How to calculate strut lengths, inside diameter and thickness?

[AA]

Hello,

My goal is to do the common conduit geodesic dome 3v 5/8 and I have started with using this http://www.desertdomes.com/dome3calc.html

I am Indonesian in Indonesia (poor village jungle area, no building code).

Questions

1. I have read many times that peoples plans online do not factor in some part of the strut. If I had to guess what it was, I cant really remember, but I think its the part where the pipe is flattened, bent and has a hole put through it. This worries me, can anyone clarify?
2. Is there any good choices for the diameter of the dome that works great with common lengths of pipe? Conduit here seems like the same as it is in the States, 10ft, and I read once that there is a size that works great with this to reduce wastage when cutting the pipe. As my first dome, I would like to do something small such as 12ft in diameter (open to something a bit bigger if it's wiser).
3. I plan to put a tarp over the dome, then fiberglass mesh, then latex cement.  With that said, is there any suggested size for the pipe? Online they always say 3/4" pipe which is available here but its either 1.2mm thick or 2mm thick. The 2mm thick conduit is 3x more expensive than the 1.2mm thick conduit....I was hoping I could get by with 1.2mm thick. Its been hard to find out the thickness of the conduit these people use in the States as they dont mention it. I read one place only and it said 1.6mm.....does that mean I have to go with the 2mm or can I get by with the 1.2mm?
4. Maybe if the conduit is too much of a challenge, I can find steel pipe here, but again I dont know the inside diameter or the thickness required, all the info online just mentions the length.

Thank you

[Bryan L]

Hello AA,

Do you mean PVC plastic conduit?

3v 5/8 doesn't have a flat base. Maybe look at Kruschke 5/9 for a flat base.

http://www.domerama.com/ has a lot of good info and calculators

1. I have read many times that peoples plans online do not factor in some part of the strut. If I had to guess what it was, I cant really remember, but I think its the part where the pipe is flattened, bent and has a hole put through it. This worries me, can anyone clarify?

The difference is small, not really enough to worry about. Just remember the strut length is measured hole to hole, so you need to add 1.5 or 2" for flattening. To flatten and bend PVC you will have to heat it. There are youtube videos on heating.

1. Is there any good choices for the diameter of the dome that works great with common lengths of pipe? Conduit here seems like the same as it is in the States, 10ft, and I read once that there is a size that works great with this to reduce wastage when cutting the pipe. As my first dome, I would like to do something small such as 12ft in diameter (open to something a bit bigger if it's wiser).

 At 12ft diameter, you will be able to get two struts per 10ft length.

1. I plan to put a tarp over the dome, then fiberglass mesh, then latex cement.  With that said, is there any suggested size for the pipe? Online they always say 3/4" pipe which is available here but its either 1.2mm thick or 2mm thick. The 2mm thick conduit is 3x more expensive than the 1.2mm thick conduit....I was hoping I could get by with 1.2mm thick. Its been hard to find out the thickness of the conduit these people use in the States as they dont mention it. I read one place only and it said 1.6mm.....does that mean I have to go with the 2mm or can I get by with the 1.2mm?

  USA schedule 40 PVC 1/2" is .109" or 2.77mm thick and 3/4" is .113" or 2.87mm thick. 

1. Maybe if the conduit is too much of a challenge, I can find steel pipe here, but again I dont know the inside diameter or the thickness required, all the info online just mentions the length.

Steel pipe is probably going to be more expensive again. 1/2" galvanized steel water pipe should be fine for 12ft diameter.

It all depends on how thick the concrete will be. Will you use resin with the fibreglass? If not, consider chicken wire in the cement.

Bryan

[AA]

Hi Bryan,

Thanks for the info!

> Do you mean PVC plastic conduit?

Nope, I mean steel pipe, as from my understanding, i'll need something strong for highwinds, earthquakes and cement cover.

> 3v 5/8 doesn't have a flat base. Maybe look at Kruschke 5/9 for a flat base.

https://www.ziptiedomes.com/customers/images/davedoucette/dave6.jpg
Isn't this flat? It seems like a 3v 5/8 standard dome (pvc though, but doesnt matter?)

