60 Meter Diameter Large Geodesic Dome

[Hesham Elfeshawy]

Hello,

I am planning to build a 60-meter diameter large geodesic dome for parties, events, or exhibitions. Actually, I cannot select aluminum for the pipes as it's very expensive, so I am considering going with iron pipes. I need your guidance and advice.

Thank You.

[Ashok Mathur]

Dear Hesham,

I am pleased to hear about your desire to build a dome of 60 meter diameter for events to be held under it.

As this dome would be under public scrutiny and there would a penalty ot be paid for any collapse or other failures, start with thinking about safety.

THe best way to impart safety to such a large dome would be to make two parallel interconnected domes. One dome would have a slightly smaller radius than the other.

Regards

Ashok

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[Hesham Elfeshawy]

Dear Ashok,

Thank you for your guidance and innovative suggestion regarding the construction of a dual dome structure for enhanced safety. However, I must share my concerns regarding the project’s budget and feasibility. The idea of building two interconnected domes, while undoubtedly beneficial for safety and stability, would significantly increase the project’s complexity and cost, which is a critical consideration for us.

Given the constraints, I’m exploring alternative solutions that would allow us to maintain the structural integrity and safety of the dome without duplicating the structure, as the budget cannot accommodate the expense of constructing two domes. I am particularly focused on material choices and engineering solutions that could compensate for the inherent limitations of iron pipes, which we are considering as a more cost-effective alternative to aluminum.

Could you possibly advise on any specific treatments, reinforcements, or design modifications that might enhance the safety and durability of an iron pipe-constructed dome? Any insights into cost-effective yet safe construction practices for large-scale domes would be immensely valuable at this stage.

Thank you once again for your understanding and support. I look forward to your expert advice on navigating these challenges.

Best regards,

Regards

Hesham El Feshawy

Sent from my iPhone

[Ashok Mathur]

Dear Hesham

Then let us begin at another end.

What is the longest strut you can safely live with?

Once that is answered, what frequency dome get you struts with that and smaller struts?

In such dome, how many hubs have a defect angle near zero or about 6 degrees?

Regards

Ashok

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On 26-Feb-2024, at 1:50 PM, Hesham Elfeshawy <shu...@gmail.com> wrote:



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[Ashok Mathur]

Dear Hesham

You may already know and appreciate the fact that shallow hubs in a dome can suddenly invert. This is not an anomaly, but a reality that geodesic structures have two resting points (equilibrium points ) for their vertices and shallow hubs under high tension, switch between the two resting points.

Geodesic structures are not rigid but vibrate around midpoint.

Hence, my concern to ask how many shallow hubs are likely to exist at the frequency you are working with?

Regards

Ashok

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On 26-Feb-2024, at 2:42 PM, Ashok Mathur <ashokch...@gmail.com> wrote:

Dear Hesham

[Ashok Mathur]

Dear Hesham 

I cannot always be negative in my thinking.

There is a site https://acidome.com/lab/calc/#1/2_GoodKarma_10V_R60_beams_120x40

which provides ready calculators at higher frequencies.

I went there and looked at a 10 frequency Dome of 60 m radius. Struts will be between 5 m to 7 m long and the angle will be between 3° to 5°.

Can you live with this?

Ashok

Sent from my iPhone

[Eric Marceau]

Hi Ashok,

Correct me if I am wrong, but with your earlier reference to a dual-shell structure, did you intend to imply that a single-shell structure would tend to dictate excessive strut weight, because of the need for the greater sectional stiffness required to provide the required vibrational stability needed to prevent "hub pop" resulting from wind-generated, audio, or pedestrian-induced harmonics?

Also, I have no direct experience with the construction/design of domes, but could such "hub pop" events lead to a potential structural collapse?

Is that why the inter-linked, dual-shell (a.k.a octet space frame) is the preferred approach on the larger structures; namely, to ensure dynamic integrity of the geometry of the structure?

Most cases I've seen show the inner and outer shells having the same size of strut, but this reference (see image at bottom)

https://technologystudent.com/struct1/monospace2.html

seems to suggest that there are designs out there that are non-homogeneous, meaning that the inner shell need not be as "hefty" as the outer shell, but provides that necessary "radial" stability to prevent the "hub pops".

Have I correctly understood the issue?  I would appreciate your feedback.

