bamboo building and culture

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Bamboo Building and Culture By Darrel DeBoer and Karl Bareis [email protected] Copyright 2000

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Small guide to Bamboo construction

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Page 1: Bamboo Building and Culture

Bamboo Buildingand Culture

By Darrel DeBoer and Karl [email protected] Copyright 2000

Page 2: Bamboo Building and Culture

The Architecture of Simon Velez 1Simon Velez , architect, CRA 2#9-54, Bogota Colombia captions written by Darrel DeBoer

OverviewThis paper is intentionally sketchy about specificsbecause of the many variables involved for someoneto try to replicate the work here: bamboo species,age, curing method, wall thickness, bolt size &material, mortar type, and especially design variables.This work is very buildable and that by knowingsome of the details of the way Velez works, we mightbegin applying some of his methods in the U.S.,especially with smaller structures for whichpermissions can more easily be received, and thereputation of the material is not harmed byimproperly stressed structures. Larger structuresshould involve Mr. Velez – there is no substitute forexperience.

Velez is a graduate architect, from the University ofColombia in Bogota. He has completed over 60projects using a controlled palette of concrete,bamboo, mangrove wood, woven palm mat lathing(or expanded metal lath) and clay roof tile.

This view is up at a ceiling through the palm matlath.

Simon Velez works from Bogota, Colombia, SouthAmerica. As much of his work has been in very ruralareas for ranchers, he has been allowed to experimentwith the locally available materials due to a lack of aregulating authority and the relative difficulty of

importing the standard building materials of brickand mortar.

The two critical breakthroughs Velez is able to teachus relate to the bolt joinery with filled internodes andthe approach which uses no sheet goods (such asplywood) to achieve extraordinary shear strength inhigh wind and earthquake areas.

In Velez’ designs, roofs framed only with bambooare capable of cantilevers as long as 28’. Especiallyintriguing when considering how much weight is inhis standard roofing of clay tile set in a fullmortarbed – he feels the heavy roof is needed tocombat the high winds, exactly the opposite ofconventional wisdom in the U.S. Clearly, we havemuch to learn.

In the image above from the book, TropicalBamboo, one can see a rare simulation of what

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The Architecture of Simon Velez 2

Europeans saw when they first came to this part ofthe Andes: a continuous, feathery guadua forest.While the botanists have classified several sub-speciesof Guadua, Velez feels that many of the plants are thesame species, and it is the different climate and soiltype, which have great effect on plant characteristicsand pole quality. For example, Bogota is too cold: alittle too high in elevation (2600 meters) for Guaduato grow. His source of poles is in the lowerelevations outside the city, but there is a significantstructural difference between the 8-inch (20 cm.)diameter coastal Guadua and the preferred 4-inch (10cm.) which grows in poorer soil and slightly coolertemperatures. When Velez works in neighboringregions and countries, he brings a supply of thefavored bamboo with him. Learning the appropriatemicroclimate for each strain of each specie is one ofour most arduous tasks in the U.S.

The species of timber bamboo preferred by Velez,Guadua Angustifolia, achieves full height (100 feet +)in 2 months, adding only strength for the next 3 yearsat which time it is harvested. It is reputed to be theonly species of bamboo capable of having nailsdriven into the culms without splitting. However, itdoesn’t tolerate frost well and will only grow in thefar southern U.S. states. He was impressed with thestrength of our Phyllostachys varieties, thoughnobody has tried these kinds of spans here.

In the trusses at the base, the wooden poles arejoined in the same manner as the roof bamboos.

Velez has developed a very interesting model forbuilding experimental structures. He builds onlywith his own well-trained crew of workers, so he isable to constantly draw upon past successes andfailures in detailing. He intentionally keepsdrawings simple, usually freehand on single sheetsof 8x11 graph paper. Full-sized details are mockedup on-site or are referenced from the memories ofpast jobs.

In traveling with Velez, I saw numerous originaldrawings sprinkled over the jobsites. Because he isfree of the contentious architect/contractor

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The Architecture of Simon Velez 3

relationship, his drawings are done completely toserve the building.

To Velez, the building is all that matters. Ifabsolutely required, the client must obtain BuildingPermits, but he won’t help. Velez views everymoment’s delay as an impediment to the mostimportant task of building. Detailed drawings areseen as another delay. The client is shown very fewdrawings. What is important is that the clientmaintains absolute faith in his ability to execute thework.

He keeps that by making drawings that embody theintent of the structure.

Most useful are the section views which are usuallyrepeated through the whole building.

The clearest concept to be seen in his drawings is thenecessity for balance. These cantilevers are verylarge, but maintain an obvious center of gravity overthe support.

All joinery is done with bolts, he never uses tyingbecause the bamboo shrinks and the joints becomeslack. Sometimes the bolts are reinforced withstraps where the forces are the greatest.

His experiments have made his buildings exercisesin statics - keeping most of the members in tension,but where compression and shear exist at the boltedjoints, he fills the internode with mortar to keep thebolts from crushing the walls of the bamboo.

With many of his center-bearing trusses (posts closeto the middle of the truss), the point of great strainis the very ridge. Across the ridge Velez puts a steelstrap which is bolted through the bamboo on eitherside. In stress tests, it is this strap or the boltswhich fail. He has yet to see the bamboo fail.

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The Architecture of Simon Velez 4

The only substantial publication of his work is abook published by Rizzoli call Tropical Bamboo,now out of print. If you can find a copy at a library,it is the best source for giving a context to Velez’work. In it, Velez wrote, “At the beginning of thiscentury, two successive fires in Manizales razed onlythe upper-class houses. The rebuilding of the citycenter and cathedral saw the first use of concrete andmarked the demise of the use of bamboo or any kindof wood. Ever since, in Colombia, bamboo andwood have been synonymous for slums and misery.”

When he does a structure that he considersexperimental, he charges little and tests at full scale.Clients don’t let him test those structures to failurelike he wants, they live in them.

These images show that bamboo used as bamboo,taking advantage of its unique qualities is capable ofso much more than solid wood. We can begin totransition to the use of structural bamboo in thiscountry by building structures half as big as these andstill feel confident in the integrity of the material.

It is important to note that in Colombia, the wealthyare now accepting a material that is inexpensive andassociated with poor people.

Pound for pound, the Guadua has a better tensilestrength than steel. The structural strategy is todesign trusses which take advantage of the tensilestrength of bamboo, then, where the inevitable shearand compression loads exist, the internodes, throughwhich bolts are placed, are filled with concrete.

A passive solar, bamboo-framed house where themortar and plaster is put to good use as thermalstorage.

Velez believes traditional joints are unreliable. Ifstrutures are to be plastered, organic ropes can’t becinched up in 3 months when the bamboo shrinks orin 2 years when the humidity rots the rope. Guaduais so strong and will definitely continue to shrinkand swell that it will overwhelm any other bindingmaterial.

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The Architecture of Simon Velez 5

He advocates a rigorous approach to structuralengineering where the stresses are spread out moreevenly throughout the structure. That way, in theory,many of the bolts could actually be removed becausethe structure is in static equilibrium. Just the keyjoints are reinforced with concrete.

One of his first structures, with no preservatives.The beetles which immediately attacked, ate the soft,starchy interior of the bamboo and then exited, havingdone no structural damage because all the strength isderived from the bamboo’s hard outer shell. (Powder-post beetle infestations in temperate, thinner-walledspecies like Phyllostachys can be much moredevastating) His early designs shared thecharacteristic of this barrel-vault truss, which putcomponents primarily in compression.

The futureA rendering of Velez’ design of the ColombianPavilion to be built for the year 2000 HanoverExposition can be found at http://www.zeri.org/ Construction progress can also be followed. As ofAugust of 1999, the full-size building has beenconstructed in Manizales.

Lessons learnedVelez’ methods of work are, in many ways, differentthan those in use here. Some of the keycomponents we can come away with include thestrong scientific basis of the design – he considersbamboo a “high-tech” material, deserving of veryrigorous detailing. His intuitive ideas come fromlong experience with the qualities of the material.

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The Architecture of Simon Velez 6

Above all, bamboo structures which employ theselong spans are still quite new and I urge extremecaution. Because just one flawed, uninformed designcan cripple future building possibilities, we should allerr on the side of being too conservative and overbuildredundant systems guaranteed to be the last tocollapse in catastrophic events.

Velez’ new office under construction

“Fish-mouth” joints on both ends of a line of polesmake precision a necessity.

An art gallery with a bed made of guadua.

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Marcelo Villegas and Simon VelezBy Darrel DeBoerI went to Colombia with the express purpose ofseeing some of the bamboo buildings of SimonVelez. What I found was significantly more. In theregion of Caldas, where the giant timber bambooGuadua angustifolia is native and still quiteabundant, there is also the work of Velez’ best friend,Marcelo Villegas, author of the book, TropicalBamboo, builder of about 8 houses,

and furniture craftsman with a 3-story workshop

and his own foundry. He makes all the tools heneeds, including a modified planer to cut theubiquitous “fish-mouth” joints used so often inColombian bamboo construction. Even the handlesof his tools are made from bamboo rhizome.

In every corner of every room is a prototype, an ideapartially born. We could have spent a week in thatone building.

Though others thought he was crazy, he felt that herequires enough bamboo that he planted Guaduathroughout his 5 hectares of coffee, phasing out the“traditional” cash crop in the next half dozen years.Being near the equator and at nearly 7000’ inelevation, every day is a pleasant temperature, verysimilar to Colombia’s National Bamboo Center’srecommended daily high temperature of between 68and 78 degrees F for Guadua. Imagine being able toplant small slips of bamboo, needing to do nothingfor them for 2 _ years, just returning in time to see 4”diameter shoots. This is the plant that once coveredthe landscape and informed the farmers where themost fertile soil was. Now relegated to non-tillableareas adjacent to waterways, drainages and steepslopes, some Guadua is still visible from any vista.

Villegas is convinced that this is the species he mustwork with, he had no interest in importing otherswhich might give different size poles, edible shootsor be resistant to Santa Fe disease, the little-understood blight that did a great deal of damageduring the last year. (A bacterium or virus may havecaused the disease, and the unusual El Nino droughtsimply made visible what had been present for years.)

The culture of bamboo creates unexpected sights.The local “lumberyard” sells no lumber from trees.Only bamboo is found – at a cost of USD$0.80 perpole – and used mostly as scaffolding or shoring,with the flattened poles made into sheets for concreteformwork, flooring, siding or ceiling finish. After astandard construction project finishes with the poles,the workers take them home and build their houseswith them. I was surprised that almost all of thepoles for sale were harvested too early, a conditionthat is very easy to see there because of the lack oflichens and mold on the poles younger than 2 years.So there are two problems, the guaduales are notrejuvenated and the available poles are weak,contributing to their reputation as a lesser buildingmaterial among the poor who seek an eventual houseof concrete. Interestingly, wood frame walls simplydon’t exist there. Brick is regarded as much quicker,while bamboo lath and plaster is faster still. 180,000

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of 220,000 people in the city of Armenia, near theepicenter of the Colombian quake, were madehomeless in January of 1999 because their houseswere built of concrete and brick. The recent bamboobuildings survived well while some of the mucholder, untreated bamboo structures known to beunsafe, collapsed. There are plans to rebuild relyingmuch more on bamboo. A question I have is whethera grading system will be implemented in time.

While it’s still unclear whether first designed byVelez or him, Villegas now makes several variationson a chair that makes interesting use of the nearlyninety degree connection of the rhizome to the culm.

When he needs a smaller angle, he harvests thebamboo on a steeper slope. But with the sub-roots(feeder roots?) coming off the rhizome averagingover an inch in diameter, digging these guys is nosmall task. With this species, the rhizome neck isconsistently around 2 feet long horizontally, and itswells to make for a very animal-like body. (see thephotograph of his lamp on page 107 of TropicalBamboo, it gets a reaction from everyone) Anotherdesign is a couch with suspended cushions.

The sophistication of the roof designs by both Velezand Villegas is worthy of a book-length discussion.The interplay of complete and separate systems oftension and compression within a single roof makesquite a beautiful experience, and a particularlydifficult challenge to represent in photographs thatcan only show a small percentage at once.

One of the most spectacular structures is also a goodstudy in the methods of work.

This tower was built to give an overview of what isvirtually the only tourist attraction in the region: acoffee plantation with a cable car. Almost preciselyon the epicenter of the earthquake, it was undamaged.Designed by Velez and built by Villegas with thedetails worked out in frequent site conferences, therewere minimal drawings and no engineeringcalculations. As an architect, it is refreshing to see aprocess with so few people looking over one’sshoulder. Both men have little faith in the ability ofengineers to appropriately analyze their buildingsbecause so few really understand the capabilities ofbamboo. During the Costa Rica Congress, I observedthe many academics present spending most of theweek focusing on the perceived limitations ofbamboo. It was quite enjoyable to watch Velezcalmly nod his head in respect and diplomacy, then totake the stage at the end of the week, and showbuilding after building that spoke eloquently of howlittle patience he truly has for the naysayers.

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Bamboo Building and CultureBamboo Building and Culture 1

Simon Velez designsbuildings with eitherconcrete or wood framewalls and bamboo roofstructures with spans upto 60 feet (27 meters),and cantilevers close to30 feet (9 meters) as seenin this clubhousestructure in Colombia.

This barrel-vaultstructure by Velez is builtin a tropical area. Withno end walls and usinguntreated bamboo,beetles immediatelyinfested the interior ofthe poles but consumedonly the starchy inner,non-structural core.

This agricultural buildingteaches lessons aboutsmaller structures thatcould be built in the U.S.Redundant members,triangulation, boltedconnections and all polesheld above ground.

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Bamboo Building and CultureBamboo Building and Culture 2

Bamboo Technologies in Hawaii has been importing bamboo poles and mats tobuild pre-fabricated structures with building permits in Hawaii

This structure was built under the direction of Simon Velez by unskilled Americans in a day

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Bamboo Building and CultureBamboo Building and Culture 3

INTROBamboo tools, utensils, food and buildings strongly influence the lives of half the world’s population.Bamboo housing has been traced to 3500 BC. It will remain serviceable for 2 years if buried underground(Hidalgo ’92) but can survive several hundred years as rafters of traditional Japanese farmhouses. Simple,quick joinery systems based on pegging and tying have evolved to take advantage of the strong outsidefibers of this hollow tube. More recent systems have been engineered to make joinery less labor-intensiveand stronger. Bamboo is that rare building material capable of long spans and allowing the same person tobe both the producer and the consumer, the builder is not dependent upon the whims of the marketplace andcan secure a long-term source of material. So, one is able to think of bamboo buildings differently fromalmost any other building material. It is the process of establishing the system then that is most important:gaining access to inexpensive land which is not valued for other purposes, choosing appropriate species,allowing the time for maturity, understanding the aesthetic of working with cylindrical materials in apredominately rectilinear society, learning to distinguish exceptional working stock, and developing adesign approach which takes full advantage of both the strength and beauty of the timber bamboo, these areour challenges.

