Bamboo as a Structural Material

2010 Bamboo as a Structural Material Client Report

G a vi v i n L e a k e - 2 0 0 6 4 18 18 2 1 K yl y l e To T o o l e - 2 0 0 5 14 14 2 0 2 P a v e l Di D i vi v i s - 2 0 0 6 15 15 4 2 2 S u p e r v i so s o r : Ca Ca r m e n T o r r e s Sa Sa n c h e z

5/ 12/2010

Bamboo as a St St r uct ur al Mat Mat eri al

Abstract This project summarises the work performed for EWB-UK on bamboo as a structural component for low cost housing in Pabal, India. In initial discussions with the partner NGO in Pabal, Vigyan Ashram, and with initial research into the academic literature and past EWB studies of bamboo, it was clear the project should have an implementation focus and so was directed towards structural systems and the associated connections. It was identified early that building with bamboo in developing nations has a significant cultural aspect; the type of house reflects the occupant wealth with traditional concrete and steel box-shaped buildings represents affluence while domes and bamboo have connotations of poverty. The structure developed has a hexagonal plan that has several structural advantages for bamboo and can be later connected in modules and in combination with the sheet m etal and strapping connections provides a cheap housing solution for India. While the hexagonal style is not quite a concrete box it is aesthetically closer to this configuration than a geodesic dome and also masks the structural bamboo. The connections, tools and instructions for the house are to be produced as a kit so once the customer has the kit can purchase their bamboo, cladding and roofing cheaply and locally. The kit also allows minimal cost by offering a low-skill do-it-yourself solution that can be built within one day by two unskilled workers with pictorial instructions to follow.

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Content Abstract ..................................... .................. ...................................... ..................................... ..................................... ...................................... ............................................ ......................... 1 Acknowledgements .................................... .................. ..................................... ...................................... ..................................... ............................................ .......................... 6 1.

Introduction ..................................... .................. ..................................... ..................................... ...................................... ............................................... ............................ 7

2.

Research ...................................... ................... ...................................... ...................................... ....................................... ................................................... ............................... 8

3.

Patents ................................... ................ ...................................... ..................................... ..................................... ...................................... ..................................... .................. 18

4.

Architecture ................................... ................ ..................................... ..................................... ...................................... ..................................... .............................. ............19

5.

Design Specification .................................... .................. ..................................... ...................................... ..................................... .................................. ................ 21

6.

Concept Generation ..................................... .................. ..................................... ..................................... ...................................... ................................. .............. 22

7.

Concept Development ..................................... .................. ...................................... ..................................... ..................................... .............................. ........... 24

8.

DfMA of the Base Plate ................................... ................. ..................................... ...................................... ..................................... ............................. ........... 26

9.

Finite Element Analysis ..................................... ................... ..................................... ...................................... ..................................... .......................... ........ 33

10.

Mechanical Testing ...................................... ................... ...................................... ...................................... ...................................... ............................. .......... 42

11.

Failure Mode Effect Analysis ................................... ................ ..................................... .................................... .................................... .................. 47

12.

Bamboo Prototyping................... Prototyping...................................... ..................................... ..................................... ...................................... ............................ ......... 48

13.

Build Instructions ..................................... .................. ..................................... ..................................... ...................................... ................................. .............. 49

14.

Modular Bamboo House Construction ................................... ................ ..................................... ..................................... ..................... .. 57

15.

Costing and Manufacturing ................................... ................ ...................................... ..................................... ..................................... ................... 58

16.

Implementation .................................... ................. ...................................... ..................................... ..................................... ...................................... ................... 61

17.

Future Work................... ..................................... .................. ...................................... ..................................... .......................................... ........................ 61

18.

Conclusion .................................... .................. ..................................... ...................................... ..................................... ..................................... .......................... ....... 62

References .................................................................................................................................. 64 Appendix ...................................... ................... ..................................... ..................................... ...................................... ..................................... ...................................... .................... 65

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List of figures Figure 1: The terminology and makeup of bamboo [2] .............................................................. 9 Figure 2: Typical Bamboo Construction in Pabal ....................................................................... 9 Figure 3: Typical Simple House in Pabal .................................................................................. 10 Figure 4: Geodesic Dome at Vigyan Ashram ............................................................................ 10 Figure 5: Percentage of fibre density through the bamboo wall ............................. .................. 12 Figure 6: Volume fraction f raction of the cellulose fibre fibr e vs. tensile strength streng th of bamboo material ....... 13 Figure 7: Compressive strength vs. Moisture content (the bamboo beams are subjected to the compression stress mainly at the house base where moisture is likely to be present due to weather conditions) .................................... ................. ..................................... ..................................... ...................................... ........................................... ........................ 13 Figure 8: Bending strength vs. Moisture content (all other structure components will be predominantly subjected to the bending stress) ....................................................................... 14 Figure 9: Relationship between Specific modulus and Specific strength to determine costperformance properties of bamboo material (upper right corner – better value) ................... 14 Figure 10: Simón Vélez ZERI Pavilion Prototype ...................................................................... 19 Figure 11: Guadua Tech Construction ....................................................................................... 20 Figure 12: Pugh Design Specification......................................................................................... 21 Figure 13: Examples of Early Concept Structures .................................................................... 22 Figure 14: The Selected Developed Concept Structure ............................................................ 24 Figure 15: Position of the strap slots to reduce tooling cost ................................. ............... .................................... .................... .. 27 Figure 16: Cut corner to minimize waste .................................................................................. 27 Figure 17: Design for the stamping to minimize waste. ........................................................... 28 Figure 18: Recommended modification of the blank shape to reduce waste [3] .................... 28 Figure 19: Diameter of the hole was determined from the minimum blanking hole related to the metal sheet thickness. The diameter of the hole is normalized for the M10 bolt. ............ 28 Figure 20: Base wing is redundant when wh en used at top of walls w alls or on roof. ............................... ................. .............. 29 Figure 21: Orientation of the shoulder at the bottom of the construction has changed from horizontal to vertical position so that the same blank can be used for bottom base as well as top roof plates. ........................................................................................................................... 29 Figure 22: Only three different angles are utilized in order to simplify the bending operation. .................................................................................................................................................... 30 Figure 23: The slots placed at the edge of the base plate significantly reduce the assembling time as the strip can be wound around the two pieces instead of running in the slots. ......... 30 Figure 24: Distance of the holes was determined from maximum diameter of the bamboo (100mm) and easy access of the spanner. ................................................................................. 31 Figure 25: Recommended clearance for different types of wrench. The most common wrench in Pabal is open-end one therefore minimum clearance of 75mm was chosen. ...................... 31 Figure 26: Position of several slots had changed to simplify final assembly. Real model made of PMMA plastic was used to realize potential issues during assembly. ................................. 32 Figure 27: Graphical representation of the structure load. ...................................................... 33 Figure 28: Impact of the wind on the bamboo structure [15]. ................................................. 34 Figure 29: Diameter of the bamboo used in the simulation .................................................... 38 Figure 30: Limit thickness of 12mm left and 1mm right. ......................................................... 39 Figure 31: Results of the optimization study, wall thickness 3.2mm, maximum stress 62MPa. .................................................................................................................................................... 39 Figure 32: Two critical points of the base plate with the ultimate load. .................................. ................. ................. 40 Figure 33: Location of the most loaded joint in the structure. ................................................ 40

