Bamboo construction

A brief history of bamboo construction

The ancient Chinese created "fire arrows," which were made of bamboo filled with gunpowder, to get more distance to their arrows. These arrows eventually evolved to become the rockets and firecrackers we are familiar with today. More recently, Thomas Edison used carbonized bamboo for the first successful light filaments. It has been used to make paper, cloth, and even Rayon.

Bamboo's tensile strength has been essential in the development of bridges. The Chinese invented suspension bridges using bamboo to cross rivers. Using only the exterior part of the bamboo, which is four times as strong as the interior, they created tension cables up to 120 meters long. Bamboo bridges were also constructed in India, and by the Incas in South America. In both cases, the structural cable was strung above the walking surface, which hung from it. And in Colombia, tension bridges were created using this amazingly strong material, with tensile strengths of up to 3,200 kg/cm2 for the species Guadua. Similar building techniques have also been used to create gabions to dam rivers and streams, where a long basket of bamboo is filled with stones with each end secured to the banks. It has been crucial to the development of many inventions. Bamboo has been used to build boats and zeppelins. In aeronautical research, structural members of kites and early planes were constructed using the material as it is light and extremely strong. A plane made completely of bamboo was built in the Philippines, while the Chinese commonly used it in their planes during World War II. Plans for bamboo planes were even available in "Popular Mechanics" magazine.

Bamboo also has a long history of use in buildings, being common to the vernacular architecture of China, Southeast Asia and Central and South America. The Chinese could span up to ten meters with their corbelling technology, and bamboo has been used extensively all over Indonesia, especially in the Celebes Islands. In Hong Kong, all scaffolding for highways construction is built of bamboo, and tied with bamboo strips only 1 mm thick. Although they have a great history of building with bamboo, today the Japanese use it only for their traditional tea houses..

Introduction 

India has presently reasonable bamboo resources with a potential  to increase the same through improved propagation techniques. Its renewability, workability and low co st have made bamboo an established traditional construction material, particularly in rural areas. These advantages together with high strength of bamboo outweigh its limitations like low durability. However, sophisticated applications of bamboo such as large spanned building sand reinforcement in concrete to exploit its high tensile strength have not been made practically possible despite attempts made in developing such uses. It is possible to improve the durability of bamboo in construction by adopting suitable treatment and improved detailing, especially of joints. Research and Development work are needed for better exploitation of this renewable resource with short rotation which in improved and reconstituted form can substitute wood in construction and packaging. Recent studies have shown that a more rational utilization of bamboo is possible through conversion of bamboo into products like bamboo mat boards rational utilization of present bamboo resources depends on the development of improved and new products from bamboo which can overcome the limitations of solid bamboo and enhance both its technical and economic value. Splitting bamboo into slivers and weaving them into mats of different pattern, shape and quality is a cottage industry in many parts of India. Bamboo mat weaving is a popular cottage industry contributing to the livelihood of thousands of people in areas where large quantities of short rotation species like Ochiandra travancorica and Och Iandra rheedi are available.

1. Significance of bamboo as a resource 

Giant grass	Harvest after about 5 years
Distributed in tropical areas	1250 known species of Bamboo, with 1500 possible uses.
Growths like telescope	2.5 billion people worldwide use bamboo, of which 1 billion people use it for housing
Diameter decreases with increasing height	Trade in Bamboo generates US $ 4.5 billion.
Growth exclusively in length	Provides Livelihood, Ecological and Food Security.
No changes in thickness	Eco-friendly Products
Height: 20-25m, Diameter: about 12 cm	Lignifications : after about 3 years

 Properties of bamboo

Tensile strength:

The fibers of the bamboo run axial. In the outer zone are highly elastic vascular bundle, that have

a high tensile strength. The tensile strength of these fibers is higher than that of steel, but it's not

possible to construct connections that can transfer these tensile strengths.

Shrinking:

Bamboo shrinks more than wood when it loses water. The canes can tear apart at the nodes.

Bamboo shrinks in the cross section 10-16 %, in the wall thickness 15-17 %.

