1600GTO Concrete Base
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I'm trying to find specs for constructing a concrete base for my 1600GTO AE with about 75-100lbs of payload on a 10" diam 42" AP pier. Any pointers/links greatly appreciated. Thanks
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Bob Enouen
Rich,
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I had the concrete contractor place an 18” x 48” sonotube from Lowe’s in the middle of my concrete pad to isolate vibrations. This was level with the top of the 12’ round pad which was about 4” thick on top of a standard tamped gravel base for my 10’ observatory so when they poured the concrete it was all filled in and finished at the same time. Make sure the pad is poured level if you want to place an observatory on it or you will be shimming it later. I then hammered drilled holes for the set bolts for the pier, and used a concrete epoxy to set them. The pier sits on nuts which allowed me to plumb the pier, and then another set of nuts lock it down to those bolts. My AP 1600 non AE has carried a 100 lb load on this pier beautifully. I shoot unguided 10 minute subs with an APPM 300 point map and enable Dec Arc Tracking with APCC Pro and NINA. I marvel at the capability that the AP team has enabled me with every time I use it. Good luck! Thanks, Bob Robert J. Enouen Cell 513-504-4410 On Dec 3, 2022, at 10:50 PM, Rich via groups.io <gibbonsrk@...> wrote:
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Thanks Bob, I was planning the sonotube route with a footer. I’ve been trying to estimate height and diameter of the concrete pier base so your 18”x48” gives me a starting point (without doing a structural load analysis). I’ll be putting the base at ground level below the observatory deck I’ll be building. I’ve been trying to find “rules of thumb” for concrete amounts, and I’ve read anywhere from 5 – 10x the mount plus payload weight. The 1600GTO is rated at ~220lb payload so I figure a system weight of ~350lbs which means I’m looking at about 2000-4000lbs of concrete (~.5 to 1 yd^3). I use a 10x42 AP pier so I’m trying to “nail down” required interface hardware. I’ve done a fair amount of searching and I’m kind of surprised there is not some kind of “turnkey” solution for this. Thanks for your real-world inputs. Rich
From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Bob Enouen
Sent: Monday, December 5, 2022 1:36 AM To: main@ap-gto.groups.io Subject: Re: [ap-gto] 1600GTO Concrete Base
Rich,
I had the concrete contractor place an 18” x 48” sonotube from Lowe’s in the middle of my concrete pad to isolate vibrations. This was level with the top of the 12’ round pad which was about 4” thick on top of a standard tamped gravel base for my 10’ observatory so when they poured the concrete it was all filled in and finished at the same time. Make sure the pad is poured level if you want to place an observatory on it or you will be shimming it later.
I then hammered drilled holes for the set bolts for the pier, and used a concrete epoxy to set them. The pier sits on nuts which allowed me to plumb the pier, and then another set of nuts lock it down to those bolts. My AP 1600 non AE has carried a 100 lb load on this pier beautifully.
I shoot unguided 10 minute subs with an APPM 300 point map and enable Dec Arc Tracking with APCC Pro and NINA. I marvel at the capability that the AP team has enabled me with every time I use it. Good luck! Thanks, Bob
Robert J. Enouen Cell 513-504-4410
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Hi Rich
One thing that you may want to consider is isolating the foundation for your pier from the rest of the observatory floor. I once rented out Roland & Marj's house in Hawaii for a family vacation, and I noticed that the foundation for his 1600 mount which was sitting on an A-P Eagle tripod was isolated from the rest of the observatory floor. You can see what I am talking bout in the photo. It is about 4 ft square. I am not sure how deep the foundation was for this section though. Mike 
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Bill Gardner
Rich, If you are building a pier and not just a concrete pad, you will want to consider digging down past your frost line to avoid the pier heaving with the seasons. I have a pictorial history of my construction. You can see it here. The pier has not moved at all through the years. Bill _____________ Pictor Observatory http://www.pictorobservatory.ca Twitter: @pictorobs Minor Planet 21350 - billgardner I'm trying to find specs for constructing a concrete base for my 1600GTO AE with about 75-100lbs of payload on a 10" diam 42" AP pier. Any pointers/links greatly appreciated. Thanks |
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Scott SCHNEIDER
Hi Rich,
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Here is a long/short answer to your concrete pier sizing question…. As you can imagine, there are many variables which go into the design of a properly sized pier/foundation. The short of it is, what works for one person may or may not work for you. It really comes down to the load you are trying bear and the bearing capacity of the soil and soil type(s) - this is where it gets complicated as most of the time there isn’t just one type of soil depending on where you are located. This is one of the main reasons there aren’t turnkey solutions to pier design, or more generally, foundations as these variables are different at every location, even possibly within your own property. For example, I’ve seen properties in San Francisco, where I am an architect, that have shallow streams running below the ground in part of the lot, one of those things you don’t know until you know…. While you may not have that you may have clay or other silty types of soil which are typically not great. Some soils can only carry 1000 psf while others might carry more like 3000 psf and some locations may even have shallow bedrock, which would be good. From a very general structural aspect a typical cantilever (which is what a pier is) should be sized in a 2:1 ratio. That is, the part going into the ground should be approximatly twice as tall as the part sticking out of the ground (this would include the mounting height above the finished grade/ground of your scope and mount). This can of course change depending on the diameter of the pair and the stiffness of the pier, concrete bearing PSI, etc (concrete has different bearing capacities depending on the mix and rebar combination you go with). You can find minimum soil capacities and other code minimum rules of thumb in your local jurisdiction’s building code book (which may just be the state code book), check www.upcodes.com. A few simple rules of thumb to follow: Make sure that the bottom of your foundation/footings are at or below the frost line at a minimum - you don’t want that thing moving when the ground freezes, thaws, or rains. Definitely isolate the pier from the rest of the structure so as to limit vibration around the pier - that is for example do not pour a concrete slab right up to the pier leave a gap with an expansion/isolation joint. As for placing a spread footing under the pier there is most likely no reason to do it, typically you would use a spread footing under walls as the purpose is to take a uniform load and spread it evenly to the ground depending on the capacity of the soil, piers by definition are more of a point type of load. Anyway, hope this is helpful. Feel free to reach out if you have other questions. Scott
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Len Fulham
Rich,
Here is a link to an eBook that deals with this topic. I find it has good info and should give you a lot of guidance. It will cost a few $ but so will your pier! https://telescopepiers.com/diy-design-guide/ You can use it to review various recommendations you may get and/or can make a complete design for yourself Just an option (no commercial connection) Len. |
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You can make a template for the support bolts and embed them in the concrete pier when it poured to avoid having to drill the pier. Use 3/4" or 1" all thread. My pier was built for a lighter mount, but it works fine with my AP1600.
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This is what I had in mind except I have an AP 10x42 metal pier. I'm about an hour east of L.A. so our frost line is basically surface level. How deep did you go and what is the diam of your pier?
Thanks, Rich |
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The footings are 24 inches. This pier was 10 inches (Sona tube). We used about 16 bags of ready mix concrete. I would do 12 inches if I did it again.
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Also put rebar in the pier and footings.
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