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Figure 34: Location of the heaviest loaded joint of the structure. ................................ ............ 41 Figure 35: Graphical view of test 1. ........................................................................................... 42 Figure 36: Yield location of test 1. ............................................................................................. 43 Figure 37: Results of the first and second bending test. .......................................................... 43 Figure 38: Graphical view of test 2. .......................................................................................... 44 Figure 39: Yield location of test 1. ............................................................................................. 44 Figure 40: Detail of the shoulder buckling after exceeding the critical load of 11kN, the detail III of Figure 37. .......................................................................................................................... 44 Figure 42: Base plate after test 3. .............................................................................................. 45 Figure 41: Graphical view of test 3. ........................................................................................... 45 Figure 43: Results of the third bending test ............................................................................. 46 Figure 44: Plastic deformation of the base plate shoulder after the third destructive test. ... 46 Figure 45: Yield location of test 3. ............................................................................................. 46 Figure 46: Sheet Manufacturing ............................................................................................... 60

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Acknowledgements Our supervisor Carmen Torres-Sanchez has been amazing throughout the project with support throughout. The technicians Duncan Lindsay and Drew Irvine for all the time and effort in producing the prototypes that made this project a success. The Vigyan Ashram NGO of Pabal in India have provided massive support. Our contact, Mr. Rohan Choukkar, has supplied insight, answers to our recurrent questions, with feedback and encouraged our progress throughout the project. engIndia and their experienced member Ms. Mariel John have also provided great insight and knowledge from experience of Pabal and past bamboo projects. EWB-UK Research director, Ms. Katie Cresswell-Maynard, has provided support and encouragement throughout the project, while Ms. Lara Lewington, our mentor, has been of a great help because of her broad experience on bamboo projects at Vigyan Ashram.

St at ement of Aca cademi demic c Hones Honestt y We declare that this submission is entirely our own ori ginal work. We declare that, except where fully referenced direct quotations have be en included, no aspect of this submission has been copied from any other source. We declare that all other works cited in this submission have been appropriately referenced. We understand that any act of Academic Dishonesty such as plagiarism or collusion may result in the non-award of our degrees.

Signed ………………………………………………………………………………………………………………………

Dated ……………………………………………………

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1. Introduction For many years, bamboo has been used as a feasible and sustainable solution as a building component of structures in developing countries in Africa, South America and the Far East. Its widespread availability and rapid growth in areas of China, Japan and India has made this grass an interesting structural material due to its affordability, easy assembly and relatively long durability. In the Far East, bamboo is broadly used in scaffolding structures [1] and, for those who have little, housing and storage solutions have also seen bamboo as a structural component. Concrete and steel structures for buildings are typically difficult to prepare and assemble, requiring skilled workers and significant access to resources (equipment, suppliers) for any truly successful result, bamboo offers an easier alternative to that process. However, in developing nations the implementation of bamboo structures seem to be generally quite poor, with planning, specification and design being abandoned in favour of ‘quick and dirty’ building techniques. This project looks to address these issues with superior guidelines and frameworks for building of bamboo structures. In developing nations there is a significant cultural aspect of the local environment that is tied to perceptions of wealth. Only the richest of those in India can afford large typically Western boxshaped brick or concrete construction houses with proper insulation and utilities. With bamboo as such a cheap material and often best used in quite different configurations from concrete, the perception is that only poor people would adopt this type of structure and so the poorest people struggling for funds would rather get into more debt and appear wealthy than to purchase something novel or unique that makes them appear poor.

Project Overview Or iginal Br Br ief While the project originally focused on research of bamboo species with the following objectives and deliverables, initial reading suggested much research has already been performed into bamboo and connections. Discussions with Vigyan Ashram highlighted the abundance of past academic and EWB work on different aspects of bamboo structures yet little work had been taken from these and put into practice as acceptable implementations. The following objectives were initially provided to the team: 1. Identify the ideal species of bamboo for use as a building and design material. 2. Recommendations on which bamboo to cultivate and how to do it the Far East, especially India. 3. An investigation into the lifespan of the bamboo and any methods of expanding it if necessary would be of interest. These would have then resulted in the following deliverables that would be yet more academic study and of less use to Vigyan Ashram than an implementation study: 1. Research on a method for assessing the strength of the bamboo. 2. Tabular mechanical properties of the three most recommended types of bamboo suitable for the area.

Revised Brief It was agreed that the project should focus much more on the structural design and implementation aspects in order to complement previous theoretical work (e.g. mechanical properties testing, finite

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element analysis of the bamboo behaviour). The following three key objectives are now much broader and more suitable for an engineering project/study: 1. Research properties and types of bamboo available in Pabal. 2. Review, invent and develop joining j oining methods (i.e. connections) for bamboo structures. 3. Design structural system for wide-scale implementation in Pabal. If time permits, it is expected to include in the project outcomes the results of physical analysis and simulation of the design structure prototypes to verify the solution. The output of these objectives should be the following deliverables: 1. Develop bamboo joining types. 2. Prototype bamboo structure and propose methods for implementation in Pabal/Pune after assessing feasibility on the prototypes. 3. Recommendations on the type of structures that can be built using the proposed methodology.

To achieve these, the project included two milestones of client presentations with the December milestone focusing on research and review, specifically: • • •

Literature review of former work and identify potential implementation of those studies. Summary of bamboo properties and types available in Pabal/Pune. Assessment of current joining strategies used in P abal/Pune.

Then the February milestone required more original and conceptual work for structures and connections to be produced with the following specific: •

Development of bamboo joining types and progress towards prototype structure for mass production of bamboo structures.

These changes allowed a plan following the Pugh design process to be developed in October 2009 and revised in January 2010.

2. Research Stakeholders Engineers Without Borders UK are the primary client with an overall mission to facilitate human development through engineering. The main areas of focus for this organisation are Habitat, Energy, Water & Sanitation, Transport, ICT, and Industry with numerous briefs in each area, Bamboo as a Permanent Structural Component is an established theme. This brief partners EWB-UK with EngIndia and so includes Vigyan Ashram in Pabal, India as a valuable on the ground contact. Less direct contact with EngIndia has been experienced however it is this organisation that enabled the links with Vigyan Ashram and the research performed and data available from their studies has been invaluable. Vigyan Ashram is a centre of Indian Institute Institut e of Education and non government organisation (NGO) based in Pabal near Pune in Maharashtra, India. Founded by Dr. S. S. Kalbag in 1983, the centre believes in learning by doing with a program for training youth that are unsuitable for academia with practical skills and knowledge.

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About Bamboo While estimates vary, there are over 70 genera divided into about 1,450 species [21]. In India I ndia there are likely 130 species, 16 of which are suitable for construction [4]. Bamboo has been used as a building component for many centuries with bamboo used for scaffold as long as 5000 years [1].