Bamboo is a native plant in every continent except Europe, once covering millions of acres in theSoutheastern U.S. Bamboo is an extremely strong fiber – twice the compressive strength of concrete androughly the same strength to weight ratio of steel in tension. The hollow shape approximates the idealshape of a beam. (Janssen ’97). In the United States, now is an ideal time to draw upon the provenbamboo-working methods from Southeast Asia and South America as this is the first time in our historywhen an unlimited, highly subsidized source of structural-quality timber does not exist in this country.While there are already thousands of timber bamboos growing in the western and southern U.S., manyAmericans have never seen one. And the whole system of growing, processing and especiallyunderstanding bamboo does not yet exist in this country. Because of the relative scarcity of timber bambooin the U.S., this discussion will concentrate on using the giant grass for its highest and best use: to takeadvantage of both the strength and the beauty.

"To compare materials, one can look into their strength and stiffness," says Dr. Janssen. "It is even moreinteresting to also look into their mass per volume, and ask, 'How much strength and stiffness can I buywith 1 kilogram?' "Strength:Material...Stress..Mass per Volume....RatioConcrete ...8 N/mm2...2400............0.003Steel .....160 N/mm2...7800............0.020Wood .....7.5 N/mm2....600............0.013Bamboo..10 N/mm2......600...........0.017

Stiffness:Material...E-modulus...Mass/Volume...RatioConcrete...25000 MN/m2.....2400..........10Steel .......210000.……...…..7800........27Wood........11000....………....600.........18Bamboo.....20000.………......600.......33

"In the first table, bamboo ranks second," says Dr. Janssen. "In the second table, it ranks first."E-modulus = Young's modulus Source: Dr. Jules Janssen, 11/29/96 Moso is quoted (Zou, 1981 & 1985) ashaving a "Tensile strength parallel to the grain" of 1,960.6 kg/sq cm. Its average density (Specific gravity)is quoted as 0.61. This converts to a tensile strength of 192 N/mm squared. 1

By comparison, Dendrocalamus asper is quoted (Surjokusumoa) as having a has a MOE of between 227and 307.27 N/mm2, between 16 and 57% stronger than Moso. D aspers average density (SG)is quoted at 0.7, which is 11.5% heavier than Moso.2

1 Zou F in 1981 and Zou H M in 1985 translated from Chinese by Lou Yiping, an associate Prof workingunder Fu Maoyi at the Fuyang Research Institute.2 Surjokusumo of Bogor University, Subyakto Indonesian Institute of Sciences (LIPI), with furtherreferences by Widjaja and others.

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Bamboo Building and CultureBamboo Building and Culture 4

Bamboo Spruce Concrete SteelTensile strength 35-300 N/mm2 90 kp/mm2

= 9N/mm21/10 ofcompressivestrength

250-350 N/mm2

Compressive strength 64-110 N/mm2 43 kp/mm2

= 4.3 N/mm212.6 - 126N/mm2

250-350 N/mm2

Shape characteristics 1.9 times stronger thana solid due to hollowcylindrical shapeEfficient incompression andbending

Because it’ssolid, moreweight to getsame load-carryingcapacity

best ascompositewithreinforcing intension zone

Most efficient intension, capable ofmost work insmallest crosssection

Fire resistance(seconds untilignition, Dunkelberg‘85)

Acts as firebreak whengrowing, (61.2untreated)

(19.1) Will not burn,but prone tospalling assteel expands

Loses elasticity,risk of quick failure

Embodied energybtu/cu.ft.

Minimal, unlessimported

Transportationcan be high

42 – 96,000(ERG ’97)

91,618 (ERG ’97)

Regenerative capacity/ year (Cooper ’92)3

80-300% (28,000 -50,000 lb./acre)

3-6% (16,000lb./acre - pine)

None None

Time to maturity 7-9 years 60-80 years -- --Subsequent maturityafter initial harvest

1 year 60-80 years -- --

Conforms to NaturalStep’s 4 systemconditions4

Yes Yes No, fails firstthree

No, fails all four

3 Though this is the only U.S. study which compared yields of bamboo and pine, W.H. Hodge of the USDAestimated that bamboo annually produces 6 times as much cellulosic material per acre as does southernpine.4 1. Substances from the Earth’s crust must not systematically increase in the biosphere2. Substances produced by society must not systematically increase in the biosphere.3.The physical basis for the productivity and diversity of nature must not be systematically deteriorated.4. There must be fair and efficient use of resources with respect to meeting human needs.

Traditional UsesBamboo has been classified as having over 1500different uses, including fences, gates trellises,and every part of a building. In South America,structures of the native timber bamboo Guaduawere popular for rich and poor until severalcatastrophic fires in Colombian cities at the turnof this century relegated the use of bambooexclusively to the poor. (Velez ’96) And,unfortunately, most of those living in thesestructures consider them a temporary step on the

way to a more “permanent” concrete house. Thework of a few – especially Simon Velez andMarcelo Villegas in South America and BobbyManoso in the Philippines – are making bamboostructures acceptable among the wealthy onceagain, which is critical for ultimate acceptance byall. It is estimated that over 800,000 people livein bamboo structures just in Guayaquil, Ecuadortoday. Similar statistics can be found for much ofLatin America. Our collective efforts at buildingcities could be considered more sustainable ifmany of these average people could be convincedto use mature bamboo, inexpensively and

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benignly treated, to make beautiful cities ratherthan considering their houses temporarysteppingstones on their way to much moreenergy-intensive structures.

In Andean Colombia, timber bamboo iscommonly used as structural posts, split openand flattened to be used as lath, finish wallsurface, ceiling surface and flooring. Flattenedpoles are actually cheaper than round ones. Veryrarely is bamboo separated by grade, age,thickness or any criteria generally accepted formaterials like wood. In Colombia, only 5-10%of the poles for sale in the “lumber yards” sellingexclusively bamboo are mature enough to beconsidered structural. Most of the poles sold areused for scaffolding and concrete formwork.Traditionally, one can usually find bamboo,whether left over from a construction project orgrowing nearby. In recent years, populationpressures have significantly reduced the supplyaccessible to the public.

The National Bamboo Project has planted 2000hectares in the last several years in hopes ofbringing back the plant that once blanketed theregion and was so critical to the establishment ofhuman settlement.

In rural Thailand, parts of Indonesia, and manyPacific islands, bamboo is used for every singleaspect of life. In most of the rest of Asia –especially Japan – bamboo is used lessstructurally and more decoratively for walls,flooring and the occasional roof frame. (Seelater discussion on Japanese Traditional CuringMethods) Much of the way a region makes useof bamboo is rooted in a tradition of isolation. Insome areas, truly inventive ideas used forcenturies would be rejected in other places asentirely impractical. For example, _” thickflattened bamboo commonly spans 5 feet forflooring in southern China and the slightlyconvex surface feels comfortable on the feet.Traditions of uniquely detailed doors have been

developed to keep livestock out of houses,window lattice is the strongest available materialto give both ventilation and personal expression,an entire house full of furniture can be built for amaterials cost of less than a day’s wage. Wherebamboo grows, it allows.

