Aligned bases with different sub divisions

[Ashok Mathur]

Dear Dave,

I just wish to share a link where you will get calculations for almost
all the frequencies and classes that you wish to use.

If you check a button, the calculations will be redone with aligned bases.

You can choose 3/8 or 5/8 truncations.

http://acidome.ru/lab/calc/#Align_5/8_Mexican_Piped_D102_4V_R4.2_beams_100x100

Another site allows you to minimise the strut numbers for the class
and division that you have chosen:
http://simplydifferently.org/

--
Ashok

[Ashok Mathur]

Dear Dave,

From the correspondence, it is clear that you have come a long way to
finalize the plan for the two car geodesic structure that you want to
build.

Allow me to divert you for a few minutes with an alternate thought
which is not based on an icosahedron but is based on octagon.

My understanding is that the key requirement is that the structure
should have a 16 foot by 7 foot opening for installing the garage
door.

In what follows, I am not aiming for accuracy or precision but for
ease of explaining/ understanding.

Why an icosahedron based dome is not very suitable.
1. Assume that the radius of the floor plan is the same as the radius
of the dome, though it is about 0.95 of it.
2. Assume that the door width is 16 ft or X ft.
3.If you are making a single frequency dome , you will have five
struts at the base whose total length will approximate the
circumference of a circle with dome radius i.e 2*pie*R.
Each strut will be one fifth of it.

4. If you are making a N frequency dome you will have 5*N struts at the base.
Each strut will be ( 2*pie*R)/(5*N) long.

5 Suppose you are using a 12 ft radius dome with five frequency
sub-division then each of 12*5 = 60 strut will be 2*3.14*12/60 = 1.25
feet long.

6. Your 16 foot door will violate (physically displace violently)
16/1.25 = 13 struts at its base. on one side. It will displace a
similar number ( may be 1 or 2 more or less) on the other side of the
dome.
7. As you go up the dome, the number of struts that will be violated,
will keep coming down.
8. Overall, your structure loses its strengths as you displace the struts.

Why I am proposing the octahedron base.
1. In an octahedron base with same radius and frequency, the number of
struts at the floor level will be 25% less than the icosahedron.The
number will be 4*N rather than 5*N.
2 Thus you will displace 25% fewer struts.
3. I am aware that octahedron at the same frequency is less spherical
than an icosahedron.
For comparable smoothness, you have to go up in frequency.
4.If that is so , for most structures, icosahedron are a better choice.
5. However, Octahedron give you a choice that icosahedron do not give.
6. Because of four fold symmetry inherent in the Octahedron, you can
take two vertically partial octahedrons and hang straight connections
between them to give you a rectangular opening with least displacement
of struts.

Links to 2 sites

A One of the best sites on Oct domes is
http://www.gardendome.com/octa_dome_types.html
Under para 3 "The Edge Zenith" you will have four images. If you look
at the bottom right hand image, you can visualize, how easy i would be
to separate the dome in two halves and hang straight rods to
accommodate a garage door.

B John Zerning has done wonderful work that you can see at
http://www.johnzerning.com/category/ellipsoid/

I wish you best of luck in whatever path you choose to follow.


--
Ashok

[Gerry in Quebec]

Dave, Ashok & others,

More grist for the design mill.... Here's an ellipsoidal layout more or less along the lines Ashok was suggesting -- though it looks more like half an Easter egg than a traditional native North American longhouse! It incorporates elements of octahedral symmetry, but if you look closely you'll see it's not simply a projection of the octahedron. It has 188 triangles. Two jpgs attached.

Cheers,

- Gerry in Quebec

[Ashok Mathur]

Dear Gerry,
Wow!
That was fast.

I am wondering if Dave would have the length that you have calculated
for the garage.
Its far more than the normal driveway length.

Is it possible for you to redo the calculations assuming that the
length of the major axis is only 30 feet while the minor axis remains
the same.

This would only mean assuming a different ( sharper) eccentricity ratio.

Thanks and Regards
Ashok

On 4/14/14, geodes...@googlegroups.com <geodes...@googlegroups.com> wrote:
> =============================================================================
> Today's topic summary
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> Group: geodes...@googlegroups.com
> Url: http://groups.google.com/group/geodesichelp/topics
>
> - Aligned bases with different sub divisions [2 Updates]
> http://groups.google.com/group/geodesichelp/t/ee3fa2a1b1f9c798
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>
> =============================================================================
> Topic: Aligned bases with different sub divisions
> Url: http://groups.google.com/group/geodesichelp/t/ee3fa2a1b1f9c798
> =============================================================================
>
> ---------- 1 of 2 ----------
> From: Ashok Mathur <ashokch...@gmail.com>
> Date: Apr 13 11:45AM +0530
> Url: http://groups.google.com/group/geodesichelp/msg/a7316eb3f1cd9648

> ---------- 2 of 2 ----------
> From: Gerry in Quebec <toomey...@gmail.com>
> Date: Apr 13 08:50AM -0700
> Url: http://groups.google.com/group/geodesichelp/msg/5d9dc360cb926fa

