In this final bonus episode, I sit down with David Trujillo to discuss the structural qualities of bamboo, the challenges of connections, durability and fire, and how engineered bamboo could play a critical role in the future of low-carbon construction.
In this podcast, we discuss the following topics:
Orin: Welcome to the Bamboo U Podcast. Thanks so much for joining me here today in Bali. It's you know, it's a real pleasure to have you and to get to learn so many incredible things about the work and the research you've been doing to figure out how to actually know how strong our bamboo buildings actually are and to really take bamboo engineering to a whole new level.
So thanks so much for joining me and you know, thanks so much for, for doing this really incredible work, that at least I feel like, and I think a lot of our listeners probably feel like, is really important for us to grow bamboo as a building material around the world.
David: Well, thanks Orin for inviting me to Bamboo U. It's fantastic to be here. I feel that when I'm here, it's not just me teaching. I'm also learning all the time. It's a fantastic location with such a variety of solutions using bamboo that I'm always in awe of everything I can take in. So, it goes both ways.
Orin: Awesome. Well, it sounds like it's a reciprocal relationship. So David, what got you into being a bamboo engineer and really a researcher for bamboo engineering
David: So, I was born and raised and went to high education in Colombia. And as some of your listeners might know there's a lot of bamboo usage in Colombia, particularly in the coffee growing region. And I think we were… Sort of came about to our professional lives in the, sort of in the light of the work that Simon Velez had done. He was a bit of like a trailblazer in this respect and influenced a generation of architects and engineers. The definitive motivation was I wanted to do something that meant more to rural communities, that meant more to low-income families.
And I thought, well, here's a cool resource that is economical, well that's what I thought, at least. I mean it can be. And strong, and beautiful, and earthquake resilient, which was something I came to realize in, after the earthquake of 1999 in the Coffee region. And so, and then afterwards I, or more or less at the same time I was realizing about climate change and, but, you know, this is a low carbon material. So it just, it had everything for me. I thought, this is the way to go, and then I wanted to look into it and design with it. And the reality was, it wasn't easy to design it because the answers weren't there. So, I said, well, then my mission is to find the answers.
And that's how I got into it. I moved to the UK 20 years ago, and as soon as I could which was 15 years ago, I got into academia and that gave me the free hand to research things a lot more than I could have done in industry.
But I'm now back to part-time in industry, two years ago in Atelier One, on a part time basis, and that's sort of now, I could say, I'm in the sharing phase of what I’ve found.
Orin: Awesome, and so what is it about bamboo that makes it so strong and makes it so incredible as a material?
David: The first thing, and probably your listeners know this, but bamboo is a grass, it's not a tree. And it's, it's a plant that sort of evolved to be tall. It wants to reach out as high as it can in as little time as it can, to beat the rest to the sunlight.
And this is probably what's led it to be, think of it like a mast of a sail is blowing onto it. So, the wind is pushing it really hard and it's fighting super-efficient in, in doing it.
So it's, it's a beautifully designed, if you like, plant; efficiently evolved plant. But so it has these incredibly strong fibers in the direction of, of what we call the axis, so longitudinally it has these very, very strong fibers. It is, people say it's very flexible, so it's relatively flexible, it's not that different to the strongest timbers in terms of flexibility, maybe it's a little lighter and stronger, so that's what it leads us to think it's flexible, because we can push it very far before it breaks, and that's where our perception of flexibility comes from.
That's how it evolved. That's its mission as a plant. We human beings then, take it and use it in something else, and we have to live with the compromises it's made because it's efficient to do that. When we want it to do something else, then we have to find workarounds. But it is incredibly strong.
Just as a reference, if you pull it, sort of parallel to its fibers, in tension, you can resist sort of an average 100, 120 megapascals, or, also known as Newtons per millimeter squared. That is very, very strong. It is about a third of how much steel, structural steel, can take. But, as I like to remind people, you know, steel weighs 12 times more, or at least 10 times more, and it's, you know, it has come about through a hugely energy-intensive process. This is just something that grows in 3 years. So, it's phenomenal.
Orin: So, you're saying that it's 30 percent as strong as steel, but a 10th or a 12th of the weight. Yeah. Interesting. And so, you know, there's a lot of like marketing out there that says the bamboo is as strong as steel. From a strength to weight ratio, and what are they talking about when they say that?
David: Well, you've, you've heard my numbers, so I said it's about a third, a third of the strength, and a tenth of a, of the weight. So, you do the math, it looks, you know, it turns out to be about three times higher strength to weight. That was tension. Which in bamboo, we struggle to exploit. So, then we go into properties of mechanics, like compression, where it's not so remarkable, but still remarkable, it's got a very efficient shape.
And then, because it's a natural material, not a man-made material, we then tend to punish it with higher levels of factors of safety. So, it's still remarkable in terms of strength to weight and what we can do with it. So, I don't think, you know, the marketing, it might be true that some aspects can have a high strength to weight ratio, but there are some situations that take that phenomenal tensile strength. It's really hard to use because you have to find a way to connect it. And that's where we struggle.
Orin: So it has a really high strength in tension. Yep. And has a really, or a comparable strength in compression to other wood, or?
David: Yeah, in compression it's stronger than most timbers. And has the added advantage that it's hollow, hollow cylinder, so it's actually more efficient in its use of that strength. So yeah, when, if you find a timber that had a comparable compression strength, it would probably take 80 years to grow.
Orin: So, we can grow something in four years that's as strong or stronger in compression as a material? And it has a more efficient shape?
David: Correct
Orin: Awesome. And just so listeners also understand, what is it about a cylinder from an engineering point of view, and particularly, I think, is it's I believe it's not just a cylinder. It's also has nodes and undulates a little bit. What is it about that shape that makes it so efficient?
David: So let's start with it being a cylinder. So, the best way to explain this is sort of through an analogy. Take bicycles, yeah? A bicycle frame is made of hollow cylinders. And the reason is that you're trying to push your metal as far away from the center to increase the characteristic, which we call the second moment of aerial or the moment of inertia, as far away as possible.
Not to make it too thin, otherwise you'll have the metal crumpling, but as far as you can to use as little metal as possible, and that you do that to have then very light bicycles. So that's what nature has done. It's pushing the bamboo far away to get a very efficient shape. You, you're pushing the materials far away, not too thin either with otherwise they’ll crumble.
And this is where the, the nodes come in because when you get this crumpling, which we'll call it buckling, the nodes help prevent buckling from happening. And this is where the plant is evolved to suit itself, not suit us - is that you will find the nodes are closer together at the bottom of the plant where the stresses on the wall are the highest.
So it's trying to prevent the buckling towards the bottom and gradually as you move towards the top of the plant, it spaces them further apart because the stresses become smaller. So, it's a very remarkably engineered plant.
Orin: So interesting to think about how it uses just enough strength to accomplish its goals of getting to the sunlight as quickly as possible.
So it's like, [it] really is a race. And I can't help but draw analogies to maybe like, our intentions with something like climate change. It's also kind of a race to like, okay, how do we lower our impact as quickly as possible? And it's almost like the bamboo has the same kind of theme where it's like, okay, how do I achieve my goals with as little effort and as quickly as possible?
So just doing, you know, being intelligent to put exactly what's needed. So, I can't help but draw this kind of analogy where this material has kind of showed up at a time when we really needed it. Or we take a notice, I should say, at a time where we really need it. So that's the upside. You know, it's super fast growing. it's really, really light and strong, and its shape is more efficient than a comparable thing like wood. What's the downside?
David: Well, as in every material, it has downsides. And it's really important to realize that that's what design is about. Design with any material is about working on its downsides.
So, those fibers I was telling you, they're primarily along the stem. At the diaphragm they sort of mix a bit. Or the node, sorry, so a big mix of it, but really it doesn't have a lot of strength in the other direction. So, if you, if you try to pull it in the other direction or you try to shear it, it's not so good.
So, we have difficulties connecting. Because in many connection styles or types, we start trying to break it in a way that induces that splitting or shearing, and that's what limits us to being able to use that phenomenal tensile strength, because we don't have an easy way to sort of get hold of it.
So that is and remains really very much the challenge of using bamboo, it's trying to have it connected, but that's one of the downsides. The other downside that bamboo has is that unlike those 80, 90, 100 year grown trees, in its very short life cycle, it doesn't accumulate naturally-occurring toxins.
So trees they have sort of a dumping ground, which is called the heartwood, and lots of chemicals that occur naturally in the tree, they just get dumped in the heartwood. So, a very old tree of a certain species, that wood has all these toxins which make it, unpleasant for fungus and insects to eat. Bamboo doesn't have that.
So, because it sort of grew so quickly, it didn't have time to accumulate the stuff. It doesn't have a high level of natural durability. You have to do something to it. And this is, sometimes people who want to remain very pure about not doing processes which are artificial, they say, oh, let's not put preservatives - they're out of their mind. We have to put preservatives into bamboo because it doesn't have natural durability.
The other thing is somehow in people's mind, they go back to that message that it's got the strength of a tree that took 80, 100 years to grow. And so they sort of think it also has the durability of a tree that took 80, 100 years to grow.