Because bamboo systems require relatively littlespace, the same small number of people can beinvolved all the way from planting throughutilization. These few can be in full control oftheir bamboo supply and be flexible enough toshift production into whichever of bamboo’s 1500uses is most in demand. There is minimal needfor infrastructure or equipment. Every part of theplant has a use and the appropriate timing of thatuse not only doesn’t hurt the plant, but encouragesfuture vigor. The groves can be located to takeadvantage of the plant’s unusual ability to quicklyprocess nutrients and water left over fromlivestock farms, sewage treatment plants andindustrial processes. In contrast to most plants,when bamboo receives excess fertilizer, it doesnot become “leggy” and out of control. Instead,the quality of the poles remains the same, as thereis a time lag while the energy is stored in therhizome for later release as next year’s culms.(Liese ’92) The structure of those rhizomes ismeanwhile very useful for holding topsoil and forerosion control. Even though bamboo is a heavyfeeder, there is evidence that mycorrhizalrelationships with soil and rhizome are developedto make the soil in a mature grove more fertile.The plants create their own microclimate withtranspiration to cool a grove as much as 10 to 15degrees F. The branches and leaves are useful asanimal fodder with a higher protein content thanalfalfa.

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Few bridge structures are this easily portable.Few building materials can be used to span along distance, then be carried away on one’sshoulders. The strength to weight ratio isthought-provoking.

CompositesFrom our orientation toward wood as the mostcommon building material, bamboo is anawkward shape and doesn’t have the forgivenessof wood when mistakes are made where nailingor gluing on another piece can often solveproblems. Our tendency is to try to makebamboo into wood. Flooring milled from thinstrips of bamboo and woven matting are twovery simple substitutions for commonly usedmaterials. These changes require no training orshift in mindset. The problems will have more todo with the inherent difficulties ofindustrialization: demand outstrippingsustainable supply, local producer economiesdestroyed by outside owners and cash economydemands, and short-sighted use of cheapmaterials, etc. For example, by far the mostcommon glue used in composites is ureaformaldehyde, which is highly sensitizing,generally accepted as carcinogenic and should beavoided. Significantly better are thepolyurethane, isocyanate and aliphatic“carpenter” glues, which are non-reactive after aday. A more sustainable future is quicklyarriving with the recent release of soy-basedglues, which can allow building materials topermanently stay out of the toxic category.Assuming we keep in mind the socialimplications of our materials decisions, andencourage local control of locally appropriatematerials for local use, many of the problems canbe solved.

Checklist for well-designed bambootruss structure§ Good solid static analysis to distribute loads

more evenly among the joints and axiallyalong the pole

§ Slenderness ratio of less than 50 (Arce ’93)§ Bolted joints with solid-filled internodes§ Dry poles that are still easily workable –

about 6 weeks after harvest is ideal§ “Good hat and pair of boots” for your

building – keep the poles out of the sun anddry

§ Find a way to obtain lateral strength – eitherthrough creating a shear panel consisting ofa mortar-bed over lath or avoid mortar

altogether and rely upon redundanttriangulation within trusses to distribute theforces

§ Refer to the engineering formulas and testingcriteria developed by Jules Janssen (Janssen’97)

In this structure designed by Simon Velez for apublic park in San Francisco, redundancy andvisual richness is found in using multiple polesalong the same line, the overhang is wide, and theonly parts touching the ground are pressure-treated wood. An alternative connection to theground would be to bolt the bamboo to a steelangle iron set into a concrete footing.

There are only 2 kinds of joints (see ‘JoineryDesign,’ for illustrations of both), along withstrategic locating of steel straps where tensileforces are greatest.

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Building Code ApprovalThrough most of the world, there is no provisionin the codes for bamboo construction. A modelnon-prescriptive code written by Jules Janssenfor the International Network on Bamboo andRattan (INBAR) is intended for inclusion in theyear 2000 International Building Code and couldhave a lasting impact on widespread acceptance.This code helps the user to analyze beams,trusses, columns, joints and composite mats. Dr.Janssen has also written, for INBAR, theStandards for Testing Bamboo, an importantwork because of the many varieties of bambooand the current difficulty of comparing testingresults by different people. In the U.S., JeffreeTrudeau and David Sands of BambooTechnologies in Hawaii are currently working ona Uniform Building Code standard for bambooand have been successful in achieving codeacceptance by first building a ferrocement housewith stay-in-place formwork (that just happenedto be bamboo). Then, once the inspectors werecomfortable with the idea, a letter was receivedfrom the County of Kauai Building Officialaddressing future projects which puts the designand inspection responsibility firmly in the handsof the designer. The signature and stamp of astructural engineer or architect is required, alongwith special inspection (UBC Section 306.a.14)to obtain approval. They also suggested that aprescriptive code be developed by the localdesign community to “provide uniformity insubmittals.” As the U.S. is expected to adopt theInternational Building Code, Janssen’s modelcode will likely be able to apply here, but a step-by-step prescriptive code will be very useful toallow approvals in jurisdictions with littleexperience in structural bamboo. The first all-bamboo structures have been approved inconformity with the current code.· No permit required – For places in the U.S.with unenthusiastic building officials, there is1994 UBC section 106.2, exempting frompermits “One story detached accessory buildingsused as tool and storage sheds, playhouses andsimilar uses, provided the projected roof areadoes not exceed 120 square feet (11.15 m2).”This provides the opportunity for anyone to getsomething built which can help convince thebuilding officials of the viability of largerstructures.

Earthquakes and WindThere are two different strategies for overcominglateral forces. One – represented by the recent,engineered Latin American structures – relies onthe shear provided by mortar on both thebamboo-lathed walls and roof. In April 1991, 20houses constructed under the instruction of Dr.Jules Janssen in Costa Rica survived a 7.5earthquake near the epicenter. The relativelylight weight bamboo structures attracted farsmaller lateral forces than the surroundingmasonry buildings which sustained significantdamage. The other approach uses theforgiveness of the traditional lashed, pinned orbolted joints of both Asia and the Americas. Inboth locations, much anecdotal evidence showsthem surviving unscathed when the much morerigid adjacent concrete structures routinely fail.Even the structures with intuitive engineeringand non-optimized joinery take great advantageof the broad elastic range of bamboo in allowingit to be pushed out of shape and return once theload is removed. It is very difficult to causefailure in pure compression or tension, andbending can be quite dramatic and still not fail.“Failure is not failure.” (Janssen ’97) The jointsare most critical.

In overcoming lateral forces in roof structures,Simon Velez and Marcello Villegas have createdthe redundant second roof. They feel it isimportant to design structures with redundantsystems, capable of both tension andcompression. A joint purely in compressionunder gravity loading might be pulled apart intension in the event of high winds or earthquake.So, a second set of rafters that triangulates withthe first, can carry those temporarily opposingforces when needed. As an added bonus, thissophisticated structure is quite beautiful.

