Paramount ME concrete pier
Posted 28 December 2012 - 03:19 PM
My college will be buying a paramount ME in about two years, and we are in the process of designing an observatory for it. Payload will be an 12" Meade SCT and later on, probably a larger-aperture RC. We are looking for advice on a concrete pier. The pier top will be at least 8 feet off the ground.
It seems like 12" concrete columns are popular, made from the standard sonotube. Is there any advantage to instead having a pier that is cone-shaped instead of cylindrical? We are looking for maximum stability and minimization of vibrations from surrounding area (isn't everyone?)
It will be completely isolated from the observatory structure.
Ideas, thoughts, advice is welcome!
Posted 28 December 2012 - 06:57 PM
building supply and got a 14 inch x 10 foot sonotube that
was substantially more durable than the sonotubes sold
at the local Home Depot/Lowes for my ME. With the 14 inch
width, the heavy duty Bisque pier adapter works like a charm.
Posted 28 December 2012 - 07:38 PM
Posted 29 December 2012 - 12:50 PM
They produce several types of forming tubes. One consideration is the amount of concrete you'll have to use. See chart at: http://www.sonotube..../sizechart.aspx
You'll want something like a 4' cube as a foundation. You should consider the need for drainage of your foundation if ground water is a problem. I don't know about a cone, other than it won't be easy to fabricate a form.
Posted 29 December 2012 - 01:53 PM
Posted 30 December 2012 - 03:30 AM
Definitely it's good to try to get a tougher sonotube material. To get the bubbles out of my 8' pier (4' below ground, 4 above) I slapped the sides a lot with my hands and rhythmically squeezed it (the concrete was pretty wet). It worked well to get out most of the air, but by the end of it the sonotube cardboard was very much saturated with water. The whole thing started to lose integrity and crumple on one side at the bottom - I had to support it with some wood to keep it steady until it dried. I haven't measured, but I think it also got a bit widened on the top as well due to my abuse, so it ended up like a reverse tapered cylinder. Still, in the end it does the job.
If you really want the concrete to settle well, I know you can rent vibrating tools that are meant to be inserted into the concrete for a very short time, shouldn't harm the sonotube at all.
Posted 30 December 2012 - 11:12 AM
Posted 02 January 2013 - 03:58 PM
Posted 02 January 2013 - 08:37 PM
I use a length of rebar by driving it up and down in the tube. Kind of like churning water. Works well enough for concrete mixed properly. Mistake is often made to use too much water in an attempt to speed/ease mixing and finishing. In the end you'll weaken the mix. I go by the 1-2-3 rule. One part portland, two sand and three stone with a ratio by weight of 0.4 water to portland. So an 80 pound bag of portland requires 32 pounds of water or a little less then 3 gallons. My mixer handles about a third of a bag of portland per batch, so that's just one gallon. This is pretty stiff. If you get your concrete mixed commercially they can add plasticizers or super-plasticizers to ease handling.
Posted 03 January 2013 - 09:13 AM
If you check at better lumber yards or masonry supply houses, there are a range of one-piece heavy-duty plastic pier forms that look somewhat like upside-down champagne glasses, that being smooth and black, make attractive finished piers. One of them over a big footing poured right into a carefully dug hole will yield a substantial and stable scope base.
Also, consider inserting a piece or two of plastic conduit in the pier before the pour for wires going to the scope. The conduits could even extend under the floor to a box mounted on a side wall......
Posted 03 January 2013 - 09:25 AM
I googled, and found these: