Observation Deck

[rdbkr99999]

I'm building an observation deck for my motocross track and I wanted to run my ideas past everyone.

Here are the details. The deck will be about 8' off the ground and 12'x12' was going to be outside dimensions. For the legs I am using telephone poles (approx 11" in diameter) that are 20' long. They are buried 3' in the ground.

The holes for the poles are dug, but not set yet. The holes were dug with post hole diggers, so they aren't perfect. I was going to use cement to fill the voids. I know that some people don't like cementing in posts, should I just fill with dirt and compact?

For the beams I was going to use 2x12s sandwiched on each side of the telephone poles and then use 2x6s for the floor joists and decking.

I've attached a couple of images that I drew up in Google SketchUp. What do you think? Do I need to build anything stronger?

 

[/pine]

from experience I don't think 3' is near deep enough if the live load is 8" off the ground and there is any considerable dead load above that ...!
just gravel (with some fines) will work best to plum the poles...

 

[rdbkr99999]

That was a concern that I had as well. I was going to see how stable the platform is and add 2x6 x-bracing to the legs if it seems like it moves much.

from experience I don't think 3' is near deep enough if the live load is 8" off the ground and there is any considerable dead load above that ...!
just gravel (with some fines) will work best to plum the poles...

 

[patrick_g]

I'm building an observation deck for my motocross track and I wanted to run my ideas past everyone.

What do you think? Do I need to build anything stronger?

Yup, I think so. The only thing keeping your design from folding worse than a house of cards is the lateral resistance of the part of the poles in the ground.

Imagine a force pushing sideways on the floor or any of the poles. What opposes it? Nothing but the resistance of the poles in the ground. The mechanical advantage (disadvantage?) given the length of the lever arm (part of the poles out of the ground) versus the little bit in the ground does not inspire confidence.

You need some triangularization (think gussets) to keep the first stiff wind after a soaking rain from folding it up.

Pat

Pat

 

[rdbkr99999]

Does this look better?

 

[tornadowatchranch]

this is almost exactly what I did last year. I have included (I hope) a link to the threads. Mine ended up being about 12x12 after all. I braced on 3 sides so we can park the 4-wheelers underneath. My son calls it his garage. I can take more pics if you are interested. The floor is about 8 feet up. The outer two boards are sandwiched 2x12. 2x10 perpendicular and 5/4 x 6 floorboards. I used 2x10 for the outer supports for the slant room and 2x8 perpendicular. At times you will probably pack a bunch of screaming fans up there so I would also worry about overbuilding. That would be a litigation nightmare if it came down during a race.

Best thing I did was to get an impact wrench to put in all those huge bolts.




http://www.tractorbynet.com/forums/projects/139822-utility-pole-fort-begun-pics.html

http://www.tractorbynet.com/forums/projects/139098-utility-pole-tree-fort.html

 

[buck12]

I have a deer stand that is 16' tall (floor is 10' above ground). It is only 4' x 4'. I did not burry it in the ground at all. It sets on cap blocks with each leg braced to 2" x 6"s drove into the ground with 2" x 4"s angled up to the legs. It has been like this for 10 years on top of a hill and has survived multiple stroms. I think proper bracing is the key not setting the post in the ground.

 

[rdbkr99999]

That's awesome! I've been looking for something similar to this for quite a while and wasn't able to find anything. Thanks for sharing!

How is the fort holding up? Is there anything that you would have changed?

I've been debating about whether it would be better for me to have a 2x12 on each side of the poles or to laminate them together with plywood in between.

As far as the load on the deck, that is a concern. Most of the design charts seem to be for a 50 lb/ft2 live load. That should give me a 7200 lb load at 12x12. If I figure 200lbs per person, that is 36 people on the deck. I'm not sure if I could even fit that many people on there. Also, we are a small track and don't get that much traffic... yet.

Thanks for the ideas!

 

[/pine]

...I'm building an observation deck for my motocross track ...

FWIW...if this is a structure that is going to be used by anyone other than friends and family...i.e., the general public...and it is on your property...I suggest getting a licensed engineer to sign off on the "as built" design...and file a copy with your insurance agent...

 

[buck12]

FWIW...if this is a structure that is going to be used by anyone other than friends and family...i.e., the general public...and it is on your property...I suggest getting a licensed engineer to sign off on the "as built" design...and file a copy with your insurance agent...

Excellent advice!