And so they expect it to do things that that sort of wood can do, which is be exposed to the elements and so forth. And again, bamboo doesn't like that. It has to be kept dry and protected from the sun and water. So, that's another downside, but again, we solve these problems through design.
And the third thing is wood, contrary to what many people's perceptions are, is pretty good in fire and that is because it burns from the outside inwards, and it has a gradual, a residual section. And, you know, if the fire brigade comes and picks out the fire, you've still got something holding up the building. The thing with bamboo, because precisely is hollow. You've got very little to burn before it's gone.
So it doesn't mean you can't work with it. But again, we have to think about these implications through design and they are workarounds that we can talk about later.
Orin: Awesome. So, I mean, those are all 3 of those topics I think are really good to kind of get into. But I want to start with the connections because I think from an engineering standpoint, that is really interesting to me and what makes me realize is so the building is basically as strong as its connections in many cases.
And what is, you know, because we use a fish mouth, which is very elegant, but high labor. You can use a nut and a bolt and a washer, which is a little bit of, you know, basically borrowed from steel construction which is less elegant, but relatively strong, especially if you fill it with mortar.
But what do you think be, you know, the golden ticket or the future, at least for round pole bamboo construction, what do you think the connection future is, and if you start to think about things like 3D printing and 3D scanning and AI on these digital design tools and what I mean, do you see there being things possible now or in the near future that would dramatically increase our ability to use the strengths of bamboo and also to mitigate some of the weaknesses?
David: Yeah, it's a very interesting question, and I sometimes think I know the answer, and then I go test something in the lab, and then I change my mind.
I have, for 25 years, believed that one of the tricks that we have to pull off with bamboo is spread the points of contact. So, I have worked with small diameter fasteners, particularly screws and using many of them. So, by using very many connectors you spread the load. I feel that, amongst other things, it makes it that if, in the event that you did have a crack, it would just take out of action a few of the screws or whatever…
Orin: Or all of the screws out.
David: Or, or the bolts.
Orin: So, it's basically redundancy.
David: Right. Redundancy. And the mortar solution is a practical one, and it depends on what you're trying to do with, with bamboo. In certain directions, it does a great job. In others, it does an okay job. And that is, you know, it's compromised, and it's done a service… well for, like, 40 years. But it works.
I think there must be something beyond that. So I'm imagining… my imagination would be a product that you could buy, a bit like you can buy for timber. The branded products like Simpsons, Strongtie, or any other brand, and you can buy it off the shelf and you'd say, yeah, that connection takes so much and you'd come and just connect it to your, to your bamboo and off you go. That's, that's how I would like it to be.
Orin: Plug and play with different sizes.
David: Yeah, plug and play in different sizes. And it would mean that the beauty of a product like the branded ones is that it's not just there available in your local hardware store. But also, you can find on the manufacturer's website how much load it can take.
And I think that's a key thing that timber engineers have available. Is that they can just say, okay, look up on a table. That's how much it takes my calculations there are double. If every engineer every time had to calculate every special connection in timber, they’d say, alright. It's too hard. And it would make it harder. And so, this is what these people being very resourceful about, inventing a product that makes life easy for engineers
Orin: I guess maybe when you're maybe that's your next venture, bamboo connections, pre-engineered bamboo connections.
David: I would love to, but I don't think I'm much of an entrepreneur. That's a problem. I'm full of ideas. I just need a partner that has the business acumen to see them through.
Orin: Anybody who’s out there…No I’m just kidding. So, we talked about joints and connections. And so, I guess it sounds like the main challenge is figuring out how to spread the load and create some kind of component that is standardized enough that we know how strong it is, but variable enough that it fits into different bamboo sizes, viven that it's a tapering, hollow, curvy pole.
So how, and, and let's get into durability because that was another point you mentioned, which is one of the downsides… what do you think? So, you know, we do a lot of bamboo building and the way we deal with durability is through chemical preservation, through boric and boric acid.
And that's one of many options. And then we put a big roof on it, you know, we properly clad and add a nice long overhang. Do you see any other potential? Things beyond treatment by design and treatment through chemical preservation that will expand the durability?
David: That's a really good question.
You know, there might be things to explore like thermal modification, which could possibly work, which is maybe you put it into an autoclave and put it at a high temperature and high pressures and so forth. And maybe through chemical modification, you could get it to work.
Orin: Sounds way better than my idea of frying it.
David: Maybe. The only concern I have - a residual one, is we'd have to understand if, because you sort of put bamboo in a very exposed location, even if with all these procedures, you don't happen to develop cracks, because maybe it's not rotting… but it's starting to crack because of cycles of wetting and drying.