Joinery DesignLashed and pegged joinery has been usedsuccessfully for millennia. It allows formovement, and if natural fibers like jute, hemp,rattan or split bamboo are used while still green,they will have a tendency to tighten around thejoint.. Unfortunately, in most of the U.S., theseasonal moisture changes will cause thebamboo to expand and contract by as much as6% across the diameter (Dunkelberg ’85),causing a slackening of the joint, and not all

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joints remain accessible for tightening. The jointof preference has become the one developed bySimon Velez in Colombia. He relies on a boltedconnection, understanding that the bolt aloneconcentrates too much force on the wall of thebamboo, therefore the void between solid nodesis filled with a solidifying mortar. . This type ofjoint is critical where the bamboo is acting intension, and has enabled structures with verylarge spans to be built.

In understanding the distinction between tensionand compression joints, it is important to realizethat a joint purely in compression under gravityloading might be pulled apart in tension in theevent of high winds or earthquake. It isimportant to design with redundant systems,capable of both tension and compression.

When loads are well distributed throughout thestructure, bolts can be used without mortar. Anexample of this is the traditional layout of ahouse in Japan. A gable roof consisting ofrafters spaced closely together is topped bypurlins running perpendicular to the rafters.Many joints are created with relatively smallloads at each.

A simple vault design can consist of piecescoped to fit together purely in compression.Because gravity holds them together, no bolts areneeded under gravity loading. But, if this vaultis placed on top of vertical walls, a horizontal

collar tie member must be added to preventsplaying. This piece must be bolted andmortared. If there is an additional lateral load,like wind, the design needs more triangulation tohold the compression-fit pieces together.

Where members of the truss come together atangles, and tension forces are anticipated, a steelstrap is placed to bridge the pieces, and the jointsfilled. Especially for center-bearing trusses,tensile loads on this strap can be quite large. Forall of the dozens of structures built by Velez, hesays, “I have never seen the bamboo fail, onlythe steel straps have failed under load testing.”

ToolsThe appropriate use of tools is difficult to teachin a book, best is to learn from craftspeople likeDoug Lingen – 530-292-9449 or Nicanor Non –218-668-2545. But a few general principles canbe discussed. Because of the lack of reinforcingfor the very long fibers in bamboo, one needs tocut, not tear or pull those fibers. In drilling, thisprinciple translates to the use of brad-point bitsfor smaller holes and Forstner bits for largerholes. In cutting, this principle forces us torotate the pole during the cut so that fibers arepushed toward the pole not pulled out to teardown the length of the pole.

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Design opportunitiesExperiments to gain the spans achieved bySimon Velez have taken place far from anyinspection. Now that these 66 foot spansand 30’ cantilevers exist, they stand as proofof what works and as a model which mightenable us to attempt only one quarter thespan and still find it adequate for most of ourneeds.

Make Use of Smaller polesIn this country, by far the most commonvariety is Phyllostachys aurea, or GoldenBamboo. Next is Phyllostachys nigra, orBlack Bamboo. These two are readilyavailable, but rarely longer than 15 feet orover one inch in diameter. The fibers arestrong, though somewhat prone to splitting.A great challenge is to find use for thesecommon varieties. One solution is to makestructural members out of split bamboo.This allows the further advantage of beingable to form curves, as in this trellisdesigned by the author. (Photograph byJacqueline Lytle)

Use curving polesIn contrast with Asian groves, acharacteristic of many of our availabletimber bamboo groves is that they were

never thinned to maximize pole production.In the new shoot’s search for light, the polecan become quite curved. This trussdesigned by the author uses the “camber” inthat large pole as the top of a bridge. Therewill be two of these trusses with joists toconnect them and a mat of split-openbamboo as the walking surface. (photographby Kevin Falkerson)

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The same idea can be applied to a roofstructure:

Use as both tension andcompression membersAs in this stool, the same member can actboth as a compressive post as well as aflexible fiber, capable of bending into tightradii.

Use custom cross sectionsAs the new shoot is forming, it can bemolded simply into, for example, a squarecross section. This ability can bring bambooat least occasionally closer to our rectangularmindset. (photo by Woody Woodworth)

Living structuresBecause of the speed of renewal anddurability of the living plant, once a masterplan for a site is created, future buildings –and especially trellises – can be anchored tothe ground. In this case, a structure isplanned and temporary poles carry thetensile fabric roof while the bamboo is givena half dozen years to mature. Once theculms are large enough, they will be bentand tied together at the center of the circle.Bob Mandich, designer.

Or, if a design calls for a strong edge, plant afence or trellis:

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Strawbale composite

The "all-grass" solution: bamboo, strawbales and thatch (not shown). It begins witha bamboo substructure formwork uponwhich the bales are laid and pinned togetherwith bamboo or rebar. Anothersuperstructure of bamboo over the top is tiedthrough the bales to the substructure creatinga composite beam to make the wholestructure integral. [architects Dan Smith andBob Theis 510-526-1935; Kelly Lerner 510-528-3765, see articles in The Last Straw #12, 14, 17 (520-882-3848)]

Use straight poles to define curvesCurved roof and wall surfaces can bedescribed with a series of straight lines, as inthis design by the author:

The structure below was created at theBamboo Hardwoods factory in Vietnam by aFrencharchitect

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Urban LandscapesFew plants are capable of such a sizeablepresence in a small footprint. Bamboo canlend texture to a façade and soften while stillallowing transparency.

Building as BasketImagine being able to weave an entirebuilding the same way as the integrallystrong baskets are made. This is a design byarchitect Shoei Yoh. A very thin concreteshell was cast around the bambooframework, covering it completely. Anotherlayer of bamboo was placed inside thestructure for decorative purposes.

Rebar /

CableOscar Hidalgo has achieved success inturning culm splits into something of a braid,increasing the surface area for adhesion(Bali ’96 v.3, p. 76). Janssen has mixedfeelings but thinks the technique issometimes appropriate (Janssen ’95, p. 49).For our use, research focus should be onusing bamboo for carrying distributed loadslike footing reinforcing and slabs rather thanfor concrete beams where loads are tooconcentrated.

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Bamboo growth strategies

The plantThink of bamboo differently. The strength of theplant has less to do with the visible portion aboveground, and much more to do with how well therhizome below ground has been storing energythroughout the year. You are only rewarded nextSpring for how well the plant has been cared for theentire previous year. Once the new shoot appears,it will never get any larger in diameter. As theplant becomes established, subsequent year’sshoots are larger than the “parent” culms.Temperature is a key factor in production of newshoots in running bamboo. Studies by the USDAdetermined that the years with the most days under40 degrees F corresponded with increases in thefollowing year’s number of shoots. Bamboo,because it is shallow rooted, has evolved a complexrelationship with certain soil microbes. Aphotosensitive algae is used by root tips todetermine optimum sunlight conditions for newshoots. Studies have begun to uncover somemysteries of bamboo nutrient uptake by closeanalysis of microscopic nutrient transfers.Scientists in Asia have begun to identify the rolethat mycorrhizae fungi have in allowing bamboo tobreak down and absorb complex minerals as wellas bring nutrients and moisture from lower strata.In the U.S. climate, with different fungi anddifferent relationships with other more deep-rootedplants, some success has been had in injectingspores of some of our fungi, and in consideringmushrooms one of the major crops of the grove.Rhizomes have low survival rates when detachedfrom the mother plant at times other than springwhen new shoots occur. But, rhizomes with eventhe smallest plants attached will have a muchhigher survival rate, leading to suggestions that theamount of shooting is regulated by substancesproduced in the culms or leaves, according toUSDA research5 in the early ‘60’s. It has beenestablished that the culm itself is capable ofphotosynthesis.6

The fiber lengths vary across the culm wall: shorterin the interior and exterior than in the center of thewall. The shortest fibers are near the nodes wherecracking is likely to first appear. (Liese ’92) Fiberstrength is significantly greater at the exterior. Oneaspect that has yet to be fully explored is the sharp 5 anonymous6 Dr. Hau-Po Mok, personal correspondence

contrast between the way wood is formed in trees – from thecambium layer outward to form bark and inward to formannular rings – and bamboo which, as a grass, forms bystretching. The structural and design implications have yetto be explored.

