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Why bamboo is the ‘green steel’ of 21st-century Asian architecture
Bamboo fibre is stronger and cheaper than steel, says Dirk Hebel
Carbon Fiber Vs Steel Vs Aluminum Vs Bamboo Pros and Cons
Is bamboo stronger than steel?

How are their comparative strengths in various directions and orientations?

I've been reading a lot online but can't seem to find definitive comparison that talks numbers and specific comparison of numbers in various directions.

Are there specific experiment(s) or research whose findings can be outlined here?

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    $\begingroup$ Look carefully at what is actually compared. In your second link it says "Our [bamboo composite] material is only a quarter of the weight of steel. In terms of strength to weight, it performs better than steel." So it's not tensile strength that is compared there, but the specific strength, which is an important material parameter in civil engineering. $\endgroup$ – Robin Jun 27 '16 at 9:18
  • $\begingroup$ @Robin - Do share more of that in an answer if possible. I can't remember all diff specific strengths/ stresses/ strain varieties from my Engg college days $\endgroup$ – Alex S Nov 16 '17 at 3:21
  • $\begingroup$ In my opinion the main point is that you have to look at the application. It does not make sense do compare steel against bamboo just for the sake of it. They are too different. This is also the core of what starrise wrote. Therefore I'm afraid I'm unable to write more about the topic. $\endgroup$ – Robin Nov 17 '17 at 7:36
  • $\begingroup$ You mention "bamboo". But what type of bamboo? Because there are many type of bamboo, and so it depends the strength. $\endgroup$ – Lavinia May 2 at 19:15
  • $\begingroup$ @Lavinia there’s many types of bamboo as well as steel. Given the content & context above I’m open to any that were studied comparatively for building materials $\endgroup$ – Alex S May 6 at 12:07
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Stating categorically that bamboo is stronger than steel is a bit like stating that automobiles are faster than planes. On its face, it is a bit shocking, and seems wrong. But a rocket-powered automobile is certainly going to be faster than a one-seat propeller plane over a short distance on a controlled track. Then again, the same rocket car is going to lose in a ground-speed race to an SR-71 blackbird by a factor of about 2.5. Note that each vehicle has its advantages and disadvantages aside from just measurement of speed. So it goes with broad material comparisons. Bamboo may be strong, but there are steels that will almost certainly be stronger. Bamboo fibers may be stronger than the bamboo itself, or even stronger than some steels, but will probably still not approach the strength of the strongest steels.

The highest strength steels have isotropic strength near $2\ \textrm{GPa}$, and have ductilities of $3\%$ to $10\%$. Kevlar fibers are near $3\ \textrm{GPa}$ but only along their length. Their transverse strength is closer to $50\ \textrm{MPa}$, and they have limited extensibility, closer to $1\%$. All of these values are available with some internet sleuthing and in many textbooks. Bamboo fiber data is harder to find, but the sources here and here (both links end at ScienceDirect, and are peer-reviewed journal articles) have interesting results. The former link has either $350\ \textrm{MPa}$ or $550\ \textrm{MPa}$ depending on preparation method, with no reported variance (though there is probably considerable variance, it was not reported). The latter link gives $650\pm175\ \textrm{MPa}$ and $800\pm100\ \textrm{MPa}$ for different preparation methods. Note that these values are all along the fiber lengths. No values were found for transverse strength, though it is probably an order of magnitude lower than longitudinal strength if the mechanisms are similar to those of non-biological polymers. And, at any rate, the fiber strengths are misleading since the fibers must be mixed into a polymer-matrix composite to be of any use (except perhaps as ropes), which will result in strength values lower than those of the fibers alone.

Measuring the strength of bamboo plants is challenging due to the variation in size and shape, and the difficulties of finding proper measuring tools, or even of what geometric values to measure. I was unable to find any information on the subject of bamboo plants.

As with all material selection problems, there are other tradeoffs worth considering depending on application and requirements. Some things to think about include ecological factors (bamboo is renewable), environmental factors (bamboo is flammable), loading factors (steel can be made ductile and its high properties are isotropic), and weight considerations (bamboo is much less dense). Another important factor is processing: steel is always initially made by casting to a generic shape then by working, or directly to shape by casting. The process is intensive but relatively straightforward and well understood. To form a bamboo composite one must separate the fibers from the remaining plant material, chop them to size, coat them with sizing to ensure compatibility with the matrix material, mix with matrix resin, and then finally form into shape. Some of these steps and how they affect properties are not well understood yet.

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