Orin: Or sunlight.
David: Or sunlight. Yeah. Yeah, correct. So maybe you have a product that doesn't rot, but what's the point if it's full of splits? It's still useless.
So, maybe then you have to do another process, which is sort of wrap it up with something. So, yeah, you know, we might get to the point where we engineer it to do that.
But then you start wondering, maybe, can we take a step back and see what other people are doing? And so one thing people are doing is just transforming it into engineered bamboo. And then it's just like timber, but made of bamboo.
Orin: Basically, if you're going to get into any kind of additional durability, you probably have to get into engineered. Basically, tear it apart and put it back together.
David: Yeah, I mean, the other strategy you could adopt is having some sacrificial layers. So maybe… in some architectural styles in South East Asia, you use bamboo walling systems that are exposed to elements. I presume know that in 5 years time, you have to change it.
Orin: Yeah, we do that with our roofs.
David: Yeah, so provided the structure is not expected to be replaced, but you know, you can do that. So, yeah. It could be that someone comes up with a clever solution. We can work around this solution. There are very few materials, structural materials, that really want to be exposed to wetting and all the elements.
You know, take steel. Steel has to be regularly painted. It has to be regularly maintained, otherwise you're going to have a problem. Concrete…Yeah, you can get it to work fully exposed, but then watch out if you have chlorides and things like that. So, even in these materials we perceive as so called durable, we have to take precautions of design to ensure they are durable.
Orin: Yeah, it's like the Golden Gate Bridge. When they finish painting on one side, they have to start again.
David: Absolutely.
Orin: So they're, they're always painting it.
David: Yeah, I mean, if you think of the utmost durable material, which is stone. Yeah. In medieval cathedrals, the reason why you had gargoyles is to throw the water as far away from the building as possible so that water didn't trickle down the side of the graves.
So every material requires care about how you get it to be as durable as possible.
Orin: You know, it's interesting you bring that up because I find that a lot of people here when we're building bamboo buildings for them, they say, Oh, well, you know, it's not… or people who would consider bamboo building… but they go, it's not that durable, the durability isn't good.
And I mean, there definitely… there's grains of truth to that, where there are certain situations where it really isn't as durable. But I feel like part of it is just that it's actually the maintenance, or the other thing is not, not even about durability, but just say, oh well, it's hard to maintain.
And actually, if you start to think about a normal house and all the works that have to be done after 5 or 10 years in any house, it's actually what's true is that the maintenance is much more specialized and not as standardized, as finding someone to refinish your bamboo house is just a little bit harder than finding someone to repaint the concrete pipes. Right?
So, I think there's almost this element where it's the early adopter syndrome where you're kind of, because you're doing something different from what everybody else is doing, everything's just slightly harder because it's not as common or available to make changes and fixes.
David: Yeah, and I suppose there's also, I think you're describing mainly the locals who have their perception of material through vernacular construction.
Orin: Well, we see it also with foreigners. Oh, they never have a bamboo house, but then they buy a villa. It's probably not even… it's often poorly built out of concrete and steel and you know.
David: But at least from the point of view of the locals, I can understand that they would have that perception because their experience in the vernacular construction was a type of construction that wasn't meant to be durable. It was something that, you know, we built for a while and then…
Because they didn't have access to chemicals to make it durable. And you know, there's bamboo everywhere, so just come and fix it. It was… when a material comes along, say concrete that lasted a long time, then they come to expect things to last long. But, you know, I think we can, we do have buildings that have been built with modern preservation systems that have been around 50 years, maybe, 40 years, something like that, and they're still fine.
So, it is an issue that, on the one hand, is that people are comparing it with probably the wrong type of things. And then, there is the other problem that every now and then someone comes along and thinks they have, they don't have to follow these rules. And, oh, I'm just going to expose the bamboo to wetting. Who cares? And this, that, and the other. And then, of course, this bamboo looks nasty in five years time. And they say, you see? Bamboo's not durable.
And they think they can be durable. I mean, our listeners can't see this, but I'm sitting on a bamboo chair. I'm looking at a bamboo table. And These chairs and tables are going to be fine, easily, for the next 50 years. Why? Because they're indoors. So, if you can keep the whole of the bamboo indoors, fundamentally, it'll be fine.
Orin: Yeah, and so that brings me to my, my next question. This is the final question related to durability. But what do you think, you know, people always ask, how long will a bamboo building last? And my best answer right now is it depends, right? For, because I don't know what kind of bamboo we're even talking about. You know, there's traditional vernacular buildings with bamboo that have lasted over a hundred years.
