The image of bamboo usually reflects the characteristic of Asian and tropical countries context. As in Indonesia, it is easy to find bamboo plant with various kind of species in almost every region of the country. Scientist indicate that 1,250 bamboo species found in all around the world and 11 percent of them are local endemic to Indonesia. Bamboo plant is environmentally friendly, easy to cultivate, can be harvested after 3-5 years, evades erosion, improves soil water content, and it is renewable. This plant has the highest growth rate in the world, which can even grow up to 100 centimeters in 24 hours. On average, its growth is between 10 and 30 centimeters per day. For the construction purposes, bamboo is preferable because it is stronger and more flexible than wood, steel or concrete.
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For generations, bamboo is widely known by the people in Indonesia as a local material used for various purposes in their daily life. Bamboo plants in Indonesia are found in both lowlands and highlands with an altitude of about 300 m above sea level and are generally grown in open areas and free of puddles (Purwito, 2008). However, bamboo is often regarded as a lower class material used by lower income people in their building. This image effects the middle to high income people to avoid bamboo to be use as material in their building design. They are more likely to choose architectural design trends that are leading to high-end technologies with modern materials, such as iron, steel, concrete, glass or brick.
Qualitative descriptive methods were used in this study to reveal an understanding the application of bamboo materials in recent building design. The discussion focuses on the use of bamboo in building design in create and innovative way to support sustainable green architecture. ‘Heart of Green School’ (HGS) building in Green School complex, Bali, Indonesia was selected as a case study to explain the use of bamboo as the main material in building design and construction, HGS is main building in the complex. Case study is needed to review the potential of bamboo as building material which is became new trend and approaches in architectural design.
POTENTIAL OF BAMBOO
Bamboo has good properties to use as construction material, i.e., strong, flexible, straight, flat, hard, easy to split, easy to be formed and lightweight material. Besides, bamboo is relatively cheap compared to other building materials because its availability and easy to found in all regions in Indonesia (Purwito, 2008). Bamboo belongs to the grass species and its tensile strength is better than steel. Bamboo can grow 10-30% faster than other trees that only reach 2-5% per year. Bamboo can grow with production of 50-100 tons per hectare (depending on species, soil and climate). Bamboo plants consist of 60-70% stems, 10-15% branches and 15-20% leaves. Bamboo plants is good to speed up groundwater recycle process, even better 240% than pine forest. Bamboo is also good for soil consolidation, since its roots have strong properties to retain soil erosion. Bamboo plants absorb CO2 as much as 62 tons per hectare per year, which is 4 (four) times larger than other forest plant species that can only absorb 15 tons per hectare per year. Bamboo can release O2 35% larger than other forest plants during photosynthesis process (J.A. Janssen in Hindarto, 2012).
Most of traditional building in Indonesia and Asia use bamboo as raw materials, mutually as structural and non-structural materials. The use of bamboo in traditional buildings is due that bamboo grows plentifully in tropical rain forest. After industrial era has begun the use of bamboo as building material become outdated. Bamboo is reflected as cheap and non-permanent materials. It is also reflected as low-class material, even called as “the poor man timber” by many modern builder (Lobokivov, 2009).
People prefer to choose brick, concrete and steel as structural and construction materials to construct the building. Recently, after global warming and sustainability issues are appeared, bamboo as building materials is widely discussed and reviewed. Good-quality woods for construction are infrequently found because of deforestation issues. Wood also requires long time to re-grow and ready to use as construction materials. Meanwhile, bamboo can be harvested in a short time, which is between 3-5 years. When bamboo grows, it also releases oxygen into the air, the ability that cannot be executed by industrial materials like steel, plastic and concrete. For the reasons, bamboo has been widely known as sustainable building materials.