>
> Dave, Ashok & others,
> More grist for the design mill.... Here's an ellipsoidal layout more
> or less along the lines Ashok was suggesting -- though it looks more like
> half an Easter egg than a traditional native North American longhouse! It
> incorporates elements of octahedral symmetry, but if you look closely
> you'll see it's not simply a projection of the octahedron. It has 188
> triangles. Two jpgs attached.
> Cheers,
> - Gerry in Quebec
>
> On Sunday, April 13, 2014 2:15:21 AM UTC-4, Ashok Mathur wrote:
>
>
>
>
>

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--
Ashok

[Gerry in Quebec]

Hi Ashok,

With a minor axis of 29.034 ft and, as you suggest, a major axis of only 30 ft instead of 46 ft 12 in, the footprint would be nearly circular instead of strongly elliptical. It might also be difficult to install a 16 ft wide door. Dave's design sets the garage length (major axis) at 41 ft. 3".

Cheers,

- Gerry in Quebec

[dave...@gmail.com]

Hi:
Didn't realize this post was addressing my questions.  Did try this model which seems better, however I get lost in the technical terms of Geodesic design.  Is this what your talking about?
This was my second option see attached.  (Didn't know you cannot post print screen images. Sorry!)

Thanks again Gerry and Ashok.
Dave Seigworth

[Gerry in Quebec]

Here are three more examples of triangular layouts that combine octahedral and lesser-circle geometry to form an oblong dome. The octahedral end sections are 5v, Mexican method. Two jpgs are attached.

- Gerry in Quebec

[David Seigworth]

Thanks Gerry:

You are working very hard on my questions and both of these design are wonderful and would like to use attachment with the 5v and even footprint.  The basis first hurdle still seems to be the reaction from the P.E.'s I have contacted. 

Example:
"If these buildings are to be permanent structures, they must comply with a number of load combinations required by the Building Code.  Load testing for all of them is time consuming and expensive.  Usually only universities have the equipment and funding to do them all.

As for breakdowns, there is a law of diminishing returns for increased breakdown divisions.  Higher breakdowns = more different member lengths and cutting angles.  Also too many breakdowns begin to weaken the entire system.

If this project is to be a house and garage for your own use, may I suggest that the path of least resistance for you is to purchase plans for a kit, then build it yourself.  Then enjoy the journey."

I am still unable to get a certificate (or whatever it is called) to present to the County Building Permit authorities.

Dave Seigworth

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[Ashok Mathur]

Dear All,

I thank Dave for adding to my literature on evaluating the strengths
of geodesic domes.

I am not in agreement with the article, and, in particular, using
Finite Element Analysis, to evaluate the strengths of Geodesic domes.

This is because geodesic domes are by definition not a structure but
are machines.

A structure is rigid and has no parts that move relative to other parts.

A machine has parts that move relative to each other.

As we all know geodesic dome , is by design,never at rest, but always
rotates about each hub.

Under pressure, the dome reacts by twisting inward such that the
radius of the dome is reduced.

Lastly, when a pressure is applied at a point on the dome, it reacts
as a whole all over the dome and not only at points near the point of
application.

Thus FEA is not really applicable to geodesic dome analysis.

So far I have seen Domerama host a report on the application of FEA to a dome.

The findings are that the strength of a strut are its strengths when
viewed as an isolated piece, and similarly the strengths of a hub are
its strengths when viewed as an isolated piece.
That is the analysis shows no synergy is present in the dome.

But Geodesic Maths and how to use it suggests very strongly that a
dome has synergy of factor of 500.

I would like a breaking strength test to be carried out on a dome to
see whether the FEA analysis is an accurate predictor of the strength
of a dome built using the same materials that were used in the
analysis.

The Domerama article does not indicate if any comparison between
actual and predicted was ever carried out.

Similarly, Mark Kubik never carried out this comparison but has left
behind a FEA tool that can be run on Excel.

I think what is needed is to find out ways by which FEA can be
modified to model the structure and machine aspects of the geodesic
dome accurately.

FEA analysis is costly and becomes more costly when you want to
evaluate two or more different models of geodesic domes that meet most
of your criteria.
This is the case with Dave right now.

Can we evolve some rules of thumb, where using capabilities limited to
simple excel sheets, relative strengths of different mode;ls can be
compared to a reasonable degree?


--
Ashok

[David Seigworth]

Wow!  Needed to read this 3 times. 

Thanks Askok

[David Seigworth]

Hi Ashok:

I believe I heard somewhere that Good Karma Domes had extensive testing done on there 4v domes.  Don't know if they note that on their website, but I will look again.

I did have another article from UK on a low profile dome set of plans, they mention putting a center post in the center for support.

Sorry for the mistake on your name.  Thanks for all your advice, keep up the conversation with everyone helping, we find a method, that will help everyone. 

Dave Seigworth