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Pouring pad at same time as piers

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#1 LoveChina61

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Posted 25 July 2021 - 04:48 PM

I am having a cement truck come put to pour my observatory's foundation so I might as well have him pour my two piers as well. I poured a pier for myself one time long ago with a 10" diameter sono-tube on a 3x3x3ft cement base and all went well. I later built a wooden deck around the cement pier and built the 10'x12' observatory on top of the wooden decking.

 

Now I am building observatory #2 in an entirely different location and want to have an all-cement floor. This time I want to have two isolated piers. Each one will have four bolts anchored deep within them and poking out from the top of the cement pier base where I can anchor a steel pier on them. But how will I pour an all-cement foundation at the same time that I am pouring two isolated cement pier bases? Am I limited to pouring a "post like" cement base for my pier that is something like 1ft wide x 1ft wide x 4ft deep in order to keep them separate and not overlapping? How have some of you done that?

 

Thanks for any direction you can give me.

 

Mike



#2 Stevegeo

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Posted 25 July 2021 - 05:27 PM

Isolating the piers and pier base from mainslab could be done, however if not taken great care the two ( or in your case three) would be a disaster as bleed from main slab to pier would potentially  induce unwanted vibration .

 

A pier could be isolated using foam around the pier itself . 

The dug hole for pier could have several bags of concrete dumped in mixed  with rerod pre set in place  , sonotube set onto that , then foamed ( spray foam) then dirt packed around that  when the foam sets up ( minutes)  a drop over pre cut  foam piece over the sonotube for pier isolation to pad in place,  then final pour of slab .  Timing of all this wouldnt be that  critical and piers and slab could cure together.  It would need careful planning and execution step by step ..

 

A prepoured pier with rebar and j  bolts  in place would be the preferred method , with the isolated  material around each pier  at pad level   thick enough below and above .. befor pad  pour is prob best.


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#3 macdonjh

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Posted 25 July 2021 - 09:10 PM

Perhaps take a look at the Pier Engineering thread here on Cloudy Nights.  Your construction will be much simpler if you can (and feel comfortable with) using an auger to drill a deep shaft as the footer for your steel piers, rather than having a big block of concrete at a shallower depth.  If you accept the "deep shaft" footer, you can:

 

Set your forms for your floor, and even place and tie your rebar, just don't raise the rebar onto chairs yet as you'll be walking on it.  Then drill your pier footer shafts with your auger and remove all the "spoils".  Set the rebar cage, the forms for the very tops of your pier footers, and the anchor bolt template with your anchor bolts.  Note that the forms for the top of your pier footers will be "double": one inner form to create the shape of the top of your pier footers (and to support your anchor bolt templates), and an outer form to keep the floor concrete from getting into contact with the top of your pier footers.

 

You could also ask your concrete contractor to pour your floor, leaving a couple of holes and come back in a couple of weeks with your auger and drill for your pier footers.  Once you get the forms for the tops of the piers and your anchor bolts set you could pour the concrete for your piers yourself.

 

When your concrete contractor arrives, he'll pour your pier footers first, making sure your anchor bolts are oriented correctly and are plumb.  Then he'll raise the rebar for your floor onto chairs (or pieces of concrete bricks) so the rebar is held near the middle of your floor slab.  Next he'll pour the floor and rake the concrete such that it fills the forms and is approximately level and smooth-ish.  Then he'll screed the top surface: he'll drag a straight edge, supported by your forms, over the wet concrete to remove excess and bring your floor to the right elevation.  I'm sure your anchor bolts will get in his way, but he'll deal with that.  Finally, after a few hours, when the concrete has just begun to set, he'll "float" the concrete with a big metal plate to flatten the concrete and make it smooth.  If you plan to leave the concrete exposed, he may recommend a "light broom finish" to slightly roughen the concrete so it's not slippery if it gets wet (like with dew when your roof is open).

 

If you decide you want a big chunk of concrete, you'll have to dig a big hole and pour that part first.  Then you'll back-fill over the top of the footer and make sure your back-fill is well and properly compacted so it doesn't settle and create a void under your floor.  Then you can build your forms, set your rebar and pour your floor.

 

An alternate to the plan above is to make the top of the "big chunk footer" the same elevation as the finished concrete floor.  Then it would be possible to execute construction is a manner similar to the deep shaft footer.

 

Good luck with your project.


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#4 mmalik

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Posted 26 July 2021 - 05:47 PM

Juggling...

