Jump to content


Photo

Pier for rooftop observatory

  • Please log in to reply
32 replies to this topic

#1 musicos

musicos

    Lift Off

  • -----
  • Posts: 16
  • Joined: 16 Jun 2010

Posted 09 February 2013 - 02:04 PM

Hi, I want to put close to 800lbs of gear (mount, photographic newton,...) on a pier 13.5' above ground. Ground is hard clay. We live in southern France, there is close to no frost zone. I wonder if it would be better to dig a deep foundation, or a large foundation. Also, I wonder about the dimensioning of the pier. I thought about a foundation 5x5', 3' deep (but I could do also 4x4', 5' deep). Then, a concrete column up to 8' above ground (size 2x2'). Finally, a 6' steel column, bolted on the concrete column, diameter approx 1', filled with sand. There are also ideas about building an enormeous tripod (or quadrupod), out of steel parts, from ground to top ("Eiffel tower"), or building a brick chimney and filling it only with sand (but how to fix the mount on it). My major issue concerns vibrations. Also, if I could find a solution which might be dismountable one day would be nice, but that is second priority. My observatory will be at the end in the 3rd floor of the atelier of my wife (who is a painter). I'll have to insulate it very well from heat influences...
You see, many questions, I'd be more than happy to get your different ideas and opinions.

best regards and a nice weekend

Torsten

#2 Lorence

Lorence

    Viking 1

  • -----
  • Posts: 854
  • Joined: 15 Sep 2008

Posted 09 February 2013 - 03:19 PM

Hi, I want to put close to 800lbs of gear (mount, photographic newton,...) on a pier 13.5' above ground. Ground is hard clay. We live in southern France, there is close to no frost zone. I wonder if it would be better to dig a deep foundation, or a large foundation.

Torsten


They have been building stone fireplaces and chimneys for thousands of years in your part of the world. Many of them are still standing. Some not to far from where you are.

Talk to the people who do the building. Any one of them will know more about what to do in your area than the entire CN group knows collectively.

#3 rimcrazy

rimcrazy

    Mariner 2

  • -----
  • Posts: 296
  • Joined: 03 Mar 2012
  • Loc: Overgaard, AZ

Posted 09 February 2013 - 03:56 PM

This is my custom pier.

Posted Image

It is on a 5'x5'x3' concrete block. The base is 48" in diameter. The height is 9.5' from base to the top. I plan on putting a 450lbs of telescope on top of this ( 20" PlaneWave with a AP1600 GTO mount). The base weight is over 12,000lbs.

A few qualifiers here. This is an imaging observatory only. Obviously with an eyepiece over 10' in the air, I'm not sitting around looking through it. I have access to custom metal fabrication. (My son is a ME with his own metal fabrication company. This helps A LOT!) The raised round concrete pier that you see is actually not by design, more evolution. This started out as a ROR observatory and morphed to a dome. With a ROR, a much shorter pier was too be bolted to the round concrete pier. Now it's just ballast. The level of the floor is actually the top of what you see as the round concrete pier. There is a 18" to 2' stem wall around the building. There is insulation between the floor and ground to keep the concrete slab thermally more constant.

#4 stmguy

stmguy

    Ranger 4

  • *****
  • Posts: 342
  • Joined: 11 Oct 2012
  • Loc: Western NH

Posted 10 February 2013 - 08:57 AM

I would go with a concrete block pier for something that big..see Brian Lula's obs in New Mexico..scroll down
http://www.heavensgl...observatory.htm

Norm

#5 csa/montana

csa/montana

    Den Mama

  • *****
  • Posts: 86525
  • Joined: 14 May 2005
  • Loc: montana

Posted 10 February 2013 - 10:25 AM

Welcome to Cloudy Nights, and especially the Observatory Forum!

Rest assured; you will get many helpful suggestions from our great members here, that have built something similiar to what you are considering. There's a wealth of information here from our kind members that love sharing it with others. Members here have a lot of experience, and gladly share it; so keep asking questions, and our gracious members will help you along.

#6 1965healy

1965healy

    The Snarkster

  • *****
  • Moderators
  • Posts: 9071
  • Joined: 23 Jun 2007
  • Loc: San Antonio, TX

Posted 10 February 2013 - 09:50 PM

http://www.cloudynig...26-DSC00740.JPG

Concrete block pier for my Obs. Roof top ROR by BYO. The pier is about 7' tall, filled with cement and rests on the concrete slab of the garage. There is a steel pier bolted to the top where it is level with a hole in the Obs floor.
You could contact Scott at Back Yard Observatories and he might be able to recommend the proper dimensions for your application.

#7 musicos

musicos

    Lift Off

  • -----
  • Posts: 16
  • Joined: 16 Jun 2010

Posted 11 February 2013 - 04:39 PM

Hi, thank's for all the comments!
I won't ask Back Yard, he's asking for money for advice. No good. I like the idea of a sand filled pier...but how to do the top plate ...