Eric

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[Eric Marceau]

Hello Hesham,

By the way, for comparison, the Expo 67 Geodesic Dome (U.S. Pavilion) was a Class I with a 76 m diameter.

That is only 25% larger than the dome that you have contemplated designing and building.

That fact should lead one to conclude that the two domes fall into the same "ballpark".  Furthermore, I think that, if Fuller thought best to use the dual-sphere configuration, rather than the single-sphere, there would have been some rather compelling reasons to do so.

I would suggest that the above historical reference point ought bring you to pause, and reflect, on whether the single-sphere configuration is the wisest path to pursue.  If, however, you can get the numbers to show your single-sphere approach is sound, and safe, go for it!

Food for thought!

Handy reference (nice photos of structural details):

https://www.archdaily.com/572135/ad-classics-montreal-biosphere-buckminster-fuller

Eric

[Ashok Mathur]

Dear Hesham

Your first paragraph has too many technical terms for me to wrestle with.

But simply dual domes give rigidness and stability.

Both domes can be identical with only a slight difference in radius. That simple appproach has a lot of waste.

The other approach is to use a different type of dome for the inner dome.

Regards

Ashok

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On 27-Feb-2024, at 6:39 AM, Eric Marceau <eajma...@gmail.com> wrote:



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[Ashok Mathur]

Dear Eric

I did not realise until after that the reply is from you and not Hesham.

Subject to corrections, the strut weight or length have very little to do with a hub popping. 

That depends almost entirely on the shallowness of the hub. In terms of Dick, it’s the deficit angle at the hub that determines the probability of popping.

Sorry for the mistake made earlier.

Regards

Ashok

Sent from my iPhone

[Hesham Elfeshawy]

Dear Ashok and Eric,

Thank you both for your invaluable insights and contributions to the ongoing discussion about the structural integrity and design considerations for the geodesic dome project. Your expertise is greatly appreciated and has significantly deepened my understanding of the complexities involved.

Ashok, your explanation about the potential for shallow hubs to suddenly invert due to the inherent properties of geodesic structures, including their non-rigid nature and tendency to vibrate around a midpoint, was particularly enlightening. This highlights the importance of carefully considering the dome's frequency and the characteristics of its hubs to mitigate the risk of such inversions. Your reference to the acidome.com calculator and the suggestion to consider a 10-frequency dome with strut lengths and angles within manageable thresholds provides a valuable direction for refining the dome's design to balance structural integrity with practical construction considerations.

Eric, your inquiry about the dual-shell structure and its role in preventing hub pop through increased vibrational stability raises an essential point about the design's overall resilience and safety. The reference you provided adds an interesting layer to our discussion, suggesting that there are innovative ways to achieve the necessary stability without resorting to excessively heavy or costly materials.

Ashok, your subsequent messages, including the historical reference to the Expo 67 Geodesic Dome and the suggestion to reconsider the single-sphere versus dual-sphere configuration, offer a critical perspective on the project. The idea that Buckminster Fuller's decision to use a dual-sphere configuration for such a landmark project was based on compelling reasons is a potent reminder of the need to carefully evaluate our design choices in light of historical precedents and proven engineering principles.

Your clarification regarding the factors influencing hub popping, emphasizing the role of the hub's shallowness and the deficit angle, further refines our understanding of the structural challenges we face. This distinction helps to focus our attention on the geometric and structural parameters most critical to the dome's stability and safety.

In light of your insights, I will delve deeper into the structural and geometric considerations you've both highlighted, with a particular focus on the frequency of the dome, the characteristics of the hubs, and the potential benefits and challenges of a dual-shell versus single-shell configuration. Your guidance has been instrumental in shaping the direction of this project, and I am grateful for your continued support and expertise.

Thank you once again for your thoughtful contributions and for fostering such a productive dialogue. I look forward to further discussions as we progress in our design and decision-making processes.

Best regards,

Hesham El Feshawy 

[Hesham Elfeshawy]

Dear Ashok,

Thank you once again for your valuable insights and for directing me to the acidome.com calculator. Your reference to a dome with a 60-meter radius, however, led to a slight misunderstanding on my part, as my original query was based on constructing a dome with a 60-meter diameter, effectively halving the size you considered.