F i gu gu r e 1: 1: Th Th e t e r m i n o l o gy gy a n d m a k e u p o f b a m b o o [ 2 ]

Bamboo has some very exciting and beneficial properties including but not limited to: • • • •

Grows 15-18cm/day Full height after 4-6 months Harvested within 3-5 years of growth (compared to 20-40 years for timber) Production energy required for bamboo (per square meter) is only 0.1% of that required for steel.

Discovering the species of bamboo available in Pabal has been relatively difficult and no method of easily identifying a species has been possible. Bamboo is known to grow widely in the area of Pabal and is construction grade and hosts similar properties to Mao Jue and Kao Jue. The commonly accepted species available in Pabal is Dendrocalamus Strictus, known as Calcutta bamboo [5][engIndia], and it is suggested that 53% of bamboo grown in India is of this type.

F ig i g u r e 2 : Ty T y p ic i c a l Ba B a m b o o C o n s t r u c t io io n i n P a b a l

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Market Pabal is located approximately 70km North East of Pune and has a population of approximately 15,000[engIndia] with 5,000 in the village of Pabal and the remaining in small houses scattered around, many in hamlets of 5-10 or larger clusters of 500-1000. Most occupancies are 4-7 member families with 2-3 children and often a grandparent, usually in dwellings of 2-4 rooms (social space, kitchen, storage for food, clothes and belongings) but some larger families often have several dwellings. The end users are to be those poorest families in India in need of a more stable, robust and safe family home. As a kit the end users will also be the assemblers. It has been identified that a simple concrete reinforced structure with corrugated roof is INR 21,000 (~GB£310). It is also noted that the poorest may earn INR 2,000/month (~GB£30) while a homeopathic doctor may achieve INR 30,000/month (~GB£445).

F i gu gu r e 3 : T yp y p i c a l S im im p l e H o u s e i n P a b a l

This project may be best implemented in small poor rural communities around Vigyan Ashram in Maharaksha and would fit well amongst other kit based housi ng projects of geodesic domes and mud-brick adobe builds.

F ig i g u r e 4 : G e o d e s i c D o m e a t V ig i g ya ya n A s h r a m

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Literature In an effort to determine the key principles for working with bamboo, academic literature, international standards and patents were searched. The previous reports from EWB students researching bamboo as a structural component were the first and most valuable resource, these focus of these works are as follows: •

•

•

•

Bamboo Housing in Pabal by Jaspreet Grewal: Bamboo species, material properties, architectural state of art. Bamboo Connections by Chris Davies: Bamboo connection taxonomy and testing of connections. Investigation of Bamboo Reinforced Concrete for Potential Use in Developing Countries by Alex Davies: Bamboo reinforced concrete study and experimentation . Bamboo as a Permanent Structural Component by Chia Bing Liang: Design of structure and computational analysis of structure and beam, engineering experimentation of connection and beam.

A very typical structural use of bamboo is for high-rise scaffolding i n East Asia, most widely used in Hong Kong this practice has been banned in China for structures over 6 stories 1. In China there are several standards for bamboo use as flooring or ply-wood sheet style substitutes however no real documentation on usage in structural settings. Colombia is another nation that makes widespread use of bamboo, however the standards are limited to harvesting and preservation despite rife use as a structural component. So while the national standards do exist in certain contexts, these seem weak and low on engineering focus, the only real progress towards international standardisation is the work of the International Network for Bamboo and Rattan (INBAR) on ISO22156: Bamboo – structural design and ISO22157-1: Bamboo – determination of physical and mechanical properties – part 1: requirements.

Mecha echani nica call Pr opert i es Extensive research and testing of bamboo properties has been done in past [1-5]. The most relevant properties that will impact the design specification and concept selection such as Young’s modulus and tensile strength are listed in thi s capture. As for any natural material also the bamboo mechanical properties wary from piece to piece and the scientific test are used as guidance for an analysis of the designed structure. It has been found that majority of the studies regarding bamboo properties and structural design have been conducted in China namely at Hong Kong Polytechnic University. Such studies focus on properties of Chinese bamboo species such as Mao Jue and Kao Jue which are not available in the Pabal village. Following discussion with Vigyan Ashram, it has been found that the properties of locally grown bamboo Dendrocalamus Strictus are almost identical to the Mao Jue and Kao Jue species. Therefore properties in this section are generally regarded as for all bamboo species.

Landler, Mark (27 March 2002). "Hong Kong Journal; For Raising Skyscrapers, Bamboo Does Nicely". New York Times. http://www.nytimes.com/2002/03/27/world/hong-kong-journal-forraising-skyscrapers-bamboo-does-nicely.html. 1

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Young’ s Modul us Young’s modulus is defined as the ratio of the uni-axial stress ov er the uni-axial strain in the range of stress in which Hooke's Law holds [1]. Determination of correct Young’ s modulus is particularly important for calculation of beam buckling, structure displacement under stress and bending properties of the bamboo beams. Unlike in steel materials the Young’s modulus of bamboo material significantly varies within the wall cross-section (the radial distance from the bamboo centre). Bamboo behaves like composite material therefore a standard strength and Young’s modulus equations for composites can be applied to determine local mechanical properties. Tensile strength and Young’s modulus are calculated from the volume fraction of the fibre and matrix, equation below [2 ].

E = E f V f

+

E m (1 − V f )

It has been determined that Young’s modulus of the bamboo matrix is 3GPa and fibre 46GPa. However, the significant variation of the fibre content throughout the wall from the centre outwards makes almost impossible to determine correct Young’s modulus of the bamboo beam. Figure 1 shows distribution of cellulose fibre through the bamboo wall crosssection [3].

F i gu gu r e 5 : P e r c e n t a g e o f f i b r e d e n s i ty ty t h r o u g h t h e b a m b o o w a l l

Tensile and compression strength Tensile/compression strength, along with Young’s modulus is an important parameter of engineering materials used in structures and mechanical devices. Similarly to the Young’s modulus tensile strength bamboo material depends on many variables. The local strength

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and Young’s modulus can be calculated from the same Equation 1. Relation of the fibre content (Vf) in a bamboo wall and its tensile strength is displayed in Figure 2 [2].

F i gu gu r e 6 : V o lu lu m e f r a c t io i o n o f t h e c e l lu lu l o s e f ib ib r e v s . t e n s i le le s t r e n g t h o f b a m b o o m a t e r i a l

The bamboo strength properties depend also on moisture content of the material. As mentioned in the previous chapter, this project deals with dried and treated bamboo that should provide the best mechanical properties. However, if such bamboo is inserted into a wet concrete, it would immediately gain the surr ounding moisture and its properties would degrade significantly. Figure 3 and Figure 4 [4] explain relationship between moisture content in bamboo material and its compression and tensile strength. It is apparent that compression strength is much more effected than bending strength which is important for design of a structure base where the bamboo columns are subjected to the compression stress and high moisture.

