Bamboo as a modern construction material in South East Asia

BAMBOO AS A MODERN CONSTRUCTION MATERIAL IN SOUTEAST ASIA Evelien Florijn – A0145263J Assignment 2, semester 1 2015 – 2016 Advanced Architectural Technology – AR5321 National University of Singapore, Department of Architecture

This essay will explore the potential of bamboo as a modern construction material within Southeast Asia. First, the physical qualities of bamboo will be explored. Thereafter, the limitations of the construction material will be discussed and certain design solutions will be proposed. The third and final part discusses the future possibilities and limitations that have yet to be overcome.

developing countries for simple constructions for housing but also as a material for farms, school buildings and bridges, scaffolding, water piping, shuttering and reinforcement for concrete (Sharma, 250).

FIGURE 1. NATIVE BAMBOO DISTRIBUTION (EL BASSAM, N. 1996)

FIGURE 2. ANATOMY OF A BAMBOO CULM (BAMBOO BOTANICALS 2015)

Bamboo is a type of grass, and commonly known because of its rapid growth that can reach up to 25 cm a day (Escamilla 2014, 118). Naturally, bamboo can be found in countries around the equator (see Figure 1). Its main qualities are that it is light, strong and versatile, environmentally friendly, accessible to the poor, a self-renewing resource, fast growing and highly productive (Sharma 2014, 253). Currently bamboo is mostly used in

Most bamboo species are hollow. Within this hollow inner area there are some horizontal partitions called diaphragms, which are denoted by ring around the culm on the outside. Together, the diaphragm and ring form a node, with the space in between called an internode (see Figure 2) (Janssen 2000, 10). The different species of bamboo can be categorized into two main categories: running bamboo and clumping bamboo

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(see Figure 3) (Janssen 2000, 36). Running bamboo grows in a linear manner, and has a more invasive character as it aims to create a forest, whereas clumping bamboo stays together to form a clump (Clune 2010).

FIGURE 3. RUNNING AND CLUMPING BAMBOO (CLUNE 2010)

The bamboo groves themselves have a positive effect on the local ecosystems, as they provide a haven for animals such as birds, iguanas, snakes, pandas, orangutans and elephants (Janssen 2000, 13). Furthermore, the extensive network of rhizomes and roots, especially those of running bamboo, binds the top one foot of soil, which is critical for land productivity and effectively resists erosion by forces of nature such as wind and water (Janssen 2000, 13).

FIGURE 4. BAMBOO PREVALENCE IN SOUTHEAST ASIA (ETHZ 2013)

Bamboo is widely prevalent in Southeast Asia (see Figure 4). Commercially important species of bamboo usually mature in four or five years’ time, after which multiple harvests are possible every second year, for up to 120 years in some species and indefinitely in others (Sharma 2014, 250).

Bamboo only flowers once every 15-100 years, so it is propagated through cuttings. In Asia, these cutting, or culm lengths are about 2-3 internodes

long, with the branches trimmed off. They are then put vertically in the soil and after 2-3 weeks roots start growing at lower nodes, whilst branches sprout from upper (Janssen 2000, 15).

After bamboo is harvested, it has to be dried before it can be used. Within construction the service life of untreated bamboo is about 1-3 years in the open and in contact with soil; 4-6 years under cover and free from contact with the soil; and 10-15 years under very good storage/use conditions (Esteve-Sendra 2012, 120; Janssen 2000, 52, 77). Therefore it is advisable to treat bamboo with a preservative.

However, preservatives can only enter through conducting vessels, as the outer layer has a high silica content and the inside is covered with a waxy layer. These vessels close forever after 24h after harvest, hence preservation has to happen before this (Janssen 2000, 56).

Bamboo does not have a very long lifespan compared to other construction materials.

However, this is no problem for applications within cities where buildings tend to have a quick turnover time, such as Singapore. Looking from this perspective, it is actually very wasteful to build with concrete when the expected lifetime is not to pass 10 years. As some bamboo elements last shorter, it is important to consider maintenance during the design process as less durable components should be replaceable without having to dismantle the structure (Janssen 2000, 151).

A unique quality of bamboo is its flexibility.