And then there are situations where I see things that are built here that are, you know, probably only going to last, you know, 20 or 30 years. So, what do you think, besides exposure, like assuming that it's properly covered, what other elements in the longer term would you be thinking about or worried about in relation to durability just from an engineering perspective?
David: Well, the main concern is where you're going to get some source of water. So, is it going to be some condensation? Is it going to be some other form of water? If you can control that, you're covered for most situations that humidity can arise.
You could have humidity in certain climates, not to be concerned here, but in certain times you can have also through the walls in the perimeter when you have risk of condensation. That's the other situation that happens, and same happens for timber, and it just requires careful detailing of those contexts.
But I think in terms of that hazard, what you would have on the tropics is insects and termites and so forth, which could also want to try to eat your building. And that's mainly addressed in preservation, but that's also addressed by creating a barrier between the ground and on your building, you make it hard for termites to get to your building in the first place.
So provided you don't sort of abandon the building to its own devices, but you're just inspecting it regularly to see that you're not getting tunnels for termites. I'm told that that is a way that you can make them last indefinitely. And there are cases of buildings that are doing very, very well when they follow all these rules.
So how long can it last? So, the answer is, I would say, provided you're maintaining it and looking after it and someone's living in the building, indefinite. What we would like to say in standards is 50 years because it's the benchmark of comparability. You know, we don't say forever because it sounds silly.
Orin: So let's talk about fire. You mentioned that one of the big issues, bamboo is a cylinder, makes it super efficient, super strong, with very little material, but then, you know, you have this fire issue, and I know that you played a really important role in developing the ISO standards for structural applications of bamboo, and I believe in the, correct me if I'm wrong, but I believe in the ISO standard, you've limited bamboo buildings to two stories, because of this fire issue, right, where, you know, obviously you don't want people in a building that is going to burn down really quickly.
So, where do you think that's the biggest concern is in relation to that? And do you think is there any way in your opinion around that? Or do you do you think that it's like, just, you know, solid. Like if it's around a round-pole building and we really want to be safe and responsible that we want to avoid you know any exits above two stories.
David: I'll start by caveating that I'm not a fire engineer, and if there’s a fire engineer listening to this podcast, they might be cringing a little at the stuff I'm going to say. In ISO we spoke, we said very little about fire because it was given, it was deemed to be outside the scope of the committee to say a lot because there's a separate committee.
The other thing to bear in mind about ISO standards is that they're voluntary and they have no jurisdiction until they're adopted by a country. And even then, they will be just voluntary because they're standards. To make them enforced, they have to become codes.
Now, so, we put that two stories thing sort of to hint at anyone writing a code that this is what we feel comfortable about. Why? Because you could imagine people can probably still escape through windows and stuff at two stories. Above that, then, you have to have pretty well thought through fire strategies. What could you do? You could address the issues architecturally. So, you could address them through means of escape.
You can enhance your means of protection, your means of alarms. So, it means, you know, maybe you can't save the building, but the key thing is saving people's lives. So, if you have better means of detecting, better means of egress, and then there are things to better understand to which I don't claim I know the answer, is one of the strategies that we use for fire is compartmentalization.
So it's creating barriers between rooms and so forth, which is a strategy that works well in an environment where we want to close doors and windows because we want to keep the heat in, or maybe keep the cold in, which is maybe a very Western way to see things. In an environment where, well, it's very open because it's, you know, it's a tropical environment, you lose maybe the compartmentalization, but maybe you gain a thing that the smoke escapes.
And remember, the first killer is not the fire, it's the smoke. So, the smoke might just go out of the building. So provided people are able to escape, it would be possibly better because the smoke issue might go up. Again, fire engineers, forgive me if I'm talking nonsense. And then the other things that would be potential that you can do that's using fire is something called encapsulation, which is where a plasterboard or gypsum board comes in, you know, timber constructions.
You hide from fire, and we could do that with bamboo, but it seemed a great shame to be using beautiful round culms and then hiding them. So, that is a technique that has been used in some type of construction to where the driver is not using bamboo so much because of its beauty, but using bamboo for its cost or its sustainability. So then they just hide it or at least they hide it in firewalls. So that's walled between two properties.
You could maybe address it by spacing buildings a certain distance. So, if my house catches fire yours doesn't. You could also, I mean I was seeing this morning online, it was this… there are these active fire detection systems that, you know, they look like these little robots with a hose and they detect a fire and they put it out in like five seconds.
Orin: They live on your wall or?
