May 24, 2008 at 10:50 pm #514
Has anyone considered using bamboo as a reinforcement bar, rather than steel?
- no corrosion
- sourced from agriculture, not industry
- lighter weight
- lower elastic modulus means some cracking under tensile loads
- Only in use since 1960s: less-developed technology
More info, including design calculations and notes on selecting and preparing bamboo culms.May 25, 2008 at 1:17 am #2372
Um, no corrosion? Bamboo never rots? In a wet environment?
- Agriculture is good, and industry is bad? Is that the implication? Care to support that?
- Isn’t the whole point of ferrocement vs un-reinforced concrete to increase tensile strenght (since plain concrete is fine at compressive tasks)? How would a lesser tensile strength addition be a benefit?
Point: Bamboo has been used in structural engineering for thousands of years.May 25, 2008 at 4:46 pm #2380
Thebastidge – This poster is making a moderate suggestion and references an academic study to back it up. You should really dial back the “shred” tone of your reply. Anyway, it’s plain to any careful reader that s/he’s not arguing that industry is “bad” and agriculture “good.”May 25, 2008 at 9:12 pm #2391
May 26, 2008 at 1:12 am #2395
- Bamboo yield strength is 4000psi = 28MPa according to the article.
- Rebar yield strength is 500MPa according to wikipedia.
- So you´d need 500/28=18 times the cross section of steel to make the same finished product with bamboo
- I haven´t read the whole article but I´m guessing that using bamboo is intended for applications with slightly lower specifications or criticality than ours.
- Just to be clear I´m not ruling anything out, just throwing some numbers out there.
- Thanks for the response! I don’t mind some grit on an internet forum, in fact I think it improves traction. IMHO your tone was productive. I’ll try to remember not to post anonymously in the future: feel free to be blunt and direct toward me. To answer your concerns:
I use “corrosion” in the sense a metallurgist would. In my field, it refers to an electrochemical process that causes metals to dissolve and/or transform to ionic compounds. Obviously organic matter can rot, though I’m not sure how fast silicate-treated bamboo would rot in the saline and slightly caustic environment at the interior of a concrete casting, floating in the ocean. I would like to know. The issue of swelling due to moisture is also worth looking into, and would seem to fit under your (likely more practical) definition of corrosion.
- While I don’t think it’s universally “better”, I do think agriculture might be in line with goals like autonomy and self-sufficiency more than heavy industry is. If it becomes possible to build new seasteads out of little more than plants, mollusc shells, and diatoms, that could be a major win. I considered elaborating, but didn’t want to add too much emphasis to that bullet point.
As to tension: I didn’t see anything in the design that puts a submerged member into pure tension. Reinforcement may be needed, even if the combination of forces is not enough to open cracks in the surface.
- I have only a couple semesters’ education on structures, and even that was half a decade ago, but it doesn’t seem that this design require the high proportions of steel that we see in bridges and such. As the paper mentions, the proportion of reinforcement needs to be higher when using bamboo versus steel to achieve a given strength. The result has lower density, is springier, and will quite likely have a different sort of toughness, any of which could be a pro or a con, for all I know. It may be that steel is preferred for some parts of the structure, but bamboo is sufficient for others.
I hope this discussion continues.
May 26, 2008 at 1:28 am #2396
- By the way, does anyone know how to get line breaks to work? I’ve tried adding up to six blank lines, and using HTML tags, but to no avail. I’ve resorted to using bullet points on alternate paragraphs.
Sorry to post twice in a row, but I checked back to the paper, and the example problem suggests using 4x the cross section, no 18x. Perhaps they used mild steel in the ’60s, or maybe Wikipedia listed a yield strength without a safety factor, and the paper had a strength that included a safety factor.
- Additionally: re-reading thebastidge’s comment, I think we may have caught another jargon problem from my original post: elastic modulus.
Just to clarify: even if you make bamboo-reinforced concrete with the same ultimate strength as steel-reinforced concrete (which is quite possible for moderate-strength, high-toughness designs), the bamboo will stretch more under a given load than the steel will. I tried to put this into layman’s terms by saying “springy”, but perhaps “stretchy” is the better term.May 26, 2008 at 2:44 am #2398
Bamboo is not consistantly the same strength for size, though for a plant it’s very impressive. In a structure this large, and subjected to various unpredictable forces, it would be really imporant to have the same strength each and every inch. That is great thinking for solving the corrosion problem though.
Bamboo, and reed boat craft is generally for lightweight boats. Since the center is hollow you’d have a lot of voids forming in your concrete when poured, which would ultimately cost more in labor and concrete than just dealing with steel to start with. There is also the problem of expansion of plant fibers when wetted.
Great suggestion! No idea should be viewed as impractical until discussed.May 26, 2008 at 10:26 am #2423
Not so plain. I hear people making essentially that argument all the time. I just wanted to verify the poster’s assumptions, it does go to credibility in my mind. The academic study referenced is excellent, this poster did a good job of providing resources along with opinions. But I challenged some ideas on their merits, without calling names or saying anything denigrating.
May 26, 2008 at 10:35 am #2424
- There are some pretty whacked-out ideas being presented in some other threads. If one is going to be moving to a dangerous and unforgiving environment, a certain measure of practicality and attempts to educate oneself on practical engineering and realistic expectations are in order. If that means calling bullshit on some ideas, so be it. Not all ideas are created equal.
