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EE/ESD Program

Title of EE/ESD project

Bamboo Bows for Load Bearing Structural Elements

Created : Oct 18 2007 / Modified : Oct 18 2007

Organization Name

Haritha Association for Learning from Environment, India

Type of the Project

National / Community Level

National

Main contents and field

Agriculture / Forestry / Research / Training / Other (Green building technology and School deucation)

Target area and people

Any typical rural area in India. Rural communities including those of tribals

Background/Problems of the project

Traditional house building, with rooms of decent sizes, require large sized timber, which come from trees that are 20 years or older for the main roof load bearing structure.
Commercial plantations to grow trees for timber are beyond the means of even big farmers, not to speak of the marginal farmers. Thus, the source of timber for the roof load bearing elements in traditional building of houses is mainly forests, which are rapidly getting depleted and denuded.
This has led some well meaning activists to call for banning the use of timber in house construction.

But we believe that the gigantic task, of greening over 160 million hectares of the wastelands in India, can only be accomplished with commercially sustainable activities, which must include rapidly renewable plantations, such as bamboo and using the same in massive housing projects.

Thus the challenge is to build with what we can grow in four to six years time.
Our solution is in using bamboo for building.
Even though bamboo has been in use for times immemorial, in house construction, it is only as roof load distribution but not as main roof load bearing structural elements.

The main difficulty in using the bamboo is to reliably join several bamboos rigidly, with several years of good performance. This is because, for all its great strength, bamboo splits easily and standard timber joints are not at all useful for bamboo joinery.
A great deal of recent efforts at global level have focused on cost effective bamboo joinery for the massive low-end house construction.

Traditional house building, with rooms of decent sizes, require large sized timber, which come from trees that are 20 years or older for the main roof load bearing structure.
Commercial plantations to grow trees for timber are beyond the means of even big farmers, not to speak of the marginal farmers. Thus, the source of timber for the roof load bearing elements in traditional building of houses is mainly forests, which are rapidly getting depleted and denuded.
This has led some well meaning activists to call for banning the use of timber in house construction.

But we believe that the gigantic task, of greening over 160 million hectares of the wastelands in India, can only be accomplished with commercially sustainable activities, which must include rapidly renewable plantations, such as bamboo and using the same in massive housing projects.

Thus the challenge is to build with what we can grow in four to six years time.
Our solution is in using bamboo for building.
Even though bamboo has been in use for times immemorial, in house construction, it is only as roof load distribution but not as main roof load bearing structural elements.

The main difficulty in using the bamboo is to reliably join several bamboos rigidly, with several years of good performance. This is because, for all its great strength, bamboo splits easily and standard timber joints are not at all useful for bamboo joinery.
A great deal of recent efforts at global level have focused on cost effective bamboo joinery for the massive low-end house construction.

Objectives/Significance of the project

Our dream: Build houses with what we can grow in three to six years.

Our solution: Bamboo Bow.

We, at Haritha, have come up with a unique and cost effective solution by using 'bamboo as a bow' to take the load of the roofs. And since bamboo matures to good 'timber' in about 4 to 5 years, it is rapidly renewable.

Significance:
Greening the waste lands - bamboo plantations - a massive economic opportunity for the tens of millions:
Bamboo has commercial uses from when it is a few weeks old (as bamboo shoots) to when it is 1 or 2 years old (for weaving bamboo ropes and baskets)
Thus a bamboo plantation can be undertaken by even marginal farmers, as the returns trickle in even in the very first years of plantation.
More over, bamboo plantations, once raised, would give annual yields for fifty to seventy years.
Thus if only there is a massive high end demand for bamboo, such as for the main roof load bearing structurals, tens of millions of marginal farmers and farm labour can take up bamboo plantations and green the vast waste lands in a commercially viable and sustainable manner while healing the badly bruised soils of the waste lands.
A good value addition at production site by primary producers:
Further, the technology of making bamboo bows is really very simple, requiring very little external inputs and thus can empower the multitude of the masses as they can easily achieve a good value addition to their primary produce, namely the bamboo.

An Insurance for generations:
And what is more, these plantations would give them the kind of insurance against ravages of nature or manipulated markets, that is unthinkable otherwise.

