Need help & inputs for quadrosphere dome design...

[imxt...@gmail.com]

Greetings from Bengaluru, India

Have been a geodesic dome enthusiast for a while now... I've specifically like this quadrosphere dome design  inspired by the Alpbau quadrospheres....  which I'm planning to build....this will be covered although I'm still not sure if bamboo with thatch if that is possible & finding the right ppl to do it.... 

This is a 50ft dome with central height of 24ft....The opening arches are 12ft high...they will also have 

Considering the practicality of the build & material availability / cost, I've increased the sections so wood struts can also be used. Mainly designed with steel tubes - 82 x 145 mm with 3.2mm wall thickness... For wood it would be 4" x 6" beams which after milling / planing would be nearly same as steel beams

For the Hubs i'm planning to use 8mm thick steel. This design uses many diff shape/size hubs due to the angles..Gusset plate in center of hub is not shown in pic but will be fixed.

I've made a scale 5ft model last year with miniature versions of same hubs and wooden struts....everything fit as per design....will share pics soon....

Purpose : pool cum indoor game room
Dome size : 50ft
central height : 24ft
Opening height : 12 ft
Shortest strut : 3.5ft
Longest strut : 6ft
strut section : 145 x 82mm steel - galvanized, 3.2mm wall thickness
Hubs : 8mm welded steel with central gusset plate
456 sections
169 hubs 
Total weight in steel, struts & hubs - Approx : 9 tonnes. ( not including cover)

My questions...I have many actually...
- How do I check technical feasibility? load/strength test etc.....I'm no engineer
- Do more sections/struts increase strength or lesser longer struts are stronger?
- what am i missing?

- any ideas for the cover with steel struts?
- Is this doable :-))

- This is mostly a DIY itch since many years....I now have the space & purpose to build it. 
- too many questions/doubts arise but I will wait for your feedback/critique before posting any more

Thanks for reading & your inputs in advance :-)
Srikanth
Bengaluru

[Dx G]

Srikanth,

  Interesting project. I will give it a little more thought, but one issue did come to mind which I did not see mentioned.

I don't know if you are in an area which is subject to storms or high velocity winds.  If you aren't concerned about high winds in your area, do keep in mind that some locations are experiencing weather events that they "never" had before, perhaps due to climate change.  So a building that is subjected to high winds, especially with airborne debris, might find the sides blown open and subjected to uplift. If so, consideration should be given to anchorage, via the foundation or footings.  The tendency (or lack thereof) of surrounding soil to change properties when wet or flooded is important in some locations.  Sometimes people think they can address this by pouring cement footings, but even those have to be designed properly to work right and not create more problems than they solve.  In some settings, helical piers are a good option.

Those are some initial thoughts to share.

Dx G

[Ashok Mathur]

Try google free wind tunnel software.

This is likely to pop up

https://www.grc.nasa.gov/www/k-12/freesoftware_page.htm

Regards

Ashok

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[imxt...@gmail.com]

Dear DxG & Ashokji

Thanks for your feedback & info. This is being built on outskirts of Bengaluru, India. This region hasn't experienced any severe weather or wind conditions at least until now....

This will be a permanent structure ....Any thoughts regarding the strut section size & overall structural strength compared to a regular 3v or 4v dome....

Ashokji - Any suggestions or recommendations who can help with the structural analysis for this design ?

Thanks
Srikanth

[Ashok Mathur]

Dear Imtx,

As I have stated for many years, there is no tool to gauge the structural strength of a tensgritty structure of which geodesic structures are a sub class.

This is because common tools likeFEMA or FEA assume that the reaction to a force is confined to that point only whereas the geodesic structures respond to the force as a whole as would any tensed string.

Secondly when force is applied to a geodesic structure, it twists around the central axis ;

no FEMA or FEA software has any component to deal with this twisting action.

But there are any number of structural engineers who will agree to carry out a structural analysis for you on payment of fee.

Your call to make ;and many people have made a call to carry out the structural analysis.

If this is going to be a permanent structure, then there are two choices of building material.

In USA, very large domes are built out of 4 inch steel pipes. You can look up Pacific domes where you will get better specifications.