> It all depends on how thick the concrete will be. Will you use resin with the fibreglass? If not, consider chicken wire in the cement.

No, I wasn't planning to do resin. I was planning to do the latex cement plan which recommends fiberglass mesh. https://youtu.be/DkE4_vUflRU The total layers of concrete I plan to do would be 3, scratch coat, brown coat, finish coat.

> Steel pipe is probably going to be more expensive again. 1/2" galvanized steel water pipe should be fine for 12ft diameter.

With what I mentioned above, what pipe dimension do you recommend if I can't get the steel conduit for a good price? The expensive option is 2mm, while the cheaper option is 1.2mm, this is not good as you mentioned the standard thickness people are using in the states is almost 3mm.

[Bryan L]

Hi Bryan,

Thanks for the info!

Your welcome. I am really interested in this. The latex cement with fibreglass is something I have been looking for.

 

> Do you mean PVC plastic conduit?

Nope, I mean steel pipe, as from my understanding, i'll need something strong for highwinds, earthquakes and cement cover.

OK I understand now, thinner steel conduit vs thicker steel construction pipe.

 

> 3v 5/8 doesnenghts't have a flat base. Maybe look at Kruschke 5/9 for a flat base.

https://www.ziptiedomes.com/customers/images/davedoucette/dave6.jpg
Isn't this flat? It seems like a 3v 5/8 standard dome (pvc though, but doesnt matter?)

 It appears flat because their hubs are not rigid and allows hubs to move in and out. I checked the strut lengths from their site and they are Method 1 lengths which wont sit flat with pinned hubs. There are options here, Kruschke being one that has 4 lengths instead of 3.

> It all depends on how thick the concrete will be. Will you use resin with the fibreglass? If not, consider chicken wire in the cement.

No, I wasn't planning to do resin. I was planning to do the latex cement plan which recommends fiberglass mesh. https://youtu.be/DkE4_vUflRU The total layers of concrete I plan to do would be 3, scratch coat, brown coat, finish coat.

 How thick with all coats? Trying to get an idea of weight load.

> Steel pipe is probably going to be more expensive again. 1/2" galvanized steel water pipe should be fine for 12ft diameter.

With what I mentioned above, what pipe dimension do you recommend if I can't get the steel conduit for a good price? The expensive option is 2mm, while the cheaper option is 1.2mm, this is not good as you mentioned the standard thickness people are using in the states is almost 3mm.

Honestly, even PVC supports the weight of a human climbing on it. I think the thinner wall conduit will be fine because the concrete is self supporting to a fair degree. 12ft diameter is not a big dome. I think the 1.2mm conduit should be fine.

My previous reply on thickness was referring to PVC thickness.

All I can suggest is, hang your weight off a piece of the conduit supported at 5 or 6' apart. If it holds you it should hold an inch or two of concrete.

If you are worried about cost, have you thought of bamboo?

Where in Indonesia are you?

Semoga berhasil

[AA]

> Your welcome. I am really interested in this. The latex cement with fibreglass is something I have been looking for.

I am really optimistic about the whole latex cement method!

> It appears flat because their hubs are not rigid and allows hubs to move in and out. I checked the strut lengths from their site and they are Method 1 lengths which wont sit flat with pinned hubs. There are options here, Kruschke being one that has 4 lengths instead of 3.

Meaning the bottom row can be wobbly or it's not fixed?, and you need the Kruschke style for example where it's rigid? I did go to the link you mentioned earlier, http://www.domerama.com/calculators/3v-geodesic-dome-calculator/ and saw "not flat at base" for 3v 5/8 and "flat at base" for Kruschke. So this was a good call, thanks!

> How thick with all coats? Trying to get an idea of weight load.

I wish I knew! My goal is to make a bunch of domes that will connect to each other and will be my home in the end. I am starting with a small dome for starters as it's less riskier than doing a big dome to start with.  All I want is some covering for the dome that can withstand potential troublemakers, heavy rain, earthquakes and highwinds. It doesn't have to be super super strong in my opinion but again...I have no idea what thickness the final concrete will be. I am guessing it won't be really thick, but that is still subjective. If you have any guesses, let me know. By the way, I am referencing this https://www.instructables.com/Latex-Concrete-Roof/

> If you are worried about cost, have you thought of bamboo?

