Brainstorming dream obs which will become real!
Posted 01 May 2013 - 09:36 AM
Posted 01 May 2013 - 03:10 PM
First, I'd consider renting a jackhammer to break up the concrete after you cut around the edge with a masonry blade in a skill saw. For a small job like that, an electric jackhammer should work fine.
How big will your cinder block base be? How many blocks on a side? If it's only one or two blocks, you can probably fill all the cavities. If it's more, you might want to only fill some and leave some empty. But at a minimum, fill the corner cavities.
Have a set of cinder blocks ready to go for the first course at the bottom. Once the concrete for the pad is poured and leveled, set the cinder blocks on the surface, buttering the ends with mortar. You want the cinder blocks to be resting on wet concrete so they adhere well, and you want it to still be wet enough to able to accept rebar. Once you've got the first course in place, jam a piece of rebar into the concrete in the cavities that you intend to fill later. Shove it down into the wet concrete so it sticks out of the cavity to the height of the finished base. If the base will be very tall, then only go up a few feet with the rebar, otherwise it will be hard to get the next layer of cinder blocks over them. You can wire on extra pieces of rebar as you go up.
Once the pad has set up, you can start adding courses of cinder block until you reach final height. Then fill the rebar-containing cavities with concrete.
Posted 02 May 2013 - 08:24 PM
The good news is the dome is going up tomorrow. They will use a forklift to raise it. Also everything is more or less on budget. Considering the extra hassles and delays I am very pleased. He originally was supposed to do this work earlier. The only additional charge is to add siding to the addition the same as the roof will be a couple hundred more.
My Dad will be at the house Saturday I'll get him to take some higher resolution photos and I will be there next weekend to inspect it myself.
It's really looking exactly like how I wanted it to. Of course I need to fix a lot of little things and I do hope to get around to paining the building as well but it seems like everything is going well.
Posted 02 May 2013 - 09:22 PM
Posted 02 May 2013 - 10:32 PM
Posted 02 May 2013 - 10:44 PM
Posted 03 May 2013 - 11:09 AM
I'm still torn about the pier again the contractor is urging me to use a big sonotube. Maybe he had a bad experience with cinder / chimney blocks but he keeps telling me it will be hard to work with. He won't have anything to do with it so it's not like he's doing that work. Next week I'll go price out the blocks and go from there. Price will not be the deciding factor but if there is a big difference either way that may steer me.
I have been looking at this pier a lot
Of course I could do the same thing with blocks. Once the dome is up I asked him to cut the largest possible hole in the floor without cutting the joists. The pier can be as big as I want up to that point and then it will shorten to fit through the floor. I will look into steel pipes in the area when I get to this point or I could even do a smaller sonotube on top. That would at least be a mixable amount of concrete. For the pad I'm going to have to bring in a truck in all likelyhood. Unless I open my own labor camp
Posted 03 May 2013 - 01:11 PM
....I'm still torn about the pier again the contractor is urging me to use a big sonotube. Maybe he had a bad experience with cinder / chimney blocks but he keeps telling me it will be hard to work with......
To put it politely, your contractor doesn't know what he's talking about.
An astronomical pier needs a large footprint to be stable. A large sonotube isn't appropriate. The weight of a large sonotube filled with concrete is considerable. A properly-sized base is a must.
A tall sonotube filled with wet concrete is a nightmare if there is a blowout. You don't ever want to deal with that.
Has your contractor considered how to fill a tall sonotube? A pumper truck is what is called for. They're not cheap and rarely available in sparsely inhabited places.
Compare this with a block pier that is cheap, has a large footprint, and can easily be built by one person.
You might want to reconsider using this contractor, too. <g>
Posted 03 May 2013 - 02:14 PM
I'm getting ready to have my pier built in the next month or so. I was showing the contractor the pier plate assembly with the 3/4" stainless J-bolts on the bottom to sink into the concrete. He was telling me there's no way I need bolts that big - he's built houses that attached with smaller bolts than that.
I explained that it didn't really matter how strongly the bolts were holding the pier plate to the concrete. The issue is that the the pier plate needs to be suspended above the pier so that there is room to adjust the height and level the plate. The bolts need to be thick and solid so that the suspended plate and attached scope/mount are held rigidly without vibrations. These are things a contractor has no experience with and could care less about.
Similarly, the design of the concrete part of an astronomical pier has to meet different requirements than normal structural concrete work. Your contractor won't be taking those requirements into consideration so take what he says with a grain of salt.
Posted 03 May 2013 - 03:21 PM
I'm simply consulting him about the pier not using him to build it. I come here for the pier advice and everything I'm reading less considering using another guy I agree with. Cinder blocks and chimney blocks it will be. I am now thinking I will use cinder for the first few feet and below the floor so rebar can go through it with ease and then possibly switch to the chimney blocks as it gets higher. Unless its better to go cinder all the way. I will then switch to either a sonotube or steel pipe when I get to the second level. This part will be narrower to avoid having to resupport the floor.
I'm so excited to get there.
Posted 03 May 2013 - 03:32 PM
Posted 03 May 2013 - 04:28 PM
Go about halfway down and find the plans.
It will give you an idea of how to build a cinder block pier.
A mason and a helper could easily build something like this in a couple of days, maybe a bit less.
There's nothing wrong with a sonotube pier for lower heights, but they become problematic for high piers.
