Nodes, diaphragms and other stuff

[shotomartin]

Is there an elegant way of removing, from the ends, the nodes from the inside of, say, a 10 ', 3" diameter culm? I can think of a bit or hole saw on an extension, or some sort of punch. Surely there is a better way. TIA.
Peter Martin

[jmbamboo]

I have used a piece of steel rebar with great success. I first punched out all the nodes with the rebar then slid the bar up and down inside the now hollow culm. The rough surface of the rebar cleans out most all of the node material making a smooth inside. I used this to make digeridoos. You can use a piece about 6 feet long and go at the 10 foot long cane from both ends.

[shotomartin]

Thanks for the rebar idea. With the node (or should I be saying septum?) removed, to what extent is the compressive strength of the culm reduced? Peter

[Strider_1952]

having split bamboo and having had a good look at the node, the bamboo seems to swell there to create the node. the little bit of the node that is remove using the above mentioned method should have no strength reduction associated with it.

[shotomartin]

Originally posted by Strider_1952
the little bit of the node that is remove using the above mentioned method should have no strength reduction associated with it. I was concerned after reading the following at http://www.networkearth.org/naturalbuilding/bamboo.html : "For structural bamboo it is important not to penetrate the septum as it is the crucial part of the bamboo for strength" and "Bamboo is unique in that it is strong in both tension and compression.... There is some controversy in determining proper testing protocols, as it is important to test bamboo which is at least three years old, and that the test should occur on a piece of bamboo with an entire internode and two intact nodes". This suggests to me that the node plays an important part in compressive strength. Thanks for your opinion based on experience. Peter.

[Strider_1952]

Forgive me, I should have explained that I was working with P. aurea and P. aureasulcata. And one should remember which bamboo they are using. I would be willing to bet that P. aurea with septem removed will be stronger that P. aureasulcata with the septem intact. Futher, if i were going to use a bamboo in a structural application I would certainally go down to the local collage of engineering and do a little testing of my own on the bamboo i was going to use.
My hope is to find out that removing the septem will help with reducing splitting, which really reduces the strength of bamboo. And if i want really strong bamboo, i split it and then tie it back together.
Also with respect to the artical, we do not have a problem with bugs down here and i would think the same would be true up there. It may be the clumpers they use or the temperature.

Have fun,

Michael

[jmbamboo]

I would be curios to know what effect removing the septum has on the strength.
I agree with you concerning P.aurea vs P.aureosulcata. When cutting and handling it is easy to see the difference in the quality of the wood.
I think a geat deal depends on what part of the culm you are using. The bottom (base) few feet of some species (P.bambusoides and P.h.pubescens for example) are extremely thick walled. In comparison the septum is of such low strength it would seem not to add greatly to the crushing or compressive strength of those sections.
Jim

[Frank McNeill]

Anyone who uses bamboo culms as structural members might be interested in a PDF file about physical properties of Sulfur-Based Wood Composites at
www.google.com/search?hl=en&q=sulfur+wood+composite&btnG=Google+Search that Suggests the possibility for producing bamboo/sulfur or bamboo/sulfur polymer cement composites, since a modified form of sulfur called sulfur polymer cement would probably be stronger than regular sulfur.

There are two sources that I know of in north america, STARcrete in Calgary, Canada at: http://www.starcrete.com/index.html and GRC Chempruf in Clarksville, Tennessee at: http://www.chemprufconcrete.com/
There is also a source in Poland, The Marbet Wil company with a web site at: http://www.marbetwil.com.pl/en/index.php There might be one more manufacturer in Iran, but I haven’t found any info about this on the Internet.
Chempruf and Marbet Wil sell additives that can be used to convert locally available sulfur into sulfur polymer cement, which might be good to know for anyone who isn’t very close to Canada, the US, or Poland.

Some of you probably know that the Taiheiho Cement Company has used crushed bamboo to reinforce concrete made from Portland cement mortar. Go to: http://www.grida.no/climate/ipcc/tectran/337.htm for an old report. The plan was to build a factory in Colombia to produce blends of Portland cement and bamboo fiber.

If anyone decides to fill reamed out culms with molten sulfur or sulfur polymer cement for use in a moist, warm environment, they might want to protect the filled culms from varieties of sulfur-loving bacteria called Thiobacilli that are ordinarily satisfied with converting Hydrogen Sulfide into dilute Sulfuric Acid. It has been discovered that this bacteria is the usual cause of failure in concrete sewers. The bacteria will attack elemental sulfur too, when no H2S is present.
There is a two part, all solids urethane coating material that can be used to protect sewers, or structures with exposed sulfur or sulfur polymer cement concrete. Madison Chemical Industries, Inc. bills itself as the: World Leader for Infrastructural Coatings”TM and is located at:
490 McGeachie Drive, Milton, Ontario Canada L9T 3Y5
Phone: (905) 878-8863 Fax: (905) 878-1449
http://www.madisonchemical.com/index1.htm

Best wishes, Frank

[Mark Mortimer]

Just a note on spetums or nodes.
I'm pretty sure I have read both views, that they do add to strength and that they don't. Can't find my sources at the moment.
But in my experience, I have found no difference. Mind you I don't tend to subject bamboo to large amounts of compression.
However, both Oscar Hidalgo and DrJules Janssen both maintain that the part of a culm most resistant to compression is the node area. I believe this to be true even if there is no septum present. It's the swelling, and the configuration of the fibres.
Cheers, Mark

[Mark Mortimer]

It is interesting, in Argentina, the bamboo cutters and sellers were convinced that removing septums would reduce cracking. I think they were correct as far as their circumstances were concerned: they used to stand bamboo against a wall in the hot sun, and you could hear then exploding sometimes. Perhaps removing septums would not let the internal pressure build up so much.
Another reason for removing septums is to avoid cupping, or retention of water in a vertical culm (outdoors with no protection). Used as a post, it makes sense to leave the top sepetum intact, so water doen't fill the top internode. But later in it's life cracks willdevelop along the culm which will let in water. If there are no spetums the water will just drain out. With septums the water will remain and cause problems.
Personally I like to leave spetums intact in my indoor furniture, as I think a culm ending on one looks better than a gaping hole or rattan lashing. Of course it makes selection of culms a longer and more difficult process as usually I have to find pairs of culms which have nodes at both ends at the right place!
Cheers, Mark

[Mark Mortimer]

More on diaphragms or nodes. I wrote an e-mail to Dr Jules Janssen to ask his opinion about it. (for those of you who don't know, he's probably THE major dude in bamboo technology). I didn't know if he'd reply, but he was nice enough to send this(it seems to contradict what I said):

Dear Mark Mortimer,
Generally there is no significant difference in strength between nodes and internodes, which means the septum does not have a significant influence.
1. This is especially the case in compression.
2. With regard to bending, some years ago we did bending tests on culms with outer diameter of say 100 mm and free span of 4 m, with removed diaphragms; we found no difference in ultimate bending strength! The main function of the diaphragms (the more common name for septums) is in a support: the diaphragm makes the culm stronger for the load perpendicular to the culm.
3. In shear there is a difference but this is mainly due to the difference in area.
4. In tension there is a siginificant difference between nodes and internodes, due to different tissue.
I hope this is the answer you need. Kind regards,
Dr. Jules J.A. Janssen.
Editor-in-Chief of INBAR's Journal of Bamboo and Rattan.
Based at Eindhoven University (B-CO), The Netherlands


Good to know,
Mark