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How to check roof stability

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#1 Eden Orion

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Posted 26 December 2018 - 03:10 AM

Hello
My name is Eden Orion, and I work at the University of Haifa, Israel.
Currently we are checking the possibility of building an Observatory on the roof of one of the buildings at the university.
The observatory will serve mostly non-professional visitors, but there is a thought of using it as a research observatory as well.
Since the plan is to place it on a roof of a building about 20 meters above the ground, how can we test the stability of the place regarding the possibility of need for a research scope.
Thank you in advance

%D7%90%D7%95%D7%A0%D7%99%D7%91%D7%A8%D7%
 



#2 jfrech14

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Posted 26 December 2018 - 04:29 AM

Assuming that you are allowed to (we weren't allowed to build one on our roof due to it not being made to have a bunch of people on it at once.. according to the city), I would get a small scope set up to monitor seeing using DIMM or something, maybe get some accelerometers to see if the building shakes a lot, etc. Determining where there is the least amount of vibrations would naturally be best. Then, checking your seeing lets you see if it is suitable for the type of research you want to do with whatever telescope you plan on getting.

 

The best location is out there on the right but it, unfortunately, looks like it has the least amount of damping. I work in a laser lab and during the day the vibrations are just awful. But, fortunately, the night is when everyone is gone and the building is the most stable.


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#3 Ian Robinson

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Posted 26 December 2018 - 06:53 AM

Surely you have an engineering faculty with expert engineers in house who have access to the best design modelling programs ?

 

Why are you not asking for their input and for them to check the design and recommend changes ?



#4 Eden Orion

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Posted 26 December 2018 - 08:11 AM

Thank You so much.
We will do some tests.
 



#5 Graeme5959

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Posted 26 December 2018 - 08:15 AM

I would suggest that you set up a photographic rig with guidescope and a tripod to try it out.  You will not be able to assess accelerometer data as you have no idea about what values would b acceptable and where any threshold would be.  Try out a semi portable rig eg on a tri-pier and get a trace for guiding. Perhaps try walking through the building & jumping one or twice to see the response.

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#6 roscoe

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Posted 26 December 2018 - 08:23 AM

Is the building in the design phase or is it an existing structure?

 

If it's still in design, perhaps some internal walls could be made to a cross-shape, with the obs directly above them? 



#7 DLuders

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Posted 26 December 2018 - 08:39 AM

Set out a shallow pan of water, and see what effect (if any) these have in creating ripples:

(1) Several people walking around & jumping on the roof

(2) Heavy traffic below (trucks, buses, trains, etc.)

 

That big cantilevered wing of the building won't be nearly as stable as the left, solid portion of the building.  Those columns look like they have pinned connections, and will rotate a bit in high winds.



#8 Moonman5

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Posted 26 December 2018 - 08:53 AM

Set up small telescope with reasonable power and focus on moon, planet or star and have people walk around. 

Magnification of image will also magnify vibration.



#9 jfrech14

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Posted 26 December 2018 - 12:30 PM

I would suggest that you set up a photographic rig with guidescope and a tripod to try it out. You will not be able to assess accelerometer data as you have no idea about what values would b acceptable and where any threshold would be. Try out a semi portable rig eg on a tri-pier and get a trace for guiding. Perhaps try walking through the building & jumping one or twice to see the response.
graeme

Taking the Fourier transform of accelerometer data will tell you the frequencies of the vibrations experienced, which is a big help assuming you are taking it properly and calibrated it. Low frequencies with a large magnitude show the culprits likely to cause issues while higher frequencies are less likely to have large magnitudes and affect the setup since it's been shown that cars, building vibrations and foot traffic are typically low frequency less than 60Hz or so, which is why optical tables have tuned damping In the low frequency range. The power spectrum of accelerometer data should reveal a lot of the building vibrations over a reasonable period of time.

Walking around the test rig is a good idea for nearby sources, but research would likely be done remotely or with people sitting down near the scope. The issue will likely be the building and nearby roads. Big buildings like this vibrate awfully.


Edited by jfrech14, 26 December 2018 - 12:50 PM.


#10 jfrech14

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Posted 26 December 2018 - 12:33 PM

Is the building in the design phase or is it an existing structure?

If it's still in design, perhaps some internal walls could be made to a cross-shape, with the obs directly above them?


I agree, something like this, for research, is important to take into account in the design phase. People don't understand how much research goes into design and placement of university and research observatories. It's different than just casual observing for a museum. The university, or those in charge, will likely want some solid evidence that a research observatory is feasible in order to spend the money.

#11 CharlesW

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Posted 26 December 2018 - 01:29 PM

You should really be talking to the building’s architect to see how much flex they designed into it. Then I’d talk to the on-site engineer to see if the HVAC equipment can be disabled overnight. The entire building could sway, not disturb a plate of water, and completely smear the stars in your image. 


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#12 Alex McConahay

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Posted 26 December 2018 - 03:53 PM

If I were you, and the building is already built, I would build it not right on the roof, but immediately off to the side. This means you can stage visitors (have them line up, attend orientations, whatever) on the roof itself, using as much as you like of the area. And then when it is time to observe, they step off the side onto a platform that is either attached to the building or not. But the telescope pier itself is rooted all the way to the ground below, with separation between itself and the building.

 

While some parts of the building look like a 20 + meter pier would be necessary, other parts of it could be done for substantially less. The extra ground space would be only the thickness of the pier. This whole arrangement would probably be less expensive than anything you could engineer (or re-engineer) to accommodate a scope on top of a building. 