CASE STUDY: GREEN SCHOOL, BALI
Green School is located in Banjar Saren, Sibang Kaja Village, Abiansemal, Badung. about 30 kilometers from downtown Denpasar, Bali. Green School was opened in May 2009, current capacity are 700 students clustered to kindergarten, elementary and junior high school level. The school was conceived by John Hardy, a silver businessman from Canada who is also founder of the Kulkul Foundation, who has lived in Bali for over 30 years. John Hardy explains that the basic idea of school construction on an area of 20 hectares is to apply philosophy of Trihita Karana, a traditional philosophy for life on the island of Bali which is referred to in the three principle i.e., harmony among people, harmony with nature or environment, harmony with God. Therefore, no manufactured materials or chemicals are used in this school. School complex is built using an organic permaculture system and is designed to adapt in perfect cohesion with soil ecology. All buildings inside school complex is made with passion to develop a civilization that respects to nature by using organic materials and renewable energy sources, such as micro hydro power, solar power, and bio-diesel. Each building was not designed by a famous architect, but was completed by a team of eclectic designers and bamboo artists in Bali.
The school complex consists of several masses which each mass accommodates different function such as classroom, laboratory, multifunction hall, office, student and teacher’s dormitory, etc. Green School building design has been through various stage of exploration in building form, structure system and construction process. The main building (HGS), which is located in the center, is two to three storage building. The building has three circular shapes that resemble nautilus shell. The three nautilus shape roof is lined together formed wide envelope for the space below. While other smaller masses have varied roof shape and form. The building in this school won Aga Khan award for the recycle category in 2010.
‘Heart of Green School’ (HGS) is two to three-story building which is stand on double elliptical plan pattern, whereas three spiral shape staircases are directed into three core system of building to lock and stabilize the building structure. The cores are the highest level and connected pragmatically all together to form a single structure building within the spiral organization. Three types of local bamboo are used in the HGS construction system, namely Dendrocalamus asper (bamboo petung), Gigantochloa apus (bamboo rope), and Bambusa blumeana (bamboo thorn). Roof of each building is covered with bundles of cogon grass (Imperata cylindrica), while combination of bamboo, clay, mud and cotton are used as walls material alternately.
HGS is designed in organic shape building, use arch, spline and other curvature shape, therefore it needs curve bamboo to achieve the form. There are two methods of bamboo bending (Dulkenberg, ), i.e., hot bending method and cold bending method. Hot bending method can be done by immersing bamboo in the lukewarm water until bamboo fibers are become soft enough to be curves using clamp; or by heating bamboo section to the desire heat (>150oC) that cause bamboo fibers become soft and easy to bend. To bend bamboo in cold bending method can be done by splitting bamboo into planks then tie it into become a bundle; or by slashing bamboo rods the curved it. Bamboo bending method can generate smooth or segmented bamboo curved as well as can increase or decrease the strength of bamboo (Maurina, 2015). Bamboo split technique is used in HGS structure, especially to support arches in the smaller masses that are functioned as classrooms. However, bamboo split method can decrease the strength property of bamboo and can cause structural deformation and deflection (Maurina, 2015). To avoid deformation and deflection of structural system, the appropriate dimension proportion to the span is needed.
Building masses, HGS are using form active structure to achieve organic shape for the buildings form. The main hall using wide span arches, that are stabilized by roof rafters, to generate the curved shape roof form. Long roof eaves create good protection from sun and rain. HGS functioned as office, which has nautilus shell shape is resolved using surface structure. The surface structure of HGS uses battens, rafters and purlins supported by bamboo pillars. The system resembles to the tent-like structure system. The round purlins play a role in giving the nautilus shell shape to the roof.
In term of structure properties, columns and cores uses Dendrocalamus asper (bamboo petung) to be able to bear the compressive force. Besides its high value strength to bear compressive force, Dendrocalamus asper (bamboo petung) also stiff and will avoid deflection risk. Small beam to support floor plate and roof frame and rafter uses Gigantochloa apus (bamboo rope) which has almost the same value on flexural strength, tensile strength and compressive strength. Whereas to bind vertical core structure are used split bamboo which are arranged and laminated all together.