Torsten

#8 Raginar

Raginar

    Fly Me to the Moon

  • *****
  • Posts: 6138
  • Joined: 19 Oct 2010
  • Loc: Rapid CIty, SD

Posted 11 February 2013 - 04:51 PM

Perhaps paying for advice isn't a bad option. He's got lots of professional experience in it.

How do you do a top plate? Honestly, I bought one. The bottom plate I made out of wood. My plate ties into a wooden pier so it's lag bolted in... if you were setting up a concrete pier you would put j-bolts in and create a steel plate around that.

Top plates are harder to make.. I'd recommend googling them and just paying for it.

#9 musicos

musicos

    Lift Off

  • -----
  • Posts: 16
  • Joined: 16 Jun 2010

Posted 11 February 2013 - 05:17 PM

Hi Chris,

I give advice for free, so I don't pay for any advice. Btw, I'm a professional astronomer, and I never had the idea of asking for payment... of any kind from amateur fellows...!

To do the metallic work of a topplate is not easy, but not really difficult. The hard work is to link it correctly to the pier, and if the pier is made of sand, it's even more tricky...

Torsten

#10 csa/montana

csa/montana

    Den Mama

  • *****
  • Posts: 86525
  • Joined: 14 May 2005
  • Loc: montana

Posted 11 February 2013 - 06:01 PM

I give advice for free, so I don't pay for any advice. Btw, I'm a professional astronomer, and I never had the idea of asking for payment... of any kind from amateur fellows...!



FYI; Scott has graciously offered advice many, many times on this forum without asking for payment, as he is also an astronomer & member here. His expertise has helped many here!

#11 Scott Horstman

Scott Horstman

    Vendor - Backyard Observatories

  • *****
  • Vendors
  • Posts: 14613
  • Joined: 11 Mar 2004
  • Loc: South Side of the Sky

Posted 11 February 2013 - 06:31 PM

I won't ask Back Yard, he's asking for money for advice. No good




I don't know where you get your information but many here can verify that I've never asked for a bleddy cent to help folks out if I can.

#12 *skyguy*

*skyguy*

    Vanguard

  • *****
  • Posts: 2028
  • Joined: 31 Dec 2008
  • Loc: Western New York

Posted 11 February 2013 - 06:53 PM

Using concrete blocks makes a strong and very cost effective way to build a tall pier. I built a 14' chimney block (16"x16"x8" blocks) pier 12 years ago for my 12" SCT ... mainly for astrophotography. I have about 140lbs. of equipment mounted on the top ... not 800lbs. ... but my pier has been proven to be very capable as a photographic platform.

Observatory and Pier

Pier Cap

12" SCT on Pier

#13 mikey cee

mikey cee

    Cosmos

  • *****
  • Posts: 8201
  • Joined: 18 Jan 2007
  • Loc: bellevue ne.

Posted 11 February 2013 - 09:12 PM

Maybe Musicos believes there would be a conflict of interest asking a vendor for "free" advice. He probably feels awkward being that forward with someone who makes a living doing this sort of thing. :shrug:Hell I don't know. Mike :tonofbricks:

#14 musicos

musicos

    Lift Off

  • -----
  • Posts: 16
  • Joined: 16 Jun 2010

Posted 12 February 2013 - 02:13 AM

@ Scott. Sincere apologies! I (mis-)understood from a too quick reading of your webpage that your offer concerns astronomy shag building advices (for purchase). Now I went back on the other pages of your site and discovered all the BYO observatories you propose, and they are really very nice!

#15 csa/montana

csa/montana

    Den Mama

  • *****
  • Posts: 86525
  • Joined: 14 May 2005
  • Loc: montana

Posted 12 February 2013 - 12:39 PM

You may be referring to Scott's very detailed plans (blueprints) for observatories. These are on paper & sent to those buying them; much different from advice.

#16 musicos

musicos

    Lift Off

  • -----
  • Posts: 16
  • Joined: 16 Jun 2010

Posted 12 February 2013 - 03:48 PM

I would like to come back to the question of the pier... :-))


#17 Mary B

Mary B

    Vendor - Echo Astronomy and Electronics

  • *****
  • Vendors
  • Posts: 3072
  • Joined: 21 May 2010
  • Loc: Minnesota

Posted 12 February 2013 - 04:40 PM

I have read much of scott's advice that has been posted in this forum, it really should be compiled into a sticky.

With that much weight I would consult an engineer but a poured column would work.

#18 Scott Horstman

Scott Horstman

    Vendor - Backyard Observatories

  • *****
  • Vendors
  • Posts: 14613
  • Joined: 11 Mar 2004
  • Loc: South Side of the Sky

Posted 12 February 2013 - 04:41 PM

We've always done them like 1965Healey's link. Preferably with a base as shown in the picture below. An isolated base can be poured but we've found that going right to the existing slab is fine.
In the picture the rebar was added right into the fresh pour and the ground was scooped out so the concrete there was a couple feet thick. You can use wedge anchors with steel added to help hold the block to the floor and once you get the whole thing poured solid, it's not going anywhere.
Another thing I like about using block is that you don't have to worry about doing a continuous pour (just add rebar at the joint) or the form blowing out.

