RESEARCH
QUESTION
How can a composite of natural and man-made material increase the durability of
bamboo construction in the modern industrialize construction?
The scientific Vernacular explores the turning points when
inputs of scientific knowledge boost the creative urges of architects for new
forms of architectural expression which were traditionally concentrated in
Vernacular Architecture; taking the leap from a stylist approach to knowledge
based and innovative approach with the use of technological science.
Bamboo has its disadvantages such as decaying, susceptible
to insect and fungal attack. The service life of bamboo is generally considered
as being too short for any worthwhile investment. A problem that compounds the
low natural durability is the hollowness of the bamboo culm, particularly when
compared with the end-to-end massive cross section of wood. If fungi or insects
attack and destroy the outer layer of the bamboo, it may mean the loss of one
quarter of its thickness compared to the total thickness of wood. The
hollowness also offers a relatively safe hiding place for the pests of
destruction. In most tropical countries, the high relative humidity of the air
adds to durability problems. High moisture content in the bamboo also creates
problem in drying process. Besides, bamboo does not contain cross fibers and is
consequently, not designed to bear weight width-wise, with the exception of the
points at the nodes. Bamboo is prone to splitting, especially when standard
construction fasteners, such as bolts, screws and nails are inserted. Special
fastening techniques are required when joining pieces of bamboo.
The diagram below shows the life cycle of an untreated
bamboo:
Since Bamboo itself brings threats towards the mission and
vision of our future development, a combination of kaccha and pukka styles can
be used to increase its characteristic thus improve durability and feasibility
of the various periods stated above. How? What is kaccha and pukka?
Kaccha is a building made of natural materials such as mud,
grass, bamboo, thatch or sticks and is therefore a short-lived structure;
Whereas pukka is a structure made from materials resistant to wear as forms of
stone or brick, clay tiles, metal or other durable materials, such structures
are expensive to construct as the materials are costly and more labour is
required.
To simplify the research question, the research will be researching on the type
of natural and artificial material used to increase the durability of bamboo.
Community in villages know by experience the durability of
the bamboos in their homeseeds. The lower part of the culm is said to be more
durable; and so is the outer part of the culm wall. The starch in the bamboo
attracts fungi and insects, therefore the selection of harvest time during the
dry season will have a better durability. Also, bamboo with flowers is more
resistant to these agents due to its depletion of starch.
The correlation between natural durability is difficult to
establish; most of the facts are based on culture and tradition from the
villages through experience than on physical reality (Kirkpatrick and Simmonds
1958).
There are various durability can be found in bamboo in
terms of its life span and service as a structural member.
Starch makes bamboo
vulnerable to be attacked by fungi and insects. Therefore, reducing start
content of bamboo is the best way to make it less vulnerable. You can reduce
starch content by:
- keeping the culm in a vertical position under a shade for a week after
harvesting
- harvesting only the mature bamboos
- harvesting in winter season
- by soaking the bamboo for 3 to 6 weeks in running water or permanent water
sources
The
durability of bamboo is directly related to how well it is treated at all
stages of its use, including how it is grown, harvested, dried, stored,
transported and installed.
Bamboo fails most
commonly through rot from excessive water contact, and attack from pests
seeking out the sugars in the starch of the bamboo, hence most pest infestation
occurs at the joints and through cracks and holes. Therefore, prevent direct
moisture contact and reducing cracking through careful handling will greatly
increase life expectancy as will surface treatments such as paint and oils.
Harvesting
When harvesting, cut the bamboo neatly and evenly immediately above a
node that is one or two nodes above the ground, to reduce the potential for
fungus to infest and degrade the plant. Using the basic principles stated above
to increase the durability of bamboo.
Leaching
In many cultures freshly cut bamboo is soaked in rivers or streams to
leach out sugars and saps to reduce pest infestation. Leaching is more
effective on smaller sections of bamboo; therefore it should be done after
cutting to length or split while vascular cells are still open. Knocking a hold
through the centre of each node along the length of bamboo will allows saps to
wash away more rapidly.
Bamboo will achieve it is the greatest strength if it is being dried
slowly, uniformly; prior to use and to prevent cracking. The curing process is
being done in a cool, shaded, ventilated and organic material free area. The
culms should be stored horizontally; rotating regularly to avoid splitting from
uneven drying. In the process of drying, the bamboo will loses its leaves and
start turning brown; going through the process of losing starch content and moisture.