This clarification significantly alters the parameters we're working with, potentially simplifying the structural complexity and reducing the construction challenges associated with a larger dome. The implications of this adjustment mean we might not need to pursue as high a frequency for the dome's design, which could, in turn, mitigate some of the concerns related to strut length, hub shallowness, and overall structural stability.

Given this updated context, I will revisit the acidome.com calculator with the corrected dimensions in mind. This will help in recalculating the necessary specifications to ensure structural integrity, while also possibly avoiding the excessive complications and costs associated with the larger scale you had kindly investigated.

Your advice has been pivotal in steering this conversation towards a more accurate understanding of the project's scope and requirements. I appreciate your patience and willingness to engage with these technical details, which are crucial for the successful design and construction of the dome.

I'll proceed with the adjusted calculations and will keep you informed of the developments, ensuring that our design remains practical, safe, and aligned with the project's original vision.

Thank you once again for your continued support and guidance.

Best regards,

Hesham El Feshawy

[Ajay Ajay]

I agree this 60m is in the same "ball park" as the Montreal Dome... which burnt in "front of my eyes" (about 3-5km away) in 1976.... but the Steel Structure.. refused to budge, as we (all Engineers) waited for the total collapse of the Dome"s Steel Dtructure that inherently weakens substantially with heat... but NOTHING HAPPENED...

My 40m dome is investigating "how far" one can take a single Strut Dome rather than revert to a dual one (as at Montreal) .. and by using Carbon Fiber Struts, that are much stronger than Steel.... (I think..??).. 

Ajay..  

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[Hesham Elfeshawy]

Dear Ajay,

Your firsthand account of the Montreal Dome's resilience during the 1976 fire is captivating. Your project's investigation into pushing the limits of a single-strut dome with carbon fiber is innovative and promising. I look forward to seeing the outcomes of your exploration.

Best regards,

Hesham El Feshawy

[Bryan L]

Hesham, I would like to clear up a point that has been made about domes with shallow hubs.

While the shallower a hubs' angle definitely increases its propensity to pop, or dimple, the stiffness of the hub and struts definitely contribute to whether it will dimple or not. There will certainly be a point of diminishing returns where, to preclude dimpling, the member strength required would become excessive in cost and or size. Unfortunately, as far as I know, there hasn't been any publicly available Finite Element Analysis performed for a given member's attributes from which we could get an idea on limitations, including propensity to pop.

Best of luck with your dome,

Bryan

[Ashok Mathur]

Dear Bryan

Does not FEMA assumes that the structure is rigid and the reaction is at the point of application.

If so, FEMA is not the tool to predict hub inversion as that would be an action outside the Universe of FEMA.

Also assume that somehow FEMA grows wings and does a good job of hub inversion, Where do you bring in the struts in this analysis, as you seem to imply is necessary?

Regards

Ashok

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[Eric Marceau]

Hi Ajay,

I was still at McGill for my 2nd year Engineering studies when that happened.  I was looking at the burn from a "high ground" of the Molson Residence up on Mount Royal.  I was very sad to see that go up in flames.  We had a near-clear view. A bunch of us pulled out some beers to mark the occasion as a regrettable milestone on the one hand (burn), but a success on the other (no collapse).

But your point, about the dual-sphere preventing the anticipated collapse, is a key insight on planning for risks of various modes of disaster.  They never anticipated fire, so they never built in a sprinkler system.

On that last point about possible risks of a given design configuration, wouldn't "carbon-fibre" struts "burn"?  If so, wouldn't that limit the application to non-life-threatening situations, such as unattended hot-houses?

Just wondering.

Eric

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[Dx G]

Hesham,

 I'm hoping that if you didn't realize you need the support of structural engineer with a background in "reticulated" domes (as opposed to only shell structures, like those made from concrete), you see the importance and value of this now.   Sure, people in this group can help with ideas, but there are a lot of considerations with any building, especially so with one of this size and type. You will need technical support by someone who is specifically looking at this structure on the specific site you select.  Here are a few examples

What kind of loads will the structure be exposed to?

  - If it is evenly covered with snow, how much weight does it have to hold?  That is in addition to the loads in normally carries when there is no snow.  (Sure, lots of places don't have snow, but you get the idea).

  - What if the load is uneven (asymmetric), like a wind from one side, or being hit by a mud slide?   What if the wind is carrying snow or sand?

