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1st floor flat roof Pier

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#1 photonboy

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Posted 27 July 2014 - 01:26 PM

Hi there,

I was wondering if anyone had any experience of placing a permanent pier on a 1st floor flat roof and imaging?

My concerns are thermal currents and I am in the process of rebuilding the roof and the room below and can therefore insulate thoroughly to try to prevent thermal issues.

The benefit of this location for me would be that i can have a permanent pier (Wife has banned this from the garden) and the roof would be secure from theft unlike my garden. Also I would be able to see a far greater area of the sky from up there.

Any thoughts from people?

Many thanks

Nick

#2 Raginar

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Posted 28 July 2014 - 11:01 AM

Hey Nick,

Welcome to the forums. There are quite a few examples of what you're doing. One guy did it recently on his second floor and was installing a sky-light. That might be a good option. It's unfortunate she's banned you from the garden :). A semi-permanent pier turned into a bird bath during the day is a good feature.

I'm sure some other guys will chime in.

#3 TCW

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Posted 28 July 2014 - 06:07 PM

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#4 roscoe

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Posted 28 July 2014 - 06:57 PM

I agree with TCW, the roof will bounce unless you install some sort of fairly significant support beneath it.

On the other hand, if you remotely image, you might be OK, as long as there are no vibration issues in the house - if a washing machine is spinning, or a door is slammed, the whole house will shake, and even a refrigerator running can cause a shimmy. As suggested, try it out with a tripod and see what happens.

#5 photonboy

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Posted 29 July 2014 - 12:10 AM

Thanks for the responses,

The structure will be built from brick but I was thinking of using 2 steel girders spanning the room and a small steel spanning these two. Then bolt a pier to the steel. Hopefully should be pretty solid but I wouldn't walk on the roof whilst imaging. My main concern is thermal currents from the house and whether these can be negated......

cheers
Nick

#6 TCW

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Posted 29 July 2014 - 12:27 AM

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#7 roscoe

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Posted 29 July 2014 - 06:56 AM

For thermal issues, if your roof is well-insulated, low mass, and light colored, your heat plume should be minimized. Stored heat rising from the brick walls could be more of an issue, but much depends on the difference between day and night temps, and amount of sun hitting the walls.
There is a CN member named Hilmi who built a rooftop obs on his home in a hot desert climate, contacting him would possibly be a good resource....as these are issues he had to consider.

#8 tassy

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Posted 21 August 2014 - 10:47 PM

This is a "cut and paste" of some info I placed on " Roof Top Options" about a week ago.  

 

I am just in the process of completing a raised observatory which is constructed on a 3m high platform approx. 3.5m by 3.5m next to my house. Telescope is a Meade 16"LX200. The pier is primarily supported by two 200PFC (parallel flange channel) beams (22.9kg/m) separated by approx. 850mm and 3.5m long. I suspected beam deflections at the centre (where the pier is supported) might cause problems which is turning out to be the case. I currently have a couple of ACROW type props temporarily providing support immediately under the pier (which is a big improvement) until I can fix something a bit more permanent. I was hoping to have the area under the platform clear so it could be used as a walkthrough but I don't think this will be possible. Can provide more details if anyone interested.



#9 photonboy

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Posted 25 August 2014 - 05:54 AM

Thanks Tassy,

 

When you say beam deflections, are you referring to movement/flexure in the pier or beam?  I was thinking of using two fairly wide "I" beams with a shorter "I" beam spanning the two, with cast-in padstones.  My thinking was that the I beam would alleviate the torsional twist issue?

 

cheers

 

Nick



#10 dr.who

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Posted 25 August 2014 - 11:06 AM

While the steel beams will help you will still be facing issues with deflection and vibration. Most likely from the support posts at the end points. A way that will work to get around this is to build a two part structure. Part one will be for the load of the pier and scope. It has it's own posts, studs, joists, and plates that are completely isolated from the second structure and do not tie into the house. Add in vibration supression materials where the peir connects to it and you should be right as rain. On top of and outside of (or inside of) the first structure you build a second structure to house you. This part can tie into the house. This way the pier and scope are completely isolated from the floor you will be walking on as well as any vibrations the house may create. You will want to over build the joists and posts as this will cut down on vibration. To the point where adding in bridging (x shaped pieces between joists), corner braces, and extra studs at narrower than usual on center points.



#11 tassy

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Posted 26 August 2014 - 07:02 PM

Hi photonboy and dr.who

Hopefully I have successfully uploaded 3 photos of my setup.

Most of the original (before props) deflections were from the up/down movement of the central beams. The central "cross" must help reducing deflections by coupling the beams together but the large span is a major contributor to the problem.  For example tilting of the pier results when someone moves from being above one beam to the other. The first beam rises as their weight is removed and the second beam sags tilting the pier. The pier is made from an old hydraulic accumulator (16mm wall thickness) and is quite rigid.

I realized well before construction began that completely isolating the pier from the remaining structure would be the way to go but in my case this would mean a very tall pier (4m) which unless it had a massive diameter would be susceptible to inverted pendulum type vibrations. Hopefully 4 props, one at each corner of the central cross will solve most of the problem.

Cheers tassy

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