Skyinsight-pier

From SkyInsight

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Contents 1 Pier Base/Footing 2 Pier design options 3 The Lower Pier 4 The Upper Pier

Pier Base/Footing

March 2005 - I'm still trying to determine the size of the footing for the pier. I know I need to go 48" deep for the frostline. At this point I'm guessing that the footing will probably need to be 4'x4'x4'. That's a lot of concrete. I'm researching to see if I can dig the hole that size and use sand and/or gravel for a portion and then the cement slab on top of that.

April 28, 2005 - I determined that the frostline is 36" so with the standard rule of thumb of 6" below frost, the current plan is to dig a hole for the pier base that is 42"W x 42"L x 42" D. The hole would then be partially filled with a concrete to create a slab that is 42"W x 42"L x 24"D. After the upper pier is set, the rest will be back filled with gravel.

Concrete Network's Footing Fundamentals

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Pier design options

The goal is to design the pier in two parts:

1. The Lower Pier - The lower half from the ground to just below the deck
   • A concrete pad with dimesions of 42"W x 42"L x 24"D will sit in a hole with dimensions of 42"x42"x42" and back filled with gravel.
   • Set into the slab will be an pier extending ~ 8' to the bottom of the deck. It will probably consist of 16"W x 16"L x 8"D chimney blocks.
2. The Upper Pier - The upper half that extends above the deck
   • This will be a four cedar 4x4s bolted/glued together that will bolt to the lower pier (via bottom plate) and hold the telescope (via top plates). The ideas is that it could be removed is necessary. I don't plan on removing it often, that would defeat the purpose, but is the need arose it could be removed and the deck opening "capped".
     
     I was looking at buying a steel pier but they are expensive. I found that some people used wooden piers (as a temporary pier in one case) and decided that it would work well in my situation. Since the upper pier will only be 30" to 36" tall, I'm not concerned about it warping. Plus, using wooden top and bottom plates (MDO) it will be easy to drill the mounting holes, unlike a steel plate, plus a rather inexpensive. Another benefit to the wooden upper pier is that I can easy attach accessory trays to the pier. But those are finishing touches I'll worry about later.

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The Lower Pier

• Cement pier
  • The obvious option for the 9ft pier is to use a sonotube and fill it with cement. The concern is that it would need to be poured from the deck, a long way to fill, leaving the possibility of gaps as shown in this project: Example 1 Example 2

• Chimney blocks
  • One alternative is to use chimney blocks: Wye Mountain Observatory
  • Using chimney block there's two options for adding stability:
    1. Add four pieces of rebar in the corners of the blocks and fill with concrete
    2. Stack four blocks side-by-side in a square creating a 32"W x 32"L pier.

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The Upper Pier

Purchasing a commercial pier could be expensive. A quick search of the Internet turns up piers in the range of $450 to $1,500. A cheaper alternative would be to build one from good "scrap". That option requires welding which I'd have to outsource.

• Options for building a pier:
  • This site shows a pier built from lumber.
  • Another lumber-built pier
  • Instructions on building a wooden pier - A picture of the design
  • Steel Pier Design by Tony Floyde
  • Permanent Pier Design by Jim Slay
• Commercially available piers (listed alphabetically):
  • Advanced Telescope Systems
  • AstroPier
  • Clear Skys Piers
  • Pier-Tech

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