Whereas in steel and wood bending leads to failure, this is not the case for bamboo. “Creep” which is increasingly deformation on the long term, is negligible in bamboo whereas it does create a profound problem in most timbers (Janssen 2000, 22). Still, to prevent failure, heavier bamboo with a greater density is preferred. When bamboo fails, it cracks, but it does not break. This means that after an earthquake, some bamboo elements might show damage, but the house will still be standing and safe to live in. Even if the houses were located near the epicentre (Janssen 2000, 24).

Apart from being more flexible than wood, bamboo is also stronger when it comes to shear,

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FIGURE 5. EFFICIENCY DURING THE CONVERSION OF BAMBOO (LEFT) AND WOOD (RIGHT) RESOURCES TO SEMI FINISHED MATERIALS FOR 3 SCENARIOS, A-QUALITY, B-QUALITY AND C-QUALITY*; ALL PERCENTAGES (VOGTLĂ„NDER 2010, 1268)

and calculations show that the structural efficiency is excellent (Janssen 2000, 24; 65). And when comparing efficiency, it turns out that bamboo is more efficient compared to wood harvesting, and results in a greater variety of A-quality products (see Figure 5) (Vogtländer 2010, 1268).

In case of hurricane or earthquake, the material will have to withstand great stresses. Steel will break down, but most structures of timber or bamboo will remain in good condition (EsteveSendra 2012, 779; Janssen 2000, 21). Damages from such events tend to concentrate in the joints.

One of the limitations is that the mechanical properties of bamboo vary depending on the size, thickness, internode distance and the quantity of cellulose fibres (Janssen 2000, 75-77). Therefore, rules of thumb and values yielded from experiments, such as compression tests, may not always have physical validity. Also, the designer has to pay attention to many details. Only air-dry bamboo is to be used, the design should allow bamboo to dry quickly in case it becomes wet, permeability of walls, floors and roofs, as these

cause internal pressures which can affect stability (Janssen 2000, 81). For common construction materials such as timber and steel, the properties of all types of fasteners (nails, screws, bolts, etc.) are known, and can thus be used for calculating the strains on any joint (Janssen 2000, 83).

Unfortunately, this is not the case for bamboo. The fundamental idea is to create structural continuity between elements, which includes force transmission in a set way and deflections that can be predicted and then kept between acceptable limits (Janssen 2000, 83). These predictions are based on calculations.

Janssen (2000, 90-92) proposes a classification system for bamboo joints using three guidelines: 1.

2.

A joint between two whole bamboo culms can be made either by contact between the full cross-sections, or by collecting forces from the cross-section to a joining element.

Collecting the forces may occur from the inside, from the cross-section or from the outside.

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3.

The joining element can run parallel with the fibres or perpendicular to them.

This then led to the formation of 8 categories that can be seen in Table 1. Per group, there are multiple types of connections that Janssens describes, mentioning the different forces that a certain joint is able to take.

Group 1

Group 2

Group 3 Group 4 Group 5

Group 6

Group 7

Joints involving full cross-section.

Perhaps the most prevalent and traditional jointing in practice; lashings used to keep the bamboos in position will fall into this category.

Joints from inside to an element parallel.

Some designers have made joints by filling the culm with mortar and putting a steel bar in it. A recent development is a wood fitting, glued into the culm. Both solutions transfer the joints to the area of steel or wood joints.

Joints from inside to perpendicular.*

an

element

Joints from cross-section to element parallel. Elements of steel or wood, however, are held in place mostly with pins from Group 5.

Joints from cross-section to element perpendicular. Jointing with pins, bolts, etc. comes in this category.

Joints from outside to element parallel.

This is a modern variation of the traditional lashings, such as the “Delft wire lacing tool” that wraps a steel wire tightly around the bamboos. This type offers a simple and strong joint.

Joints from outside perpendicular.*

to

longitudinal direction has cellulose fibres, which are strong and stiff, whereas the transversal direction has lignin, which is soft and brittle.

Another constraint comes from the shape, as the form of bamboo is hollow and varies in size, thickness and form. Internodes and open ends can be easily crushed, therefore joints are best placed at or near nodes, which occur at varying distances (Janssen 2000, 114). Hence, it is difficult to find the right pieces of bamboo for certain elements as they have to have nodes at the desired joints.