- Thanks to the original poster for his follow-on comments explaing further. I’ll comment on that next.
Thanks Joel, and if I was offensive, I do apologize. I was more interested in addressing your points than etiquette, that is sometimes a failing when discussing online that I try to address.
- I take your comment about corrosion. but I was getting at the point that specific means of failure or not, the durability is important, and rot and corrosion essentially amount to the same thing from a functional standpoint. I think you heav already acknowledged this so I won’t belabour the point. Sometimes I try to encourage a certain rigorously critical mindset towards untried ideas rather than feeling super strongly about a given idea.
- The tensile strength is important, as is shearing strength. The more internal displacement, the more ballast has to be at the bottom to keep the structure upright. while gravity is somewhat counter-acted by buoancy, there will still be a lot of weight hanging down a long, narrow structure.
- I’m cool with organic solutions, as long as they are cheaper and better (and the ratio to decide between better/cheaper is a sliding scale). I wasn’t sure of you were leanign toward organic because of economics and engineering or because you worship Mother Gaia and hate engineers as the Great Satan. It makes a difference in ho wmuch time I spend reading/responding to your subsequent posts.
There’s something wrong with the setup of the forums. They’re still working out the bugs. You can switch to plain text editor and add
and it will work, but if you have done any auto-formatting, it will screw up some other things that you will then have to fix. for now it is easier to use numbered or bullt point lists interspersed with normal paragraphs.May 26, 2008 at 8:14 pm #2452
In chapter four of the paper there is a table with properties of bamboo. I figured “Allowable tensile stress” meant yield strength. I´m no engineer though so don´t take my word for it. And I guess you need to take MOE into account as well… so forget that 18 times cross section number. It´s probably wrong.May 26, 2008 at 8:15 pm #2451
The link suggests splitting the bamboo into long, thin strips to prevent voids, and treating it with water glass or tar to avoid swelling. Other chemicals could be added to this waterproofing treatment to slow rotting: I’ve heard a mix of sodium chromate, copper sulfate and boric acid works, which sounds similar to anti-fouling chemicals. The strips are bent hot, and laid up like re-bar, but with about 4x as much cross-section of reinforcement.
AFAIK, the whole idea with ferrocement is trading off skilled for unskilled labor. I think the higher volume-fraction makes inconsistencies less of an issue, but of course it would be wise to inspect everything and to test representative samples.
JoelAugust 21, 2009 at 11:44 pm #7526
How is this relevent to seasteading?August 22, 2009 at 7:29 am #7528
I really like the idea of bamboo because it can be grown on a good sized Seastead and used for expansion projects. While it may take roughly 10 to 20 times more for the same stength, bamboo may cost sufficiently less than steel to much using it economical. It may end up being more expensive though because it may need special treatments to prevent rot. Personally I think the future of construction may be in growing structures more than building them.August 25, 2009 at 4:40 pm #7575
on ETV and various reinforcements were discussed for concrete and the one I liked the most was plastic matting. The stuff they showed was mostly orange in color with 4″ holes in it on big rolls. Bamboo would work for reinforcing concrete but it would rot just like steel rusts and corrodes only a lot faster I think. One point that was made was that the Pantheon in Rome is made of unreinforced concrete like most of the ancient Roman stuff and that if it had been steel reinforced it wouldn’t have lasted this long. The Romans didn’t build ships out of concrete but a plastic reinforced concrete ship might really last forever…January 23, 2010 at 7:18 pm #9319
Bamboo is a great solution if your design objectives are coming from a certain place.
Bamboo can likely be preserved by sealing it in beeswax or thermo plastic. It would then make a great exoskeleton for a geodesic dome exoskeleton. The rigid monolith designs being proposed modeled after oil rigs are the wrong direction IMO and will garuntee that seasteading stays a scarce novelty.
If seasteading is to become a new frontier: it is necessary to design around cheap, easy, and “renewable” materials in the spirit of the “RepRap” project. This is my opinion, however I suspect that it is also an accurate prediction of the most promising direction towards meeting our objective.
We can talk about these things or we can experiment and have 6 people living on a manmade island for less than $1000 dollars by the end of the year.
Step 1: Homeless shelter
Is this the future/vision of the seasteading institute? Maybe their vision is a little more top heavy in terms of barriers to entry in exchange for more comfort. Great. That’s a good thing. These visions are not in conflict, and the research SHOULD be done in parallel as findings which are of no use to one goal, may be the keystone to another. This saves both projects time as they don’t re-cover territory.
In the mean time: this forum seems like an excellent place to move forward with prooof of concept systems.
Anyone who wants to talk about a frame design:
fill up your bathtub, get some balso wood, popsickle sticks, plaster of parris, syringes, and balloons and experiment! It is human to embrace new visionary ideas with defeatist attitudes. Prepare for this. It’s easy to shout down an idea, but it’s hard to argue with results.
Get a fish tank and experiment with preservation techniques for biological building materials.
We’re looking over the cliff of a new frontier. We can be the ones to TAKE ACTION and make leaps of faith, or we can stand on the edge and plan on the best way to approach the problem.
Thank you everyone for your ideas, and for sharing them on this forum. It is a great brainstorming resource to draw from. Don’t let anyone convince you that you need a million dollars to escape the rat race. It’s been done with plastic bottles. Let’s lash together some bamboo and make history. If bamboo doesn’t work then maybe crushed seashells as a composite will. The devil is in the building materials. It’s all architorture from there.
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