David: They live like on your wall, on your ceiling. And the moment they, they're like always scanning for heat and the moment they detect heat of a certain temperature, they turn their nozzles to the fire and put it out. It is phenomenal. There’s a great footage of it online.
Orin: AI robot firefighter in your house.
David: But, yeah, maybe that's the way. Just put out the fire before it's a problem. Again, maybe it's not a favored system because it's an active system. It requires that maybe electricity supply’s not damaged, so that everything's working properly. So, I don't know where law and authorities stand on active systems of firefighting. But I think all these could come in the mix, as a way to address this, and maybe we could push to, you know, three, four stories. Are we going to make skyscrapers out of this? No, I don't think so. Not in its round form.
Orin: So, so that that's a great segue. So we're definitely, you know, I think, I think we're in agreement. We're not going to be making skyscrapers out of bamboo poles. But I think what is surprising, or at least was surprising to me when I learned about it a few years ago, is we may actually be making skyscrapers using bamboo as an engineered material. And do you see that really being something that will take off in the next, you know, 5 or 10 years?
David: Wow. I think… I think engineered bamboo is a very interesting product. It's, so for the listeners, it's just changing bamboo, breaking it up, and then gluing it again. So it becomes sort of rectangular, so a bit like timber, but made out of bamboo. And you can, depending very much on the processes, retain a lot of its strength and its stiffness.
It transfers many of the characteristics that it had as a bamboo species to be engineered and so some species produce better engineered bamboo than others. And I think it can be very promising because, as I say it is strong, it is relatively stiff compared to timber. Particularly tropical bamboos are thicker, strong, and stiff.
And you can also imagine that it's something that production could be ramped up. So, you were saying about, you know, climate change, and I was sort of nodding, people can’t see me nodding, thinking, yeah. It's the beauty is that we could imagine a scenario where we ramp up production fairly quickly. If we want to ramp up tree plantation you can… but trees won't grow to the size we need them to be by the time we need to be solving the problems around climate change fast enough.
So, you know, they can be part of the solution. And obviously when we already have trees like in North America and Europe, great, use them. But in many parts of the world, we just don’t have that commercial forest and we can't go around chopping down our primary forests. So, what we need to do is a solution that we can deploy quickly. And that's where bamboo comes in. And if we want to really transform the construction industry. Poles are only part of the answer. We would need engineered bamboo.
Orin: Yeah, so, you know, let's talk a little bit about your research, because what I've learned just talking to you over the last couple of days is you're doing some pretty important tests and learning some pretty important things that I feel like, for whatever reason, engineers haven't really explored as fully as they could have. And it looks like you've like starting to see some patterns. Is bamboo isn't just one plant. Like wood, there's oak, there's pine, there's beech, there's… with bamboo is the same, you know, we've got asper, we've got guadua, we've got moso, we've got strictus, we've got all kinds of different types of bamboo.
And so you know, that then brings up the issue, if you're going to actually test the material properties of 1 bamboo, then that's not necessarily the next bamboo. And I'm curious just from your work, what are the patterns that we're seeing between the bamboo? And what are the differences that you're finding in testing different types and trying to find, you know, some ratios and things like you mentioned where the people pull up a table, like the timber guy does and figure out exactly how big the beam needs to be.
David: Yeah, that's a really interesting point you make, and it's true that the bamboos are different, as they are the trees. But when you go and build in North America or in Europe with timber, you don't go and say, oh, can you please send me a pine? Or can you go and please send me a fir? You go for a timber that's been gone through a process of grading, and you know it's going to do the job, and its strength is there within that.
So, you stop worrying about species. Unless you want species for an aesthetic reason, or some other reason, you’re generally not worried about the species. And that's what I would like us to get to with bamboo, where we just wouldn't have to worry about, you know, the engineer says, well, bamboo, maybe of a certain, there might be some slight variations between species.
So it's one of these that we don't know the pattern fully yet, but some patterns are emerging. So, listeners, again don't go away and immediately start designing with these patterns I'm going to say.
But some patterns are emerging. And the patterns that are emerging are that tropical bamboos, particularly the ones of fairly thin walls, have similar sort of strengths in terms of those that are governed by their fibers, like compression and tension and bending.
They have sort of similar stiffnesses. I'm starting to suspect that stiffness is also maybe affected by the way they grow. So, there's some bamboos that are clumping, they grow very close together. There's some that are running, so they spread apart. And then we have some intermediate ones, like the Guadua genus, that do something in between.
