The Bamboo Solution

Tough as steel, sturdier than concrete, full-size in a year.

By Mary Roach|Saturday, June 01, 1996
RELATED TAGS: MATERIALS SCIENCE
Bamboo expert jules janssen is admiring a stalk of Bambusa vulgaris. A popular ornamental, the plant can be seen in Chinese brush paintings and along the quiet pathways of Buddhist monasteries. But the beauty of this particular piece, in Janssen’s eyes, has nothing to do with its graceful proportions or its polished yellow hull. It has to do with the 78 newtons per square millimeter of compression force it has just withstood.

Janssen is not a botanist but a civil engineer. He works in a basement lab at the Eindhoven University of Technology in Holland. There, amid the shudder and clang of rebar and aluminum, he ponders the biomechanics of lignin and nodes. While his colleagues grapple with the finer points of better bridges and faster freeways, he gives thought to the pleasing practicalities of bamboo houses.

Janssen believes that for building affordable housing in tropical countries, bamboo is usually best. Ounce for ounce, bamboo is stronger than wood, brick, and concrete. Consider the aforementioned compression test. What that figure means is that, compared with, say, concrete, bamboo can withstand twice as much force bearing down on it. A short, straight column of bamboo with a top surface area of 10 square centimeters could support an 11,000-pound elephant.

The compression test is carried out on a menacing 12-foot-tall machine, equal parts guillotine and sledgehammer, in Janssen’s Bamboo Laboratory. He is taking me on a tour of the facility. A large sign on the machine’s hull says DRUKBANK.

Is that Dutch for ‘danger’? I am picturing my hand flattened like a bamboo rake.

No. It is Dutch for ‘compression machine.’

Janssen is the quintessential engineer, as dry and straight as his stalks of Bambusa. He is 60, with wire-rimmed glasses and prominent ears that frame his head like bookends. For someone who has devoted 21 years to the study of bamboo, he remains more or less dispassionate about the plant itself. He is not a member of the Dutch Union of Bamboo Lovers. He has a potted fern in his office, but no bamboo plants. There is a bumper sticker on his wall that reads I © BAMBUSA, but I don’t buy it. I ß BAMBUSA is perhaps more apt.

Part of Janssen’s lab is set up inside a lofty glass greenhouse, where stalks, or culms, of cut bamboo are stored on their sides, wine- cellar style, in floor-to-ceiling racks. A cloud of humidified air is falling out of a pipe near the ceiling, like knockout gas in a James Bond movie. Off the back is a room with more bamboo-testing devices: shear testers, bending machines, creep gauges--everything short of an 11,000- pound elephant. Many Janssen has had to invent or modify himself: you cannot fit a round bamboo peg into a square lumber shear tester.

Janssen is showing me a technique he devised for measuring bamboo’s tensile strength. A wire is embedded lengthwise along a stretch of bamboo cylinder. Current is passed through the wire while a mechanized tug- of-war takes place at either end. As the bamboo is stretched, it squeezes the wire and increases its resistance. The resulting dip in current yields a precise measure of tensile strength. In this regard, bamboo is as strong as steel.

Janssen explains the importance of quantification. Everyone who has worked with bamboo knows it is strong, but exactly how strong was a question no one had bothered to answer. Quantification of a material’s specific strengths and weaknesses is critical to its acceptance as a building material. Without a formal grading system, such as exists with lumber, or any international standards or building codes, bamboo has thus far failed to see widespread use in large-scale housing projects. It’s a problem, Janssen observes. A lack of codes and standards can be interpreted as ‘It is forbidden to build with bamboo.’ Janssen and an international task force of bamboo researchers are currently working on an international model for bamboo building codes.

This is not to say that no one ever builds with bamboo. On the contrary: Countries as geographically and culturally distinct as New Guinea, Colombia, Bangladesh, and Thailand have built traditional bamboo structures for centuries. But these are village-scale, one-at-a-time efforts. Large government-funded, bureaucracy-approved projects have been reluctant to embrace bamboo--until now, thanks largely to the efforts of Janssen and a group of international bamboo experts and enthusiasts. Since 1974, when aid workers in Southeast Asia approached the Eindhoven University for advice on how to construct bamboo trusses large enough to support a school roof, Janssen has volunteered his services as a consultant to tropical countries seeking information on cultivating and building with bamboo.