 

Note, if the building has not yet been built, it is simple enough to build the building around a pier that goes straight to the ground and is not in contact with the building itself.

 

Alex



#13 jfrech14

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Posted 26 December 2018 - 05:58 PM

From a Google search, the building already exists and they are trying to put an observatory in. The roof may be an excellent place for outreach but likely not for research. A building next to it, as suggested, might be the better option. However, at a university that option was likely the first go to if the money was available. So, it likely isn't and the money would go to the instruments.

Edited by jfrech14, 26 December 2018 - 06:17 PM.


#14 Steve Haverl

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Posted 26 December 2018 - 06:32 PM

Good  lord people, this is a university, not Uncle Bob’s garage ! Involving the structural engineering faculty is the obvious solution.



#15 jfrech14

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Posted 26 December 2018 - 07:07 PM

I'm going to say that since it is a university, the engineering firm has been contacted and have given the green light and perhaps are involved IF the project has been approved or moved to the next stage of planning. I read the question mostly as how to test the site to see where the best stability is for a research scope not just in terms of vibrations but seeing and everything involved with the observatory. A structural engineer won't know everything about the needs of a telescope and the faculty in structural engineering likely won't know the building because it was contracted. But, they are good people to involve. But, not good enough to only involve them since they have their own research and classes. Having been involved in something like this before, when you propose something like this you need to come to them with a solid plan and support for building it. If the cost of a research telescope will be a lot more, they need to justify it to the department or university. It's likely not always as easy as "just contact the engineer." It costs money, money that might not be given to the project yet. He came here for ideas, and the request seems general. What might be obvious to some people might not be to others and it might not even be correct or is assuming too much. Maybe we should wait to hear more specifics about the questions he wants answered and what stage the project is in.

Edited by jfrech14, 26 December 2018 - 07:12 PM.


#16 Alex McConahay

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Posted 26 December 2018 - 11:29 PM

>>>>> A building next to it, as suggested, might be the better option.

 

Let's be clear, here.....I am not suggesting building a whole building next to the current one. I am suggesting only having a pier run to the ground, completely free-standing from the existing building. If need be, build a deck that people can walk around on. Attach it to the attached to the current building, or make it free standing.  But I am only advocating that whatever you do, have a freestanding pier to hold the scope. 

 

Alex


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#17 jfrech14

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Posted 27 December 2018 - 12:01 AM

>>>>> A building next to it, as suggested, might be the better option.

 

Let's be clear, here.....I am not suggesting building a whole building next to the current one. I am suggesting only having a pier run to the ground, completely free-standing from the existing building. If need be, build a deck that people can walk around on. Attach it to the attached to the current building, or make it free standing.  But I am only advocating that whatever you do, have a freestanding pier to hold the scope. 

 

Alex

That is what I thought you meant, and what I meant. So, good call clarifying it since mine made it sound like I meant a whole building  


Edited by jfrech14, 27 December 2018 - 12:02 AM.


#18 DeanS

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Posted 27 December 2018 - 11:07 AM

We did some testing at our local university when they suggested they wanted to put an observatory on top of a 5 story parking garage.  We used a webcam at about F/40 on on a 10" scope.  I drove a car starting at the bottom of the garage.  You could see every time I went over a speed bump :) 

 

We played back the video to them but they still put the dome up there.  They also figured that there would be little traffic at night, but lighting is the biggest issue.  Oh, and the university hospital has lots of helicopter traffic which lands on a nearby building does not help much either.  Those big life flight birds going directly overhead make a lot of noise and vibrations.

 

When we asked about why not put it out at one of the agriculture research farms away from the city, they said it is a teaching university and students need easy access which would not be the case if it was 10-20 miles way.

 

Dean

 

University of Kentucky

MacAdam Student observatory

https://pa.as.uky.edu/observatory



#19 DeanS

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Posted 27 December 2018 - 11:16 AM

Here is a small picture of it.  They actually had the building pre-assembled into sections on the ground and air lifted it into place using a huge construction helicopter.

 

After talking with the current director of the observatory, he thinks they ended up using cranes but did originally talk about air lift.   He was going to try and find some construction photos.  But regardless, it vibrates and is closer to the lights :(

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Edited by DeanS, 27 December 2018 - 09:57 PM.


#20 jfrech14

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Posted 27 December 2018 - 01:04 PM

We had a dome on top of our physics building. The city and university said nobody is allowed up there because they didn't build the roof for people to be up there. So, they had to make it remote and when it failed, they wouldn't let students up there to work on it and no faculty felt qualified to work on it because we don't have astronomy. I convinced the chair to clear it out one year and the scope hadn't been touched in ages and now there's just an empty dome that nobody is allowed to do anything with. They wouldn't even let it be taken apart. And judging how much my laser lab shakes on the 2nd floor, the roof must have been awful. However, a local community college built an awesome research grade observatory in the middle of a white zone, so... i guess it depends on who the chair is sometimes. How bad dis it end up being?

Edited by jfrech14, 27 December 2018 - 01:06 PM.


#21 Alex McConahay

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Posted 27 December 2018 - 05:55 PM

I have been in several rooftop (or decktop) observatories that did not have piers going to the ground. (University of Redlands, and Ohio State, and several others, that I cannot exactly recall. They have all had issues with vibrations. 

 

Never plan your life around everybody staying still while you observe. (It's Okay to have an observatory on the roof, because the students are not there during the night time when it will be used!!!! ) It just does not work. 

 

Alex


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