On the other hand, storing in a silo as another alternative for its drying
place where shades and ventilation are present. Also, split, woven bamboo is
another strategy for drying to take place quickly.
Kiln
Drying
Using
the present level of drying technology, it is not feasible to dry bamboo poles
due to its incidence of cracking and collapse. However split bamboos are
preferred instead.
Air
Drying
Air drying takes up 6-12 weeks depending on the moisture content and the wall thickness.
Mature culms are preferable; thus it
will not pose any problems of splitting under the sun.
Smoking
(Baking over Open Fire)
The bamboo is stored above the fireplace for few days after applying oil on the
surface; until the colour turns into slightly black. This causes rapid drying
of outer shell and decomposition of starch. However, excessive heat might
develop fissure or crack in fresh bamboo when you apply heat to the freshly cut
bamboo; therefore using a gentle fire and rotating the surfaces constantly is
recommended.
Transport
and Storage
Bamboo culms should be loaded and unloaded by hands; not thrown from the
truck. They should be stored carefully so that air can circulate around each
culm and being protected from ground water and rain; keeping it away from
direct contact with soil due to its route for pests and moisture retention in
it.
Surface treatments such
as application of sumps oil, paint, varnish or other chemicals being applied in
a diluted form to allow deep penetration although surface treatment are not as
effective as penetrative treatments thus require regular top up treatments..
Focus should be given to joints, ends, cracks and nodes as the area has the
most pest infestation. Starch coatings within the culm have to be removed by
boiling or abrading with wet sand if a burning process is required. The
Japanese have refined an artificial method of obtaining a similar colouring
using sulphuric acid mixed with mud.
Treatment of Fresh
Bamboo
Freshly cut culms being
placed upright in containers of concentrated solutions of water-borne
preservatives (5-10%). The treatment takes between 7 and 14 days, losing the
preservative solution in the container and made up to maintain the initial
level of solution.
Sap Displacement
Bamboo culms are
prepared to size and submerged in Borax/Boric Acid solution which is a water
soluble preservative for several days. Preservative rises by wick action as the
sap is sucked up. The preservative enters the culm through ends and holes
drilled in internodes. The soaking process is long enough for the chemical to
soak through the entire structure of the culm.
Modified
Boucherie Process
The Boucherie method was pioneered by Dr Walter Liese of Hamburg University. Borax
is water soluble; it will leach out with continued exposure to rain, losing its
effectiveness. In this method, the preservative is passed under pressure
through the culm till it comes out at the other end of the culm. This can be
applied only to fresh bamboo within 24 hours after the harvest.
Dip
Diffusion Process
Fresh culm with high moisture content (above 50%) are kept submerged in
solution for a diffusion period of 10 to 20 days. This method can be applied
only to split and swan bamboo strips since the moisture causes difficulties for
the penetration to occur. Steaming and quenching, followed by diffusion under
drying conditions is another variation of diffusion process.
Treatment
of Dry Bamboo
Soaking
Air
dried bamboos have only to be submerged in the preservative solution (oil or solvent
type) for a period. The penetration is predominantly by capillarity. If
water-borne preservatives are used, the process is called ‘steeping’. But the
soaking treatment with organic solvent (such as pentachlorophenol, copper,
abietates) works better than steeping in water-soluble preservatives.
Hot
and Cold Method
The bamboo to be treated is submerged in a tank of preservative that is
directly heated by fire after being maintained at a constant temperature for a
period, the tank is allowed to cool. During the cooling process, the
preservative is drawn into the bamboo. The hot and cold method can be used for
green or dry bamboo culms with either Boron or Creosote.
Pressure Treatment
Round and half split
bamboos of thick walled species can be treated with creosote (fuel oil) under
hydraulic pressure. The problem of under pressure can be resolved by drilling
holes or notches between, but this leads to spillage. Therefore, a
vacuum/pressure schedule helps to ensure more inform penetration.
Protection by Design
The design of bamboo is to ensure its good nodal placement and protecting the
bamboo from weather and pests.
Large roof overhangs
prevent direct wetting of bamboo walls in heavy rains; thus using drainage
channels or gutters to discharge water from the building at a certain safe distance.