 

 

1. Rebars and bracing/centering them

 

2. Sono and bracing them

 

3. Sono and vibration isolating them from the pad

 

4. Templating and balancing/aligning/orienting them

 

5. Etc.

 

...will be quite difficult if not impossible if pouring pad at the same time. I would advise first taking due care of the piers and once all up and ready, then pouring the pad. May be pour the piers yourself and then call in the pad support. Regards


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#5 syxbach

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Posted 27 July 2021 - 08:57 AM

Mike

 

You can do these at the same time, although finishing pier then the pad is preferred. 

 

Basically you pour concrete into your pier foundations and the sono tubes. Then put 6 inch dirt (dirt, gravel, etc.) on top of your foundations. This is for isolating the pier foundation from the pad. After the foundation is fully covered, you can pour the rest of concrete to form your pad. 

 

You can check my observatory building log. We processed these at the same time because the workers wanted to finish the project in one day. The pier performance is great.

 

https://www.cloudyni...bservatory-wto/

 

Yuexiao 

 

 

I am having a cement truck come put to pour my observatory's foundation so I might as well have him pour my two piers as well. I poured a pier for myself one time long ago with a 10" diameter sono-tube on a 3x3x3ft cement base and all went well. I later built a wooden deck around the cement pier and built the 10'x12' observatory on top of the wooden decking.

 

Now I am building observatory #2 in an entirely different location and want to have an all-cement floor. This time I want to have two isolated piers. Each one will have four bolts anchored deep within them and poking out from the top of the cement pier base where I can anchor a steel pier on them. But how will I pour an all-cement foundation at the same time that I am pouring two isolated cement pier bases? Am I limited to pouring a "post like" cement base for my pier that is something like 1ft wide x 1ft wide x 4ft deep in order to keep them separate and not overlapping? How have some of you done that?

 

Thanks for any direction you can give me.

 

Mike


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#6 Galaxyhunter

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Posted 27 July 2021 - 09:09 AM

I did an "All in One" pour.  I bored three holes (12" x 4' deep) for three legs of my mount. I poured the slab &  pier legs at once.  After, I saw cut the three pier leg to separate it from the slab.  Easy peasy.  I filled the saw cut gap with silicon.

 

Saw Cut


Edited by Galaxyhunter, 27 July 2021 - 09:10 AM.

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#7 LoveChina61

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Posted 28 July 2021 - 02:18 PM

Mike

 

You can do these at the same time, although finishing pier then the pad is preferred. 

 

Basically you pour concrete into your pier foundations and the sono tubes. Then put 6 inch dirt (dirt, gravel, etc.) on top of your foundations. This is for isolating the pier foundation from the pad. After the foundation is fully covered, you can pour the rest of concrete to form your pad. 

 

You can check my observatory building log. We processed these at the same time because the workers wanted to finish the project in one day. The pier performance is great.

 

https://www.cloudyni...bservatory-wto/

 

Yuexiao 

Yuexiao,

 

How long did you wait for the pier foundation to dry before piling 6 inches of dirt on top of it?

 

Is there any vibration whatsover being passed from floor foundation to the pier foundation via/through the 6 inches of dirt that is sandwiched between the two?

 

Thanks much!

 

Mike



#8 LoveChina61

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Posted 28 July 2021 - 02:22 PM

Yuexiao,

 

How long did you wait for the pier foundation to dry before piling 6 inches of dirt on top of it?

 

Is there any vibration whatsover being passed from floor foundation to the pier foundation via/through the 6 inches of dirt that is sandwiched between the two?

 

Thanks much!

 

Mike

Yuexiao,

 

I know that I must use some rebar inside the base of the pier foundation, but did you have rebar running up into the sonotubes as well?

 

Thanks,

 

Mike



#9 robbieg147

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Posted 28 July 2021 - 02:59 PM

One way would be to cast the two pier bases complete with starter bars for the concrete piers, then pour the piers up to approx 25mm above the finished floor of your observatory complete with holding down sockets for the steel piers.

 

Carefully line the piers with expansion board and then backfill around the piers to underside of hardcore.

 

Place hardcore and finally pour your observatory floor slab. Pour sealant between the 20mm gap between concrete pier and floor.

 

I would not try and do it all in one go myself?


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#10 speedster

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Posted 29 July 2021 - 12:40 AM

It's really quite simple.  Let's say your piers are 12" diameter by however deep.  Build a 1x6 cedar box about 16" square and center it over the holes.  Locate and support the boxes with two 2x boards spanning from slab side form to slab side form.  Pour the holes and the boxes, then pour the slab.  The 2x boards are removed after pouring but before finishing, as soon as the concrete is stiff enough to hold the boxes in place.  After all is cured a couple of days, chisel out the box boards or just leave them.  If you want to get fancy, make the box sides a little wedge shaped, thinner on the bottom, so they come out pretty easily.  This gives you a pier top that is flush with the floor.  If you want a different pier height, change the height of the box.  Other ways of accomplishing the same thing - depends on your design - but forming it all for one pour is easy.  Just have the bottom of the box in the dirt, or backfill against it from the slab side, so the slab concrete does not touch the pier concrete.