  - What about earthquake (seismic), or other issues such as sinking, shifting or settling of the foundation?  Is anyone evaluating the soil that will support the structure?

The list can get very long.  Some things are rather simple and easy to understand, others are not.  Just to give you a feeling of the scope of an analysis, take a look through this publication about the South Pole dome.  Don't get too bogged down in the equations, the mathematical models and the vocabulary. The main thing, at first, is to look at the kinds of things that were under review.  

                   https://apps.dtic.mil/sti/tr/pdf/ADA193833.pdf

      Also keep in mind this publication is pretty old, and a lot of things have changed.  If you are interested in learning how things are done now, there are hundreds of research papers and articles about why structures like this fail, and how they can be built to better withstand forces that conspire to collapse them.  A few titles I see include:

-Dynamic Analysis of Geodesic Dome Structure

-Deformability of single layer diamatic space frame Domes under non-symmetrical snow load and earthquake shaking
-A Comparative Study of the Structural Performance of Different Types of Reticulated Dome Subjected to Distributed Loads

-Seismic performance evaluation of single-layer reticulated dome and its fragility analysis

I'm not trying to scare you away from the project. I admire what you are doing, and am hoping you have a good success.  My only intention in sharing this is to help you go into this with your eyes wide open, in case all of this was not already obvious to you.  

Dx G

[Bryan L]

On Tue, 27 Feb 2024 at 23:41, Ashok Mathur <ashokch...@gmail.com> wrote:

Dear Bryan

Does not FEMA assumes that the structure is rigid and the reaction is at the point of application.

If so, FEMA is not the tool to predict hub inversion as that would be an action outside the Universe of FEMA.

Also assume that somehow FEMA grows wings and does a good job of hub inversion, Where do you bring in the struts in this analysis, as you seem to imply is necessary?

Regards

Ashok

Hello Ashok,

not at all. FEA takes into consideration the characteristics of the material in question. The user then defines loads at whatever points and direction they wish. The software then calculates distortions / failures of the whole structure.

A typical manner is too assume pinned hubs, which doesn't include any hub distortion - it only uses the struts.

But I am sure an engineer skilled in the use of the software could include characteristics of the hubs. 

A complete analysis would even include the characteristics of any bolts / screws / brackets used to connect struts and hubs.

This is required for many types structures (buildings, aeroplanes) to find the potential points of failure.

[Ashok Mathur]

Dear Bryan

There is enough fighting going on in the world to fight with friends.

I concede that a skilled software engineer can do anything whatsoever!

Regards

Ashok

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[Ashok Mathur]

Dear DxG

In the context of a geodesic dome, I regard the term asymmetric load as an oxymoronic  I. E. pompous sounding with no meaning in the context.

For a rectangular structure that react only at the point of application of the load, the term has a significant meaning.

But geodesic domes react as a whole and don’t care where the load is appliedso no asymmetric loads!

Regards

Ashok

Sent from my iPhone

[Dx G]

Ashok,

 Actually, you are mistaken on that point.  Numerous research papers contain results of exposing domes and shell structures to loads that are evenly applied vs. those that are unevenly applied.  If you have any doubts, find your nearest neighborhood dome, and hang some sacks of sand from each hub. You will find the structure can stand immense loads - if, that is, they are symmetric.  If you then start removing some of those sacks from only one side of the dome, even though the dome now has less load than it did when you began, with sufficient starting load, you will see the dome deform or even collapse on one side.    This was investigated in detail back in the early dome days of the ones at the south pole, Montreal, Spokane and others that are well known now.   There were some significant historic dome collapses, and this phenomenon became clear in engineering investigation and forensics .  It was also of interest to NASA.

   Since I agree with you, we don't want to fight with friends, I would avoid using such terms as "pompous", even if readers may incorrectly assume you were directing it at them.  Part of the measure of a relationship is not how well we agree, but rather, how well we disagree.  People who are well meaning and have good intentions, bearing no ill will to others, can differ on opinions, but should not be being subject to being demonized for doing so.  We already see that happening too much now, and I hope we don't see that among contributors in this group.  Rather, we can learn from each other, and as one US president was told in a debate once, when he said we literally went to war with another country because he was "certain" he had weapons of mass destruction, his opponent in the debate aptly said, you can be certain, and you can be wrong.   He was interviewed later, and drew on a famous quote, which is, Life has taught me to keep my words sweet, due to the inevitable consequence of having to eat them.  I always suggest we attach issues and problems, not people. 