And the pattern, I think I'm seeing, but again I need to validate this, and this is, we need, we have to get data from other people, we have to make sure we've done the tests correctly and so forth. But I think you might be able to sort of be able to group, so maybe the clumping bamboos have a characteristic, the ones that separate a bit more have, the guadua genus, has sort of their own characteristics, and maybe the running bamboos have their own characteristics, and so forth.
And maybe we'll be able to spot patterns, and I've studied, at least in terms of strength, there are not many differences. Stiffness, there seems to be some differences between these. Thick-walled bamboos seem to be quite different. And then in shear strength, which is not so much governed by the fibers but by the meaty material between the fibers, which is called the parenchyma, and this material between them, at least between tropical bamboos, we seem to be getting a similar sort of number.
So it's thinking, maybe we don't have to test them so much. That has to be seen from the moment we have to just keep testing until we know the answer. But and I mentioned shear because it tends to be the most critical strength property in the design of bamboo.
Orin: Awesome. So, you're saying that there's a possibility that the sheer strength between different species really may not be that far apart.
David: No and in Europe, at least for timber, that was sort of a conclusion they arrived at. They said, let's just say we'll have the same shear strength. And so even if you go for a very strong pine or a fairly weak pine, you'll get the same shear strength. Presumably they arrived at a similar conclusion.
Orin: Awesome. And what's different about thick-walled bamboos?
David: Well, firstly, thick-walled bamboos tend to be smaller, and the tests, rigs, and test procedures have all been thought through for slightly bigger bamboo. Secondly, particularly the shear test, is hard to do with thick walled bamboos.
So, we might have to come up with a new test. So that's one of the first things. So, what we have is sort of tentative data, and so far, its shear strength seems to be slightly lower. But that shouldn't dishearten us because thick-walled bamboos have other characteristics which are very exciting. One of them is that you can nail it.
Generally with bamboo you try to avoid nailing, but thick walled bamboos you can nail in. So, you can start imagining the possibilities emerge. I think connections probably might be easier. So, it's a really exciting field, which has been poorly explored and developed. I also think maybe some engineered products that you can develop within thick-walled bamboo might be easier.
So I think it's a completely different world to what we think of, so far, we've thought of as bamboo. It is like, it's a semi timber. [00:41:21]
Orin: Awesome. And so, what are you most excited about moving forward in your research and in exploring bamboo further in the next, I guess, in the next five or ten years?
David: Ah, that's a problem with me. I've got so many things that are on my mind that I'd like to do and so limited time and resources. But one thing I would like to do [is] progress connections to the point that, as I described, we get to a point where engineers can fairly reliably understand. So that would be something like, how to put… I'd like to put to bed. I don't want to spend too much more time on bamboo connections. I want to get to the point where we've got something that engineers can work with and, even if it's not the best solution, it's a satisfactory compromise and they can work with bamboo poles to the point that it's safe. And that's the key thing. We need bamboo connections to be safe.
And that is because in seismically active locations, we reckon that it's at the connections where all the yielding is going to happen, all the energy dissipation has to happen. So, we need to get to the point where we have a connection that's reliable, you can predict its strength, you can predict its stiffness, you can trust that it's not going to be affected if a lot of spitting happens and that it will fail in what we call a ductile manner when you push it to the back. If I come across a connection that has those characteristics, I'm going to be happy and I think I'll probably say “Done. Mission accomplished.”
Then in terms of other things that I want to do is I'd like to help shape the market in the sense of that engineers can say, okay, I feel confident that this product can take so much load. And that's why I got involved in all this work around grading. It was just to make sure you have something that an engineer can start working with and say, yeah, I'm going to, and they don't even have to worry about the species. They can say, I am going to use a class A, 100 hundred mil diameter bamboo. And they don't have to even worry what species it is, because they know the supplier has gone through the process, that’s rigorous, that they, that's the bamboo they're going to get on site.
Orin: The architects would be really happy too. Because right now, there's so much variation that can happen, even in the design process, just because the bamboo you order and the bamboo you get may not be exactly the same.
David: I think grading is a very interesting topic and how do you go about shaping the market? It's, it's a tricky one… but that's why I got myself into a field that I'm finding interesting and I didn't get into it because I thought, this is so exciting. If anything, I think it's slightly boring, but I realized that if we didn't get into it, we wouldn't shape the market so that we can then create a market that has parity with timber where you just say, I want a piece of softwood that does this and people know two by fours. And you can design with it and work with them. So, so that's my second topic, which has been the whole thing around grading, characterization, and helping people understand how to build these supply chains in their country.
And then, the thing that I've recently discovered, and I discovered here at Bamboo U, is Pinboo.
Orin: Maybe describe what Pinboo is, just so our listeners understand.
