Kruschke method to level 5V dome (calculator)

[Circoluzion Ong]

Dear all

First of all, hello to everyone! My name is Christian from Peru; we are an ONG (www.circoluzion.org) in environmental education and have quiet some experience in constructing 4V domes (although always based on the existing online calculators…thank you for everybody that helped to develop them!!).

However, we were asked to build a 7m radius 5V 4/9 (or 7/15) dome. Honestly, I have no experience on the fact that you have to cut either at 7/15 or 8/15. So I was wondering if someone knows of a calculator for 5V but with the Kruschke method to make it flat (on domerama.com I came along a 3V calculators with Kruschke method).

On the other hand I was asking myself how uneven a "normal" 7/15 5V dome would be...does it really make a huge difference? If there is no possibility to include the Kruschke method in 5V domes….does anybody has an idea how I would have to adapt the base struts in order to get it flat.

I would really appreciate to hear from you guys soon.

Best wishes & abrazos desde Peru

Chris

[Ashok Mathur]

Dear Chris,

I think all your answers on simplydifferent site:

https://simplydifferently.org/Geodesic_Dome_Notes?page=4#5V 7/15 Icosahedron Dome

8/15 is also covered.

Similar domes with levealized base and optimized number of struts are also covered.

Become familiar with the sites way of naming dome variations first.

If you can not find what you want, let me know as right now  m travelling.

Regards

Ashok

[Ashok Mathur]

Dear Chris,

I am enclosing a single sheet containing data from the two sites, first, simplydifferent and secondly from Dome Calculator.

At the bottom of the two data set, is a small comparative table that should show that the data from simplydifferent has been optimised in some way. The number of struts vary tremendously after the first two rows of triangles.

I suspect that it has been made with  flat base and optimised for length variation.

Regards

Ashok 

Regards

Ashok

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[Ashok Mathur]

Dear Chris,

I hope this 3rd email from in a short time does not irritate you.

From your original email the impression that I get is that you want to design a big dome.

If so I would like to draw your attention an old thread in this group regarding an usual truncation of a dome called shallow iscoa cap.

The link starts from here

https://groups.google.com/forum/?hl=en#!searchin/geodesichelp/shallow$20cap/geodesichelp/KGNXxvrkdfg/pKoLIRbHe8QJ

In brief if you take into account only the cost of struts and the sheathing of the dome surface, then compared to 7/15th or 8/15th version, a shallow cap saves about 40 % of that cost.

Because the struts and sheathing are lighter, it is economical to expand some of the savings into building a 7foot riser wall.

See Gerry's spread sheet for details.

Regards

Ashok

Regards

Ashok

On Fri, Jul 31, 2015 at 11:29 AM, Ashok Mathur <ashokch...@gmail.com> wrote:

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[Gerry in Quebec]

Hola Chris,
If you use the Google search function, concentrating it on this
geodesic discussion group, you may find exactly what you are looking
for. There are several 5v icosa (class I) layouts that might be
suitable for your needs. The most comprehensive 5v icosa "truncatable"
(Kruschke-type) design I know of (level base at various truncations
above and below the equator) is the one by Bucky Fuller and Shoji
Sadao at Southern Illinois University, Edwardsville Campus. It's the
University's spiritual centre.

I am on a super-slow dial-up Internet connection for a few days, so
communication is difficult (and precious). Maybe others here can give
you details sooner.

- Gerry Toomey, Quebec, Canada

[TaffGoch]

Christian,

Here's a 3D SketchUp model that I produced a couple of years ago, depicting Kruschke subdivision, frequencies 3v, 4v, 5v & 6v.  Radius of each sphere is 1.0 (unity.) You can scale it, in SketchUp, to any radius/diameter you need, by using the "Tape Measure" tool. (Don't use the scale tool, as it is not numerically accurate, in most cases.)

(I don't recall having shared this model before, therefore, other readers might want take note, and save the model file for their potential future use, if needed.)

-Taff

[Circoluzion Ong]

Dear all

Thank you very much for all your answers & documents. I will go through them and get back to you.

Anytime you come along Peru, please let me know to invite you to stay at my place.

Have a good day!

Chris 

[Gerry in Quebec]

 

 

A footnote to Taff's SketchUp models.... Like the Mexican method, the Fuller-Kruschke "truncatable" method for class I domes begins to break down (stray from symmetry?) at frequency 6. In Taff's model of the Kruschke spheroids, some of the strut paths of the 6v -- the ones running through the pentagon edges --  follow neither lesser circles nor great circles. See the attached jpg, based on Taff's model of the 6v. So, at the 7/18 and 11/18 truncations, the 6v dome does NOT sit exactly flat. But at the three intermediate truncations -- 8/18, 9/18 and 10/18 -- it does sit flat. While it's possible to tweak the numbers to make the dome sit flat at 7/18 and 11/18, without undermining overall icosa symmetry, this would eliminate the level-base feature at other truncations.

- Gerry

[Circoluzion Ong]

Dear Ashok

Thank you very much for your help. Please note that the struts from "simplydifferently" and "Desert Dome" are the same…they only have a different assembly diagram!

Safe travels

Chris

[Circoluzion Ong]

Dear Taffgoch

I can't thank you enough for the document you posted…on the other hand it resulted in a few more questions I still haven't found an answer to:

For example, dome 4V:

If I compare the lengths of the struts that I get from the online calculators (in this case I used Domerama, Desert Dome & Simplidifferently) I get other lenghts than when I measure the struts in your model. How can I adapt your model to the lengths I get from the calculators?