F ig i g u r e 7 : C o m p r e s s iv i v e st s t r e n g t h vs vs . M Mo o i s t u r e c o n t e n t ( t h e b a m b o o b e a m s a r e s u b j e ct ct e d t o t h e c o m p r e s s i o n s t r e s s m a i n l y a t t h e h o u s e b a s e w h e r e m o i s t u r e i s li li k e ly ly t o b e p r e s e n t d u e t o w e a t h e r c o n d i t io io n s )

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F i gu gu r e 8 : B e n d i n g s t r e n g t h v s. s . M o is is t u r e c o n t e n t ( a l l o t h e r s t r u c t u r e c o m p o n e n t s w i ll ll b e p r e d o m i n a n t l y s u b j e c t e d to to t h e b e n d i n g s t r e s s )

Comparing mechanical properties of bamboo fibre with other engineering materials it can be found that bamboo fibre has equivalent tensile strength of 650MPa with tensile strength of steel (500-1000MPa) and much higher flexibility determined by lower Young’s modulus value of ~50GPa compared to steel’s ~200GPa [3]. Ahby [5] compared Bamboo mechanical properties with other engineering materials and concluded that bamboo fibre material has specific strength comparable with engineering alloys, ceramics, and bone. In terms of weight-cost relation bamboo fibre provides even better value than steel [5].

Bamboo

F i gu gu r e 9 : R e l a t io io n s h i p b e t w e e n S p e c if if ic ic m o d u l u s a n d S p e c if if ic ic s t r e n g t h t o d e t e r m i n e c o s t p e r f o r m a n c e p r o p e r t i e s of o f b a m b o o m a t e r i a l ( u p p e r r i gh gh t c o r n e r – b e t t er er v a l u e )

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Connections Bamboo has proven to be a very effective structural material however, connecting culms of bamboo together has long been a problematic issue. The Th e reasons for the difficulty in connecting bamboo culms are listed below. •

•

•

Bamboo has a circular profile which is a geometric shape that is inherently difficult to connect with other members. Bamboo is hollow which means there is no support in the middle of the culm, so it cannot be subjected to high compressive forces perpendicular to the culms surface. As Bamboo is a natural material the culms vary in diameter, wall thickness, length and quality.

Bamboo has been used as a building material for thousands of years and so numerous connection systems have been developed. All of these connection systems have their advantages and disadvantages depending on: the design of the structure, cost, time-frame, the skill of the builder, the availability of materials and the capabilities of local manufacturing facilities. Many of the connection systems compromise the natural mechanical properties of the bamboo by either requiring an opening (hole or slot) to be created in th e wall of the bamboo culm or putting the culm under high compressive forces that are perpendicular to the culms axis, which can cause the culm to collapse in on itself. It must be noted that if an opening in the culm is required, a circular whole is the best option as it resists the highest amount of stresses and the worst option is a square, rectangular or triangular slot as this causes high stress concentrations in the corners of the opening. When constructing a connection or designing new connection system a number of rules must be followed to ensure for a good connection, these rules are listed below; 1. 2. 3. 4. 5. 6.

Avoid openings in culms (e.g. drilling dri lling & cutting) Construct joints near nodes (Stronger & protects against water penetration and insects) Treat the bamboo culms (To prevent against rotting) Securely fit joints (e.g. Edge preparation & correct level of tightening) Make durable connections (e.g. Materials, Design, Quality) Reinforce culms under high point loads (e.g. Wood Core Inserts & concrete reinforcement)

The criteria from the revised project brief allows the evaluation of numerous connection systems. From relevant literature it is possible to determine which systems are the most appropriate to the project. The criteria that is required from the connection systems are detailed below: • • • • • • •

Strong Durable Simple to construct (for an unskilled workers) Fast to construct Low cost Manufactured from readily available materials Can be Manufactured Locally

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Mortice & Tenon Joint

Double Horn

Pegged Joint

Appr ppropri opri ate Connect onnection ion Sys ystt ems C o n n e c t io io n M e t h o d S im i m p l e La La s h i n g s

(Lashing: simple elastic lashing)

Gusse t Plate & Bolting

(Steel, timber, plywood plates)

S le le e v e J o i n t

(Wood, plastic & metal connectors

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Ad v a n t a g e s

Disadvanta ges

F e a s i b i li li t y

-Fast -Inexpensive -Lightweight -No drilling required -Can connect bamboo in any direction -Flexible connection, allows for a degree of movement

-Security of connection dependant on skill of worker -Connection becomes lose over a small period of time due to movement of structure

-Materials are readily available -No tools required -The simpler the lashing method the more people can use this system.

-Very strong & rigid -Can connect bamboo in many directions on the same plane. -Triangulated plates helps to relieve stress around joint

-Relatively heavy -Materials can be -Requires drilling easily sourced for bolt holes in -Can be bamboo manufactured on -In some mass for arrangements a slot ‘connection kits’ it required in the -Easy to assemble bamboo when in kit form -Time consuming -Relatively expensive

-Simple assembly -Fast assembly

-Very weak connection -Can only Connect bamboo in one direction -Diameters of connector have to be exact and custom to each bamboo

-Materials are readily available -manufacture is relatively simple by means of turning or a lathe or using ‘hole cutters’

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-Ability to fit into a -Manufacture can range of bamboos be difficult with different -Manufacturing a diameters connection that can -Fast assembly connect bamboos -Easy assembly in multiple directions is (Connector fit inside difficult. bamboo culms) -Over-tightening the connection can split bamboo S t e e l I n s e r t & C o n c r e t e -Very strong -Requires -Easy to assembly connection ‘Hub’ to Fill -Steel rod carries connect multiple stresses and not bamboos with the bamboo together -Aesthetically -Time consuming pleasing to manufacture -Relatively heavy E xp xp a n d a b l e J o i n t

-Materials can be easily sourced -Complex manufacture reduces feasibility

-Materials can be easily sourced -Connection ‘hub’ may be difficult and expensive to manufacture

(Threaded rod at end) Wood Core Insert

(Adds additional strength when loaded in the tangential direction)

-Shear stress distributed evenly across bamboo -Increased ability to accept a higher bending moment -Can be treated as a timber component, so drilling etc is acceptable

- Diameters of inserts have to be exact and custom to each bamboo -Not all bamboo has a perfectly circular cross section

-All materials are readily available -Manufacture is very quick and simple

All the connection types have their advantages and disadvantages. The connection systems listed will be used as a knowledge base to aid the concept generation and development process for both new bamboo connection systems and bamboo structural design. It must be noted that a new bamboo connection system may be adapted from one of the existing system listed and it may also be an amalgamation of different parts of these connection systems. Once the connection system for the new bamboo structure is finalised the corresponding connection systems will be analysed in much greater detail.

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3. Patents World-wide patents related to the bamboo constructions and joints for bamboo structures were reviewed with no conflict identified. identi fied. Only the two most relevant patents are described following:

Sect ion ional al Bamboo Bamboo Bui Buill di ding ng St r uct ur e - US 27037 2703724 24 y y y

The connection uses plastic or wooden plug with a thread in the middle Both such modified ends are joined by two side bolt For angular joints a special segments are used

Method for Preparing a Terminal Assembly for Bamboo - US 6957479 y y y y

Author cuts off grooves from the upper side of the bamboo Such end is squeezed together and thin metal washer is pulled over Bolt is then inserted into the cavity which is subsequently filled by epoxy Bamboo rods are joint by threaded segments

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4. Architecture With both the cultural implications and the architectural aspect of this project, research i nto modern architectural use of bamboo was performed. It was found that while bamboo has been used for centuries, few architects and engineers engi neers are still utilising bamboo as a structural component.

