Click here if you are having trouble logging into the forums
Privacy Policy |
Please read our Terms
of Service | Signup and
Troubleshooting FAQ | Problems? PM a Red or a Green Gu
uh, User
1965healey
The Snarkster
Reged: 06/23/07
Loc: San Antonio, TX
|
Re: Pier for rooftop observatory
[Re: Scott Horstman]
#5676452 - 02/12/13 07:16 PM
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Musicos, is it possible for you to post some pictures of what you want to mount and where you want to mount it?
|
*skyguy*
Pooh-Bah
Reged: 12/31/08
Loc: Western New York
|
Re: Pier for rooftop observatory
[Re: musicos]
#5676586 - 02/12/13 08:53 PM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Quote:
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/inČ... 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 inČ contact area), each tire exerting only 32 lbs./inČ on the concrete pad. How do you get the 32 lbs./inČ 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./ftł) 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./inČ (4400/16x16)... a little more than 1/2 the weight per inČ 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! 
|
musicos
member
Reged: 06/16/10
|
Re: Pier for rooftop observatory
[Re: *skyguy*]
#5676956 - 02/13/13 02:14 AM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
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
|
Scott Horstman
Vendor - Backyard Observatories
Reged: 03/11/04
Loc: Too Far North, USA
|
Re: Pier for rooftop observatory
[Re: musicos]
#5676967 - 02/13/13 02:35 AM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
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. 
|
*skyguy*
Pooh-Bah
Reged: 12/31/08
Loc: Western New York
|
Re: Pier for rooftop observatory
[Re: Scott Horstman]
#5677437 - 02/13/13 10:58 AM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
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.
|
jrcrilly
Refractor wienie no more
Reged: 04/30/03
Loc: NE Ohio
|
Re: Pier for rooftop observatory
[Re: *skyguy*]
#5677449 - 02/13/13 11:04 AM
|
|
Edit
|
Reply
|
Quote |
Quick Reply
|
|
|
Quote:
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.
I've never experienced any problems with mine either (chimney blocks on slab floor). Of course, if someone WERE to be walking around in my garage at night, I'd want to know about it - but I believe I'd have to find out about it some other way. 
|
|
6 registered and 10 anonymous users are browsing this forum.
Moderator: csa/montana, Chris Erickson
Print Thread
|
Forum Permissions
You cannot start new topics
You cannot reply to topics
HTML is disabled
UBBCode is enabled
|
Thread views: 1240
|
|
|
|
|
|
|
Previous
Index
Next
Threaded