  So, I'm not saying you are a bad or malicious guy, just suggesting you wordsmith your postings so we don't confuse you, with them.

Dx G

 

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[Ashok Mathur]

Dear DXG

By coincidence in next 15 days I will get try what your suggesting.

If you take wire in tension and you add weight any distance from the two ends, it reacts in the same way.

Why does it behave differently in another structure?

Regards

Ashok

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On 28-Feb-2024, at 9:07 PM, Dx G <yipp...@gmail.com> wrote:



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[Dx G]

Ashok,

  Try this and see what you find.  Take two weigh scales with hooks and connect them with wire or line a few feet apart.  Hang a weight on the center of the wire. Note the reading on the two scales. Then move the weight along the line, closer to one scale then the other.  Note any changes to the weight on the scales.  

     Consider those two points as dome hubs.   Perhaps you will observe "asymmetric" (uneven) loading.   You can also see this in trusses use in floors, roofing, etc.   You will also see this in compression if you put a board across two scales a few feet apart, and move the load off dead center.

  If you find this:

"If you take wire in tension and you add weight any distance from the two ends, it reacts in the same way."

   I would be most interested in learning more about it.

Dx G 

[Ajay Ajay]

Eric,

So.. we were BOTH witnesses to an historical event as far as Geodesic Domes are concerned.. and feel we will take the image of the "fire" and acrylic panels flying up in the air with us ..  forever..  as well as the integrity of the Dome... which did not flinch an inch as fire engulfed everything around it.. Feels like ... yesterday..

Thanks for pointing out the Fire Hazard of the Epoxies etc.. used to hold the Carbon Fiber together.. I will look into this but I am sure the "fire-proof" CF will provide some degree of flame retardancy to the Structure. 

Then there are flame retardant paints etc.. too.. looks more-n-more interesting.. Thankx...

Let us see where this voyage "into the unknown" (single Struts) takes us..  as I solicit help from all... directions.. 

Regards,

Ajay..  

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[Eric Marceau]

Hi Ajay,

I knew about the flame-retardant properties of carbon-fibre epoxies.

However ... if a sustained fire exposes such carbon-fibre struts to the ongoing heat/flame/ionic stream, those struts (both the resin and the carbon-fibres themselves) will combust with the oxygen in the air/flame.

There is no way around that eventuality ... unless you conceive carbon-fibre struts that are metal-coated, to prevent direct exposure  to the flame/oxygen of either the resin or the carbon.  That would imply some kind of cap/seal at each end of the struts to protect the inner surfaces from exposure of convective currents thru the core of the struts.

For the outer surface, I'm not sure if "tin" would have a sufficiently high melting point to resist to flames long enough to allow any kind of flame extinguishing to take place.

Fun times at the Geodesic ranch!

Eric

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[Ajay Ajay]

Yup... Fun Times are finally here... again.. 👍🏽👍🏽👍🏽👍🏽

Ajay

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[Hesham Elfeshawy]

Dear All,

I want to express my heartfelt gratitude to each of you for sharing your valuable insights and expertise in our discussion. Your contributions have been incredibly enlightening and have enriched my understanding of dome construction in profound ways.

After careful consideration of all the input provided, I've decided to pursue an inflatable dome solution for our event needs. This decision is driven by the desire to mitigate the high costs associated with traditional geodesic domes and to alleviate concerns about structural collapse. Additionally, the inflatable dome offers the flexibility of easy setup and storage, making it a practical choice for our intermittent event requirements.

Your collective knowledge and guidance have been instrumental in shaping this decision, and I'm truly appreciative of the wealth of information you've shared. I look forward to implementing these insights as we move forward with our project.

Thank you once again for your invaluable contributions and support.

Warm regards,

Hesham El Feshawy

[Ashok Mathur]

Dear DxG

This what I imagine a tension scale to look like. Essentially it is a spring that can be attached to a wire at both its end and it will measure the tension the wire is undergoing.

One end of the wire is attached to a hook in the walll; the other end draws down over pulley at the end of it different weights can be drawn.

By cutting the wire in between and creating hooks at the cut ends, this scale can be inserted anywhere in the wire.