I should clarify. I am not too worried about the cost because I am optimistic that this project will be worth the money spent and be actually better quality than the average (in my opinion...cutting-corners) houses that my people usually do here. I just want to spend my money the best way I could by carefully planning it out (the best I could), save up money for the budget (and some extra for surprises) and stick to that, versus not planning the best I could do and then spend more and more money.

Here is a change...I am thinking I now want to bump it to 16ft in diameter because the height will be more suitable for me, versus the low height that you get with a 12ft wide dome.  

I think I will be successful with finding galvanized steel pipe for a better price and strong quality if I was to go with conduit. Now with that said, here are some estimated prices. 

1. Out of these choices below, do you think there is any that stands out to choose?
2. Also, if the lowest diameter dome I would consider is 14ft, is there a sweet spot number for the dome that I should choose (I am open to whatever, doesnt have to be 16ft) that would work best with the 6m/19.68ft steel pipes, where I would not have extreme wastage when I have to cut them? 

Values converted
* Inside Diameter 

* Thickness 

* Length 

* Price 


Pipa Besi Galvanis 3/4″
2,60 mm
6 m /19.68ft
$14

Pipa Besi Galvanis 1″
3,20 mm
6 m /19.68ft
$21

Pipa Besi Galvanis 1 1/4″
3,20 mm
6 m /19.68ft
$28

Pipa Besi Galvanis 1 1/2″
3,20 mm
6 m /19.68ft
$32

> Where in Indonesia are you? Semoga berhasil

Thank you! It means so much to get help for this project.  I am in Kalimantan. 

[Ashok Mathur]

Dear AA

After having crossed 70 years of age, I have turned philosophical.

Let me share some philosophy with you.

There is a price to be paid for ignorance and it better to be ready to pay for it.

In practical terms it means that some material that you use will turn out to be weak or too strong.

Between a 3/4 inch pipe and 1 inch pipe, the 1 inch pipe already has 33% more material for same thickness of steel . But the inch pipe is always slightly more thicker and cost increase of about 40% per running foot is okay.

My advise to you is two fold.

For your first dome use 3/4 inch pipe with thicker steel inside it.

Secondly tarp is a useless expensive idea. Instead use jute lining with chicken wire mesh to ferro cement the dome.

Here is a link to a dome that  my students built.

https://www.acmathur.me/domes/angled-iron-icosahedron-based-dome

It has a link to ferro-cement and has pictures of ferro cementing being carried out in part with jute and chicken wire mesh.

More links on ferro cementing can be given 

Sent from my iPhone

On 23-Jul-2021, at 8:54 PM, AA <subway...@gmail.com> wrote:



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[Bryan L]

Hi AA,

Meaning the bottom row can be wobbly or it's not fixed?, and you need the Kruschke style for example where it's rigid? I did go to the link you mentioned earlier, http://www.domerama.com/calculators/3v-geodesic-dome-calculator/ and saw "not flat at base" for 3v 5/8 and "flat at base" for Kruschke. So this was a good call, thanks!

Domes are typically designed with uniform radius. If you have an even frequency dome, 2, 4, 6, etc, there is a natural, level, truncation plane at the equator. If you look at the pics of any dome, any other truncation is not level (doesn't sit flat - some hubs lower than others).

The Kruschke method gets around this by placing hubs in successive planes so that truncations other than the equator, still sit flat. It introduces one extra strut length.

If the hubs are not rigid, allowing some change in radius, a 3v 5/8 for example, can appear to sit flat because some hubs move in a bit and some out.

Your method of pinned hubs wont allow that change in radius. Which is a good thing because it makes the structure more strong.

It is possible to design a 5/8 with a flat base, but there are from memory an extra two strut lengths.

