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Any Opinions or Advice / Concrete Block Platform Observatory

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#1 Hobby Astronomer

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Posted 07 December 2020 - 12:29 AM

Hello All.

 

Just wanted to get some input from people here.

 

Location is Northern Mexico.

 

Objective: A concrete deck on the second story of a small building for astrophotography and EAA with my children. My skies are bortle 6 where this structure is located. I often travel to a location with bortle 2 skies to image in the no-mans land of the desert. So imaging is meant to be done with a tripod instead of a pier, and so I can pack up from the deck and head off to the desert once a month.  My previous setup was imaging off three red bricks for the tripod.

 

The deck is to be 10 feet by 15 feet. The walls of the 2nd story deck will be 6 feet tall made with cinder blocks. Here are photos of construction in progress.

 

My questions and concerns:

 

I expected the primary posts or frame structure to have legs of 12" x 12" in concrete. The guy building this has put in only 7" x 5" and I am concerned. I had several discussions with him regarding the need for the platform to be very very stable and vibration free. Will the 7" x 5" legs generally work?

 

The next thing is the thickness of the upper deck. Does this need to be 4" thick on the concrete or would 6" be better.

 

Any input would be appreciated.

 

WhatsApp Image 2020-12-06 at 11.04.55 PM.jpeg

WhatsApp Image 2020-12-06 at 11.05.28 PM.jpeg


Edited by Hobby Astronomer, 07 December 2020 - 01:10 AM.


#2 Hobby Astronomer

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Posted 07 December 2020 - 12:31 AM

These photos show the rebar for the structure of the building. The concrete is only 5" x 7" for the rebar section which represent the true supporting structure of the building and the deck above.

 

Based on my discussion with the contractor concerning a footprint of 12" x12" for the structure... is 7" x 5" not going to work for a vibration free deck?

 

Does this need to be demo'ed and restarted over using a 12" x 12". I do not want to be difficult with the contractor but I am concerned this is a material weakness in the design.

 

WhatsApp Image 2020-12-06 at 11.04.19 PM.jpeg

 

WhatsApp Image 2020-12-06 at 11.04.36 PM.jpeg


Edited by Hobby Astronomer, 07 December 2020 - 01:15 AM.


#3 Hobby Astronomer

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Posted 07 December 2020 - 12:33 AM

This is the first floor structure. The second deck floor will be build above. The ceiling is 8 feet from the floor.

 

WhatsApp Image 2020-12-06 at 11.04.03 PM.jpeg

 

WhatsApp Image 2020-12-06 at 11.03.27 PM.jpeg


Edited by Hobby Astronomer, 07 December 2020 - 01:13 AM.

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#4 Hobby Astronomer

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Posted 07 December 2020 - 12:34 AM

WhatsApp Image 2020-12-06 at 11.03.38 PM.jpeg



#5 Hobby Astronomer

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Posted 07 December 2020 - 04:18 PM

Well I appreciate everyone's assistance with this issue. 

 

Thank you so much. 

 

So I called a client and got a meeting with a structural engineer and we came up with a plan to fix this. 

 

Everything in orange highlights the new modifications to be implemented. Should work out great. 

 

Deck to be 5" thick. Cross beams to be added to the design. Vertical support doubled up.

 

Should be great after everything is completed. 

 

Great to have friends with talent to compensate for my lack of expertise in concrete.

 

HA 

 

WhatsApp Image 2020-12-07 at 3.08.02 PM.jpeg


Edited by Hobby Astronomer, 07 December 2020 - 04:21 PM.

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#6 speedster

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Posted 13 December 2020 - 02:25 AM

The new interior frame, in red, isn't helping walls at all.  If your little guy in the picture pushes on that corner, block walls act as diaphragms and transfer the load to the ground.. That is good.  The stiffness of the skinny columns is not an issue.  The concrete second floor is horizontal diaphragm.  Also good.  It's quite easy to make a stronger wall for less effort and eliminate the concrete columns entirely.  Too late for that now but your walls will work fine with no additional work and the proposed addition of the red stuff won't make them any stiffer.  The red beams are reducing the span of the concrete floor and will stiffen it.  How much depends mostly on their depth.  8" deep as shown isn't going to do much.  You already have walls for vertical support so you can notch the bond beam, fill the cells of the block below, and completely eliminate any need for new columns.  Regardless of the thickness of the deck, it won't be vibration free. Sorry.


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#7 MalVeauX

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Posted 14 December 2020 - 01:58 PM

Well I'm super interested to see how this turns out.

 

I kinda like the idea of a two story observatory for visual and minor imaging maybe. What a great fun thing with the kids too, to have a little fortress observatory with a crows nest with a scope on top.

 

Dang I'm wanting to try something now....

 

For no vibration, your mount would need to be basically isolated from the structure entirely. So no matter what you employ, it will take on vibrations from anything and everything, though they should be minor.

 

Very best,


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#8 Hobby Astronomer

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Posted 15 December 2020 - 04:01 PM

Well just to give an update the project has come to a halt.

 

My next door neighbor contractor had a fit over the new plans. He said I was crazy and got emotional. Threated to quit the project. Said I owned him money and I told him I am not advancing more until you start getting some production. 

 

Short discussion he invited the mafia over. So I got to meet those people too. The police department of the town got shut down by the Army about 10 years ago. So those local guys are law and order. So we settled up. He wanted about $800 more than the work was worth but everything is settled and we are happy neighbors again with no bad feelings. 

 

So I am going to invite three local buys to bid the plans and the specs to finish up. Low bidder with references gets the job.