Si món Vél élez ez One of the best known architects of bamboo structures, the Colombian architect Simón Vélez, has developed a unique approach to building with bamboo. He builds only with his trained crew and keeps paperwork minimal with simple drawings and freehand sketches on graph paper, CAD is only used to produce documentation for purchasers. The designs are manifested in “generously overhanging roofs, ingenious load bearing structures, sophisticated joints, and an innovative combination of materials”. While he is known for bamboo structures such as the ZERI pavilion for Hanover and his nomadic museum in Mexico City, Velez insists that he is not a bamboo architect but rather a roof architect and just designs structures that suit bamboo although he is also known to also work in concrete or mangrove wood.

F i gu g u r e 10 10 : S im i m ó n V é le le z Z E R I P a v il il io io n P r o t o t y p e

Velez has produced several seminal bamboo structures, ranging f rom his massive and groundbreaking ZERI pavilion to his work on low cost housing. The 2000m 2 ZERI pavilion and nomadic museum are the two largest structures ever built from bamboo with the pavilion being prototyped and tested full-scale to appease the German authorities. Meanwhile the low cost house was 60m 2 over two levels and designed to be built by the poorest of Colombia on a self-help basis for the low cost of $5000.

Gauda Tech The bamboo species of Latin America is Guadua Angustifolia (Kunth), with very favourable properties for construction it is used by the rich and the poor and has contributed to the success of bamboo as a building material in Colombia. Team L

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F i gu g u r e 11 11: G u a d u a T e c h C o n s t r u c t i o n

Guada Tech is a modern system of terminals and joints that can be used with treated Guadua poles to create temporary and permanent structures. One of the best examples of this usage 2 is the low cost housing structure shown in FOLIO that incorporates Guadua bamboo and connections with Esterillia panels (Guadua poles broken into sheets manufactured with high heat and pressure like ply wood) while the roofing is a combination of recycled plastic tin foil and paper pressed with heat. The model assembles in 4-6 hours and comes in a box weighing less than a ton.

2

http://koolbamboo.blogspot.com/2008/05/bamboo-emergency-low-income-housing.html

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5. Des esii gn Speci peciff i ca catt i on A design specification was developed from primary re search (discussions and meetings with Vigyan Ashram) and secondary sources (literature, reports), this can be seen in appendix A. The following image shows the Pugh design specification categories with the most important sections darkened.

F i g u r e 12 : P u g h D e s i g n S p e c i fi fi c a t i o n

Some of the key metrics of this specification include the target price of INR 8000 and a life in service of 50 years, both proposed by the original brief. Both the low cost and simplicity of construction are the key factors the original brief requires. It was also identified that as NGOs, there should be no patent conflicts or licensing requirements as these will be nearly unsurpassable for the operating parameters of the organisation. The types of bamboo suitable need to be clearly discussed and issues identified, while the design should not fail when using most types of bamboo there may be cases where a type of bamboo is completely unsuitable and with around 130 species in India alone, identifyin g every possible situation is not possible. For this project a single story, single room building is the goal. The building should perform admirably with the usual summer highs of 45C and winter lows of 10C and maintain a reasonable temperature differential of at least 10 degrees, the wind and rain (monsoon) conditions possible be considered. Packaging of everything without bamboo should be possible with standard pallets (ISO standard 6780). This building should be possible to build within one day by two unskilled workers and maintenance should be possible without risk. Safety is a key feature f or shelter, habitat and building projects so a factor of safety of 3 will be employed as extra re-assurance.

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6. Concept Gener enera at i on Design of the structure for the bamboo house and the connection system development were carried as two separate activities but were performed concurrently. Designing these separately ensured that a limited number of constraints were enforced during the concept generation phase and the team were free to design the optimum structure and the optimum connection system for bamboo and the consumer.

Init ial St St r uct uctur ure e Conc Concept epts s Concept Generation Due to the nature of the product it was felt that quick sketch models of structures would be quicker to produce and more valuable than sketch drawings. The initial concepts were generated for the bamboo structures aimed to incorporate triangular and geodesic forms as it was noted from research that these types of structures are very stable, structurally strong and self supporting. It must also be noted that that the concepts aimed to put the bamboo culms under sheer bending loads rather than compression (axial) loads as bamboo performs better as beams rather than vertical columns. In total four early concepts were generated and can be seen in the folio on page 6. The concept generation task aimed to be divergent in nature producing many different types of structures. The concept generation phase provided a good foundation for the development of the structures.

F i gu g u r e 13 13 : E xa xa m p l e s o f E a r l y C o n c e p t S t r u c t u r e s

Concept Evaluation To ensure that the development of the structures was on the correct path, the early sketch models were presented to the client for evaluation. This very early evaluation of concepts limited the risk of re-work and back-tracking as well as providing extremely useful feedback on the client requirements which was vital during the development stages. The clients were excited by the diversity of the concepts and the opportunity for development. Two main points came out of the client evaluation that were firstly, the clients noted that upright columns could be used alone within the structures, as the diameter of the bamboo would be large enough to withstand the compression loading of a roof. This increased the flexibility of the forms that could be used during the development of the Team L

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structures. Secondly, it was pointed out that the Indian people prefer traditional concrete and box-shaped housing, which is composed of primarily square and rectangular forms particularly the roof.

Initial Connections System Concepts To enable effective concept generation for the connection systems, guidelines and rules were set out before the concept generation exercise. The designers aimed to follow the guidelines and rules during the concept generation exercise. C o n n e c t io i o n S ys ys t e m G u i d e l in in e s •

• • • • • •

•

Ability to connect bamboo culms of varying diameter Strong Durable Simple to Construct Fast Construct Low Cost Manufactured from Readily Available Materials and standard components Manufactured Locally

C o n n e c t io i o n S ys ys t e m r u l e s

1: Construct joints near nodes (Stronger & protects against water and insects) 2: Avoid openings in culms (e.g. drilling & cutting) 3: Securely fit joints (e.g. Edge preparation) 4: Make durable connections (e.g. Materials, Design, Quality) 5: Reinforce culms under high point loads (e.g. Wood Core Inserts)

Each team member generated three connection concepts each, thus giving a total of nine concept connection systems. The concepts can be seen in the folio on pages 7 and 8, details are given on their design feature, advantages and disadvantages. The concepts that were generated were designed to connect bamboo culms together without any focus on what structure they might be suitable for. The generated concepts would be developed to suit a particular structure during the concept development stage, once the final structure design is known. The connection concepts were evaluated through team discussions which were facilitated by a concept scoring matrix, which can be seen in the folio on page 8, right. The evaluation criteria incorporated aspects of both the concept generation guidelines and connection rules and are listed below: •

•

•

•

•

•

•

•

•

•

•

Severity of the bamboo damage Skill requirements for installation Ability to assemble a complex structure Long term strength sustainability Labour requirements for the bamboo reparation Appearance of finished joint Applicability to variable bamboo diameter Low volume manufacturing cost High volume manufacturing cost Strength in axial direction Strength in the radial direction

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From the matrix it is evident that concept nine was the best concept connection system. It scored well for all the evaluation criteria. Concept nine had a number of distinct advantages including: • • •

•

Ability to connect bamboo culms of varying diameter with the same strength. The connection plate can be cut and formed in many different configurations. A consistently secure connection (high repeatability) can be made by an unskilled worker. The strapping system (jubilee clip/pallet strapping/industrial cable-tie) is formed from standard and readily available materials/components.