Fire resistance:

The fire resistance is very good because of the high content of silicate acid. Filled up with water, it

can stand a temperature of 400° C while the water cooks inside. 

Elasticity:

The enormous elasticity of bamboo makes it to a very good building material for earth-quake endangered

areas. Another advantage of bamboo is its low weight. It can be transported and worked easily, the use of cranes is mostly unnecessary. 

Advantages of bamboo  

In general 

• fast growing natural material
• binding of CO2
• sustainability
• available in large amounts (countries of origin)  

As a building material  

• high mechanical strength
• high flexibility (earthquake-proof)
• inexpensive and sustainable
• innovative application for representative buildings with high span widths)
• application as whole Culm or as pre-fabricated
  product (e.g. plates)  

As a space frames  

• thrust load: maximum utilization of the mechanical properties of the bamboo profile
  (tube with reinforcements)
• better environmental performance for use of whole bamboo culms than for processed
  products.
• prefabrication of construction elements:
  • easy and fast application
  • no adjustments at the construction site
  • quality assurance by prefabrication
• Joint construction transferable from other materials (e.g. steel etc.)
• reusability of beams and joints

Bamboo preservation in general 

With increasing moisture of the bamboo increases the danger, that the bamboo will be attacked by animals or vegetable pests like fungi, beetles and termites. So the best time for harvesting is the

drier and cooler season when the insects are less active. The pests can attack living bamboo canes and felled ones and can perforate them to such an extend that it becomes unusable. 

• Passive methods

  

  Covered bridge from Jorg Stamm

Simple constructive measures like lifting up the pillars or an out jutting roof can help to extend the

life time of the bamboo distinctly.

• Active methods

• Smoking:

Another possibility to preserve the bamboo is smoking

it in its own resin. The smoke makes the rind unpalatable

to insects which therefore decline the bamboo.

• Heating:

The canes are heated in kilns to ca. 150°C for a short time,

so the structure of the outer zone changes and becomes 

more resistant against insects. The poles can crack up easily.

When you cook bamboo, the starch and nutrient content will 

be reduced. The Problem is to find a container that is big enough to cook the canes in it.

• Immersion:

Freshly cut canes are immersed in water for 4-12 weeks. 

The nourishment for insects (starch and sugar) is

removed. Streams are more suitable than stagnant

ponds. Saltwater is not suitable, because the salt will

stay in the bamboo and can bring moisture and fungi into the 

canes. 

• Impregnating coatings:

Coatings with borax are ecological and widely used. In addition,

lime slurries, rangoo oil or slurries from lime or cow dung are

also used. Using insectices is ecological not acceptable.  Oven to smoke bamboo

These are kerosene, DDT, PCP and others

   These methods prevent the invasion of pests during changing the surface of the bamboo or

remove the nourishment of the insects. To protect the bamboo from fungi and mould, the moisture

must be kept away. To preserve the bamboo inside of the pole, all diaphragms have to be perforated or all segments drilled. The life time of not-persevered bamboo will be 2 1/2 years, of persevered bamboo 10 years

 Scopes

Bamboo material offers a surprisingly large number of applications and uses. Bamboo as a building material in the bamboo architecture is using for several constructions. In the following some of these construction will be represent.

• Bamboo scaffolding

Because of the favorable relationship between 

Load-bearing capacity and weight, bamboo can

be used for the construction of save scaffoldings

even for very tall buildings. 

Bamboo canes used for scaffoldings 

Lashed cane extension:

Even at their connections the canes are not

treated in any way. Only lashed joints are used.

The cane extension is carried out by lashing the 

cane ends together with several ties. The ties 

are arranged in such a way that a force acting

vertically downwards wedges the nodes in the

lashing. With larger cane diameters the friction

can be increased by tightening the rope

between the canes.

The vertical and horizontal canes used for

scaffolding are almost exclusively joined using

soft lashing. This technique has the great

advantage that the joints can be retensioned to

the right degree without difficulty and also

quickly released again. Lashed cane extension

• Bamboo houses

Bamboo houses are without exception skeletal 

buildings having raised floors with main posts

which are anchored in the ground. Typical

bamboo elements are canes, halved canes,

laths, beading, bamboo boards and rope ties.