 

Hope we can get things back on track by this weekend. 

 

Christopher 



#9 speedster

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Posted 15 December 2020 - 04:41 PM

Sorry to hear about the mess.  One way to avoid the added red stuff is to use conform metal deck to form the floor.  3C18 has a construction clear span of 11'-10" so no new beams or temporary shoring needed.  6" concrete depth is good for #82 psf (6" depth between flutes, 3" depth above flutes).  6x6 W1.4xW1.4 welded wire fabric for reinforcing.  Dowel new slab into columns.  That will be far stiffer than typical residential second floor construction.


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#10 Hobby Astronomer

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Posted 15 December 2020 - 07:39 PM

Sorry to hear about the mess.  One way to avoid the added red stuff is to use conform metal deck to form the floor.  3C18 has a construction clear span of 11'-10" so no new beams or temporary shoring needed.  6" concrete depth is good for #82 psf (6" depth between flutes, 3" depth above flutes).  6x6 W1.4xW1.4 welded wire fabric for reinforcing.  Dowel new slab into columns.  That will be far stiffer than typical residential second floor construction.

 

One way to avoid the added red stuff is to use conform metal deck to form the floor. 

 

3C18 has a construction clear span of 11'-10" so no new beams or temporary shoring needed.  We were planning to use .5" rebar. It is readily available in Mexico and the guys know how to use it.

 

6" concrete depth is good for #82 psf (6" depth between flutes, 3" depth above flutes).  We were planning to go with 5" per a structural engineer. Will 6" make a difference. I have heard that the amount of rebar is what makes a roof strong and too thick of concrete (Mexico, and Mexican Concrete) beyond 12 cm can crack. Should we look at 6" instead of 5"? 

 

6x6 W1.4xW1.4 welded wire fabric for reinforcing.  I think we were going to create this structure with Rebar. But this seems easy to get my hands on and looks like it would reinforce the concrete in addition to the .5" rebar if laid on the bottom of the large concrete slab wee will pour. I like this.

 

Dowel new slab into columns.  Yes yes. That is in the plans. Great point. 

 

That will be far stiffer than typical residential second floor construction. Thanks four your kind input. 

 

HA



#11 Hobby Astronomer

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Posted 27 February 2021 - 06:54 PM

WhatsApp Image 2021-02-27 at 4.51.49 PM.jpeg

 

Well we got the project started again. This is now officially a take over project.

 

New guy on the job. Seems all of my neighbors have some degree of concrete expertise. This guy lives in across the street from my house.

 

I changed the design again. Building a structure inside of the structure the original guys started.

 

My new guy did not argue of specifications. He did as I asked.

 

We ended up constructing a 10'x10' Platform inside of the building.

 

.5" Rebar every 6" on the deck.

 

8 Pillars 12" wide.

 

The deck is about 5' above the original slab.

 

Let me add more photos


Edited by Hobby Astronomer, 27 February 2021 - 06:54 PM.


#12 Hobby Astronomer

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Posted 27 February 2021 - 06:55 PM

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#13 Hobby Astronomer

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Posted 27 February 2021 - 06:58 PM

WhatsApp Image 2021-02-27 at 4.49.40 PM.jpeg

 

I built a frame above the original slab. Photo does not show the amount of rebar going in at the base of the structure.

 

12" Pillars will be supporting the deck above.

 

Concrete is Quikcrete 5000 series.



#14 Hobby Astronomer

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Posted 27 February 2021 - 07:00 PM

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#15 Hobby Astronomer

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Posted 27 February 2021 - 07:01 PM

WhatsApp Image 2021-02-27 at 4.48.44 PM.jpeg

 

Adding more block to the structure. The upper deck has walls about 6' high.



#16 Hobby Astronomer

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Posted 27 February 2021 - 10:17 PM

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#17 Hobby Astronomer

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Posted 27 February 2021 - 10:18 PM

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#18 Hobby Astronomer

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Posted 27 February 2021 - 10:20 PM

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#19 Hobby Astronomer

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Posted 27 February 2021 - 10:21 PM

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Getting serious with the rebar



#20 Hobby Astronomer

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Posted 27 February 2021 - 10:30 PM

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#21 Hobby Astronomer

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Posted 27 February 2021 - 10:31 PM

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#22 Hobby Astronomer

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Posted 27 February 2021 - 10:32 PM

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#23 Hobby Astronomer

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Posted 27 February 2021 - 10:36 PM

WhatsApp Image 2021-02-27 at 4.45.26 PM.jpeg

 

After one week of water curing time to before seeing how the deck worked out. I cannot believe that wood supported about 3 tons of freshly poured concrete.

 

Deck is solid. 6" thick with 64 pieces of 1/2 rebar. Quikcrete 5000 series concrete.

 

Happy with the result of the deck.

 

HA


Edited by Hobby Astronomer, 27 February 2021 - 10:36 PM.

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#24 Hobby Astronomer

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Posted 27 February 2021 - 10:39 PM

WhatsApp Image 2021-02-27 at 4.45.10 PM.jpeg

 

View to the north. Overhead I can get about 6 hours of narrowband time on a target before I am in the trees.


Edited by Hobby Astronomer, 27 February 2021 - 10:43 PM.


#25 Hobby Astronomer

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Posted 27 February 2021 - 10:41 PM

WhatsApp Image 2021-02-27 at 4.44.58 PM.jpeg

 

View to the south east. Camera is about 5'4" high for the picture. Wow. Perfect.




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