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Equipment Discussions >> Observatories

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*skyguy*
Carpal Tunnel
*****

Reged: 12/31/08

Loc: Western New York
Re: Cinder block pier new [Re: StarmanDan]
      #5654029 - 01/31/13 10:28 AM Attachment (21 downloads)

Quote:

Quote:

I only filled the first 4' of block with concrete and left the rest of the pier hollow. I've had absolutely no problems with vibrations when imaging. I've found this pier to be extremely stable even without filling it completely.




I have contemplated this too, but am stumped as to how I would interface the mount to the pier. How did you manage yours?




I made a top-cap out of 3/4" plywood with a sheet of 1/4" hard rubber on the bottom (to absorb vibrations). It's bolted to the block at the corners using lead shields drilled into the block. Also, since the main attachment point for the wedge is at it's center, I embedded a length of 1/2" threaded rod into the concrete fill at the pier's base and ran it up and through the center of the block and through the top-cap ... to hold down the cap and to install the wedge. I also placed the threaded rod inside a 2" PVC pipe, filled with sand, to dampen any vibrations.

My 14' chimney block pier has far exceeded my performance expectations over the past 11 years. BTW, did I mention it cost me only $70 for materials and was built in only a few hours ... spread out over 2 days ... by myself and a friend with no block laying experience.


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barbarosa
scholastic sledgehammer


Reged: 04/11/10

Loc: "lamorinda", CA
Re: Cinder block pier new [Re: *skyguy*]
      #5654874 - 01/31/13 06:41 PM


I have to ask why any rebar is required.

Block/mortar or brick/mortar has worked for zillions of chimneys and walls. Most two-story brick/tile flue masonry chimneys here are still standing after the '06 and the '89 Loma Priata quakes. In fact, near the sections of freeway that collapsed in Oakland there are chimneys built before 1900 that neither cracked nor collapsed.

I am getting ready to do some sort of pier so these threads are educational.


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Gastrol
Pooh-Bah


Reged: 11/04/11

Loc: los angeles
Re: Cinder block pier new [Re: barbarosa]
      #5654946 - 01/31/13 07:44 PM

I can see your point in not needing rebars, especially piers with a wide stance. But in my case without rebars, my 10" diameter concrete pier, about 6' tall including gear can develope a crack at the footing and possibly break.

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roscoe
curmudgeon
*****

Reged: 02/04/09

Loc: NW Mass, inches from VT
Re: Cinder block pier new [Re: Gastrol]
      #5655355 - 01/31/13 11:52 PM

One of the most important reasons for putting rebar in a pier in colder climates is to prevent damage when the ground freezes. Frozen ground is larger than unfrozen (a volume of ice is 1/5 larger than the same volume of water) and when the ground freezes, the surface lifts, could be as much as 3-4 inches if the frost penetrates 3 or more feet, which it will in cold climates when under a structure which keeps an insulating blanket of snow away. When the soil freezes near the surface, it will adhere to the sides of the pier and attempt to lift it up. Rebar keeps the top part from being torn off the bottom part.
R


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stmguy
sage


Reged: 10/11/12

Loc: Western NH
Re: Cinder block pier [Re: roscoe]
      #5655621 - 02/01/13 06:11 AM

There also is a product that you can bind the blocks together on the outside of the blocks. I've used it and it works well.

There are different names but it usually has fiberglass fibers imbedded in it

http://www.quikrete.com/athome/Video-Dry-Stack-Wall.asp
Norm


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Gastrol
Pooh-Bah


Reged: 11/04/11

Loc: los angeles
Re: Cinder block pier new [Re: stmguy]
      #5656212 - 02/01/13 11:54 AM

Quote:

There also is a product that you can bind the blocks together on the outside of the blocks. I've used it and it works well.

There are different names but it usually has fiberglass fibers imbedded in it

http://www.quikrete.com/athome/Video-Dry-Stack-Wall.asp
Norm




I've used fiber imbedded stucco on dry-stacked cinder block walls and also as final render on my brick pizza oven. Resists cracks, adds strength, and very easy to apply.


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HunterofPhotons
Pooh-Bah


Reged: 04/26/08

Loc: Rhode Island, USA
Re: Cinder block pier new [Re: roscoe]
      #5656278 - 02/01/13 12:33 PM

Quote:

.... Rebar keeps the top part from being torn off the bottom part.
R




Just out of curiosity, have you ever seen a monolithic concrete pour separated in this manner?

dan k.


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roscoe
curmudgeon
*****

Reged: 02/04/09

Loc: NW Mass, inches from VT
Re: Cinder block pier new [Re: HunterofPhotons]
      #5657113 - 02/01/13 08:54 PM

Dan,
We rebuilt a falling-down deck a few years ago, that was built over a fairly steeply slanted backfill against a foundation, where the piers had been destroyed by frost action. There is a phenomenon called 'ground creep' that happens on hillsides, where when the ground freezes, it lifts perpendicular to the surface - it goes up at an angle - but when it thaws, it drops straight down. The piers we replaced, which were not re-enforced, had been pulled apart about 12-15" down, the bottom sections staying in place, the top parts having moved downhill in 20 or so years about 6", which of course made the 4x4 posts connected to them very crooked, and started the deck collapsing. There was enough dirt between the upper and lower part that at first we thought the initial piers were indeed only 18" tall, only after digging some more did we find the bottom halves.
Properly re-enforced ones would not have pulled apart, but in this hillside case, would likely still have begun to tip because of the creep action. We replaced the old 6" ones with 12" versions, with much larger footings, planning that the larger footing diameter would better resist tipping forces, having more area on the uphill side to press against the soil above. Because of the higher-than-normal side thrust on them, we bent 3/4" rebar into a 'u' shape, with 3 shorter pieces laid in the bottom of the U half way down the footing, spread out into a 6-pointed cross. So far, they're still straight up.
Russ


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HunterofPhotons
Pooh-Bah


Reged: 04/26/08

Loc: Rhode Island, USA
Re: Cinder block pier new [Re: roscoe]
      #5658283 - 02/02/13 02:41 PM

Thanks, Russ.
I've never come across such a situation even though the bulk of my construction experience has been in New England.
It's easy to underestimate the power of frost heaves unless you've seen what they can do. Wet ground seems to command the same low level of respect as the Monty Python rabbit. "But it's just a rabbit!" <g>

dan k.


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StarmanDan
Post Laureate
*****

Reged: 08/27/07

Loc: Deep in the heart of Texas
Re: Cinder block pier new [Re: HunterofPhotons]
      #5658640 - 02/02/13 06:08 PM

Does frost affect bedrock the same as normal soil? I've seen what frost can do. During one particularly bad winter my father would go out to the pool and chop up the 4" thick ice that had accumulated each night to keep our 30K gallon pool from cracking. In the process the pool had lifted about 4" out of the ground. Fortunately we had a gradual thaw and the pool settled without cracking.

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roscoe
curmudgeon
*****

Reged: 02/04/09

Loc: NW Mass, inches from VT
Re: Cinder block pier new [Re: StarmanDan]
      #5659079 - 02/02/13 11:00 PM

If it's real bedrock, it's the Earth's crust, and even frost can't lift that..........but it will flake pieces off the top if there are any cracks that water can seep into...... Aside from bedrock, frozen ground will lift absolutely everything. My friend's garage/equipment shed, which is built on a re-enforced concrete slab, and has a full second floor, and often a bulldozer and log skidder parked in it, lifts about 4" every winter.
R


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