Original forest "types" for the Phyllostachys genus show aclose associative affinity to deciduous hardwood forests ofsubtropic and mild temperate zones surrounding China. In atwenty year forest analysis in Hunan Province, supplementalmulch of bamboo leaves and pine needles proved the mosteffective at inducing nutrient absorption. Both of theseunrelated plant families have evolved symbioticmycorrhizae. Bamboo's ability to occupy a shallow soilzone and absorb nutrients from surface litter which containtoxic alkaloids is due to the quick fungal breakdown of theelemental nutriments before the toxins kill the delicatefeeder roots. A mulch of rice hulls was found to be the mosteffective at both providing minerals and raising soiltemperature to induce much earlier shooting (when pricesare higher) and dramatically increasing the number ofshoots. (Bali, ’96 – Qungen et al)

ControlOne reason the running bamboos have attracted the ire ofneighbors is that the rhizomes can travel as much as 30 feethorizontally in a year with no visible signs of growth.Those intending to use the culms intensively welcome thisaggressive search for nitrogen and water as the edges of thegrove can be easily contained with plastic rhizome barriers,two foot deep ditches or using mulch as a growth medium,allowing the rhizomes to be easily dug. [photo of SanLeandro mulch planting] If an existing grove hasoverstepped its bounds, remember that the straight rhizomeis the lifeline back to the mother plant. Follow the line ofshoots back to the acceptable spot and sever the rhizomethere. Then find a member of the American BambooSociety to remove any traces of your timber bamboo, or cutthe poles near the ground and break off with your foot anynew shoots you see emerging over the next few months.Soon there will be nothing to sustain the rhizome and it willgive up.

Running bamboos produce a limited number of viablerhizome buds, sometimes spaced a foot apart. If a plant isdivided leaving no buds, the plant will not spread.

In places where bamboo naturalizes, it is almost nevercultivated. This means that it is only available in the forestwhich is owned by all, yet when population pressures cometo bear, it is those places with unclear ownership that areoverharvested first. Because bamboo is such a valued

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resource, there is never a question of bambootaking over. The problem is much more often theopposite. With edible bamboo shoots selling for $4per pound retail and a 24” pot of mature timberbamboo selling for $1500, 5 gallon plants routinelyretailing for $50, there is a much greater fear ofbamboo poachers than of the plants taking over.Conversely, there is a threat from gophers, deer andneighboring goats when the plants are small.

Species selection related to climateFor structural use, several species stand out andlend themselves to specific climatic selection.While wind should be avoided and water ever-present, the most significant factor in site andspecies selection is temperature. Several large,strong temperate Phyllostachys running bambooscan withstand 0 degrees F., and appreciate hot,humid summers: P. bambusoides, P. heterocyclapubescens (moso), P. nigra henon. One clumpingtimber spans the range between the temperaterunners and the tropical clumping types: Bambusaoldhamii, hardy to 15 degrees F. (although its newshoots happen in November and December, so eventhough the plant may not be killed, it can be setback a year with a hard freeze) The tropicalclumping varieties like the other Bambusas,Guadua and the strong Dendrocalamus species (D.brandesii and D. asper) will barely toleratefreezing, although extensive research withinterplanting among trees, avoiding frost pocketsand using mineral-salt fertilizers is being carriedout in Australia (Cusack ’97) which has foundsuccess in resisting temperatures 9 degrees F.colder than the species was previously seen totolerate. But, again, for those of us in the northernhemisphere, the vulnerable shooting season is thecoldest time of year here.

Daphne Lewis details species selection for growersin the U.S. Pacific Northwest, covering thePhyllostachys varieties related to size, hardiness,quality of poles & edible shoots, forage quality andflowering dates. (Lewis ’98)

Water sourcesThrough most of the West, the rains happen in thedormant season for running bamboo. The time ofmost intensive water need, in late Spring when thenew shoots occur and late Summer when therhizome growth occurs, is the dry season. So,especially here, bamboo is inextricably tied to caregiven by people and well meshed with urbansystems. Eighty million gallons of sewage andstormwater are processed each day in the city of

San Francisco, the amount can double on a rainy day. All ofthe treated freshwater is eventually dumped into the ocean.In fact, the waste created by people is often ideal forbamboo: the phosphates in soap, the nitrogen in food wastecan make greywater a very consistent source of sustenance.The secret to growing giant moso seems to be to water itevery day, so a constant source of industrial greywater cansolve several problems. In places where septic systemswon’t percolate the soil, the EPA now encourages sand filterevapotranspiration systems (http://www.nsfc.wvu.edu),where a plastic liner keeps any effluent from reaching theground. All water must exit through evaporation ortranspiration. In this system, bamboo with shallow roots,great height and large surface area of transpiration canaccelerate the transpiration system. It is easier to grasp thepotential when one enters a large grove as the new shootsare emerging. Water droplets are pushed ahead of every tipof new growth and it literally rains there. [Diagram ofWatson Wick]

Checklist for obtaining construction-qualitypoles§ Age – 3-5 year old culms best, depending upon species§ Starch content – harvest at right time of year to

minimize beetle/fungus attack (see chart)§ Appropriate species for the intended use (Lewis, ‘98)§ Sufficiently adapted to local humidity – especially for

interior use§ Stored out of direct sun, preferably vertically§ In the running bamboos, use the bottom 5 feet or so for

other purposes as it is usually crooked, has nodes tooclose together and density characteristics different thanthe rest of the pole

§ Treated for insects and fungus if used outside (thinkwood)

CautionsGiant timber bamboo is the wrong scale for our mostcommonly created American landscape: the suburban singlefamily lot. The rule-of-thumb is that a mature grove wantsto be in radius the same as the height. So, a sixty foot highPhyllostachys henon grove will expand to a 120’ diameterand find stasis and comfort in the micro-climate created foritself. There are, however, many useful smaller species,especially mountain clumping bamboos hardy enough formany colder areas. Consult the ABS species list.

It takes longer to achieve a mature grove (4-10 years) thanmost people are willing to stay in one place.

New plantings of bamboo are extremely fragile, as therhizomes may have just been cut – somewhat like anumbilical cord – from a single organism that may havecovered thousands of square feet. Until the canopy growshigh enough to shade the ground – usually several years –

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the new plants are subject to quickly drying out,neighboring hungry horses, gophers, or an ill-timedfrost. One quick mistake can be fatal to a newgrove.

Bamboo supplyCurrently available timber bamboo poles in theUnited States consist primarily of culled, older,ungraded, highly blemished and fumigated (uponimport) material from China. What we have towork with does not at all resemble the Kyotosystem (see the harvesting and curing section),which we might hope to emulate.

