sucka's gonna be permanent.  The pier will eventually be moved or removed, even if some time in the distant future. And having a huge piece of concrete above ground level's gonna be a problem.



#5 PeteM

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Posted 08 September 2020 - 02:00 PM

The foot of the Bisque pier is 11" square and uses 4 bolts slots in each corner (6.25" out from the pier center). So a 12" diameter footing would put the j-hooks on the edge. I can get an 18" auger bit and sonotube easier around here than a 16"...so that is why for the large diameter. I am mounting an A-P1100GTO on this and once I recover from that purchase, I plan for a 14" RC or CDK, so I will be pushing 70lbs easy. But for now it is the little 8"RC. For sure going to go with the top being a couple inches below ground. I just moved and my old ROR observatory had a 12" diameter concrete pier 48" out of the ground...that was brought up by a few showing agents. Luckily the eventual buyers of the house never asked about it. I did put a concrete bird bath bowl on top. :)
 



#6 macdonjh

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Posted 08 September 2020 - 09:35 PM

The foot of the Bisque pier is 11" square and uses 4 bolts slots in each corner (6.25" out from the pier center). So a 12" diameter footing would put the j-hooks on the edge. I can get an 18" auger bit and sonotube easier around here than a 16"...so that is why for the large diameter. I am mounting an A-P1100GTO on this and once I recover from that purchase, I plan for a 14" RC or CDK, so I will be pushing 70lbs easy. But for now it is the little 8"RC. For sure going to go with the top being a couple inches below ground. I just moved and my old ROR observatory had a 12" diameter concrete pier 48" out of the ground...that was brought up by a few showing agents. Luckily the eventual buyers of the house never asked about it. I did put a concrete bird bath bowl on top. smile.gif
 

Glad you're planning for adequate "cover" for your anchor bolts.  I think you've got a good plan.

 

To expand on Peterson Engineering's comment, though: you could leave the 18" diameter footing several inches below grade, and then use extra long anchor bolts to get the base of your steel pier above grade level.  You wouldn't even form the 18" diameter section since it'll be below grade.  Then, you could use a short section of 12" diameter Sonotube to form the short section between the top of the 18" section and your steel pier.  In essence, you'd be grouting your steel pier.  

 

When it came time to remove your pier, you could unbolt your Bisque pier, use a sledge hammer on the small 12" section, and finally cut the bolts off below grade.



#7 PeteM

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Posted 08 September 2020 - 09:51 PM

Glad you're planning for adequate "cover" for your anchor bolts.  I think you've got a good plan.

 

To expand on Peterson Engineering's comment, though: you could leave the 18" diameter footing several inches below grade, and then use extra long anchor bolts to get the base of your steel pier above grade level.  You wouldn't even form the 18" diameter section since it'll be below grade.  Then, you could use a short section of 12" diameter Sonotube to form the short section between the top of the 18" section and your steel pier.  In essence, you'd be grouting your steel pier.  

 

When it came time to remove your pier, you could unbolt your Bisque pier, use a sledge hammer on the small 12" section, and finally cut the bolts off below grade.

I do like the idea of going from an unformed 18" to a smaller diameter formed so it would leave it possible to remove it down the road. But below is a screen shot of the piers bottom plate and the middle of the attachment point is 6.25" from center, so j-bolts would be coming up outside the 12" and the outer corners of the pier would be hanging in the air. That is why I am planning on just going 18" top to bottom. Though I thought about a 18" square form on the top 3-4" now since that would be easy to do with 2x4's and allow for easily alignment of the j-bolt template.

 

mx pier bottom plate.JPG



#8 Travellingbears

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Posted 09 September 2020 - 07:43 PM

Pete

 

I’m using the 10” diameter 42” high ME pier myself.  In my scenario I did 42” depth (frost line is 30”) and pier hole was shaped 18x24 with rebar cage. I was pouring directly against undisturbed earth and only added a rectangular wooden form at top which helped limit spill-over from my small 1.6 CY mixer. With finish of pour at grade (smoothed with trowel) and I got the wooden jig with j-bolts positioned and aligned North. My pier is adjusted at base via series of nuts and is about 1” off the concrete. My finished floor in observatory is up about 10” up from grade so the exposed part of pier is 32” high where my ME II rests within the observatory.

 

An unhappy anecdote: I had to remeasure my N alignment in the field during the pour because I’d knocked out a fixed marker on ground with my cement mixer (I was pouring from north side) that I intended to reference when I set my jig in cement. I get out compass and try to align on my jig board which is set in cement and ‘whoa’ its too near the bolts and starts to deflect. That wasn’t the ‘magnetic declination’ that I was intending to compensate for in my polar alignment.