This way of construction offers the following

advantages: pre-fabrication, simple assembly,

simple replacement of structural parts; the Bamboo house as a skeletal building

bamboo elements can be easily dismantled and 

reused.

Posts, battens, rails, purlins and rafters from the

longitudinal and transversal bamboo framework.

Normal cane diameters are 5 - 10 cm. Walls,

floors and roof are linings rather than stiffening

elements of the non-rigid framework because

braces and diagonal stays are absent in those

planes. The structural safety of the skeletal

structure is almost exclusively provided by the

posts anchored in the ground. The only vertical

and horizontal forces acting on the structure are Portable bamboo house

wind pressure, roof moisture, live loads and

dead weight. 

The framing is connected by articulated joints. 

All the framing bars can slightly move in relation

to one another. Although each part is able to

transfer all axial and transversal forces. Rigid

connections or joints are very rarely used.

Above all the structure must be able to

withstand dynamic loads, for example wind

gusts.

The building materials as well as the structure

have a high elasticity and low mass. This is the 

reason, why this houses are secure from an Proposed Two storey Bamboo House 

earthquake. at IPIRTI, Bangalore. 

• Bamboo roofing 
  
  

The simplest roof covering is formed by bamboo 

shingles which are as long as the rafters. To

produce the shingles the bamboo canes are

halved along their length and the diaphragms are

removed. They are threaded to the ridge and

placed in Roman tile fashion. These shingles

are nit fixed at the eaves. They are held in

position by their own weight.

The next roof covering is being composed of

double layers of shingles. Each row of shingles

is threaded onto a strip and tied to a pole with

simultaneously functions as purlin and roof

batten. Therefore the purlins are arranged in  Halved bamboo canes in roman

pairs. tile fashion.

The multi-layer shingle roofing is the most

expensive and heaviest type of roofing. Instead 

of a roof covering one can call this a roof wall 

having a thickness of up to one meter. The rows

of shingles are fixed to the roof battens by an

inserted key which prevents them from sliding 

off. Layer is placed upon layer up to the ridge.

The roof structure is made of solid timber.

The lancet shingle roofing is very expensive. Double

layers of bamboo  Lancet shingle

These are cut from bamboo laths in the length of  shingle

the segments. On the back of the lancet shingle

a tongue is split away from the bark layer and 

this tongue is inserted between pairs of roof 

battens. The shingles are placed with their 

concave side upwards. Because of the better

drainage the shingle should contain no nodes

outside the batten area.

In comparison with covering consisting of  Bamboo cane on the ridge Palm leaves on the

.

stranded palm leaves the bamboo leaf cover has  ridge

some disadvantages. The lancet shape, the

fanning-out of the bunches and the twisting of

the leafs necessitate more layers of leaf 

bundles, a steeper roof pitch and more solid

substructure. But these roofing is not rain proof

after longer periods of rain.

Roofing's with shingles made from bamboo

shavings have a thick layer and are

exceptionally wind and rain proof. These

shingles look like brushes with long bristles.

They are bent over a batten and sewn together. 

When using organic materials for roofing, the

ridge is the most exposed part of the rain-proof

layer. With hard roofing materials a half of a

large diameter bamboo cane is placed on the

ridge joint with the convex side up. Bamboo roof

With soft materials the parting at the ridge has

to be covered with an especially carefully applied layer of material. 

This layer is secured by bars against being lifted off by the wind. The roof surfaces are protected against the wind by wide-mesh lattices of bamboo strips. At the verges securing boards made from halved canes

are tied into the rafters with inserted keys. Bamboo houses usually have no gutters. An exception are gutter-type purlins, whose water catching function is, however, only secondary.