The largest and most successful of these efforts has been the National Bamboo Project in Costa Rica. Beginning in 1987, Janssen organized and oversaw the development of 700 hectares of bamboo plantations, the training of local builders, and the construction of more than 700 low-cost homes--at a cost of about $4,500 apiece. The project was so successful that in 1994 plans were laid to build an additional 1,000 homes annually.

The impressive economy of bamboo housing stems largely from the material’s extraordinarily low cost of production. The energy needed to produce bamboo is approximately half that required for wood. For one thing, bamboo grows quickly, up to three feet a day. While a tree can be harvested only once every 20 years, bamboo can be harvested every year. Also, the harvesting is simpler--a machete or hacksaw is all that’s needed--and sawmills are unnecessary.

Bamboo compares even more impressively with concrete and steel. It requires one-eighth the production energy concrete does to create material of the same bearing capacity. With steel--which must be smelted, poured, forged, alloyed, cast, and tempered--the figure is closer to one- fiftieth.

Janssen and his Costa Rican colleagues were especially pleased with the results of what Janssen calls an unplanned full-scale test. In April 1991 an earthquake of magnitude 7.5 struck Costa Rica. Twenty bamboo houses stood at the quake’s epicenter. Jorge Gutierrez, the project’s technical supervisor, recalls driving to the site that day, passing several collapsed concrete homes and hotels. Fearing the worst, he arrived to find all 20 houses intact. Not one of them had a single crack, he recalls.

The key to bamboo’s temblor-worthy nature is its light weight. If you remember from your secondary school, says Janssen, force equals mass times acceleration. The larger the mass, the stronger the force. Concrete’s ponderousness magnifies an earthquake’s force.

The force to be reckoned with here is shear. Shear happens when two forces moving in opposite directions collide and slide past each other, like the blades on a pair of scissors. If we have an earthquake, that means the earth is moving horizontally, says Janssen. A house has a mass, which takes time to accelerate, and therefore lags behind the earth it sits on, rather like Dagwood Bumstead’s fedora as he dashes out the door in the morning. When the earth then reverses direction, it slams into the force of the house moving forward, inflicting extreme shear. Bamboo weathers shear exceptionally well, considerably better than other building materials. Though wood is light, it has weak points: grain lines and large knots, where branches leave the trunk. Both can give way under stress. Bamboo has neither.

I ask Janssen what else about the biology of this plant serves to make it such an engineering wunderkind. As it’s noon, I suggest we talk over lunch. Janssen looks down at his feet, engineer’s feet, clad in somber-hued socks and chunky sandals. I, um, usually go home for lunch. He looks up. I can call my wife and have her set another place. . . .

To understand why bamboo is strong, it helps to have a piece in front of you. We are seated at the Janssens’ dining table, examining a bamboo pencil holder. Janssen points to the rim of the cup, which affords a tidy cross-sectional view of a culm of bamboo. The little black spots, he explains, are cellulose fibers, which run along the length of the culm, ferrying nutrients between the leaves and roots. The lighter-colored filler material is lignin. The cellulose is very strong, Janssen says, while the lignin is relatively weak and soft. With a composite, you take the advantages of both materials.

Janssen likens bamboo to reinforced concrete. The lignin is the concrete; it holds the cellulose fibers in place and keeps them from buckling. Lignin alone, like concrete alone, would crumble under the weight of a roof. The cellulose takes the role of the steel reinforcement bars. Cellulose on its own, like rebar, would buckle. Together, however, cellulose and lignin are an unparalleled show of botanical brawn, the whole being greater than the sum of the parts.

Janssen picks up his milk. Lunch at the Janssens’ has the predictable constancy of an engineering formula: open-face sandwich divided into six pieces, plus milk, plus apple, peeled and quartered. Janssen wipes his mouth and continues. Bamboo is hollow. Do you understand why this is an advantage? Because the tube is a very strong form. He puts his plate on top of the pencil holder to represent a load. If the bamboo were not shaped like a tube, he asks, if instead the same amount of material were squeezed in together to form a narrow rod, what would you have? Something much skinnier. It would be like Charlie Chaplin’s walking stick.