I wish I knew! My goal is to make a bunch of domes that will connect to each other and will be my home in the end. I am starting with a small dome for starters as it's less riskier than doing a big dome to start with.  All I want is some covering for the dome that can withstand potential troublemakers, heavy rain, earthquakes and highwinds. It doesn't have to be super super strong in my opinion but again...I have no idea what thickness the final concrete will be. I am guessing it won't be really thick, but that is still subjective. If you have any guesses, let me know. By the way, I am referencing this https://www.instructables.com/Latex-Concrete-Roof/

I read the instructables link. It is not thick, wont be heavy to any degree. No aggregate (small stones). Looks promising. Some degree of flexibility... I saw in the link from your previous post, in Central America, they transported half a small house with the roof intact. No damage, no problems...

Here is a change...I am thinking I now want to bump it to 16ft in diameter because the height will be more suitable for me, versus the low height that you get with a 12ft wide dome.  

I think I will be successful with finding galvanized steel pipe for a better price and strong quality if I was to go with conduit. Now with that said, here are some estimated prices.

3/4" will be fine at that size.

 

I have been playing with some numbers. First, dome strut sizes (called chord factors) have a nice property in that they are directly proportional to the radius. The chord factors are given for a dome of unit (1) radius (doesn't matter whether feet, inches, metres - the numbers are the same). So if you want a radius of 2, multiply the chord factors by 2, etc.

Here are the chord factors and strut counts for a 3v Kruschke at 5 metres diameter, allowing 50mm extra for flatenning the ends.

30 * 0.874266158390934
20 * 1.15264089708268
35 * 1.00572546410081
80 * 1.10372197798304

165 struts for a total of 172.778952175553 metres...

I am going to say that, at 5m (~16ft) diameter, 3v is overkill. You see the struts are close to 1m, rather smallish triangles and a lot of work.

At that size, a 2v (4.96m) would probably be more appropriate.

30 * 1.40540198340685
35 * 1.58272429209974

65 struts for a total of  97.5574097256964 metres. 5 or 6ft struts are typical and with 3/4" pipe,

There wont be a lot of wastage from 6m lengths. You can get 2 of each from one length, but need two more lengths to get the extra 5 * 1.5827. So I count 17 lengths for 2v. But you would need around 30+ lengths for the 3v.

I don't want to put you off, but a tarp will not wrap around a dome without a lot of folding. You will probably have to think about cutting triangles and wrapping, stapling / sewing them around your struts.

[AA]

Bryan

> Domes are typically designed with uniform radius. If you have an even frequency dome, 2, 4, 6, etc, there is a natural, level, truncation plane at the equator. If you look at the pics of any dome, any other truncation is not level (doesn't sit flat - some hubs lower than others). The Kruschke method gets around this by placing hubs in successive planes so that truncations other than the equator, still sit flat. It introduces one extra strut length. If the hubs are not rigid, allowing some change in radius, a 3v 5/8 for example, can appear to sit flat because some hubs move in a bit and some out. Your method of pinned hubs wont allow that change in radius. Which is a good thing because it makes the structure more strong.  It is possible to design a 5/8 with a flat base, but there are from memory an extra two strut lengths.

Thanks for explaining, you saved me a lot of time!

> I read the instructables link. It is not thick, wont be heavy to any degree. No aggregate (small stones). Looks promising. Some degree of flexibility... I saw in the link from your previous post, in Central America, they transported half a small house with the roof intact. No damage, no problems...

This is the reason I am choosing this method over ferrocement, as I think it will be lighter yet as strong or stronger. I can get 1sqm of fiberglass mesh for $1 USD. The latex/bonding part will be a premium but I think it will be worth it, at least to do a test. If its a failure, then ill consider the ferrocement way which seems to be solid just like Ashok has done (thanks for the info Ashok, I checked your link too!)

 

> I have been playing with some numbers....

Again, thank you, saved me a lot of time because I find this part really challenging to figure out and kinda stressful!  Good call on the 2v, I think its a wise choice, easier to setup, more affordable, good for a starter dome, still get good sqm floor area. 

1.  What is a simple way (if im correct) to express the following in English? Since its 2v, its less round and the bottom row is angled inward versus 3v 5/8 where its more round, and better suited  if you are up against the wall, eg. desk or yourself. Im still going to stick to the 2v.