• Door shutters of bamboo mat boards 

Paneled doors of bamboo mat boards

One of the expensive items in a building is door shutters. It often accounts for 10 to 15 per cent of the total cost of a building. In view of the high cost of traditional door shutter made of wood and wood based panels the bamboo mat boards can profitably be used for making aesthetically appealing and functionally adequate door shutters at a competitive cost. Bamboo mat boards of 2, 3, 5 and 7 ply are ideally suited for making hollow core flush doors and paneled doors. Bamboo mat boards of 3 ply and above can be used as infill panels in conventional paneled doors. Depending on the design, thickness of the board can be optimized to achieve greater economy. Figure 6 shows various types of bamboo mat board paneled doors using different thickness boards. A 7 ply, 5 mm thick board is adequate in a single panel shutter whereas 3 ply, 2.5 mm thick can safely be used in a double door shutter having a maximum panel width of 30 cm. Even thin door panels are impact resistant, durable and strong. In recent times, bamboo boards have become a favored material for paneled doors. It is easy to make low cost paneled door shutters by laminating panels of bamboo mat board and stiles and rails of thin sections of wood with either gluing or nail gluing. A few experimental doors of this type used under exterior conditions are still in good condition after 12 years. Thin bamboo mat boards of 2 ply and 3 ply make excellent skin for hollow core functional flush doors due to high modulus of rigidity and good impact resistance of the board. Bamboo mat board hollow core flush doors as shown in Figure 7 require only core battens of secondary species or plantation species of wood like eucalypt or rubber wood, butt joined and fixed with corrugated iron fastener and face skin bonded with room temperature setting adhesive or fixed with cup screws, thus making the fabrication very simple and ideally suited for rural housing. Hollow core bamboo mat board doors are 40-50 per cent cheaper than any type of conventional door shutters and can be made on a "do it yourself' basis.

• Bamboo truss

For pitched roof construction, trusses of different span according to the size of room form the important components of the house to sustain the roof loads. Trusses transmit the load to the ground through columns or walls. When the top and bottom chords and strut members are properly jointed by suitable fastening devices, a truss can resist the compressive and tensile forces conglomerate and as such give a stronger support to the roofing materials even against storms and earthquakes. Like a nail jointed timber truss, a bamboo truss is also designed with criteria fulfilled in respect of stresses, spacing's size of members etc. As compared to the intuitional practice of making the roof by lashing two pieces of bamboo culms at ridge point . The modern methodology of fabricating bamboo truss by jointing the top and bottom chords and also the strut members by gusseting or wiring is considered to be better. The latter has the advantage of covering more space without any sign of sagging for the designed loads. There is no difficulty to fix them with the top of columns. Trusses made with bamboo (4 m span) have shown on laboratory test a very high load deflection ratio. Fabrication procedure is also simple. A layout, according to its span and slope (generally 30°) is made on the ground or floor of workshop. Selected bamboo pieces are sized and placed over the layout. End faces in the joints are cut with minimum gap in between the meeting members which are preliminary fixed by slender wires. As per the configuration of joints, gusset plates, preferably of 12 mm ply or 20 mm thick harder timber planks are cut and placed on both the faces of the faces of the joints These are then fastened by 3.55 mm dia nails or better by mature bamboo branch pins of 7-8 mm dia (solid) driven through pre-bored holes. At least two nails/pins should be in one jointing member (Figure 1) so that the joint is tightened to enable the whole act to resist untimely the oncoming loads.

• Bamboo purlins

Bamboo culms either in the full form (round) or in half split (in case of bigger dia bamboo) form are used as purlins . They are duly wired with specially driven bamboo pins near the nodal points in the top chord of the trusses to support the roof grid and roofing materials.