Also I was using the 3DS Max where the same program draws you a geodesic sphere (you can choose the frecuencies) based on the icosaedric symmetry and all the struts again had a different length.

How comes? (sorry, I am just getting into it & these are probably some beginner questions)

I would really appreciate you could give me an explanation. The positive thing is that I work with flexible unions, therefore I can build my domes based on any lengths the different calculators give me without having to take into account the angles.

Analyzing your models I am tempted to apply the 6V model and cut it at 8/18 as pointed out also Gerry.

Also, I would be greatly thankful if by any chance you would share also models of further frecuencies (7V, 8V, 9V, …..) in order to analyze if it wouldn't be better to apply higher frecuencies because I am using wooden struts with a diameter of 3cm.

To everybody: Do you have any experience on building 15 to 18 meters (diameter) domes with wooden struts. What is the máximum length you would recommend in order that the struts dont break? (I am using 3 cm diameter struts)

Again, thank you for everything!

Hope to hear from you (or anyone) soon.

Greetings from Peru

Chris

[Circoluzion Ong]

Dear Gerry

Thank you very much for your observations…they drove me to the idea to apply a 6V dome and cut it at 8/18 (it allows to make a big circle without getting too high).

Do you have any experience of constructing big domes with wood? I would really appreciate to have an interchange on that since I am not sure how long I can make my struts (my unions allow a diameter of 3cm).

Please let me know if you have some information.

Best regards

Chris 

[Ashok Mathur]

Dear Chris,

The book " Geodesic Maths and how to use it" by Hugh Kenner has a discussion on this topic.

It defines a slenderness ratio for a strut which is its length divided by its diameter.

Though the book is available for reading online, I will just go by memory that the ratio is about 20 for wood.

That means the longest strut you can have would be 60 inches for a diameter of 3 inches.

Regards

Ashok

Regards

Ashok

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[Gerry in Quebec]

Hi Ashok,

A few points about the 5v icosa Dome Calculator on the Desert Domes website and the counterpart calculator at the Simply Differently website:

 

 -- Both calculators use class I, method 1 geometry.

 -- Simply Differently uses more precise chord factors for its calculations than does Desert Domes.

 -- Both calculators give the same strut lengths and numbers of struts (organized by strut length). This is true for both the 7/15 and 8/15 truncations. (Desert Domes calls these truncations 3/8 and 5/8.) The differing numbers in the table you posted have to do with the fact that, for the Desert Domes calculator, the listed strut counts pertain to the 5/8 (8/15) version of the dome, while, for the Simply Differently calculator, the numbers pertain to the 3/8 (7/15) dome.

 -- The 5v dome layouts from these calculators do not yield a level base at either the 7/15 or 8/15 truncations. (No optimization involved here.)

-- The two calculators use different letter-labels for the various strut lengths.

- Gerry in muggy Quebec

[Gerry in Quebec]

Hello Chris,

The maximum safe strut length depends on many factors and, at a dome diameter of 15 to 18 meters, I'd recommend submitting your plan to an engineer for structural analysis, especially if the dome is to be used as a residence, office or public building. Factors that could or do determine strut length include wind load, seismic risk, wood species and grade used for struts, cross-sectional area of struts, hub design and composition (e.g., steel, aluminum, wood, plastic), spherical profile (e.g., 7/15 versus 8/15 truncation), the use of in-triangle blocking, type of paneling/sheathing) and method of attachment.

 

I've worked on a few large-dome projects, mostly on the design side (calculations). In all but one case, structural engineers were involved. Here's a link to images of a 15.5 meter dome in Vermont, made with wood struts. (The photos were taken a few years ago, at the start of construction. The building is now finished.) There are two dome frames, one inside the other, connected by wood gussets. The owner-builders used the services of a structural engineering company and an architect.

 

https://groups.google.com/forum/#!searchin/geodesichelp/vERMONT/geodesichelp/Gg32ZLBCpAk/cwGL4fp3k00J

 

If you were to use a flat-based 6v icosa design for, say, a 9/18 (hemispheric) dome 18 meters in diameter, your longest strut length would be 2 meters. You mentioned that your struts have a diameter of only 3 cm. Are they bamboo poles or solid wood? In either case, this is probably not strong enough to build that type of dome.

 

If you post more details of the dome size, intended use, and materials you plan to use, maybe members of this group, myself included, can provide specific suggestions and dimensional information (e.g., lengths and angles).

 

- Gerry in Quebec

[Ashok Mathur]

Dear Gerry

Thanks for pointing out that I was mistaken.

Regards

Ashok

Regards

Ashok

[Gerry in Quebec]

You are most welcome, my friend. And I hope you will reciprocate when my turn comes :-)

[kbs...@gmail.com]

Dear Taffgoch,

Could you please do a tutorial about the "Method-Krushke"? I've found your 3v and 4v models and this one as well, which were very helpful, but I would like to know how to draw them in Sketchup and to be able to draw some higher fequency geodesic dome with the same method. So please, when you have some time, make a tutorial similair to your "Geodesic_dome_construct.skp". That one is perfectly detailed and very helpful.

Thank you in advance.

kbsztk