Janssen stands up and does an engineer’s impersonation of the Little Tramp, leaning into a bending, bowing cane. It’s no good.

Likewise, if you took the same amount of material and spread it more sparsely, creating a solid bamboo column of the same circumference, you would also lose strength. The more densely packed the fibers and lignin, the stronger the bamboo. The tubular form makes the most of however much material you’ve got. And because it’s hollow, it weighs very little, thereby creating that sine qua non of the building world: something strong but light.

Why, given all this, does bamboo need an international advocate? Why isn’t everyone building with it? Is it only a matter of standards and codes? Janssen shakes his head. Bamboo has disadvantages as well. For starters, pandas and humans are not the only species that eat bamboo plants. Termites and beetles bore into the culms and feed on the lignin. To prevent this, bamboo must be soaked in preservative, a process requiring equipment and technical expertise that many villages lack.

Fungus is another concern in the tropics. You need a roof with a nice big overhang so the walls don’t get wet in the rain. And good air circulation, so if the rain is coming horizontally because of strong wind, it will allow the bamboo to dry. Wet bamboo will rot in a matter of weeks. A well-constructed bamboo home, on the other hand, will easily last 30 years.

Being hollow also has drawbacks. Because of this, bamboo burns very quickly. Janssen recalls an afternoon on campus when he burned a pile of insect-infested bamboo. Fortunately, we had a fire brigade present. Goodness, it burned like hell! In turn-of-the-century Shanghai, a fire in a densely inhabited bamboo building left 500 people dead in half an hour. For safety reasons, multistory bamboo buildings are rare. It’s possible to build them, Janssen says, but you would never do it, because of the fire risk. With a one-story, single-family dwelling, fire poses little danger. Bamboo houses are open and lightweight, explains Janssen. If something happens, everybody can get away through the doors, the windows, even the walls.

Bamboo’s tubular form presents certain structural conundrums as well. Joints, for example. One can’t very well nail two hollow tubes together, and putting rods through them weakens them. This is a serious problem. For no matter what a house is built with, it’s only as strong as its joints. Traditionally, culms of bamboo are lashed together, a technique Janssen dismisses as old-fashioned and weak. You spoil the good mechanical properties of the bamboo, he says, peeling an apple wedge.

Janssen and his colleagues have expended considerable effort devising alternative joint structures. One current solution is to insert solid wood cylinders into the ends of the bamboo. The cylinders give way to squared wood planking, which can then be joined like a conventional wood joint--that is, cut, coupled, and glued, nailed, or dowelled.

By far the largest obstacle Janssen faces is attitude. Bamboo has always been viewed as the poor man’s timber, he says. From a social point of view, as soon as you belong to the middle class you will not use bamboo anymore, because that does harm to your status. Therefore you switch to brick or timber or concrete. This is beginning to change now, but slowly.

Attitudes are particularly glacial on the government level. Janssen recalls a project in Burundi for which he submitted a proposal. Though his bamboo structures would have been cheaper, cooler, and more aesthetically pleasing than other options, his proposal lost out. Probably to concrete. He shrugs. There was nothing to be done. The country’s leaders wanted a modern, Western-style development project. You have this a lot in countries with a colonial history. There is a strong link between bamboo and a nation’s colonial past. The leaders and the people say, ‘We are not a colony anymore. We are modern and new, and so we build with steel and brick and reinforced concrete.’

After lunch, Janssen’s wife suggests we move to the living room for coffee. The topic turns to bamboo’s future as a Third World building material. Janssen’s tone is one of guarded optimism. After 20 years, the scale is inching the other way. Projects similar to the one in Costa Rica are under consideration in Tanzania, Bangladesh, and several other tropical nations.

Another positive sign is that the timber people are starting to get nervous. In Costa Rica they have been spreading rumors, Janssen says. They are saying a bamboo house will last only two years, that it will not survive an earthquake. Janssen doesn’t mind. If they did not react to defend their interests, it would mean we posed no threat. That they are reacting as they are means we are becoming successful.
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