David: Yeah. By the way, I prefer calling it dowel-laminated bamboo. That would be the name I would give it, but someone else called it Pinboo, so we'll go with the name that everyone gave it.
Orin: Well, here we call it Renggang.
David: Rungan.
Orin: Renggang.
David: Rengan. Okay.
Orin: Harder to say.
David: Even harder. You get a piece of bamboo, and you cut it into slats/slits/splits and you put them side by side, and you put a bamboo dowel through them, you drill the bamboo, and you put it through it, and it fits it in place.You don't need to have glue, you just put it all together. And it makes a board. How thick is this board? Well, customarily, it's done 40 mil. Why? Because.
Some people say, oh, it's the optimal use, but it's peculiar that people are right, it's the optimal use but for very different species. So, in Colombia, where it was invented, they use 40 mil. And I think, here with Dendrocalamus asper…
Orin: You can go a little thicker probably.
David: If you went a little thicker, it'd be cool. Now, what excites me about Pinboo is that you could do incredibly boring buildings with it. And so you guys are like, what?! And the thing is what excites me about the idea of Pinboo is that we could mass produce it.
So, it's not a solution around the beauty of bamboo, it is a solution about everyone using bamboo. Particularly those people who aspire to have a concrete house. So, they think a box is the place to live in, and that's the sign of your status, and we can give you your bamboo box. And then you can clad it on the outside to look like a brick house and the inside you put the plasterboard so you could hide the bamboo if you didn't want to see it, and also get rid of that fire resistance we were worried about. And then you can imagine now we're talking about a technology of transition.
So I like it because I'm sort of thinking… what next? And engineered bamboo is really cool and it's coming along its way and all that. But that is… the investments to set up an engineered bamboo plant is big. And what I think about Pinboo that I like, is that the investment is relatively small.
Orin: Yeah, I mean, the main investment is labor.
David: Yeah, but you could gradually technify that process - you start it first very labor intensive and you gradually get it a bit more technical, and a bit more technical, and gradually, gradually…
Orin: That's true. Yeah, it wouldn't be too hard to make a machine do it.
David: And you can see an avenue, a route to massification, a route to industrialization, that doesn't require an outset, large capital investment.
So, one of the things, I'm going to geek out here… There was this economist in the UK, German origin, who lived in the UK, called E. F. Schumacher, who wrote a famous book called Small is Beautiful. And he theorized around something he called intermediate technologies. And intermediate technologies were technologies that would - his concern was unemployment - And so he put, you know, if you bring this massive machine that's going to leave people out of work, it's not a great machine.
On the other hand, being very primitive is not great. So, we need something that sits in between. And that's what he termed intermediate technology. And I think Pinboo is that. It is something that sits between the huge investment we need to make to do with the engineered bamboo product and continue building the bamboo poles. So it sits somewhere in between and it excites me a great deal because I think, yeah, this could be that technology that gets us from one place to the next.
Orin: So can we build a Pinboo house but forget the concrete and the drywall?
David: We would need…we could… Someone suggested an idea to me - the gaps, Pinboo, the slats have gaps between them.
Someone suggested earlier you have to fill those gaps with clay. It would require more maintenance from the one I've described, but you could fill that with clay in the inside, and it might give it a decent fire resistance. Maybe you could put some other finish in the inside if you wanted to. And on the outside you'd need to do some form of protection from wetting, which could be bamboo that's sacrificial, you know. You lose it, five years come and you come up with another bit of flattened bamboo, so, you know.
Orin: We're near the end of our podcast time, but I do have one more question related to this Pinboo thing. So and just also, just to touch on this, we use Pinboo a lot as a floor, right? So for the second story floor, a lot of our buildings we use this and then we usually put either veneer or, or splits on top. Sometimes we would be perforated, so I can really picture it as a floor because that's how we use it.
But I'm trying to imagine, if you're going to use it for, like, a wall or a ceiling, how would you go about, would you still need a main structure to fill it in with Pinboo, or do you see the actual material being strong enough to actually be able to make the house?
David: If you're going to do a house that is a very cellular distribution, okay, so by that we mean we have a lot of walls, and these are load bearing walls, it could be just a room.
If you wanted a more post-and-beam sort of construction, with pretty big windows and pretty large open spaces, then you'd probably still have to frame it with something else. But a fairly cellular sort of construction, you could just use it.
Orin: Sounds like we should propose like… a tiny rendering of this Pinboo house.
David: Next time you invite me to Bali, let's go for it.
Orin: Awesome. So, thanks for joining us today, David. It's been a real pleasure.
David: It's been a pleasure to be here. Thank you very much for inviting me.