Posted 03 May 2013 - 10:04 PM
Thanks for the link Dan, I think I will be doing something similar, although that pier looks MASSIVE. I understand I want the pier to weigh somewhere between 25x and 50x maximum load on top, but is that about the only guideline I have to go by as to how big it should be? I was planning a 40x40 slab but that's not set in stone (yet). I can certainly go bigger, that number just seemed good to me but I will make sure it's good before I start..
Initially the load on the top will be less then 100lbs however as I am hoping to use this for the rest of my life there could one day be a paramount or ap mount and 14" HD or 16" RC, so I'd like to build this so it will be good for a 200-300 LB load just in case. I plan on living a while and doing imaging the rest of my life.
Edit some rough calculations :
If I do a 40x40x60" pad that will require 7380lbs of concrete. If I use the 16x6x8 blocks HD sell and make the pier 36x32 I would need 12 pier level. I don't have the ceiling height but I guess it's around 10 feet maybe slightly less I'd need a 180!! blocks x 40lbs per block that is 7200lbs + the 7380 for the pad puts me at 14380 + the rest of the pier should bring it past 15000 which would allow for a 300lbs load and still maintain the 50:1 ratio.
edit again, so the blocks apparently weigh 45lbs now.
On the US home depot they are 28lbs. Either weight should work though.
Posted 04 May 2013 - 08:30 AM
Not sure where the 25-50x came from, but seems reasonable as a guideline. I think it just highlights the fact that you want a big mass for the base. There are other things to consider.
If you have roughly 14K pounds in a pier, you want to be sure the soil underneath it will support it without it sinking or tilting to one side over time. Digging down to a reasonable depth helps because the soil is more stable and compacted. But still, you need to know what the load bearing capacity of the soil in your area is so you provide enough surface area for the pier.
For example, clay is rated at about 2K pounds per square foot. To support the load you'd need about 7 square feet. Your 40" x 40" base provides 11 square feet so you should be good to go if your soil is clay. Most soil types are at least 2K pounds per square foot or more, so you're probably fine, but you might want to check on the soil types in your area from your local building department.
Posted 04 May 2013 - 11:00 PM
The dome is up and it looks exactly exactly how I wanted it to. Having something come together like this really is amazing. Obviously there is a lot to do still but it's going better then I could have hoped.
Posted 05 May 2013 - 06:12 PM
Posted 07 May 2013 - 11:46 PM
Wow! Looks wonderful! Should have a great view of the sky at that height. Now for that last pesky detail - the pier!
Yes the pesky pier.
Small bit of good news. I found a company who does excavation. I can likely get them to dig down to the frost line. Even better good news is its the same guy who plows the driveway so he already knows the house / my Dad. I'll give him a call friday and see if he can come by on the weekend. I still have to cut the concrete of course, at least this is someone who can do it whenever I won't have to be there. He's one of those island guys who doesn't have a computer. Such a different world there, no wonder there is no light pollution.
Posted 08 May 2013 - 08:40 AM
Posted 12 May 2013 - 10:10 AM
I decided I'll break up the middle of the concerete anyway. The sledge hammer route is so hard! I consider myself pretty strong but this is wearing me out. I have abou an 8" round hole in the middle of my 40x40 area. The good news is under the building it's just sand. Sand and a lot of rocks. With my gloved hands and a pry bar I've been able to get about 18" deep. I should have no time digging down to the frost line. I was thinking breaking the concrete would be easier then digging. I do want to do some of the work myself. In part to save money in part because id like some of my own sweat but hopefully not blood to be put into the construction of this observatory. This is the one for life.
Also I bought 12 concrete blocks just to visualize my pier. They had 3 sizes I stuck with the 16x6x8 ones I assumed I was going to work with. They have 8" and 12" wide ones as well. Now for the 12" ones id use a lot less blocks but in concerned they will be too heavy to work with especially at higher heights. I can also put more rebar in more blocks. I'm not sure if I will fill them all the way but at the bottom for sure and probably the top.
Do you think I should stick with my 280 or so 6" wide blocks or drop the number and use bigger blocks? Just trying to make sure I do everything as right as I can.
Also it's amazing to be under the dome! It's actually snowing now despite the fact it was 25 degrees here earlier in the week. I saw a ton of turtles when I got here yesterday but now it's back to winter. I've never seen snow this late in the year in my life!
Posted 12 May 2013 - 10:32 AM
Do you think I should stick with my 280 or so 6" wide blocks or drop the number and use bigger blocks?
Not sure I understand the question. Why would wider blocks reduce the number? Seems like wider blocks would just make the wall thicker.
The most commonly used size is the 8" wide block, mostly because it is half the length of the block which makes it easier to turn corners and have everything line up when the blocks are laid out in half-block overlapping layers. So, if you use 2.5 8-inch blocks per side, that would take up your 40 x 40 area as shown below. Was that your plan?
Posted 12 May 2013 - 10:58 AM
I was also under the assumption I had to fill the middle with blocks is that not correct? This would mean I'd need a lot less blocks. This is why I thought wider blocks would mean I will need less.
The 8" wide now seems like the way to go.
Posted 12 May 2013 - 11:20 AM
Congrats on your observatory project! Looks like you're getting close and it's exciting to see it come together.
I helped a friend build an observatory that was high up like yours. Thankfully it was well documented here on CN. You might want to see how we did the pier before you start constructing yours.
Here is a the link to the archived observatory thread.
Good luck with your project!