 

Dave

 

pic below was taken in April 2020 when I originally had the 8” MX pier on the pad before I built the observatory 

 

Pier base leveling adjustment

Edited by Travellingbears, 09 September 2020 - 08:11 PM.

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#9 PeteM

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Posted 09 September 2020 - 08:51 PM

Pete

 

I’m using the 10” diameter 42” high ME pier myself.  In my scenario I did 42” depth (frost line is 30”) and pier hole was shaped 18x24 with rebar cage. I was pouring directly against undisturbed earth and only added a rectangular wooden form at top which helped limit spill-over from my small 1.6 CY mixer. With finish of pour at grade (smoothed with trowel) and I got the wooden jig with j-bolts positioned and aligned North. My pier is adjusted at base via series of nuts and is about 1” off the concrete. My finished floor in observatory is up about 10” up from grade so the exposed part of pier is 32” high where my ME II rests within the observatory.

 

An unhappy anecdote: I had to remeasure my N alignment in the field during the pour because I’d knocked out a fixed marker on ground with my cement mixer (I was pouring from north side) that I intended to reference when I set my jig in cement. I get out compass and try to align on my jig board which is set in cement and ‘whoa’ its too near the bolts and starts to deflect. That wasn’t the ‘magnetic declination’ that I was intending to compensate for in my polar alignment.

 

Dave

 

pic below was taken in April 2020 when I originally had the 8” MX pier on the pad before I built the observatory 

 

Dave, thanks for the notes on your install and the picture. That helped answer a few questions for sure. I was wondering how far below frost line to go (seems I will go 54" (42+12). Seems like a "safe" amount. One question: what size j-bolts did you use? I just got mine from McMaster-Carr (1/2"-13 x 12") pretty sure that is what SB recommends, but I have been considering going up to 5/8" since the slots are 3/4" wide.



#10 Travellingbears

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Posted 10 September 2020 - 08:07 AM

Pete

 

To summarize I used 5/8” galvanized since I found some with longer threaded shank (2”+) at local hardware.

 

I had originally purchased some 1/2” diameter with 12” length (standard recommendation) and threaded portion was only around 1.5”. At the time I was thinking of following Bisque recommendation and placing pier directly on pier pad (vs up about 1” on adjustable nuts). I’d planned on adding layer of self-leveling after ‘rough’ pour cured to handle minor irregularities so pier would have been bolted up with adding thickness of just a leveling washer (if needed) to be ‘level within tolerances’. I would have painted concrete with sealer prior to placing pier to help isolate surfaces a bit for prevention of corrosion.

 

When I changed to ‘adjustable nut’ scenario and I knew that 1/2” sets’ threaded shank was not long enough then I went back to the ‘goof center’ (local hardware store) and came back with different bolts (5/8”) since couldn’t find 1/2” galvanized with adequate length of threaded shank. 

 

With larger 5/8”diameter it’s important that the template has bolts set well aligned since less tolerance to fit in slotted holes than 1/2”. For designing my template I flipped pier vertically so base was up and took a 20x20 1/2” thick piece of plywood and traced four slotted holes and the perimeter of the base onto template. I drilled in middle of each elongated slots (so bolts at mid-span for East-West adjustment when doing polar) and put j-bolt on template (nut/washer used on top and bottom). I then tested alignment by placing template on pier (bottom of pier was still flipped vertically) and slid down onto slots (1” of shank was exposed). It fit onto the four slots with a bit of angle to push fourth side down. Once in slots I tested by rotating of template to left and right to ensure that it was square enough on slots. It worked as expected so I was confident that I’d be able to sit pier on bolts once moored in concrete. 
 

Before actually sitting template in concrete I coated the underside of wood with vegetable oil (let soak in) which helps a bit when lifting/releasing template on concrete. I unscrewed the top visible nuts and removed washers. Then pulled off template. I had left the template positioned a bit above the surface of concrete so I was able to remove the bottom side washer and nut after was removed. I then cleaned bolt threads a bit and put the square 2” slotted plate on bolt against concrete and added arrangement of washers/nuts that you see in earlier photo. 
 

Dave

 

photo below with template in concrete on day of pour
 

Checking level on pour

Edited by Travellingbears, 10 September 2020 - 08:08 AM.


#11 PeteM

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Posted 10 September 2020 - 03:31 PM

Dave, I appreciate all the extra info on your install. This is really going to be helpful with mine. My 1/2" j-bolts have 2.5" of threads on them, but I do like the idea of the square plates, washers, nuts for a bit more leveling control. Have you found any issues with vibration, etc with that arrangement or is it pretty rock solid. Guessing your ME and PW is on this pier?