If you insert it near the wall, it will give one reading; shift it to the middle, it will give the same reading, it will give it the same readingwhen you shift it to the near the pulley. 

Wires under tension have identical tension through out the circuit.

Regards

Ashok

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On 01-Mar-2024, at 10:29 AM, Ajay Ajay <ajgo...@gmail.com> wrote:



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[Dx G]

Ashok,

 Thanks for the clarification.  However, perhaps we have a different concept of the question at hand.   The way I see this, it is the strut that is exposed to the tension or compression.  I see that as your wire line.  What appears to me to be important is the load at the two ends. Those are, essentially, the hubs.  In general, a dome covered with snow could possibly be supporting equal, or near equal loads at many, or all hub points.  In contrast, the load imposed by a snow drift, or sand piling up from wind coming from only one direction, would impose an asymmetric load on the structure.  That is what I thought we were discussing, since that is what brings down a dome.  This is why I suggested the hanging bag test.  Maybe I missed something there.

Dx G 

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[Ashok Mathur]

If I may venture to guess , you’re missing the role of reaction in the whole picture.

You see  the assymetric  loading of compressive forces, its reaction is a point reaction and equal to the load applied at that point.

Therefore it is routinely ignored.

In an tensgrity structure , a tensional reaction is instantly set up across the entire circuit and the tensional force is independent of the point of action.

You may be seeing more and better than me.

Regards

Ashok

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On 01-Mar-2024, at 9:36 PM, Dx G <yipp...@gmail.com> wrote:



To view this discussion on the web visit https://groups.google.com/d/msgid/geodesichelp/CAF1iHD7Sb8%2B9QOYEr%3DL5goF9s7fd6RO1%2B7v_fknY11R%3D7498Tg%40mail.gmail.com.

[Eric Marceau]

Hello Hesham,

I'm sure that I speak for all who responded  when I say we were each happy to help in whatever ""small" way we each could contribute towards you decision-making and eventual success for your events.

May we ask what the name of that event would be, so that we can keep an eye out for what eventually transpired?

Thank you,

Eric

To view this discussion on the web visit https://groups.google.com/d/msgid/geodesichelp/abb16219-98c9-4531-924a-ee55a2dbbd31n%40googlegroups.com.

[Hesham Elfeshawy]

Dear Eric,

Thank you so much for your kind words and for the invaluable support you and everyone else have provided. It truly means a lot to me and has significantly contributed to my confidence and decision-making process as I navigate through this journey.

Regarding the event, I deeply appreciate your interest and eagerness to follow up on our progress and eventual success. At this moment, however, I've decided to keep the details of the event confidential. This decision is not made lightly but stems from a strategic approach to ensure we maximize our chances of success and maintain an element of surprise within the competitive landscape.

Please rest assured, as soon as we are in a position to share more details publicly and celebrate our milestones, you and all those who have shown support will be among the first to know. I am eager to share our journey with you and look forward to celebrating our achievements together.

Once again, thank you for your understanding and continued support. It's incredibly motivating to know I have such a supportive group behind me as we embark on this exciting venture.

Warm regards,

Hesham El Feshawy

[Eric Marceau]

Hi Hesham,

I completely understand the need for "secrecy" to avoid having competition stealing your audience and the credit for originality/uniqueness of your event!

We look forward to your formal announcement and, again, wish you success for all your efforts!

Eric

To view this discussion on the web visit https://groups.google.com/d/msgid/geodesichelp/d1c4fc9d-8379-4952-a452-977908e27c5an%40googlegroups.com.

[Gerry in Quebec]

Here are other images of the Expo '67 double-grid network, posted here on June 21, 2017. The PDF shows Antiview snapshots of the dome. The computer model is based on the original technical drawings produced by the Fuller & Sadao architectural firm in 1966.

https://groups.google.com/g/geodesichelp/c/fIuS_UfEP6c/m/j4Cm1sylAQAJ

  - Gerry in Québec

On Monday, February 26, 2024 at 8:09:26 PM UTC-5 Eric Marceau wrote:

Hello Hesham,

By the way, for comparison, the Expo 67 Geodesic Dome (U.S. Pavilion) was a Class I with a 76 m diameter.

[Hesham Elfeshawy]

Thank you  Eric