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#1 Nick Rose

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Posted 07 February 2013 - 07:43 PM

We are fixing up our backyard but putting in new grass and taking out some trees. With one of the locations where the tree is coming out, I'll be putting a concrete pier. I will have a 3'x3'x3' base with a 12"x48" pier. They'll be rebar attaching the pier to the base. But what do I do with the base should I have rebar in it or will the mass of the base be enough.

#2 Alex McConahay

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Posted 07 February 2013 - 08:19 PM

At the price of a few sticks of rebar----add it in. Even if the concrete cracks at some point, the rebar will keep the mass together.

Alex

#3 dobsoscope

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Posted 08 February 2013 - 08:22 AM

You can put a piece of mesh reinforcement in the base.
Would also suggest that you wrap up the part which is below ground in gauge 1000 pvc sheeting.

#4 Nick Rose

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Posted 19 February 2013 - 12:25 AM

I'm now thinking if I should go some what smaller on the base. Where I live in California there is no frost line and you really don't have to go deep to get to hard soil.

Also people that have done concrete base/pier. What size and did you mix the concrete your self?

#5 Bob Moore

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Posted 19 February 2013 - 01:17 AM

nick take a look here
https://www.dropbox....home/Public/LBO

thebase is 4'x4'x4' with re-bar

#6 wolfman_4_ever

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Posted 19 February 2013 - 01:44 AM

Hey Bob. Your link doesn't work.. It asks you to login..

Nick, plan for an earthquake.

My pier pedestal is 7' x 7' at the base and is 6 feet deep. It is shaped like a block pyramid with rebar reinforcement everywhere.. My soil is a mixture of dirt and sand.. Almost 4 tons of concrete or 2 square yards..

If the ground moves from the "big" one, not much is going to stop it.. It's the bunch of smaller ones i'm more concerned about.

#7 Nick Rose

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Posted 19 February 2013 - 02:21 AM

So 2'x2'x3'deep with rebar wont be good for a base. The reason I what to go a tad smaller is because I want to do this myself. 3x3x3 is 27cu.ft. where as 2x2x3 is only 12cu.ft. so the smaller would be easier.

#8 Midnight Dan

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Posted 19 February 2013 - 06:53 AM

Nick:

Personally, I think people go a bit "overkill" on the base of these piers. I think 2' x 2' x 3' is more than large enough.

I have a porch/deck at the rear of my house, and each post is setting on a mini 'pier'. Basically an 8" diameter sonotube going 4' into the ground (due to frost line), with a 12" diameter footer. These have not budged for the past 15 years.

Compared to a building, astronomical piers have to support almost nothing in terms of weight. Unless your pier is going very high, such as with a roof-top observatory, then you really don't need much in the way of a base.

-Dan

#9 John Fitzgerald

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Posted 19 February 2013 - 07:52 AM

Nick:

Personally, I think people go a bit "overkill" on the base of these piers. I think 2' x 2' x 3' is more than large enough.



I have a porch/deck at the rear of my house, and each post is setting on a mini 'pier'. Basically an 8" diameter sonotube going 4' into the ground (due to frost line), with a 12" diameter footer. These have not budged for the past 15 years.

Compared to a building, astronomical piers have to support almost nothing in terms of weight. Unless your pier is going very high, such as with a roof-top observatory, then you really don't need much in the way of a base.

-Dan


I concur. My pier footer is not very big and has not moved in 10 years. It's actually only about 5 cubic feet and 38 inches deep and holds a 6" refractor on a 4" heavy wall pipe pier.

#10 JAT Observatory

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Posted 19 February 2013 - 09:11 AM

My base is 18"x18"x3' I mixed the concrete myself. The bottom of the pier flares out to form a footer. There is no rebar in the base. It been supporting the setup shown below for over 10 years with no issues.

Posted Image Posted Image

#11 JJK

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Posted 19 February 2013 - 09:27 AM

My base is 18"x18"x3' I mixed the concrete myself. The bottom of the pier flares out to form a footer. There is no rebar in the base. It been supporting the setup shown below for over 10 years with no issues.


Is that a can of diet Pepsi on the pier?

#12 JAT Observatory

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Posted 19 February 2013 - 09:31 AM

Yep the pier has a built in beverage holder :grin:

#13 Alex McConahay

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Posted 19 February 2013 - 09:48 AM

>>>>>Nick, plan for an earthquake.

My friend, with an observatory in Landers, CA, said his pier, which was polar aligned before the quake, was 18 degrees off after......