#12 Travellingbears

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Posted 10 September 2020 - 08:29 PM

Pete

 

Confirmed that I’ve got ME II/OAE and PW 14” on 42” ME bisque pier. The ‘adjustable bolt’ arrangement was originally tried out with MX+ on my 48” MX pier when I first poured pier in March. Since ME and MX pier have same base size/hole pattern it was easy swap during observatory construction. I didn’t use pier during observatory construction and finally brought out ME II/OAE and PW in late August. I’m still at ‘roll-out’ stage with this new PW scope and have not imaged with it yet. As long as I’ve got my gear balanced properly on mount I would expect things to be pretty good. As with any new imaging arrangement I could also be troubleshooting for a while. 

 

Dave


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#13 PeteM

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Posted 16 September 2020 - 02:15 PM

How many have poured their footing with j-bolts embedded before you received the steel pier? I am not sure when I am getting the SB pier and since I have their bolt pattern diagram, I thought I could just use that to make the template/jig and get the concrete poured while the weather is still warm and decent. Guess I am also wondering if anyone has done this and got their pier to find out the bolts do not line up!



#14 Stevegeo

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Posted 16 September 2020 - 03:10 PM

How many have poured their footing with j-bolts embedded before you received the steel pier? I am not sure when I am getting the SB pier and since I have their bolt pattern diagram, I thought I could just use that to make the template/jig and get the concrete poured while the weather is still warm and decent. Guess I am also wondering if anyone has done this and got their pier to find out the bolts do not line up!

And that's why we have DRILLS.... seriously there are ways to get around  this easily. Dont sweat it.

Been there overcome that.

 

Stevegeo 



#15 Travellingbears

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Posted 16 September 2020 - 03:39 PM

Pete 

 

It’s likely that plenty of folk trust a printed template guide to prep their pier template/jig and set bolts w/o advanced shipping of pier. Since I had received my pier before pour (received pier in October and dug pier following March) I did ‘hands-on’ pre-check by testing pier template/bolt jig on the pier itself before setting jig into concrete.

 

When swapped later from MX pier the bolt pattern already in concrete was ‘similar’ fit onto ME pier. So Bisque QC seems consistent. But key was really my QC in getting bolts positioned to match template distances and squarely bolted onto the wooden framed template and then template aligned onto surface of concrete. 

 

Dave


Edited by Travellingbears, 16 September 2020 - 03:42 PM.


#16 macdonjh

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Posted 16 September 2020 - 04:02 PM

How many have poured their footing with j-bolts embedded before you received the steel pier? I am not sure when I am getting the SB pier and since I have their bolt pattern diagram, I thought I could just use that to make the template/jig and get the concrete poured while the weather is still warm and decent. Guess I am also wondering if anyone has done this and got their pier to find out the bolts do not line up!

That's how the professionals do it.  Use a bit of plywood to make a template.  "Install" your anchor bolt in your template using nuts.  Pour your pier and sink your anchor bolts.  Remove the nuts and your template after the concrete "kicks" so you can float the top of your pier footer with a trowel for a smooth attractive finish.  Install your pier when you're ready.



#17 PeteM

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Posted 17 September 2020 - 02:24 PM

Thanks guys! I got word today that the SB pier is 6-8wks out from being delivered, so I am confident now from your replies to make the plywood template accurately and get the footing in. Then start on the observatory around it. Of course making the footing accessible from inside the obs. Probably will get everything done in time for the winter perma cloud to roll into Michigan.



#18 Bill Lee

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Posted 24 September 2020 - 10:37 AM

Believe 18" to be overkill.  It's what I did shocked.gif   You don't mention what's to be mounted but for anything under 100#  I'd suggest digging a 48" hole and using a 12 sonotube in sort of an inverted mushroom.  Leave the top of the concrete about 2" below ground level as that sucka's gonna be permanent.  The pier will eventually be moved or removed, even if some time in the distant future. And having a huge piece of concrete above ground level's gonna be a problem.

I agree. I had a 12” diameter, non-reinforced, concrete pier, holding an AP1600 holding 120+ lbs of equipment. It was 4’ above ground and 4’ below ground. It worked perfectly. Solid as a rock. I didn’t bother with remesh or rebar, since it was always in compression. As long as you’re not planning on hitting with your car, you’ll be fine. (You’d probably do more damage to the car than the pier.) It had j-bolts in the concrete to which I attached the mounting plate (1.5” thick aluminum).