2. What do you think would be a good foundation for the 5m 2v dome? I was thinking, a ring of 1ft wide, 2ft deep concrete with rebar + rocks + cement + sand. 

> I don't want to put you off, but a tarp will not wrap around a dome without a lot of folding. You will probably have to think about cutting triangles and wrapping, stapling / sewing them around your struts.

Regarding the tarp, which you and Ashok touched on, I was thinking to use it based off Instructable's page saying "Something we have started doing, which we would highly recommend, is putting a vinyl tarp on top of the frame, and then the fabric. Not only does this make less mess when applying the latex concrete, it also provides a waterproofing backup, should a hairline crack appear."

Note, I dont mind the "mess" as in if the late concrete hits the ground or gets on struts (I could clean/sand it off the struts im guessing if I dont want to clean it), and as far as the waterproof backup, that does sound nice, but maybe not needed or less concern if I already plan to put liquid rubber as the final outside coat. Maybe that doesnt even help re: possibility of cracks but just being a nice waterproof coat....

When you say "a lot of folding" does that mean making the tarp flat on all of the triangle facets?

3. Do you think I should just skip the tarp?

4. What option(s) do you suggest for finishing the inside of the dome?

[AA]

Forgot to add about the tarp, yes it sounds like it will be troublesome getting in place, I was thinking maybe epoxy on the struts to make it bond to the facet and be in place, but if you think I can just skip it, ill save the money and time!

[Ashok Mathur]

What finishing options inside a dome?

Domes produce uneven unexpected echoes!

Smooth walls amplify this.

So my advise is that you make rough surfaces that do not produce a regular echo.

I hope others will add to this.

Regards

Ashok

Sent from my iPhone

On 26-Jul-2021, at 10:24 AM, AA <subway...@gmail.com> wrote:

Forgot to add about the tarp, yes it sounds like it will be troublesome getting in place, I was thinking maybe epoxy on the struts to make it bond to the facet and be in place, but if you think I can just skip it, ill save the money and time!

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[Bryan L]

AA,

> I read the instructables link. It is not thick, wont be heavy to any degree. No aggregate (small stones). Looks promising. Some degree of flexibility... I saw in the link from your previous post, in Central America, they transported half a small house with the roof intact. No damage, no problems...

This is the reason I am choosing this method over ferrocement, as I think it will be lighter yet as strong or stronger. I can get 1sqm of fiberglass mesh for $1 USD. The latex/bonding part will be a premium but I think it will be worth it, at least to do a test. If its a failure, then ill consider the ferrocement way which seems to be solid just like Ashok has done (thanks for the info Ashok, I checked your link too!)

I have no idea about it's strength. Just that it is obviously strong enough to self support and withstand some movement. You could always make a section as a trial, so you can get a feel for it. E.g, is it strong enough to walk on.

1.  What is a simple way (if im correct) to express the following in English? Since its 2v, its less round and the bottom row is angled inward versus 3v 5/8 where its more round, and better suited  if you are up against the wall, eg. desk or yourself. Im still going to stick to the 2v.

 Yes the 2v has only 10 struts at the bottom vs 15 for 3v. So it is less "round" in floor plan.

The 3v lower ring of triangles actually angle out a little so there will be more usable space close to the walls. You will have something less than 20m^2 floor area.

2. What do you think would be a good foundation for the 5m 2v dome? I was thinking, a ring of 1ft wide, 2ft deep concrete with rebar + rocks + cement + sand.

 I would think 300mm deep x 150mm wide would be enough from a weight point of view. Domes don't "catch" anywhere near as much wind as vertical walls. 300 * 150 will have about 0.7m^3, which is, if I'm correct, more than 1.5 metric tonnes. I am not sure what wind would be required to lift that. An engineer would know. Do you get typhoons there?

From an earthquake point of view, it gets down to soil type. Anything will sink in sandy / silty soil. Would it crack and deform under movement? With rebar and appropriate stones, it will be pretty strong. That is another one for an engineer. Maybe 450 * 225mm.