India’s largest geodesic structure is an aviary built at the site of Narmada Dam. It is made of rectangular cross-section of MS beams. I think they are 4“ x 2“.

I can get you full details from the Builder.

You can use either of the two materials. Rectangular cross-section  allows you to screw down a roof panel on the structure with ease.

With round cross-section, you will need an intermediatary Double sided tape to prevent rainwater from entering the structure.

At Bangalore, the rains are heavy and even with rectangular cross-section you may opt for a Waterproofing layer between the beams and the  roofing material.

Regards

Ashok

Ps You are welcome to talk to me . just write an email to ashokch...@gmail.com for my phone number

To view this discussion visit https://groups.google.com/d/msgid/geodesichelp/94984876-73f3-4792-91de-292b627370bbn%40googlegroups.com.

[Ashok Mathur]

Dear Shrikant,

If you have some bent for mathematics or engineering, I can forward a Thesis where parts are a very clear exposition  of the special characteristics of tensgrity.

By itself, the thesis is largely free of maths.

Regards

Ashok

[Paul Kranz]

Ashok: I built a geodesic dome garage (https://www.google.com/maps/place/5626+Connell+Rd,+Plant+City,+FL+33567/@27.9454036,-82.1792851,63m/) that a structural engineer did not do a structural analysis on because it was a geodesic dome. After he signed the plans, the architect asked him, "Aren't you going to do a structural analysis on it?" To which the engineer replied, "What for? It's a geodesic dome. That'll be $500, please."

Paul sends...

To view this discussion visit https://groups.google.com/d/msgid/geodesichelp/CAD-a3Oj8Qy-qPnm%3DAKTtvp4iN3ZC3gGcw8ZuF50Vfgn7Mdo5FA%40mail.gmail.com.

--

Very high regards,

 

Paul C. Kranz, LMFT

Kranz & Associates, LLC

ReviveTheFlame.com

[Dx G]

Srikanth,

 If you go to the top of our group list and type in "structural analysis" in the search box (says Conversations to the left) you will find some discourse we have had about dome structural analysis and quite a few reference items.  Likely nothing is better than having a good, qualified engineer involved in the project, but review of some of these references will help you get a much better idea what the issues are and be able to ask much better questions during the planning.  In most cases, you can skip over any math that is of no specific interest, and still get the gist of the scope of the analysis.  

There are also some items relating to the use of Bamboo.  There are many research and training organizations (quite a few in India) the specialize in bamboo for construction, and some include domes.

   

https://www.youtube.com/watch?v=UFGTjbSSd6M  not much information here but might be some leads for you

Dx G

[Ashok Mathur]

The recent discussion triggered by Srikant's desire to build a quadosphere has led me to reexamine my views on (non existent) ways of calculating the strength of a tensegrity structure.

Thanks to the good design of the group, it is possible to revisit the past discussions with just a few key words.This has been pointed out by Dx.

I have chosen another way.

Tensegrity Structures and their Application to Architecture by Valentín Gómez Jáuregui is a MSc thesis posted on this group some time ago. 

I am enclosing it again for ready reference.

It lists properties of a tensegrity structure which make it clear why FEMA or FEA tools just will not work on a tensegrity structure.

Instead of asking everyone to wade through the entire thesis (which incidentally has a wonderful bibliography), I have made a point-wise two page extract for easy reading.

This is enclosed.

Some time ago I had mentioned my frustration in not finding Rene Motro book in prominent US libraries.

The founder of the group had come to my help and showed me how to get to the book.

The book deals with serious attempts of mathematical analysis of tensegrity structures.

But I found that the book has no mention of any software developed by the French group that does structural analysis of a tensegrity structure.

I used Claude, an free AI tool, to check my understanding of the work of Rene Motro,

Extracts are enclosed.

I have no hopes that the positions on any side will change- but re-examination may happen.

Regards

Ashok

Regards

Ashok

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From: Ashok Mathur <ashokch...@gmail.com>
Date: Thu, 8 May 2025 12:42:04 +0530
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Subject: Re: Need help & inputs for quadrosphere dome design...
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