 

My brother-in-law just pulled it out with the excavator when he dug out the ground for the garage/sun room/warm room/observatory. 


Edited by Bill Lee, 24 September 2020 - 10:42 AM.

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#19 PeteM

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Posted 24 September 2020 - 08:39 PM

Thanks Bill, since I am mounting the Software Bisque MX/ME pier to this, a 12" diameter would put the j-bolts on the edge, so going with 18" would put the j-bolts about 2.75" away from edge. Plus my local rental store for the powered auger has 12" and 18" augers...so I am going big just because of that. At least it will stop a car. Good to know about you not using rebar. My last concrete pier similar to yours had rebar and pretty sure it did not do much for the use.



#20 macdonjh

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Posted 25 September 2020 - 12:26 PM

Thanks Bill, since I am mounting the Software Bisque MX/ME pier to this, a 12" diameter would put the j-bolts on the edge, so going with 18" would put the j-bolts about 2.75" away from edge. Plus my local rental store for the powered auger has 12" and 18" augers...so I am going big just because of that. At least it will stop a car. Good to know about you not using rebar. My last concrete pier similar to yours had rebar and pretty sure it did not do much for the use.

Having your anchor bolts near the edge is bad practice.  Much better to have 2"-3" of "cover", like you said you'll have with an 18" diameter footer.

 

Rebar doesn't have much effect on a pier as Bill Lee said.  But it is concrete, and I simply can't pour concrete without rebar, I just can't.  


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#21 speedster

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Posted 25 September 2020 - 06:03 PM

Piers are not always in compression.  Differential soil forces and freezing are 2 things that can put them in tension in addition to physically pushing on them.  Unreinforced concrete still has 3,000+psi compressive strength but only about 300 psi in tension.  Will it break?  Not likely.  But, if we are fussy about thousands of dollars of equipment on top of the pier, how does it make sense to omit a key element of the pier to try to save $30?


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#22 PeteM

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Posted 25 September 2020 - 08:09 PM

Piers are not always in compression.  Differential soil forces and freezing are 2 things that can put them in tension in addition to physically pushing on them.  Unreinforced concrete still has 3,000+psi compressive strength but only about 300 psi in tension.  Will it break?  Not likely.  But, if we are fussy about thousands of dollars of equipment on top of the pier, how does it make sense to omit a key element of the pier to try to save $30?

I do plan on putting in rebar, you are right...$30 is nothing compared to mount going on top. One question: below what outdoor temp is it a bad idea to pour? I plan on pouring the footing in the next couple of weeks. With temps getting down in 40-60 range from what I hear. Guessing it will just slow the cure time?



#23 Travellingbears

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Posted 26 September 2020 - 09:56 AM

Pete

 

I poured back in late March in Maryland when it was mid-50’s during day. Used sakrete bags with normal amount of water (vs adding acrylic fortifier) for the 21+ bags into hole with rebar cage. Was seeing setup pretty quickly (normal). I removed wood template (it was left 0.25” above surface of concrete) after 36-hrs. I set MX+ pier/MX+ mount onto adjustable bolts on day 3 after pour and did PA check with polemaster later that evening. Waited another 3-days (day-7 after pour) to put scope (FSQ-106) and try to do SkyX session.

 

Dave


Edited by Travellingbears, 26 September 2020 - 09:57 AM.


#24 HunterofPhotons

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Posted 26 September 2020 - 10:36 AM

Piers are not always in compression.  Differential soil forces and freezing are 2 things that can put them in tension in addition to physically pushing on them.  Unreinforced concrete still has 3,000+psi compressive strength but only about 300 psi in tension.  Will it break?  Not likely.  But, if we are fussy about thousands of dollars of equipment on top of the pier, how does it make sense to omit a key element of the pier to try to save $30?

 

Can you furnish a link to an astronomical pier that has pulled apart from tension forces?  As you said, not likely.

It's not about saving $30.  The mob think on this forum has promulgated the notion that concrete isn't 'strong' unless rebar is in the mix.  Since most of the people here have never done concrete work they put in the rebar, usually by pounding the rebar into the base of the pier hole and then pouring in the concrete.  How ironic is it that they've assured the eventual cracking of their concrete pier?  Rebar must be fully encased in concrete or else it will rust, expand, and crack the surrounding concrete.  

 

dan k.



#25 PeteM

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Posted 26 September 2020 - 02:28 PM

So there really is no need for rebar in a telescope footing? Or if it doesn't hurt, what is the proper installation procedure? (pour about a foot of concrete in and then stick the rebar in, careful not to hit bottom?)




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