This is an area where the dome is superior to traditional structures. The dome is an integral, self supporting structure and resists collapse. Whereas timber frame needs a lot of bracing to resist earthquakes and masonry just collapses.

Regarding the tarp, which you and Ashok touched on, I was thinking to use it based off Instructable's page saying "Something we have started doing, which we would highly recommend, is putting a vinyl tarp on top of the frame, and then the fabric. Not only does this make less mess when applying the latex concrete, it also provides a waterproofing backup, should a hairline crack appear."

Note, I dont mind the "mess" as in if the late concrete hits the ground or gets on struts (I could clean/sand it off the struts im guessing if I dont want to clean it), and as far as the waterproof backup, that does sound nice, but maybe not needed or less concern if I already plan to put liquid rubber as the final outside coat. Maybe that doesnt even help re: possibility of cracks but just being a nice waterproof coat....

When you say "a lot of folding" does that mean making the tarp flat on all of the triangle facets?

3. Do you think I should just skip the tarp?

 Wrap a towel around a ball. What happens? There are lost of folds. Maybe many smaller tarps would suffice, but I think something to support your mesh while you apply the concrete.

I noticed on the instructables link they mentioned other mesh types. They suggested 80% shade cloth. Probably a lot cheaper than fibreglass.

4. What option(s) do you suggest for finishing the inside of the dome?

 

Anything you like that is not too hard to attach to the pipe. In the tropics, I think of things like bamboo slats.

One thing about round pipe as the structure, it is not so easy to attach things to it. Whether pre-drilling or using self tapping screws, they want to run off. You can make triangles of your material and attach individually.

I have a plan to use steel house frame studs as a frame. I believe can even get them cut / formed to length. The machine just spits them out from a cut list.

Bryan

[Ashok Mathur]

Dear AA

Some what in  a minority of one in the geodesic help group, I have been consistently saying that the standard tool for measuring strength, Finite Element Analysis, has fatal flaws when it comes to measuring the strength of a dome because a dome behaves very differently from FEA assumptions.

See this link for my arguments

https://acmathur.me/domes/does-finite-element-analysis-need-improvement

Regards

Ashok

 

Sent from my iPhone

On 27-Jul-2021, at 7:45 AM, Bryan L <bhla...@gmail.com> wrote:



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[Bryan L]

One thing about round pipe as the structure, it is not so easy to attach things to it. Whether pre-drilling or using self tapping screws, they want to run off. You can make triangles of your material and attach individually.

I don't mean to put you off building it. If you are handy with power tools it wont be a problem...

[Ashok Mathur]

Consider using a hollow square tube of roughly the same diameter.

It will be slightly more expansive and in some sense, slightly less weak.

But rest of making the dome will be convenient.

Regards

Ashok

Sent from my iPhone

On 30-Jul-2021, at 10:52 AM, Bryan L <bhla...@gmail.com> wrote:



One thing about round pipe as the structure, it is not so easy to attach things to it. Whether pre-drilling or using self tapping screws, they want to run off. You can make triangles of your material and attach individually.

I don't mean to put you off building it. If you are handy with power tools it wont be a problem...

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[Travelling Telescope]

 Hi AA,

As you are in Indonesia you could - if you are interested in a cheaper option - try bamboo. I've just finished a 10 meter 3/5 Krushke  (flat base) dome made entirely from bamboo and rope. 2 tools I found crucial are a good hole saw or 2 and a quality mitre saw. Can advise if interested. 

All the best

Chu

To view this discussion on the web visit https://groups.google.com/d/msgid/geodesichelp/DF7EF1C7-EC6B-4972-8922-05BC9FF17A8A%40gmail.com.

[Ashok Mathur]

Dear AA

You should try a bamboo dome but as your second dome.

The anxiety in your mind by using bamboo at the first attempt at a dome may cause “ unforced errors” as tennis calls it.

There is a full sequence of bamboo dome building on the link already sent by me.

Regards

Ashok

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On 30-Jul-2021, at 4:51 PM, Travelling Telescope <daniel...@gmail.com> wrote:



To view this discussion on the web visit https://groups.google.com/d/msgid/geodesichelp/CAApebLzR4o81zG9gTymq67xRs2PCshtesZBqg6Qa4UbyW2kdDQ%40mail.gmail.com.