Attached Files



#19 musicos

musicos

    Lift Off

  • -----
  • Posts: 16
  • Joined: 16 Jun 2010

Posted 12 February 2013 - 04:51 PM

Hi Scott, and thank's for the advice!
I have the situation that my original slab is only 4" thick.
I will therefore have to cut out the existing slab, dig in depth, etc....I did not know beforehands that I would one day
construct a rooftop observatory at this place!

best regards and thanks
Torsten

#20 Scott Horstman

Scott Horstman

    Vendor - Backyard Observatories

  • *****
  • Vendors
  • Posts: 14613
  • Joined: 11 Mar 2004
  • Loc: South Side of the Sky

Posted 12 February 2013 - 06:10 PM

I won't say that digging a 3'x 3' hole wouldn't be better but a 4" slab is generally 2500psi so technically if you did a 32"x32" block column right on the slab, providing your fill is solid, you can have 256,000 lbs (if I'm doing the math right, it's been a long day, someone correct me if I'm wrong) sitting there with no worries.

Back in the day we used to run block service chimneys from the basement up through 2 floors and out the roof and those sat right on the slab.

#21 1965healy

1965healy

    The Snarkster

  • *****
  • Moderators
  • Posts: 9071
  • Joined: 23 Jun 2007
  • Loc: San Antonio, TX

Posted 12 February 2013 - 07:16 PM

Musicos, is it possible for you to post some pictures of what you want to mount and where you want to mount it?

#22 *skyguy*

*skyguy*

    Vanguard

  • *****
  • Posts: 2028
  • Joined: 31 Dec 2008
  • Loc: Western New York

Posted 12 February 2013 - 08:53 PM

I have the situation that my original slab is only 4" thick.
I will therefore have to cut out the existing slab, dig in depth, etc....I did not know beforehands that I would one day construct a rooftop observatory at this place!


A 4" concrete slab should easily hold the weight of your proposed pier. Concrete has an extremely high compression strength ... on average, 3000 lbs/in²... and it will rarely fail/crack from the excessive application of weight. For example, an automobile weighing approximately 3200 lbs. can remain parked on a garage floor for decades without cracking the concrete ... why? ... because the weight is spread across 4 tires (25 in² contact area), each tire exerting only 32 lbs./in² on the concrete pad. How do you get the 32 lbs./in² answer ... well, you can do the math, or just measure the inflation pressure on each tire! They're both the same number ... neat!

Now, taking a look at your pier ... assuming 16"x16" cement blocks and a 14' height ... the weight of the pier filled with concrete (145lbs./ft³) will be about 3,600 pounds. Adding 800 pounds of equipment will make the total weight 4,400 pounds. Therefore, the weight of the pier and equipment on the 4" concrete pad will be only 17 lbs./in² (4400/16x16)... a little more than 1/2 the weight per in² of an average car on a concrete garage pad.

Of course, this is assuming the concrete pad is in good physical condition and underlying substrate material meets standard construction codes. Overbuilding a structure can be a serious waste of resources, time and money ... however, it will help you to sleep better at night! :)

#23 musicos

musicos

    Lift Off

  • -----
  • Posts: 16
  • Joined: 16 Jun 2010

Posted 13 February 2013 - 02:14 AM

Hi, thank's for your comments.
I'm not worried that the slap cannot carry the weight of the pier, I'm worried that any mouvement of a person walking on this slab and close to the pier will translate 15' higher as strong vibrations...well, that's the reason people "disconnect" the pier from the rest of the building...
I'll try to integrate a photo later on...

cheers
Torsten

#24 Scott Horstman

Scott Horstman

    Vendor - Backyard Observatories

  • *****
  • Vendors
  • Posts: 14613
  • Joined: 11 Mar 2004
  • Loc: South Side of the Sky

Posted 13 February 2013 - 02:35 AM

Once you have that whole mass in place, unless your having Irish Dance classes in the garage, I can't see it moving at all if someone came in, and I'd be surprised if your camera would see it too. :)

Just going by experience, I've never heard anyone complain about vibrations or movement by simply attaching to the slab.

Of course you do remove all doubt by doing an isolated footing but for the added expense.

At our old house we had a high speed railway about 2 miles away. Freight trains traveling up to 70mph.
I had a pretty good chunk of concrete in the ground for my pier in the observatory and Saturn would start shaking before I could hear the train whistle. :lol:

#25 *skyguy*

*skyguy*

    Vanguard

  • *****
  • Posts: 2028
  • Joined: 31 Dec 2008
  • Loc: Western New York

Posted 13 February 2013 - 10:58 AM

My 14' chimney block pier is attached directly to the garage floor pad. There's approximately 46,000 pounds of concrete in that pad. People walking around the garage during imaging sessions have had absolutely no effect on the telescope's performance. From my experience ... from the past 12 years of imaging using this pier ... I would not be concerned at all about placing a tall pier directly on a large concrete pad.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics