Bamboo Domes A possible solution An Alternative view
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Ashok Mathur
Jul 26, 2022, 2:02:37 AM7/26/22
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Dear List members,
As you know I had given upon large bamboo domes using poles and am advocating making large nexorades with bamboo splits.
There were two reasons as to why I had given upon domes.
Firstly beyond 3V they require costly hubs that are to be manufactured with some precision, or free hubs that self-algin which are even more costly to manufacture.
Nexorades have no hubs but need tightening points without drilling any holes in the bamboo.
Because of a post sent by an acquaintance, I have had to rethink my whole approach and wish to share as much details as possible with the list. I hope some people do add more to the topic.
The enclosed paper is by an organisation called Domebambu.
It describes initially the construction of a
geodesic dome 20 meters in diameter and frequency 3V and covered area of 314 m², and from
this event, Domebambu started a successful path, consolidating as a company specialized in the manufacture of domes.
I have been able to locate more links given below but the Instagram links I have not been able to follow as I am not a member.
I am unable to locate many details on the 3V hubs they have used
Link to their website translated into English
Original website Empresa | Domebambu (fredericorosalino.wixsite.com)
One more page?
Instagram site where more projects can be seen
Regards
Ashok
Ashok
Dx G
Aug 13, 2022, 6:30:26 PM8/13/22
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I was digging around in my library and was reminded of this hub connector. Some time ago I considered several improvements to what I see in the patent, but the general idea is quite useful. For one thing, unlike many other connectors, it allows for different face and axial angles, whereas other designs are fixed. In any case, it appeared to me that this form factor might be worth considering for bamboo, as it lends itself to simpler fabrication than some other hubs or strut ends. Much like electrical terminal connectors which have a similar general form, the implementation might work better with bamboo if the sleeve went on the outside of the strut, especially since this connector can accommodate variation in the end diameter of the strut.
If others had not considered this approach before, I thought it might inspire a few ideas.
5165207
Ashok Mathur
Aug 13, 2022, 10:21:33 PM8/13/22
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Dear DxG,
Thanks for the link.
As the patent appears to be in the public domain now, it can be used royalty-free.
Many articles on constructing 4V domes from conduit pipes use a similar arrangement.
On first glance, the patent uses a crimp in each strut to be more effective. Such a crime can not be put in bamboo, but workarounds may be there.
As there is only just one main component to be fabricated, and it does not change in any manner, whatever the dome frequency you use it for, it should be economical to fabricate.
Thanks
Ashk
Regards
Ashok
Ashok
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John Hurt
Aug 14, 2022, 9:04:31 AM8/14/22
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I am certain I am lacking "vision" on this, but I don't see how the Oehlke connector could be used with bamboo.
And I must be missing something about the purpose of the Oehlke connector, as I could not understand why a separate end piece on each strut is necessary.
My first metal dome was using the "Desert Domes" method - where you flatten the ends of the EMT conduit strut with a press, then bend the flattened end the correct angle, drill a hole and bolt it to the other struts to make a hub - all one piece.
It seems to me that the Oehlke connector involves a lot more work than the Desert Domes method, and could slip out the end of the metal strut under tension if the crimp failed. (Of course, I am not that good at reading someone else's patent.) I could not find that anyone was currently manufacturing the Oehlke connector. If they have a website, let me know.
The best information on this thread about building bamboo domes was the Ottenhaus thesis - PDF link at the bottom of this page: https://repository.tudelft.nl/islandora/object/uuid:c666f4b5-fb81-413f-9197-d7d1825c870d?collection=education
On pages 21-27 of the thesis, the author points out several different types of connectors that would attach the bamboo to the hub, with the pros and cons of each approach. The author has done a tremendous amount of work.
The author notes that the problem with bamboo is, it is easy to split when you drill it or attach something to it, it tapers and is wider on one end than the other., and it has these "nodes" every 8 to 12 inches where there is a joint or "ring" around the bamboo culm or stem that is knobby and obtrusive.
The internodal areas (between the nodes) of the bamboo stem are hollow and will crack, while the nodes are solid, tough, and walled off on the inside. Around page 49 of the thesis, Ottenhaus actually tests the different types of bamboo for cracking in the internodal regions. (That is a really good lesson for all of us, to actually build a prototype or actually test a hypothesis in the real world. I have a lot of good ideas I have never "reduced to practice" to see if they would actually work.)
By page 62, the author is providing an analysis of the nodes of bamboo as related to construction.
The nodes can randomly occur anywhere in the bamboo. So when I was cutting my bamboo struts a precise length, I found that the saw blade can end up just before a node, or just after a node, or exactly on top of a node. I threw at least half my struts away, because the nodes ended up in the wrong place, or bamboo would taper and be either slightly too big or just too small for a good connection - or the bamboo would just crack after I cut and drilled it.
In her conclusions on page 125, she states: "Q1: What are the limiting parameters in the design of bamboo geodesic domes and
can a maximum diameter be derived?
Answer: The limiting factor is often the strength of tensile connectors."
I believe her preferred connector for bamboo is on page 113.
Dx G
Aug 14, 2022, 12:14:42 PM8/14/22
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John,
All perfectly legitimate questions and justified points. Thanks for
sharing your insights. I was actually the person who posted the
referral to the Ottenhaus work, and did review that some time ago.
Although she did a terrific job, I didn't see anything like the Oehlke
connector in her extensive repertoire. The fact that her work (along
with other published work) has been so extensive in testing things
that did not work, opens the door for finding what might. Many things
we have and use today are actually a result of the same process.
As to the conduit connector approach (vs. whole struts), the
difference is whether or not you want flexibility in design or
possibly reuse. A few examples:
1) If a dome was hideously damaged, you might be able to reuse the
connectors, whereas whole struts that are badly damaged may need to be
replaced. The latter requires a manufactured strut rather than just
plain pipe, tubing, etc.
2) Shipping connectors has advantages over shipping (or storing)
complete struts. For emergency use, disaster situations or remote
locations, pipe, tubing, 2x4s and other materials may be available on
site or nearby. The connectors enable the use of such "plain"
materials for domes with minimal fabrication, and lend themselves for
use with any strut length. This would not be the case with whole
struts.
3) There is no question that one would have to test the connector to
see if the sleeve, or some variation of it, would work with bamboo.
-Where struts are in compression, it looks to me like the sleeve
would hold well, and even add some strength at the end for crush and
burst resistance.
-Where the strut was in tension, keeping the bamboo from slipping out
of the sleeve is not a trivial issue. If simply
bolting/screwing/pinning through a hole(s) in the sleeve is not
effective, there are methods that may be. I've worked with a number
of "friction fit" systems that are surprisingly simple and enormously
effective. Some are "releaseable" and some are permanent, and don't
even require adhesives.
4) Unlike manufactured or machined strut ends, as you point out, with
bamboo we are dealing with tapered ends with nodes. Likely it would
take testing to get adequate hold without damaging the end of the
bamboo strut (something Ottenhaus addressed) but I suspect there may
be some approaches that would work, which include clamping, adhesives,
caulking, and quite a list of others. The fact that others, like
Ottenhaus, did such extensive work, allows us to consider methods they
did not, rather than wasting time on "good ideas" that they already
adequately tested. I have eccentric clamps that are used in both
interior and exterior applications, without puncture, that have
tremendous strength in even thin materials that aren't as durable as
bamboo walls. Even if one does not find inspiration for their own new
system, I often find solutions used in one industry that are virtually
unknown in others, and are already available off the shelf. I've even
seen some good ones done with things like plastic ties :-)
5) If using the connectors in compression works, but the problems
with tension cannot be immediately overcome, one could use a different
type of strut where tension is needed. Although this approach does
dilute some of the advantages of using a dome made entirely of bamboo
struts, when you look at how many struts in a dome are in compression,
it still does provide a substantial use of bamboo.
6) Another factor which is often overlooked by the general public is
plant breeding. Most people do not realize how massive improvements
have been made in just a few decades in plant based items we use every
day, even from "conventional breeding", before the use of current
genetic technologies. This could create improved bamboo so superior
for building that no one would ever bother to use the materials
available now that we are "struggling" with.
In any case, those are a few thoughts to share on the issues you
raise. I remain convinced that bamboo needs to remain on the radar
screen, as it offers many possible value assets, even if it does not
work as is, at present.
Dan G.
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All perfectly legitimate questions and justified points. Thanks for
sharing your insights. I was actually the person who posted the
referral to the Ottenhaus work, and did review that some time ago.
Although she did a terrific job, I didn't see anything like the Oehlke
connector in her extensive repertoire. The fact that her work (along
with other published work) has been so extensive in testing things
that did not work, opens the door for finding what might. Many things
we have and use today are actually a result of the same process.
As to the conduit connector approach (vs. whole struts), the
difference is whether or not you want flexibility in design or
possibly reuse. A few examples:
1) If a dome was hideously damaged, you might be able to reuse the
connectors, whereas whole struts that are badly damaged may need to be
replaced. The latter requires a manufactured strut rather than just
plain pipe, tubing, etc.
2) Shipping connectors has advantages over shipping (or storing)
complete struts. For emergency use, disaster situations or remote
locations, pipe, tubing, 2x4s and other materials may be available on
site or nearby. The connectors enable the use of such "plain"
materials for domes with minimal fabrication, and lend themselves for
use with any strut length. This would not be the case with whole
struts.
3) There is no question that one would have to test the connector to
see if the sleeve, or some variation of it, would work with bamboo.
-Where struts are in compression, it looks to me like the sleeve
would hold well, and even add some strength at the end for crush and
burst resistance.
-Where the strut was in tension, keeping the bamboo from slipping out
of the sleeve is not a trivial issue. If simply
bolting/screwing/pinning through a hole(s) in the sleeve is not
effective, there are methods that may be. I've worked with a number
of "friction fit" systems that are surprisingly simple and enormously
effective. Some are "releaseable" and some are permanent, and don't
even require adhesives.
4) Unlike manufactured or machined strut ends, as you point out, with
bamboo we are dealing with tapered ends with nodes. Likely it would
take testing to get adequate hold without damaging the end of the
bamboo strut (something Ottenhaus addressed) but I suspect there may
be some approaches that would work, which include clamping, adhesives,
caulking, and quite a list of others. The fact that others, like
Ottenhaus, did such extensive work, allows us to consider methods they
did not, rather than wasting time on "good ideas" that they already
adequately tested. I have eccentric clamps that are used in both
interior and exterior applications, without puncture, that have
tremendous strength in even thin materials that aren't as durable as
bamboo walls. Even if one does not find inspiration for their own new
system, I often find solutions used in one industry that are virtually
unknown in others, and are already available off the shelf. I've even
seen some good ones done with things like plastic ties :-)
5) If using the connectors in compression works, but the problems
with tension cannot be immediately overcome, one could use a different
type of strut where tension is needed. Although this approach does
dilute some of the advantages of using a dome made entirely of bamboo
struts, when you look at how many struts in a dome are in compression,
it still does provide a substantial use of bamboo.
6) Another factor which is often overlooked by the general public is
plant breeding. Most people do not realize how massive improvements
have been made in just a few decades in plant based items we use every
day, even from "conventional breeding", before the use of current
genetic technologies. This could create improved bamboo so superior
for building that no one would ever bother to use the materials
available now that we are "struggling" with.
In any case, those are a few thoughts to share on the issues you
raise. I remain convinced that bamboo needs to remain on the radar
screen, as it offers many possible value assets, even if it does not
work as is, at present.
Dan G.
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John Hurt
Aug 14, 2022, 5:58:41 PM8/14/22
to Geodesic Help Group
Thanks Dan!
I am looking at planting some bamboo this fall, either the Mosu or
Phyllostachys Nigra 'Henon' timber bamboo here in Tennessee - zone 7a. If you have any suggestions, that would be great.
We used to "torture test" our domes to find out what makes them fail. When a 250 lb person hangs from a hub on one side of the dome, the 120 lb zip ties will fail on the opposite side of the dome - from tension, not compression.
So the tension/compression changes depending on where the stress is located, and the direction of the force applied. (We use 350 pound Stainless Steel zip ties for serious domes.)
Also, with our hubs, the higher frequencies can experience a hub inversion. This never happens with a 2v or 3v dome, but the pentagons and hexagons for the higher frequencies are "flatter" and more prone to an inversion if the force is placed on a single hub. Also, if the zip ties are not pulled tightly, this lets a hub inversion occur.
But once you skin the dome, like attaching chicken wire to the struts with zip ties, there is no more chance of a hub inversion, and the strength of the dome goes up 30%. Spray it with cement, and it is an entirely different animal.
I think the same is true with a bamboo dome - that once you put a skin on the dome that is attached to every strut and hub, you won't have problems with tension at the boundary between the bamboo and the connectors.
And so the connectors could be fairly "cheap" if the dome is to be skinned and not just hubs and struts.
I saw a YouTube video where a person was splitting the bamboo into strips, then weaving the strips like a basket over a frame, then covering the strips with a cement roof.
Dr. George Nez pioneered using latex cement for roofing his geometric roofs, you can see more here:
Thanks for all of the information, it has been very helpful.
John Hurt
Dx G
Aug 16, 2022, 9:50:26 PM8/16/22
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Ashok,
I agree. However, what I thought might be a better approach is to put
the sleeve on the outside of the bamboo, rather than inside as done in
the patent diagrams. This would also provide some additional
strength/reinforcement at the end of the bamboo strut and perhaps
prevent splitting and other forms of fatigue related structural
faults. Since this doesn't cause a point load at the end of the
strut, it may work better than bolts and other fasteners that could
compromise the end. This is typically how electrical connectors work.
Those have a tab with a hole, typically used to secure the connector
with a screw, and then the wires are placed inside the sleeve. I've
seen the smaller versions of these for light wire used to make dome
models with wooden dowels, but those connectors also come in some
rather large sizes. I've read several accounts of people working with
bamboo for dome struts and other construction uses requiring
connectors, but I have yet to see this approach taken or otherwise
shown to have downsides. If it does not work, it would be useful to
know why, as this may point us to what will.
thx
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I agree. However, what I thought might be a better approach is to put
the sleeve on the outside of the bamboo, rather than inside as done in
the patent diagrams. This would also provide some additional
strength/reinforcement at the end of the bamboo strut and perhaps
prevent splitting and other forms of fatigue related structural
faults. Since this doesn't cause a point load at the end of the
strut, it may work better than bolts and other fasteners that could
compromise the end. This is typically how electrical connectors work.
Those have a tab with a hole, typically used to secure the connector
with a screw, and then the wires are placed inside the sleeve. I've
seen the smaller versions of these for light wire used to make dome
models with wooden dowels, but those connectors also come in some
rather large sizes. I've read several accounts of people working with
bamboo for dome struts and other construction uses requiring
connectors, but I have yet to see this approach taken or otherwise
shown to have downsides. If it does not work, it would be useful to
know why, as this may point us to what will.
thx
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Dx G
Aug 16, 2022, 9:50:26 PM8/16/22
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John,
Good exchanging thoughts with you.
In case its any help, there are a number of places that promote
bamboo, provide information and sell propagation material. This one
had information on materials for up north, which have surprising
environmental range. Sure did surprise me, as I thought of bamboo as
tropical.
https://www.bamboogarden.com/browse-bamboo
Do watch yourself, as the spreading types can be a challenge, as
opposed to the clump types that stay put. I'm doing some background
work on what is grown and how it is processed, as that varies a great
deal. The industry seems to be developing, so I expect some current
problems will be overcome in a short time frame. Why not, a new crop
takes 4-6 years and can be harvested on a rotating basis without
constant replanting.
I'm somewhat enamored with the idea of just popping the Oehlke
connector (or some augmented version) on the ends of bamboo poles for
a dome frame, but time will tell if that is realistic. HL Menken once
famously said, for every complicated problem there is a simple answer
that won't work.
I appreciate your remarks on testing. The point about structural
stress shifting a strut from compression to tension is an important
issue that is easily overlooked. I do see a lot of info on the web
concerning structural testing of domes and shell structures, although
another good guy to visit with would be JJ in Alabama.
https://www.newagedomeconstruction.com/dome-test-and-shelter
With respect to hub inversion and related failure modes, I've been
working on a simple arrangement that utilizes the same principles of
any truss, more commonly seen on linear ones in rectilinear structures
for roofs, floors, etc. My models look good, but will need to go
bigger to see if its really scalable. We often have rain on snow
here, so that makes for a real good collapse test, as snow is a good
sponge and that weather can (and does) bring down whole buildings if
they are not built to the right live load specs, especially when
accompanied by wind in excess of 40mph.
Thanks for the links, I'll take a closer look at those. I do remember
people who really liked GrailCoat, but it looks like they had some
serious product failures and may disappear. The coating industry is
pretty big and I'm sure there are good choices.
Dan G.
> To view this discussion on the web visit https://groups.google.com/d/msgid/geodesichelp/450c25cc-c3b4-4327-bb0b-15ef9dad90a7n%40googlegroups.com.
Good exchanging thoughts with you.
In case its any help, there are a number of places that promote
bamboo, provide information and sell propagation material. This one
had information on materials for up north, which have surprising
environmental range. Sure did surprise me, as I thought of bamboo as
tropical.
https://www.bamboogarden.com/browse-bamboo
Do watch yourself, as the spreading types can be a challenge, as
opposed to the clump types that stay put. I'm doing some background
work on what is grown and how it is processed, as that varies a great
deal. The industry seems to be developing, so I expect some current
problems will be overcome in a short time frame. Why not, a new crop
takes 4-6 years and can be harvested on a rotating basis without
constant replanting.
I'm somewhat enamored with the idea of just popping the Oehlke
connector (or some augmented version) on the ends of bamboo poles for
a dome frame, but time will tell if that is realistic. HL Menken once
famously said, for every complicated problem there is a simple answer
that won't work.
I appreciate your remarks on testing. The point about structural
stress shifting a strut from compression to tension is an important
issue that is easily overlooked. I do see a lot of info on the web
concerning structural testing of domes and shell structures, although
another good guy to visit with would be JJ in Alabama.
https://www.newagedomeconstruction.com/dome-test-and-shelter
With respect to hub inversion and related failure modes, I've been
working on a simple arrangement that utilizes the same principles of
any truss, more commonly seen on linear ones in rectilinear structures
for roofs, floors, etc. My models look good, but will need to go
bigger to see if its really scalable. We often have rain on snow
here, so that makes for a real good collapse test, as snow is a good
sponge and that weather can (and does) bring down whole buildings if
they are not built to the right live load specs, especially when
accompanied by wind in excess of 40mph.
Thanks for the links, I'll take a closer look at those. I do remember
people who really liked GrailCoat, but it looks like they had some
serious product failures and may disappear. The coating industry is
pretty big and I'm sure there are good choices.
Dan G.
Ashok Mathur
Aug 22, 2022, 8:50:16 AM8/22/22
to geodes...@googlegroups.com
I have looked at various hubs for joining bamboo struts with each other. Almost all require you to drill s hole at each end. The good ones then use a means to put a hold on the circumference around the two holes and reduce the chances of bamboo splits.
The structure that I want to presently design is a green house about 24 feet wide , 12 feet high and 50 feet in length; two of them are needed.
Gerry has designed such a green house with multiple extensions and they are visible on John Hurts website. They use a 3v dome as end points and simple extensions. For my desired parameters, the longest bamboo strut is just 7 feet.
Very attractive structure for making with bamboo but for one thing.
The site receives at least one cyclone each year with winds in excess of 120 k mph.
The extra load may split the bamboos that have holes drilled in them.
But if instead of a dome base, the structure was designed as an nexorade, then no holes need to be drilled, and outer bands of ms iron could allow the structure to be woven and connected.
Taff has posted an animation that shows how a dome transforms itself into an nexorade with change of eccentricity.
A nexorade of 2v should do the work.
I do not have the maths skills to do the calculations.
Will somebody help.
Thanks
Ashok
Sent from my iPhone
> On 17-Aug-2022, at 7:20 AM, Dx G <yipp...@gmail.com> wrote:
>
> Ashok,
> To view this discussion on the web visit https://groups.google.com/d/msgid/geodesichelp/CAF1iHD7soKyj-VfWCGRivSVH_EhEmzrQ1WmgUs000ygCACs0ug%40mail.gmail.com.
The structure that I want to presently design is a green house about 24 feet wide , 12 feet high and 50 feet in length; two of them are needed.
Gerry has designed such a green house with multiple extensions and they are visible on John Hurts website. They use a 3v dome as end points and simple extensions. For my desired parameters, the longest bamboo strut is just 7 feet.
Very attractive structure for making with bamboo but for one thing.
The site receives at least one cyclone each year with winds in excess of 120 k mph.
The extra load may split the bamboos that have holes drilled in them.
But if instead of a dome base, the structure was designed as an nexorade, then no holes need to be drilled, and outer bands of ms iron could allow the structure to be woven and connected.
Taff has posted an animation that shows how a dome transforms itself into an nexorade with change of eccentricity.
A nexorade of 2v should do the work.
I do not have the maths skills to do the calculations.
Will somebody help.
Thanks
Ashok
Sent from my iPhone
> On 17-Aug-2022, at 7:20 AM, Dx G <yipp...@gmail.com> wrote:
>
> Ashok,
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