However, engineers have found solutions to this problem. One of these is a joint design by Christoph Tönges shown in Figure 6 (Vogtländer 2010, 1265).

element

Joints for split bamboo. This too is a modern development. Thin pieces of galvanized steel are fastened with nails.

Used in prefabricated housing.** * Groups 3 and 7 (in parentheses) have some theoretical significance, but hardly any practical application. ** Group 8 does not fit into the system, but has been included since this group of joints is very important.

Group 8

TABLE 1. BAMBOO JOINT CLASSIFICATION (JANSSEN 2000, 91)

A major constraint for bamboo joints comes from the fact that bamboo is an anisotropic material, meaning that properties in the longitudinal direction are completely different from those in transversal direction (Janssen 2000, 114). The

FIGURE 6. COMBAM JOINT DESIGN BY CHRISTOPH TÖNGES (WWW.CONBAM.DE 2004-2015)

As of yet, there is no worldwide standard for bamboo, however, to ensure construction safety it would be good to create one.

Another limitation for bamboo is that like wood, it deteriorates and decays fast when in contact with damp ground. Therefore it is unsuitable as a foundation material. A solution to this problem is to add an extension at the lower end using concrete, which penetrates the bamboo for about 400 mm (the length of an internode) and extends outside the column for over 600 mm. The concrete is poured into the bamboo culm kept in upsidedown position. A piece of PVC tube, cut lengthways and wrapped around the bamboo is being used as formwork (Janssen 2000, 28; Sharma 2014, 251).

Issues with moisture often occur in low-income housing as they do not have the funds for more advanced engineering techniques (Janssen 2000, 53). Hence, when used in building construction, one cardinal rule is to ensure that the bamboo is kept dry. This means that it should be kept free from splashing rainwater by a watertight

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foundation and by an overhanging roof. Correct design of all building details is a must as no chemical treatment will be good enough to solve the problems caused by incorrect design (Janssen 2000, 55).

A similar problem occurs when bamboo is used as reinforcement for concrete. In general, it is essential for the reinforcing material to be stronger and stiffer than the concrete, meaning that the deformation should be less and thus the reinforcing material should have a higher Emodulus (Janssen 2000, 128). Interestingly, bamboo has enough tensile strength, but the Emodulus is inadequate. Hence, theoretically, bamboo fibres are useless as reinforcement.

However, research and experiments indicate that bamboo is a very good reinforcement. Especially because of the positive tensile strength and the low price. That being said, there are some practical disadvantages that have to be overcome. A major problem is the bonding between concrete and bamboo. When steel reinforcement is used, concrete shrinks around it during the hardening process creating a firm bond between the steel and concrete, however, bamboo absorbs the moisture from the concrete, and will shrink up to four times more when the concrete dries and shrinks (Janssen 2000, 131). In general, constructions that use bamboo reinforcement are less safe than required. In order to create a safe construction that includes bamboo as concrete reinforcement, it is essential to prevent the shrinkage of bamboo and create better conditions for bonding. One option is to put the bamboo in melting bitumen or apply the hot bitumen with a brush, as a moisture barrier, and coat the bitumen with coarse sand while the bitumen still is fluid, to ensure bonding (Janssen 2000, 132).

Bamboo can also be used as flooring, however, as the bamboo has to be kept try, these houses are often built on stilts (Sharma 2014, 251). This has the advantage of keeping the bamboo dry at all times, but also ensures better ventilation and creates an extra space below the floor that can be used for storage or keeping (small) livestock (Janssen 2000, 157). The material can be used in different ways to create a structural floor. It can be

made from flattened bamboo, woven mambo mats, or split bamboo.

However, water is not bamboo’s only enemy. Fire safety is a key issue, as bamboo can easily catch fire. Options to prevent this include fire retardant treatment, which is very expensive, or covering woven bamboo walls with plaster (Janssen 2000, 149).

Only few countries have ‘official’ standards regarding quality, durability and safety of bamboo constructions. In most cases there are construction methods based on local traditions. Experience can be considered as informal, non-codified “standards” (Janssen 2000, 87). Usually they develop such standards by trial and error, resulting in surprisingly sound construction principles that are tailored to the material.