<20210311_175746.jpg>

[AA]

@Chu and Ashok

The bamboo is a good idea, thank you.  Im saving this for one of the domes after my first one (Ashok, I saw you already suggested this)

@Bryan

Thanks for all the tips!

@everyone

1.  I think I will skip the tarp.  I found another seller of fiberglass mesh, for .60 cents sqm, and shade cloth for 0.35 cents sqm. I think im going to stick with the fiberglass mesh especially since I found a cheaper rate than before.  I wonder how much mesh I would waste if I was to cut it to fit triangle facets, and fasten the mesh with zip ties to stay in place and maybe it will prevent sagging inside the triangle facet. Got a better idea? I think I can compromise on the wastage.

2.  When I mentioned finishing the inside of the dome, I meant I dont mind if the struts are exposed.  I am guessing I could just do 1 layer of cement on the inside. What do you think?

3.  Ashok mentioned square tubing. I have that available here. I like how it will be flat, but my concerns are I dont know example types to get (width/thickness), and will the ends flatten the same way?

[Ashok Mathur]

If you imagine a square and place an equilateral triangle inside it, you ware 50% of the tarp.

So expect 40% to 50 % waste if you were to cut individual  triangles.
If you to cut three side by side triangles together, the wasteage would  about 33%.

If you cut five of them together, which is possible, wasteage would be 20%.

At step 1 if you join together the cutout pieces, you could get away with just the wastage of the overlap.

Regards

Ashok

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On 04-Aug-2021, at 11:55 AM, AA <subway...@gmail.com> wrote:

@Chu and Ashok

To view this discussion on the web visit https://groups.google.com/d/msgid/geodesichelp/fbc7495f-4d9a-41f3-ba5f-5dea9eed0416n%40googlegroups.com.

[Ashok Mathur]

A simple experiment will show the way as to how to choose a entire conduit vs square pipe.

Buy waste lengths of about 3 to 4 feet of each of them of nearly same cross- sections say 3/4 inche each.

Load the pipe in the middle of its length till it bends.

Try the same weight with the square pipe.

Regards

Ashok

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On 04-Aug-2021, at 5:35 PM, Ashok Mathur <ashokch...@gmail.com> wrote:

If you imagine a square and place an equilateral triangle inside it, you ware 50% of the tarp.

[Levente Likhanecz]

hi AA,
i donno, if you can insert a flatbar into the end of hollow square
tubing, like the attached pic.
just cut into the hollow square with angle grinder, then weld a flatbar into it.
then not much headache of flattening/bending to angle, drill the hole.
structural strength i donno of this solution, but use at least same
thickness of flat bar, as the wall thickness of hollow square twice.
(same meat)
or can consider diagonal insert of flat bar.

[Levente Likhanecz]

hi AA,

i played with the idea of squre hollow strutting some further.
i guess the attached square2.png require less angle grinding/cutting.
and square3.png i closed the end of hollow square (iguess it
strengthens the strut and avoid corroding.

cheers, lev

[Rotozon dot com Pabaithai dot com]

Dear Sir:

As you mention 1.5-2.0  inch for flaten  

My qqestion is it for one side so   two sides need to time two

Thanks

Somchai Pimachon

bhla...@gmail.com

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Jul 23, 2021, 11:07:57 AM

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to Geodesic Help Group

Hello AA,

Do you mean PVC plastic conduit?

3v 5/8 doesn't have a flat base. Maybe look at Kruschke 5/9 for a flat base.

http://www.domerama.com/ has a lot of good info and calculators

1. I have read many times that peoples plans online do not factor in some part of the strut. If I had to guess what it was, I cant really remember, but I think its the part where the pipe is flattened, bent and has a hole put through it. This worries me, can anyone clarify?

The difference is small, not really enough to worry about. Just remember the strut length is measured hole to hole, so you need to add 1.5 or 2" for flattening. To flatten and bend PVC you will have to heat it. There are youtube videos on heating