Hence, we expect the benefits to the rural masses through sustainable livelihoods to be really on a massive scale even while solving the gigantic task of greening the wastelands to heal ecology and environment.

Description of the project

The beginning: A 10th class project
It all started with our efforts at utilizing the thin and small sized timber that we can get from 6 to 8 year old plantations. We tried to join these up to make I beams T beams and so on. As a 10th class student experiment, such built up shapes were compared for their load bearing ability for a given material used.

The Bow:
And in the process, the bow shape was identified as one of the best. Adding two cross ties to the one horizontal tie of the bamboo is found to substantially improve the bow's load bearing feature. It was then recognized that bamboo is a wonderful element that would fit to be bent as a bow with spans of 10 ft to 15 ft and that two or more bamboos can be joined easily to make a bow of over 24 feet span.

Real houses with bamboo bows:
The beginning: The first shed with 20 ft span was built in the old campus of our Haritha Ecological Institute, in 1990.

Scaling up: Then , in 1994-95, when we decided to build a 20,000 square feet (sft) living /class room space in a 12 acre farm land campus for our institute, 24 ft span, twin bamboo bows became the standard load bearers for a variety of roofings - from corrugated GI sheets to thatch of palm leaves or grass.
We continue to live under these after 11 years.

The Ferro cement Band : a rigid tie for bamboos
Our continuous search led us to ferro cement band to rigidly tie bamboos. It is simple, cost effective and long lasting. And lots of scope to introduce the latest in the rapidly advancing cement technology.

Great scope for innovation:
Efforts for better products with bamboo for main line construction continue. The great strides in the materials technology of glues, resins and epoxies are to be closely watched and implemented for bamboo so that bamboo can challenge steel in every construction, save the fire places.

Materials/equipments used in the project:

No more than ordinary carpenters' and masons' tools have been used thus far. Special work tables are used for some bows.
>> We could benefit from such things as concrete spraying machines and foam concrete technology.

Pictures and maps

Time span/Timeline

Basic proof of concept of a bow: 1989First bamboo bow testing : 1989 1. First bamboo bow shed : 19902. Scaling up to 20,000sft living /class room space with 24 ft bamboo bows as the main roof load bearing structurals 1994-953. The ferro cement Band tie for bamboos : 20014. 24ft x 18 ft Shed with a single Giant Built up Bamboo Bow Beam: 20025. Several Houses(over 15) withGiant built up bamboo bow beams : 2002- 2003ferro cement domed roofs: 3 housesthatched roofs: 8 houses : 2003- 20046. Ferro cement domed roofs over : 2002-2003several bamboo bowssmall houses : 10 housesLarge sheds : 20 ft span and 40 ft long : 17. New type of bamboo bow beams, bamboo bow supported A frames and rectangular beams 2005

Result/Self evaluation (success or failure) including its reasons

1. Single bamboo bows of 12 ft to 14 ft spans for lightweight thatch roofs are the simplest to build.
2. Two bamboo bows involving just the binding wire ties are simple to make, but providing a few bolt and nut ties at critical locations is better.
3. The simplicity of design, ease of fabrication of the bamboo bows and possible rapid growing of abundant bamboo supplies are the strong points in favour of bamboo bows as the main load bearing structurals.
4. The possibility of soil erosion control and nursing to health of degraded soils on a large scale, through massive bamboo plantation is a major ecological benefit while the extensive use of bamboo bow as the main load bearing structural element would be the major economic driving force for the success of the bamboo plantations. Greening of wastelands through the bamboo route can become an economically viable option, and leads to improved ecology.
4. Trying to surround the bamboos of the bows with sand cement mortar even with rice husk ash is not recommended as it resulted in failure of the structure.
5. The bamboo bow as a load bearing structure has won a national award from Housing and Urban Development Corporation, India in April 2005.

Other learning from the project

1. The long term creep properties of bamboo under different load conditions are to be studied and well understood before the bamboo is considered as a serious modern engineering material.
2. Building with bamboo as a part of school activities for learning different concepts is possible and should be taken up after extensive investigation.

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