LongevitySome species have a higher starch content andleave themselves open to earlier attack from fungusand insects, so much of the information onlongevity has to do with local conditions: withmore rain, humidity, and tropical climate, thequicker bamboo will return to compost. If buriedunderground, in most places, bamboo will survive acouple of years at most. In tropical rainforests withno preservative treatment, houses are expected tolast from 3-5 years intact, rarely will they lastlonger than 15 years. The whole structure is rebuiltin a matter of days as part of an accepted rhythm.In the Colombian Andes, one of the stronger,longer-lasting species, Guadua angustifolia hastraditionally been used untreated for posts, beams,flooring, roof structure and lathing for plaster wallsin houses now over 90 years old. This is onlypossible using culms that are at least 3 years oldwhen cut and the plaster on the ceiling and wallsprotects from beetle damage. (Hidalgo ’92) InJapan, temperate, running bamboos have been seento last hundreds of years when used as ceilingstructures receiving the smoke from unventedcooking fires. (see the section on curing)

Cracking can be the first step toward breakdown asinsects are then allowed access and the strength ofthe tube is lessened. Exposure to the sun anddramatic changes in humidity combine to increasethe frequency of cracking. Both the interior andexterior shell of the pole are watertight and theappearance of cracks on a hot, dry summer day isaccompanied by a loud popping sound as thepressure finally equalizes in the pole. Some timberspecies, like p.n.bory seem predisposed to crackingmore often than others, but the splits can beminimized by both evading the sun and keeping thehumidity high, or at least constant. And, for fenceor gate structures which are not attempting to span,the common technique is to punch out the nodes

with a steel rebar or by making an incision along an unseenside to encourage splitting to happen there. In designingstructures, it is very important to keep the forces axialwithin the length of the bamboo, and not place anyimbalanced or eccentric loads.

Bamboo Harvesting and Curing TechniquesThere is a huge compendium of stored knowledge intraditional bamboo cultures-- a living tradition kept bycraftsmen following methods that have proven effectiveover generations. In one of the most rigorous systems, stillkept alive today in Kyoto, each specie of bamboo required aslightly different harvest and curing procedure with keyseasonal factors dictating once-yearly maintenance to cleanup groves and produce useful byproducts.

Methods traditionally used to preserve bamboo culms forlight construction fall into two categories:The first principle is a clear grasp on local growingconditions that can be manipulated to give best results.Bamboo needs a moist well-aerated soil to spread rapidlyand produce high quality poles.

The second principle of culm preservation is the method ofdrying. Because there are no radial fibers in bamboo, thehard outer layer won’t transpire and, if dried too quickly,will split due to its watertight quality and shrinkage aroundthe solid node. In regions where bamboo thrives, wintertemperatures seldom stay below freezing long enough tocreate the super-drying effect found in Europe and theEastern United States. Three to four months of air drying issufficient to slow-cure the poles. These months of curingshould be cool, the area well ventilated and free of organicmaterial that could harbor pests. Most importantly, theculms should be stored horizontally out of direct sunlight toprevent uneven curing.

Harvests and Grove MaintenancePropagation of small plants is labor-intensive and slow,especially for the running bamboos. So, the price of plantsin the U.S. will probably remain at a premium. Planting agrove of timber bamboo in loose soil like sand and mulchallows for easier propagation and digging of rhizome.Groves can be a high value use for wet soil especially. Themajor work season should fall during the plants' dormantmonths, and the work in a mature grove involves harvestingvery young edible shoots and mature poles. In China, theproportion of harvest is to take 80% of the shoots as food tothin the grove and leave 20% to mature into well-spaced (2-3 feet apart) poles. These will be marked with the year oftheir shooting and taken after 3-5 years. Ideally, polesshould be harvested about 6 weeks before use, as they willhave shrunk to their expected size, while still maintainingthe working characteristics of green bamboo. In earlyspring, walking in the grove should be avoided once the

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shoots are expected. Several varieties, notablyMoso, push moisture ahead of the new shoot, so avery clear wet spot can be seen on the ground justbefore the arrival of the new culm. Those withtough feet will walk through the grove barefoot tofeel the arrival of new shoots so that soil and mulch

can be mounded over the new arrival postponing by severaldays the contact with air, which causes the shoot to becomeinedibly fibrous.

Bamboo harvest seasons in Western U.S.Running bamboos Clumping bamboos

Edible shoots March - June October – DecemberRhizome divisions Just before shoots begin January – FebruaryPlant divisions Avoid heat of summer January – FebruaryLeaves as animal feed Anytime, esp. after pole harvest Anytime, esp. after pole harvest3-5 yr. old poles April - June January – February

Once the grove is mature, culms selected forstrength and durability should be in their third tofifth season of growth, and harvested when sugarlevels are at their lowest. In the tropics of SouthAmerica and Asia, this corresponds to the dryseason. On the west coast of the U.S., the besttime may be late Spring once shooting has endedfor the running species.

SidebarWet season harvests have three immediateproblems:1. fungal contamination from the humid

conditions2. insects are active during the same wet

season,3. excess pole moisture makes them

difficult to fully cure -- traditionalharvesting techniques apply to regionswhere bamboo evolved within theforest.

Bamboo Aesthetics and History ofPreservationBefore exploring the process of curing bamboofor interior uses, it is worthwhile acknowledgingthat the cultures of Japan and China are attractedto bamboo's natural green color and understandthe value of perfectly unblemished poles. Theeffort of harvesting bamboo on the day of use tomake, for example, cups and a sake dispenser,demonstrates a kindred affirmation in theimmediate utility of bamboo, respect for theguest, generating frequent comments on thebeauty of the freshly harvested culms. For thistype of "instant" construction there is of courseno preservation method – the materials areselected fresh and used immediately. The "new"green color reflects an esthetic of renewal.

While the older waxy green color, short-lived,expresses strength and special awareness of a season orannual festival. Structures of green bamboo can berather large-scale and always exude functionality--common booth displays for bonsai plants or a shed stallwith a canvas cover. The roof material is also of atemporary nature; the most traditional covering,(seldom used since the advent of blue polyethylenetarps), would be a Sasa palmata bamboo leaf thatching– woven onto a light bamboo frame over Phyllostachysnigra f. henon rafters. Larger structures can alsoincorporate P. bambusoides posts and beams withsimple lash and mortise joinery. This temporarystructure is light and easy to assemble and disassemblewith easily replenished local ingredients.

Permanent structures in Japan usually rely on heavierstructural materials such as wood posts and pine logbeams, with bamboo incorporated as rafters and purlinsfor the ceiling, over which some formof thatch is applied. The model for this type offramework comes from the thatched roofs offarmhouses which, until this century, was the mostcommon rural roofing material. Thatch was easilyavailable, and the periodic re-thatching was a chance toreplace bamboo weak rafters. What allowed this typeof roof to last more than ten years or so were the flue-less fireplaces of the traditional farmhouses. Thesmoke wafting up through the bamboo and thatchcoated the entire surface with an acidic film similar incomposition to creosote which slowly dried andpreserved the bamboo framing and Miscanthusjaponica thatch. The resulting bamboo ceiling framecan last several hundred years and be highly resistant toinsects. Traditional untreated and uncured bamboostructures without the benefit of this smoke curing, aresaid to only last for ten years before the bamboo isinfested by powder post beetles. Selecting bamboo asan interior ceiling frame wisely keeps bamboo well

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away from destructive moisture, which isinvariably, the problem in using bamboo as afoundation.