Bamboo flooring can be protected through building on a slightly sloping site
and using raised masonry or concrete footings. This can be applied on bamboo
columns and wall panels to reduce the risk of termite infestation through the
direct contact towards the ground surface.
Bamboo has got a round profile
therefore creating connections will be leading to difficult geometric
structures at the knot. Various connections can be used; for example, friction
tight rope connections, nuts and bolts connection, positive connections,
interlocking connections. Besides that, bamboo is hollow in the middle of the
cane; therefore it can be reinforced by pouring concrete inside.
Traditional Methods
Joint Bracing
While bamboo has been used for centuries, the traditional methods
of lashing bamboo together are not appropriate for the design of long span
trusses. These lashed connections also do not fully utilize its strength; it
solely rely on friction, transferring load between members is limited thus
require more members to do the same job. Therefore joints in bamboo always have
been difficult because it is hollow, has nodes and resists only a little shear
stress. Many traditional joints suffer from weakness or deformation. Many
joints cannot take advantage of the strength of the culm itself and a special
problem is to design a joint for tensile forces.
Modern Methods
Bolting Joints
Modern connections have been proposed by Huybers, Shoei Yoh and Renzo
Piano. These connections solve the issues of complex geometries by joining the
members in various ways. These connections require puncture of the bamboo walls
sine all fibres in a bamboo culm run parallel once a bolt is placed through it
and the connection loaded in tension, the bolt acts like a wedge and splits the
bamboo. Also the puncture allows moisture to enter the culm and accelerate
decay.
Nodal Placement
With an understanding of the bolt alone concentrate much on the
wall of the bamboo, the void between the solid internal nodes is filled with
solidifying mortar where every bolt penetrates each of the bamboo culm. Members
of a truss come together at angles and tension forces are anticipated, a steel
strap is placed to bridge the pieces. It is important to design with redundant
system that is capable of both compression and tension. This frame truss system is certainly preventing bamboo from bending
and buckling in the middle of the culm. Larger
holes were drilled into the bamboo to insert the mortar into the joint
segments. The mortar was mixed with the optimal quantity of water; the bamboo
pieces where then duck taped together to maintain their positions as they were
filled with mortar and left to cure for a week. Once mortar is cured, the tape
can be removed.
Bamboo +
Mortar + Rebar
Though holes were drilled into bamboo segment to insert re-bars. This re-bars will absorb most of the stress moments and allow the bamboo structure to sustain high stress impacts as occur during earthquakes. Bamboo tends to shrink with time making the string joinery slack and insecure. Therefore the joinery system relies on bolts and mortar-fillings maintaining their shape over time. Bamboo filled with mortar are reinforced by an additional the rebar is embedded in mortar, the load is transferred evenly
across the member's cross section and can transfer high axial loads to the bamboo.
Bamboo + Mortar + Rebar + Clamp
The bamboo is cut at the end axially crosswise to generate a cone by tightening a steel clamp. The cone is filled up with mortar so that the cone is able to transfer its force to the outer high tensile fibres. A common steel clamp is also placed at the end of the member to provide confinement of the bamboo and prevent splitting of the bamboo. Because the rebar is embedded in mortar, the load is transferred evenly across the member's cross section and can transfer high axial loads to the bamboo. Finally, the incorporation of the steel gusset plate makes the bamboo easy to connect in any configuration desired.
New Joints
In order to allow bamboo for spatial and light structures, it is important to have a durable joint which does not bring much weight to the structure and which works under high forces to take advantage of the high resistance of bamboo fibers. The alternative joints for bamboo and by some techniques which are already used in steel constructions. The joint is light, strong and appropriate for easy assemble and disassemble.
Based on the various methods to increase the durability of
the bamboo from its own solid wall towards its connectivity on the building
structure, bamboo can almost become a universal element. This research has
provided a proof of concept for the durability of bamboo itself can be developed
by using the natural methods and artificial methods; thus increasing it
durability on structure by roughening the inner surface of the bamboo member,
filling a portion with mortar, embedding re-bar and welding several of these
members to gusset plate. Having both of these characteristics can then be used
to construct and span moderate distances, thus providing a safe and predictable
behavior. This research will help facilitate the future use of bamboo in a cost
effective solution to many parts of the world.