• Bamboo walling 
  
  

Bamboo reinforced mud walls (25 cm thick) can be made by using split bamboo duly dipped in hot bitumen. Vertical pieces (half split) are inserted by about 25 cm into the ground at about 30 cm apart. Similar pieces are horizontally run with same spacing's and are wired to keep them in position. Then properly molded mud mixed with rice husk, cinder and little amount of lime and water is dashed on layer by layer and extended upward by keeping the above vertical bamboo grid in the centre. When dried, extra earth is trimmed off from the surfaces of wall, 2 cm mud lime cinder mortar is applied and finally a finishing with lime putty is given to have a pleasing look. In eastern India there is an extensive use of light bamboo walls even in timber houses. They can be easily made and fixed in position with necessarily fixture at comparatively lower cost. Board walls are made by flattened bamboo culms with nodal diaphragm removed or by half split bamboo arranged vertically or at 45° angle and duly battened and nailed to cover the whole wall. Coarse mats made of split bamboo skins (thickness divided into inner and outer skins) woven in a variety of designs are also used to cover wall gaps. These are generally strengthened by 6 x 2 cm wooden battens put on both sides in a pair duly nailed preferably at top, bottom and middle .

1. Bamboo reinforced concrete 

The use of bamboo as reinforcement in Portland cement concrete has been studied extensively . Bamboo has been used as a construction material in certain areas for centuries, but its application as reinforcement in concrete had received little attention until the Clemson study. A study of the feasibility of using bamboo as the reinforcing material in precast concrete elements was conducted at the U. S. Army Engineer Waterways Experiment Station in 1964.Ultimate strength design procedures, modified to take into account the characteristics of the bamboo reinforcement were used to estimate the ultimate load carrying capacity of the precast concrete elements with bamboo reinforcing. Bamboo was given recent consideration for use as reinforcement in soil-cement pavement slabs in which the slabs behave in elastically even under light loads. For this case ultimate load analysis was shown to be more economical and suitable for use. The results of these investigations form the basis of the conclusions and recommendations presented in this report. Further studies will be required before complete confidence can be placed theoretical designs based on the material presented here. 

Selection and preparation of bamboo

Selection

The following factors should be considered in the selection of bamboo culms (whole plants) for use as reinforcement in concrete structures: 

1. Use only bamboo showing a pronounced brown color. This will insure that the plant is at least three years old. 
2. Select the longest large diameter culms available. 
3. Do not use whole culms of green, unseasoned bamboo. 
4. Avoid bamboo cut in spring or early summer. These culms are generally weaker due to increased fiber moisture content. 

Preparation

Sizing : Splints (split culms) are generally more desirable than whole culms as reinforcement. Larger culms should be split into splints approximately 3/4 inch wide. Whole culms less than 3/4 inch in diameter can be used without splitting. 

Splitting: Splitting the bamboo can he done by separating the base with a sharp knife and then pulling a dulled blade through the culm. The dull blade will force the stem to split open; this is more desirable than cutting the bamboo since splitting will result in continuous fibers and a nearly straight section. Table II shows the approximate net area provided by whole culms and by 3/4-inch-wide splints, as well as the cross-sectional properties of standard deformed steel bars and wire mesh. 

Seasoning: When possible, the bamboo should be cut and allowed to dry and season for three to four weeks before using. The culms must be supported at regular spacing's to reduce warping. 

Bending: Bamboo can be permanently bent if heat, either dry or wet, is applied while applying pressure. This procedure can be used for forming splints into C-shaped stirrups and for putting hooks on reinforcement for additional anchorage. 

Waterproof Coatings: When seasoned bamboo, either split or whole, is used as reinforcement, it should receive a waterproof coating to reduce swelling when in contact with concrete. Without some type of coating, bamboo will swell before the concrete has developed sufficient strength to prevent cracking and the member may be damaged, especially if more than 4 percent bamboo is used. The type of coating will depend on the materials available. A brush coat or dip coat of asphalt emulsion is preferable. Native latex, coal tar, paint, dilute varnish, and water-glass (sodium silicate) are other suitable coatings. In any case, only a thin coating should be applied; a thick coating will lubricate the surface and weaken the bond with the concrete. 

Construction principles

In general, techniques used in conventional reinforced concrete construction need not he changed when bamboo is to be used for reinforcement. 

Concrete Mix Proportions

The same mix designs can be used as would normally be used with steel reinforced concrete. Concrete slump should be as low as workability will allow. Excess water causes swelling of the bamboo. High early-strength cement is preferred to minimize cracks caused by swelling of bamboo when seasoned bamboo cannot be waterproofed

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