7. Concept Development Developed St St r uct ur e Conce Concept pt s The developed structure concepts were constructed using larger wooden sticks and built to a scale of 25:1. Building to this scale made the models more tangible and made it easier to visualise the final structure. Before the development deve lopment of the structures began, three key criterions were set out. Firstly, the structures should have a form of square roof to ensure that it is accepted culturally. Secondly, the structure should be based around an inherently strong shape. Thirdly, the structure should be modular in design, thus allowing multiple structures to be connected together to form larger structures. The idea for the modular design was spawned from the needs of the consumer, with the target market of poor familities there would be little capital funds to spend on a large home or structure however they would have enough money to buy a small structure that could over time be extended by adding more structures/rooms. Joining the structures could be used when more family space is required or to add differen t spaces such as storage or business premises.

F i g u r e 14 14 : T h e S e le le c t e d D e v e l o p e d C o n c e p t S t r u c t u r e

The developed structures can be seen in the folio on page 9. The images are annotated and give details on the design features for each structure; these were evaluated by in-depth team discussions which covered criteria such as: •

The strength of the structure

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• • • • • • • •

The number of connections required The number of bamboo culms required The floor space and enclosed volume of the structure The skill requirement for installation The ease of maintenance and repair The weather protection that the structure provides The amount of cladding required The aesthetic of the structure

The team unanimously agreed that concept C, folio page 9, was the best overall concept structure and would provide the basis for the final structure design. The idea for the hexagon shape of concept 9 was generated from an analogy with bee hives and honey combs. The hexagon shape is an inherently strong shape and is a very modular 'friendly' shape; one hexagon structure could potentially have six other hexagon structures seamlessly connected to it. It was also agreed that the beneficial features from concept b, folio page 9, were highlighted for integration into the final design. Such as the diagonal support struts in the walls, the overhanging roof for increased protection from the rain and the raised floor of the house which eliminates the risk of flooding and increases in creases the lifespan of the bamboo floor beams. At this stage the final structure was loosely defined and therefore the development of the connection system could be initiated.

Developed Connection System Concepts The hexagon structure that was selected required two key connection designs; the connection points at the bottom hexagon and the connection points at the top hexagon which also connects the roof. The team aimed to develop 'concept 9' from the connection system concept generation exercise to provide a connection system for these two connection points on the selected structure. Through a team design exercise two connection plate designs were generated. One for the bottom hexagon connection points and one for the top hexagon roof connection points. T he connection plates were modelled on CAD and laser cut in PMMA plastic to enable the designs to be evaluated though physical modelling. These models can be found in folio page 10. The key output from the physical modelling of the connection revealed that the two connection plates could be amalgamated to produce a simple universal connection plate that could be used throughout the full structure, including the connection points at the roof. The physical modelling also helped define key sizes for the final connection plate design such as the position of the slots and the bolting holes which are used for the connection. These were refined during a design for manufacture and assembly (DfMA) exercise which is detailed in the DfMA section of the report.

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8. DfMA of the Base Plate Design for Manufacture Considering the limited range of the material available in Pabal village and limited manufacturing processes, mild steel (low carbon) was chosen to be most appropriate material for the base plate. The manufacturing process of the base plate would depend on production volume. For a small to medium production of up to 10,000 pieces, the cheapest option would be laser cutting, abrasive water jet cutting or plasma cutting. Above this 10,000 threshold the base plate should be stamped. Tooling cost for the 300x300mm die and punch would be in range from £15,000 to £45,000 [17] depending on the die material, accuracy and complexity. Another significant factor of the tooling cost is the punch footprint area. Boothroyd in 2002 [18] empirically analyzed the relationship between the plate area and the die cost and based on this our parts would cost at least $800. This is a rather theoretical cost and so with inflation of 5% would be $1300, still very low compared to real quotes.

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Des esii gn f or Punchi ng Strap Slots The original position of the straps was to be inside of the metal sheet, in this case an extra punch would be needed to cut out the rectangular hole. Therefore to reduce the tooling cost without compromising functionality the slot feature was mov ed to the sheet edge so that the slot cut-out could be included in the main body of the die.

F i gu g u r e 15 15 : P o s i t io io n o f t h e s t r a p s l o t s t o r e d u c e t o o l i n g c o s t

Mat eri al Ut il is isa at ion During the stamping process material utilisation is important for efficient manufacturing and to minimise excess. Each individual part has to fit on the blank and leave minimum waste after the stamping process. For this reason the corner of the diagon al shoulder was cut off shown in Figure 16 and saved 8% of the raw material (4cm strip) and therefore significantly reduced its cost. S a ve ve d m a t e r i a l

F i gu gu r e 16 16 : Cu Cu t c o r n e r t o m i n i m i z e w a s t e

Amount of the waste material was also reduced by including the diagonal streng thening shoulder only on one side of the blank. Based on the FEA simulation, diagonal strengthening of the structure would be sufficient in every second plane and there is no need for supports in both diagonal directions so one diagonal shoulder was modelled on one side. Therefore, the blank can be compounded on one sheet of the metal very efficiently, see Figure 17.

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Waste material

Used material

F i gu gu r e 17 1 7 : D e s ig ig n f o r t h e s t a m p i n g t o m i n i m i z e w a s t e .

F i gu gu r e 18 18 : R e c o m m e n d e d m o d i fi f i ca c a t i o n o f th th e b l a n k s h a p e t o r e d u c e w a s t e [ 3 ]

Minimum Hole Diameter According to the rules of the design for the punching tool the h ole diameter should not be smaller than two times thickness of the blank [19], therefore the minimum size of the slot should be 6.5mm. If the construction is going to be fixed to the concrete base, normalized bolts are likely to be used, so the standard size of the hole for the M10 bolt is 10.5mm and 11mm. The 10.5mm diameter of the hole was chosen for this design.

ø10.5m

F ig i g u r e 19 1 9 : D ia i a m e t e r o f t h e h o l e w a s d e t e r m i n e d f r o m t h e m i n im i m u m b la l a n k i n g h o l e r e l a te te d t o t h e m e t a l s h e e t t h i ck c k n e s s . T h e d i a m e t e r o f t h e h o l e is i s n o r m a l iz i z e d fo f o r t h e M 10 10 b o l t .

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Par t Simi lari t y Despite the redundant features on the blank that are not used at every joint, they are kept on the blank in order to reduce diversity of the base plate types, and lower the manufacturing cost. The blank shape is identical for all joints of the structure with different combinations and pairs of bends. For example the diagonal strengthening shoulder is not used in the roof or support joints and the wing that fixes the structure to the base has no purpose on the roof as shown in Figure 20. Orientation of the base plate shoulders used for bottom connection changed from horizontal orientation to vertical orientation so that identical shape of the blank can be used for both locations as in Figure 21.