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#11 macdonjh

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Posted 29 July 2021 - 07:56 AM

Yuexiao,

 

I know that I must use some rebar inside the base of the pier foundation, but did you have rebar running up into the sonotubes as well?

 

Thanks,

 

Mike

Having rebar between the pier footer (the below grade part) and the pier itself is more important than having rebar in the footer.  The footer is just a lump of concrete.


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#12 syxbach

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Posted 29 July 2021 - 08:46 AM

Probably within half an hour. We did not wait for a long time. If you looked at the attached image, we poured the concrete in to the big hole first, then sono tubes. We ensured that the foundations are connected to the sonotubes. After the workers make the fundation flat, the pier flat, they transferred dirt on to top of the foundation until the dirt was filled to the pad bottom level. Around 6 inch.

 

No vibrations. So far all our mounts can guide perfectly. Mine AP1000 mount can go down to 0.3 arc rms guiding, which is the best the mount can provide. 

 

Yuexiao,

 

How long did you wait for the pier foundation to dry before piling 6 inches of dirt on top of it?

 

Is there any vibration whatsover being passed from floor foundation to the pier foundation via/through the 6 inches of dirt that is sandwiched between the two?

 

Thanks much!

 

Mike

 

The foundations are cylindrical. The workers installed circular rebars (a lot of rings) inside. I highlighted them in red. You can see from these rings, they installed another 3~4 L-shaped rebars which extended into the sonotubes (highlighted in blue).

 

Yuexiao

 

 

Yuexiao,

 

I know that I must use some rebar inside the base of the pier foundation, but did you have rebar running up into the sonotubes as well?

 

Thanks,

 

Mike

 

Attached Thumbnails

  • Rebar.jpg

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#13 LoveChina61

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Posted 02 August 2021 - 07:36 AM

Great! Thank you all very much for the valuable information and excellent suggestions.

 

 

Mike



#14 LoveChina61

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Posted 04 August 2021 - 11:44 AM

When pouring cement down the sonotube, how were some of you able to prevent the cement from just flowing right out of the bottom of the sonotube?

 

For example, in Yuexiao's case he needed to make sure that the top of the pier foundation ended up being 6 inches from ground level so that he could cover it with dirt and then pour the entire observatory's cement foundation on top of that. He poured the sonotube at the same time that he poured the pier's base cement foundation.

 

When I poured cement into my sonotube at the same time as pouring the base for my previous observatory, it just ran out of the bottom of the sonotube and kept filling up any and all available spaces that it could flow into.

 

Did you periodically stop the cement pouring process and let the underlying cement dry before you continued filling up the sonotube step-by-step? Hopefully the crew that comes in to do the cement pout will be patient enough to let me do that.

 

Mike



#15 HunterofPhotons

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Posted 04 August 2021 - 12:52 PM

When pouring cement down the sonotube, how were some of you able to prevent the cement from just flowing right out of the bottom of the sonotube?

 

........When I poured cement into my sonotube at the same time as pouring the base for my previous observatory, it just ran out of the bottom of the sonotube and kept filling up any and all available spaces that it could flow into......

 

 

Mike

 

I'll assume that you were writing about concrete, not cement.

Your mix was too watery if it was flowing all over the place.

Concrete is not like water which seeks its own level.  Concrete can maintain differing levels in one pour.

Search 'concrete slump test' to determine concrete consistency for future projects.

 

dan k.


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#16 LoveChina61

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Posted 04 August 2021 - 02:01 PM

I'll assume that you were writing about concrete, not cement.

Your mix was too watery if it was flowing all over the place.

Concrete is not like water which seeks its own level.  Concrete can maintain differing levels in one pour.

Search 'concrete slump test' to determine concrete consistency for future projects.

 

dan k.

Great. Thanks, Dan. Yes, I was mixing it at home by myself and evidently made it too watery. You can see how it was bulging up in the picture below.

 

Mike

 

tn_gallery_79015_4314_1407448876_25300.j


Edited by LoveChina61, 04 August 2021 - 02:02 PM.


#17 macdonjh

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Posted 04 August 2021 - 10:02 PM

I'll assume that you were writing about concrete, not cement.

Your mix was too watery if it was flowing all over the place.

Concrete is not like water which seeks its own level.  Concrete can maintain differing levels in one pour.

Search 'concrete slump test' to determine concrete consistency for future projects.

 

dan k.

+1

 

Unless you put a concrete vibrator in it...  I have a funny story (not astronomy related, though).




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