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Bolts to hold down a pier

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10 replies to this topic

#1 t-ara-fan

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Posted 22 August 2019 - 11:50 PM

I am drawing up a steel pier for my Mach1GTO and EdgeHD-8.  The pier will be 48" long, 8" Schedule 40 steel, with a 12" square 1/2" thick baseplate.  The top will be a 1/2" thick 8.625" diameter plate with threaded holes on top to mate with the Astrophysics ADATRI (Mach1GTO adapter).

 

No rat-cage in the design.

 

Will four 12" long 1/2"-13 L-bolts into an 18" diameter concrete pier do the trick? 



#2 scngc7317

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Posted 23 August 2019 - 12:22 AM

this is what I made, high nuts welded to the plate with all-thread to plug the hole and grab on to the concrete in the ground.

Top pier bolts to the in ground part, wood support to keep straight & level till concrete dries

All adjustments are in the mount, pier just needs to be straight & level.

 

1077
 
 
3149

Edited by scngc7317, 23 August 2019 - 12:34 AM.


#3 TOMDEY

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Posted 23 August 2019 - 03:32 AM

Sure, that sounds good!

 

My only recommendation would be to not use those cheap washers and square nuts that come with the bolts. Get 1/2-13 stainless, which have much better threads and won't ever try to rust on. I'm sure you have already noticed that. I'd still stick a little grease or Vaseline in there, too. Re-bar in the concrete might also make sense.

 

Pictures here, showing some 1/2 x 8-inch anchors and some 1 x 30-inch anchors. The giant ones were certainly overkill, but fun to use. Those are the same ones they use on those gargantuan stanchions that support the truss-work sign supports that bridge across expressways! I tend to over-build things... Sort of Russel-Porter-ish... The scope above all this is 36-inches, so maybe it made sense to think big. Tom

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#4 Peterson Engineering

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Posted 23 August 2019 - 08:19 AM

Based upon personal experience may it is suggested that an 18" concrete pier is overkill for anything less than a 24" scope.  Yikes! 

 

Think ahead to when you or someone else may need to remove this sucka.

 

As to the bolts, even the lowest grade 1/2" bolts have a breaking strength of 10,000 pounds.  Yes, as a professional engineer I assure you that they'll be adequate.

 

Clear skies,

 

Pete


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#5 rimcrazy

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Posted 23 August 2019 - 09:32 AM

My personal preference is to use threaded inserts as opposed to embedded bolts.  On a pier that is probably not much of a difference but on a pad where perhaps you initially place a scope and then decide you want to move it, a treaded insert is flat to the surface as opposed to bolt that you would have to cut off.  Epoxy's to hold an insert these days are stronger than the concrete and won't fail for all practical purpose.



#6 t-ara-fan

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Posted 23 August 2019 - 12:28 PM

Thanks all. You guys on CloudyNights are very helpful.

 

My only recommendation would be to not use those cheap washers and square nuts that come with the bolts. Get 1/2-13 stainless, which have much better threads and won't ever try to rust on. I'm sure you have already noticed that. I'd still stick a little grease or Vaseline in there, too. Re-bar in the concrete might also make sense.

That is the plan.  I am getting 1/2" diameter 12" long SST L-bolts made at a price of CAD13.45 each (call it USD10) which seems a good price.  And will use SST nuts.  Good idea to put some thread lube in there.

 

Based upon personal experience may it is suggested that an 18" concrete pier is overkill for anything less than a 24" scope. 

 

As to the bolts, even the lowest grade 1/2" bolts have a breaking strength of 10,000 pounds.  Yes, as a professional engineer I assure you that they'll be adequate.

 

Clear skies,

 

Pete

18" is pretty big.  0.96 tons.  My buddy and I are building identical observatories, and he has an AP 1100GTO that will sit on a 10" pier.  With a square base plate, his pier has holes on a 12" diameter.  To get the bolts at least 2" from the edge of the concrete pier, that would be a 17" diameter.  18" is the next standard size up.

 

My pier for my Mach1GTO will be only 8".  To keep things simple, both in-ground concrete piers will be the same, hence 18". Maybe I can get a bigger mount one day?!?!?  My bolt pattern will support it.

 

10,000 pounds?  So you are saying I should NOT put a 48" snipe on the end of my wrench to tighten the bolts? cool.gif


Edited by t-ara-fan, 23 August 2019 - 12:38 PM.


#7 Stevegeo

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Posted 23 August 2019 - 03:18 PM

Instead of Vaseline,   use Never Seize , dab it on the threads, run the nuts on and tighten down.....10yrs from now you'll thank me when it's time to take it off... I prefer the grey (which has aluminum), but the copper works equally well.



#8 John Fitzgerald

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Posted 23 August 2019 - 07:08 PM

I bought four galvanized L-bolts .  They were 5/8" x 16", so that's what I used.  It was overkill for a 4" nominal pipe pier, but you have to use what you can get.



#9 my-spot

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Posted 23 August 2019 - 08:48 PM

I had a custom pier made back in 2002. It is 48" x 6.5" diameter aluminum 1/2" thick with a 3/4" thick gusseted base plate. Uses three 3/4-10 threaded rods into a 16" dia concrete pier. Never had an issue with flexure or vibration or with the bolts rusting. My rig is not as big or heavy but this works for me and is as strong as I will likely require.

 

I am moving my observatory next week and am taking the pier with me. The pier is rendered in this image.

Dome Layout

Had a new bolt pattern fabricated which was shipped to the new site and sunk in concrete last month.

bolt cage

I have a raised floor in my dome and didn't want to seal around the concrete so I raised the bolts a few inches so they poke through the floor with some clearance holes with 3/8" plate adding stiffness just below the floor.

Dome Floor Construction

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#10 speedster

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Posted 24 August 2019 - 01:40 AM

Well, bigger is better, right?  To put it in perspective, a lowly 1/4" wedge anchor, not embedded or epoxied, is about a buck, has 877 pound pull-out and 1082 pound shear.  Three in the pier will hold down well over a ton.  If you push as hard as you can on the top of a 48" steel pier, you might put 30-40 pounds of pull-out force on an anchor. 



#11 John Fitzgerald

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Posted 24 August 2019 - 09:13 AM

Well, bigger is better, right?  To put it in perspective, a lowly 1/4" wedge anchor, not embedded or epoxied, is about a buck, has 877 pound pull-out and 1082 pound shear.  Three in the pier will hold down well over a ton.  If you push as hard as you can on the top of a 48" steel pier, you might put 30-40 pounds of pull-out force on an anchor.


That makes me feel good about my 5/8 inch embedded bolts. I estimate they are 13 inches down into the concrete. LOL


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