No use in this type of the connection

F i gu gu r e 2 0 : B a s e w in i n g i s r e d u n d a n t w h e n u s e d a t t o p o f w a l ls ls o r o n r o o f .

F i gu gu r e 2 1: 1: Or O r i e n t a t i o n o f t h e s h o u l d e r a t t h e b o t t o m o f th t h e c o n s t r u c t i o n h a s c h a n g e d fr fr o m h o r i zo z o n t a l t o v e r t i ca ca l p o s i ti ti o n s o t h a t t h e s a m e b l a n k c a n b e u s e d fo r b o t t o m b a s e a s w e l l a s t o p roof plates.

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Des esii gn f or Bendi ending ng Bending angles of the base plate were designed for minimal variance; there are only three angles employed 30°, 60° and 45° therefore, the bending press can be set on three hard stops. This could significantly reduce the fabrication time and cost of the joint. Figure 22 below shows all three angle alternatives that repeat across the structure.

4 5°

30 °

60 °

F i gu gu r e 2 2 : O n l y t h r e e d i ff f f e r e n t a n g le le s a r e u t i l iz iz e d i n o r d e r t o s i m p l if if y t h e b e n d i n g o p e r a t i o n .

Design for Assembly Strap Slots The second purpose of the slots being placed at the edge of the base plate, as shown in Figure 23, is simple assembly. The metal strap does not have to be fed through a slot and so can be wound around both base plate and bamboo beam. Much less plastic deformation of the low carbon strips will occur due to the reduced manipulation for this configuration.

F i gu gu r e 2 3 : T h e s l o t s p l a ce c e d a t t h e e d g e o f t h e b a s e p l a t e s i gn gn i f ic ic a n t l y r e d u c e t h e a s s e m b l in in g t i m e a s t h e s t r i p c a n b e w o u n d a r o u n d t h e t w o p i e ce c e s in i n s t e a d o f r u n n i n g in i n t h e s lo lo t s .

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Distance of t he Holes Holes Holes that are used for fixing of the structure to the concrete base were designed so there is easy worker access for bolt tightening even with maximum bamboo diametersat maximum diameter of used bamboo as in Figure 24. To determine the minimum clearance between spanner and shoulder, the chart in Figure 25 was used and based on usage of open-ended wrench so was set at 75mm.

75mm

120mm F ig i g u r e 2 4 : D is is t a n c e o f t h e h o l e s w a s d e t e r m i n e d f r o m m a x im im u m d i a m e t e r o f t h e b a m b o o ( 10 10 0 m m ) a n d e a s y a c ce ce s s o f t h e s p a n n e r .

F i gu gu r e 2 5 : R e c o m m e n d e d c le l e a r a n c e fo f o r d i f fe fe r e n t t yp yp e s o f w r e n c h . Th Th e m o s t co co m m o n w r e n c h i n P a b a l is i s o p e n - e n d o n e t h e r e fo f o r e m i n im i m u m c le le a r a n c e o f 7 5 m m w a s c h o s e n .

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Dis istt anc ance e of t he Slot Slot s Distance of the slots was estimated to enable assembly of the base plate, bamboo and metal straps. Each position of the slot was optimized in CAD assembly model. A concept model of the base plate was cut from PMMA plastic to determine how the assembly works together in reality. Some positions of the slots and also their dimensions were modified based on the full scale model.

F i gu gu r e 2 6 : P o s i t io i o n o f s e ve v e r a l s l o t s h a d c h a n g e d t o s i m p l if i f y f in in a l a s s e m b l y. y. R e a l m o d e l m a d e o f P M M A p la l a s t i c w a s u s e d t o r e a l i ze z e p o t e n t i a l is is s u e s d u r i n g a s s e m b l y. y.

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9. Fi ni nitt e El El ement Ana nall ys ysii s Several iterations of the FEA were run to test various design options of the structure. Firstly the applied load on the structure was calculated. Secondly simulation could be carried out with the real load figures.

Est imat imation ion of t he St St r uct uctur ure e Loa Load Vertical Load •

•

•

Load of the bamboo beams used as support for the roofing material was calculated from the weight of roof covered by corrugated metal and one adult worker standing on top of the construction. The metal thickness generally used for such corrugated roofing is 0.5mm [20] with a planar weight of such material at (7800kg/m 3 density of metal) 7.8kg/m 2. Hexagonal shape of the base with maximum length of the beam at 2m.

• •

Figure 27, area of one roof segment is 1.73 m2 creating force of 13.5kg.

Top view

One worker (90kg) the construction 1/6th area of the roof = 1.73m2 Equal to 13.5kg weight of roofing

Bamboo weight of 10kg

F i gu gu r e 2 7 : G r a p h i ca ca l r e p r e s e n t a t i o n o f t h e s t r u c t u r e l o a d . •

There are 6 such segments creating total load of 81kg – 810N. Assuming that there will be no column in middle of the room, this load of 810N will be carried by 6 bam boo columns placed in each corner. Additional force of 10kg due to bamboo own weight is added to the calculations. Worker has to climb up in order to assemble the roof, his weight is 90gk equal to 900N therefore in worst w orst case scenario is subjected to the maximum force of (810N+100N+900N) = 1910N.

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Hori zont al Load Load Wind force from the side of the structure is calculated for maximum wind speed of 100 kilometres per hour.

F = A x P x Cd [14,15] F= horizontal force A – area of the house from side P – wind pressure for 100km/h = 478N/m 2 Cd – flow coefficient

Flat area of the house = 4m 2, with Cd coefficient 2 – F1= 3824N Angular area of the house = 5.5m 2, wind Cd coefficient 1.2 –F2= 3150N

Total force of the wind of speed 100km/h on side of the house is 6974N ~ 7kN. Illustration of the wind impact on the structure is in Figure 28 .

F i gu gu r e 2 8 : I m p a c t o f t h e w i n d o n t h e b a m b o o s t r u c t u r e [ 15 15 ] .

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FEA Analysis of the Structure F Run 1

A force F=1810N was applied on the roof of the bamboo house to find out the critically stressed locations. This process was particularly efficient for improving static performance of the structure. The figure shows extensive stress in the upper joint area. Based on orientation of the stressed corner, it is suggested to be tension stress. It could be eliminated by adding a ribband. The maximum stress in this structure was 4.1MPa (10% of the bamboo ultimate strength).

Run 2

The ribband (dotted red line) that strengthens the upper corner was added to the structure and the maximum local stress decreased by 20% to 3.2MPa. Aim of this optimization was to load all beams of the construction equally so that the roof load would be more equally distributed. Therefore the ribband was moved to the middle of the roof beam.

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Run 3

Placing the ribband to the middle of the roof resulted in even better reduction of the maximum stress to 2.3MPa equal to 10% of the bamboo ultimate stress which proofs the robustness of the hexagonal structure.