The bamboo ceiling prototype of the countryfarmhouse has metamorphosed into the elegantbamboo elements used in the Japanese TeaCeremony. The refined utensils and architecturalelements all derive from the "rustic" esthetics,often called 'wabi sabi'. These mood-evokingterms refer to the simplicity sought in theunderstated designs reserved for the tea roomarchitecture. As the actual tea room is neverlarge enough to accommodate a fire, thepreservation techniques for the bamboo curtainsandwindow frames and ceiling are somewhatunique.

Traditional JapaneseCuring MethodThe winter harvest and curing previously notedis followed by a short secondary curing. Thissecond curing lasts only one or two weeks. Firstthe bamboo poles are selected to match oneanother in size and evenness of internodalspacing, determined by the culm's locationwithin the grove. Near the center of a maturegrove the culms have fewer branches and muststretch to reach the available sunlight; thischaracteristic also creates very evenly spacednodes without branches for several meters fromthe ground, and these poles have somewhatthinner walls which makes them dry uniformlyfrom bottom to top. After careful selectivegrading the bamboo is transported to a specialcuring yard set up with peeled Cryptomeriajaponica drying racks. At this point the partiallyaged poles are pale green in color. Apprenticesare set to work leaning the poles vertically in thesun-- the season is usually dry but withoutintense sunlight or high winds. During thesecondary curing the poles are turned constantly-- each pole must be turned two or three times aday to keep sunlight from splitting the culm.After having been spun approximately twentytimes they are ready for the final process ofsmoking the poles quickly to preserve them withthe creosote naturally in the smoke. Thecharcoal pits are constructed at ground level twoto three feet wide by the length of the pole –twelve to fifteen feet long. Each pole issuspended over the pit by two workers standingat either end of the pit and slowly spinning theculm between them until the light green color

begins to vanish. This final process takes less than fiveminutes. It is important that the pole has receivedenough time in the yard prior to this final processing. Ifthe culm has been dried too quickly the baking cure willresult in a blotchy "finish". The Japanese expressionfor the final curing is 'roketsu-dosu', which refers toremoval of the exterior culm wax, which naturallyoccurs on the outer surface of bamboo. The wax isquickly wiped off while the pole is still piping hot,leaving a highly polished surface. While still warm, thepoles are flexible and can be straightened. As soon asthe poles have been wiped and cooled in a well-ventilated rack they are stored upright in tidy storagebarns, ready for use. At this point the color is an eventan shade which will very slowly patina over time.

Recently, a method of boiling bamboo culms in causticash solution has been used in Japan. The methodemployed is to follow the curing process for threemonths and then to boil the culms for twenty-fiveminutes. This method is less time consuming andexpensive, but does not leave a satisfactory polish onthe culms and brings a lower price for the finishedproduct. In Costa Rica, culms are boiled in caustic sodato remove the wax so their dark flame-finish will applyevenly.

The insects are most interested in the starchy fibersclosest to the interior of the culm. But neither thesmoke nor the boiling methods effectively reach thosefibers. Holes can be drilled into each internode to allowsome penetration, but since there are no radial fibers inbamboo, full treatment is not always possible,depending upon species. In tropical regions especially,it is most advisable to treat with a pressure-injectionsystem, like the Boucherie.

Preservation with Borate SolutionThe "Boucherie" method was pioneered by Dr. WalterLiese, of Hamburg University. This technique replacesthe starchy sap of the just-harvested bamboo with aborate/borax salt solution to make the cellulose andlignin fibers indigestible to insects and microbes. Theculms selected must be of mature age and themachinery close enough to be processed in the first dayafter harvest while the sap remains fluid and capable ofcapillary action. The dye-marked solution is pressure-fed until it is seen at the far end of the pole. Borates areused as fire preventative in various insulations, but notesting has been done to our knowledge on the fire-resistance of the bamboo poles treated with borates.More information on this method has beendisseminated through the INBAR bamboo researchnetwork in India, and the borate is a less toxic (tohumans) method to preserve bamboo culms — although

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it appears to be difficult to incorporate inindustrial-scale production methods

Finishing the surfacesCareful handling keeps bruises and imperfectionsfrom spoiling the clearest possible finish. Again,if the culms are not thinned and are allowed togrow too close together, they will cause a greatdeal of surface damage to one another.

With the natural waxy coating of bamboo –especially the older culms – there is no strictrequirement for applying a finish. If a stained ortorched finish is desired, the wax must beremoved first, usually by boiling or by abradingwith wet sand.

Regardless of color or striping when alive,almost all bamboos dry and turn a consistentlight brown. One exception is P. nigra, whichcan maintain the black color, especially if keptout of the sun. Another exception is P. nigrabory, also known as Leopard bamboo because ofthe spots that remain even after drying. TheJapanese have refined an artificial method ofobtaining a similar coloring using sulphuric acidmixed with mud.

A dark brown patina is obtained with the smokecuring method described above under “JapaneseCuring Method.”

Bibliography§ Arce-Villalobos, Oscar, ’93, Bouwstenen

24: Fundamentals of the Design of BambooStructures, Eindhoven University, theHague, ISBN 90-6814-524-X

§ (Bali) various authors, ’96, Bamboo, Peopleand the Environment, Proceedings of theVth International Bamboo Workshop,International Network for Bamboo andRattan, New Delhi, ISBN 81-86247-15-7

§ Cooper, ’92 (see Liese)§ Cusack, Victor, ’97, Bamboo Rediscovered:

Growing and Using Non-Invasive, ClumpingBamboo, Earth Garden Books, Trentham,Victoria, Australia ISBN 0 9595889 8 1

§ (ERG)various authors, ’97, AIAEnvironmental Resource Guide, Wiley, NewYork, ISBN 0-471-14043-0

§ Dunkelberg, Klaus et al, ’85, IL31: Bambooas a Building Material, Institute forLightweight Structures, Karl Kramer Verlag,Stuttgart, ISBN 3-7828-2031-2

§ Glenn, H.E., ’56, Seasoning, Preservative andWater-Repellent Treatment and Physical PropertyStudies of Bamboo, Clemson Agricultural College,Clemson, S.C.

§ Hidalgo, Oscar, ’81, Manual de Construccion conBambu, Estudios Tecnicos Colombianos, Bogota

§ Hidalgo, ’92 (see Liese)§ Janssen, Jules, ’95, Building With Bamboo,

Intermediate Technology Publications, London,ISBN 1 85339 203 0

§ Janssen, Jules, ’97, Bamboo: A Grower &Builder’s Reference Manual, HCABS (PO Box1390, Keaau, HI 96749)

§ Lewis, Daphne, ’98, Hardy Bamboos for Shootsand Poles, self-published (tel. 206-781-1437)

§ Liese, Walter; Hidaldo, Oscar; Cooper, Gib; et al,’92, Bamboo and its Use – InternationalSymposium on Industrial Use of Bamboo,International Tropical Timber Organization,Beijing

§ McClure, Floyd, ’53, Bamboo as a BuildingMaterial (reprinted by American Bamboo Society,’96)

§ Velez, Simon; Marcelo Villegas et al, ’96, TropicalBamboo, Rizzoli, New York, ISBN 0-8478-1192-1