But the limitations of bamboo extend beyond the physical. One of the critical issues is that it has a reputation of being a “poor” man’s material (Janssen 2000, 143). This stigma prevents the material from flourishing whereas it has a lot of potential. The stigma could be overcome by creating aesthetically pleasing designs that not only compromise of housing. As consumers see the possibilities of bamboo construction, they will become more familiar with it and generate a more positive attitude. Another way is to enhance customer value through innovative designs, using technology to diverge the attention away from the material (Vogtländer 2010, 1261).

A great example is the German-Chinese House pavilion design for the Shanghai Expo in 2010 by Markus Heinsdorff (see Figure 7) (Heinsdorff 2015).

The architect describes the building as: [a] 2-storey bamboo and Membrane Building with a 330 square meters walkable exhibition area for the world exhibition in Shanghai. The innovative art building as the German pavilion at the EXPO exists with 8 m height, 25 m width and 10 m depth to a great extent of bamboo canes and bamboo laminates. The building is constructed with new developed connecting and procedure technologies for bamboo. Principals are the German Federal Foreign Office and the Goethe Institute. It represents the events series „Germany and China –

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Moving Ahead Together", which was realised from 2007 to 2010 in five "mega cities" of China and also devoted itself to the topic „sustained urbanization" (Heinsdorff 2015)

qualities of membranes such as ETFE or PTFE make them perfect to be used in irregular façade patterns. Also, it avoids the problem of creating frameworks for glass windows or panels.

However, what still is a major constraint is the building height. Southeast Asia is experiencing rapid population growth, which will result in denser cities that will need higher buildings. Hybrid structures could be a solution, in which for example only the top two or three storeys are constructed using bamboo. Also, lightweight elements such as balconies and canopies could be made from bamboo.

Furthermore, for large scale production, bamboo needs to be standardized. Standard measurements and joint structures will place bamboo in closer reach of architects, as it requires less in depth material knowledge as opposed to working with the “raw” material.

FIGURE 7. GERMAN-CHINESE HOUSE, SHANGHAI EXPO A. FRONT ELEVATION B. SIDE ELEVATION C. INTERIOR (HEINSDORFF 2015)

What is interesting about his design, is that it uses a membrane as a façade material. The flexible

Bamboo has great potential as a construction material in Southeast Asia. Not only for vernacular housing but especially for modern design implementation. It is fast growing and can be harvested many times. The bamboo groves create diverse ecosystems, and the root system prevents soil erosion. Even though there are some challenges such as the short lifespan, irregular form (length of internodes), and vulnerability to moisture and fire, these can be overcome by (small) adaptations. There is little cause for problems if great attention to details is paid during the design process, especially when designing the joints. Innovative and aesthetically pleasing design can overcome the existing stigma, creating a positive association with bamboo as a construction material. Membranes and bamboo have great potential to be used together as the membranes provide enough flexibility for irregular designs. The only limitation to overcome is building height to accommodate the expanding cities of Southeast Asia, but for now it can be used in lower designs or as lightweight additions to hybrid structures.

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BIBLIOGRAPHY Bamboo Botanicals. Anatomy of a Bamboo Culm. Port Coquitlam, 2015.

Clune, Bob. Rhizomes. Davis, 2010.

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Esteve-Sendra, Chele, and et. al. . “Bamboo, From Traditional Crafts to Contemporary Design and Architecture.”

Procedia, Social and Behavioral Sciences, 2012: 777 - 781.

ETHZ. Southeast Asia Bamboo Habitat. Zurich, 22 March 2013.

Heinsdorff, Markus. Expo Shanghai. 2015. http://heinsdorff.de/en/work/installations/expo-shanghai (accessed November 21, 2015).

Janssen, Jules J.A. Designing and Building with Bamboo. Technical report, Technical University of Eindhoven, Eindhoven: International Network for Bamboo and Rattan, 2000.

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(Sharma, Dhanwantri en Mehta 2014) (Vogtländer, van der Lugt en Brezet 2010) (Esteve-Sendra en et. al. 2012) (Escamilla en Habert 2014)

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