Alex

#14 Midnight Dan

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Posted 19 February 2013 - 11:53 AM

If the earth moves, it isn't going to really matter how big your base is. Entire buildings, roadways, etc. will shift in the right kind of earthquake.

-Dan

#15 wolfman_4_ever

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Posted 19 February 2013 - 02:04 PM

Nick, plan for an earthquake.

If the ground moves from the "big" one, not much is going to stop it.. It's the bunch of smaller ones i'm more concerned about.



#16 JJK

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Posted 19 February 2013 - 02:27 PM

If the earth moves, it isn't going to really matter how big your base is. Entire buildings, roadways, etc. will shift in the right kind of earthquake.

-Dan


But a more substantial base will provide better support for all shakers, except the "big one".

#17 frolinmod

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Posted 20 February 2013 - 12:15 PM

My pier footer is not very big and has not moved in 10 years.

Mine is moving at over 3cm/year to the Northwest and there's not a darned thing I can do to stop it because the whole Pacific plate in this area is apparently doing the same. It's moved over 126cm Northwest since I've lived here. :help: :roflmao:

#18 gdd

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Posted 20 February 2013 - 12:40 PM

Mine is moving at over 3cm/year to the Northwest and there's not a darned thing I can do to stop it because the whole Pacific plate in this area is apparently doing the same. It's moved over 126cm Northwest since I've lived here.




Is the pier still on your property? :question:

Gale

#19 Bob Moore

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Posted 20 February 2013 - 02:06 PM

I fixed it here is the good link. https://www.dropbox....w2vj/7O54w9XQyb

#20 Kunama

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Posted 20 February 2013 - 02:37 PM

Nick:

Personally, I think people go a bit "overkill" on the base of these piers.

-Dan


In some cases "overkill" is an understatement, I have spend the last 15 years supervising concrete formwork construction and have built multistorey buildings on footings smaller than some of these pier bases.

The secret is in the base preparation and reinforcement, dig the hole then COMPACT the ground well before laying down plastic, then 'chair up' a sheet of steel mesh about 3" off the ground, another sheet about 3" below the finished concrete level and then fix 6 L-shaped anglebars 1/2" diameter to the bottom mesh arranged so they end up inside the proposed pier with at least 1" of concrete to the face of the pier.

I think a base area of 3' x 3' and 18" deep would be as big as you would ever need. My own pier base will be 2' x 2' x 18".

Just my 2 cents.

#21 jazle

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Posted 20 February 2013 - 06:32 PM

Calculate where the center of mass will be. Add more cubic feet to the base until it's at least a foot below ground level. Then you won't have to worry about it "going anywhere" from being top heavy if your soils are saturated.

#22 JJK

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Posted 20 February 2013 - 06:39 PM

Nick:

Personally, I think people go a bit "overkill" on the base of these piers.

-Dan


In some cases "overkill" is an understatement, I have spend the last 15 years supervising concrete formwork construction and have built multistorey buildings on footings smaller than some of these pier bases.

The secret is in the base preparation and reinforcement, dig the hole then COMPACT the ground well before laying down plastic, then 'chair up' a sheet of steel mesh about 3" off the ground, another sheet about 3" below the finished concrete level and then fix 6 L-shaped anglebars 1/2" diameter to the bottom mesh arranged so they end up inside the proposed pier with at least 1" of concrete to the face of the pier.

I think a base area of 3' x 3' and 18" deep would be as big as you would ever need. My own pier base will be 2' x 2' x 18".

Just my 2 cents.



Matt, a footer for a building and a foundation for a telescope pier are two different animals. The former has to accept the load from above, whereas the latter has to do that plus not budge one iota. At high magnification, a small displacement at the scope translates to a significant change in the EP.

Also, it is important to get the base of the foundation below frost line (i.e., well below 18" deep).

#23 Kunama

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Posted 20 February 2013 - 11:06 PM


[/quote] Also, it is important to get the base of the foundation below frost line (i.e., well below 18" deep). [/quote]

My apologies, I did not realise that San Mateo, California suffered frosts or had a frost line.

#24 Nick Rose

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Posted 20 February 2013 - 11:19 PM

San Mateo does not have a frost line, at least as I know of.

#25 mikey cee

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Posted 20 February 2013 - 11:46 PM

Don't overkill your project like some commercial or government projects. When putting rebar, pencil rod and wire mesh into place make sure you leave enough room to fit in a "little" concrete! :roflmao: Mike :foreheadslap:






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