Run 4

Also horizontal force of 7kN was added to the simulation to simulate wind from side of the structure. Location of the maximum stress moved from the upper corner to the bottom of the construction. Its value was 42MPa, considerably higher than effect of the vertically oriented load. Diagonal bamboo beams were added to the structure to support walls of the building in horizontal direction.

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Run 5

Adding the diagonal supports reduced the local stress at the base of the construction to 21MPa. Detailed design of the base connection has to be carefully optimized and tested. The maximum stress at the connection is as 50% of the bamboo ultimate stress, equal to safety factor 2. Mechanical testing of the connections would be appropriate to assure stability of the structure.

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FEA FE A of of t he base base plat pl ate e Bamboo beam modelling •

•

•

Size of the bamboo was determined from the material available locally at Pabal village. Standard sizes between 2” and 6” are generally available, therefore size of 80mm ~ 3.5” has been chosen for the FEA in Pro/Engineer, see Figure 29. Internal structure of the bamboo including distance between the nodes and increased wall thickness at the node location were manually measured and scaled from the bamboo sample shipped from Pabal. The maximum allowed stress in the bamboo was derived from Ming Lu (2002) [11] empirical experiments on dry and wet bamboo where the recommended maximum compression stress for dry bamboo was determined to 58MPa including safety factor k=2.

F i gu gu r e 2 9 : D i a m e t e r o f t h e b a m b o o u s e d i n t h e s i m u l a t io io n

Concept des design ign of t he met al bas base e plat e •

•

•

Dimensions of the base plate were estimated from the initial stage sketches. Width of the slot in the base plate holding the strap was derived from the real size of the low carbon steel strap selected from the supplier. Thickness of the base plate was drafted as a model parameter and was the only variable optimised by the FEA based on maximum allowed stress (complex stress including tension, compression and sheer). The maximum allowed stress in the base plate was determined from standard allowed stress of the mild steel with yield stress of 300MPa, safety factor k=2 and assumption that the material in the slots is subjected to the shear stress in which case the maximum allowed shear stress can be calculated as 60% of the maximum allowed tension stress.

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•

These considerations led to the final value of 75MPa as maximum allowed complex stress in the steel sheet. Figure 30 below displays two thicknesses of 12mm and 1mm that were entered into the optimization calculations as model limits.

F i gu gu r e 3 0 : Li L i m i t t h i c k n e s s o f 12 12 m m l e ft ft a n d 1m 1m m r i g h t .

Set up of of t he simul imula at ion/ opti mizati on Constrains of the model were determined from the real situation where the edges of the slots will likely take all applied load if the joint is properly assembled by metal straps. All factors described in previous chapter were entered into the Mech anica module of the Pro/Engineer software which optimized the base plate thickness without exceeding the maximum allowed stress. The final value of 3.2mm base plate thickness was calculated to be an ideal solution with the maximum stress of 62MPa as can be seen on Figure 31 below.

F i gu gu r e 3 1: 1: R e s u l t s o f t h e o p t i m i z a t io i o n s t u d y , w a ll l l t h i ck c k n e s s 3 . 2 m m , m a x im im u m s t r e s s 6 2 M P a . •

As expected the maximum stress was identified to be at location where m etal straps support the structure, detail in Figure 32 right. Also some bending stress was found in the ‘neck’ location, Figure 32 left.

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F i gu gu r e 3 2 : T w o c r i t ic ic a l p o i n t s o f t h e b a s e p l a t e w i t h t h e u l t im im a t e l o a d .

Whole system has been modeled as parametric therefore any ch anges in the base plate thickness or dimensions would automatically update and remodel the metal strap shape and dimensions. The particular joint in the simulation was chosen based on assumption that this location would be subjected to the greatest load in the whole structure. As displayed in Figure 33 and Figure 34 below.

F i gu gu r e 3 3 : Lo L o c a t io i o n o f t h e m o s t lo l o a d e d j o in in t i n t h e s t r u c t u r e .

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Modelled Connection

F i gu gu r e 3 4 : L o c a t io i o n o f t h e h e a v ie ie s t l o a d e d j o i n t o f t h e s t r u c t u r e .

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10.. Mechanical Testing 10 In order to validate the FEA process and test actual behaviour of the base plate when subjected to load, a full size and real material model was manufactured and mechanically tested in the mechanical engineering laboratory. The original design of the base plate used in FEA changed according to the DfMA. The design and dimensions of the mechanically tested sample are identical to the final product.

The destructive mechanical tests were carried out to determine ultimate forces. Orientation and setup of the applied force was estimated to represent reality as close as possible. The force amplitudes captured by the hydraulic press were modelled in Pro/Engineer Mechanica to determine real internal stress in the material.

Bending Test 1 This bending test was derived from the real situation scenario where the vertical and diagonal beams are fixed to the base plate and on the top beam is load of a roofing worker. Such situation would create identical setup as below, Figure 35.

Force

Clamped

F i gu g u r e 3 5 : G r a p h i c a l vi vi e w o f t e s t 1. 1.

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The first bending test begins at 0N load and 0mm displacement. The base plate behaves according to the Hooks law and the flexible deformation continues until reaching the yield point I, Figure 37. From the point I, the plastic deformation takes place and the base plate starts to collapse as displayed in Figure 36. One can read out the maximum load from the diagram to be 6.5kN before the base plate collapses if fixed at the bottom.

Bending test A Displacement [mm] -12

-10

-8

-6

-4

-2

0 0

-2,000

-4,000

I -6,000

II

] N [ d a o L

-8,000

Bending Test 2 When the stress reached the yield point during test 1, the base plate was clamped in upper location, Figure 38. This was to simulate behaviour of the base plate when subjected to the maximum load when top section of the base plate is fixed. This situation could occur when a roofer is laying down the corrugated metal sheets and standing at the top of the bamboo structure. This clamping setup of the tested sample resulted in change of the curvature of the diagram Figure 36, detail II. Meaning, the basepate is more rigid when clamped on both top and bottom

III -10,000

-12,000 F i gu gu r e 3 7 : R e su s u l t s o f t h e f ir ir s t a n d s e c o n d b e n d i n g t e s t .

locations. The flexible F i gu g u r e 3 6 : Yi Yi e ld l d l o c a t i o n o f t e s t 1. 1.

deformation of the sample continued up to the force of 11kN after which the sample buckled (collapsed), Figure 36, detail III. After that point, even lower force than 11kN would lead to bending of the base plate.

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Force

Clamped

F i gu g u r e 3 8 : G r a p h i c a l v ie ie w o f t e s t 2 .

F i gu g u r e 3 9 : Yi Yi e l d l o c a t i o n o f t e s t 1. 1.

F i gu g u r e 4 0 : D e t a i l o f t h e s h o u l d e r b u c k l in in g a f t e r e x c e e d i n g t h e c r i t ic i c a l lo lo a d o f 11 11k N , t h e d e t a i l I I I o f F i gu gu r e 3 7 .

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Bending Test 3 The third test was carried out in order to simulate the force that would be required to bend the shoulder in planar orientation. This force can be in reality created by wind in horizontal direction that acts as a force perpendicular to the structure wall. Such bending force can be found at the bottom of the structure or at the base of the roof. Clamped

Force

F i gu g u r e 4 1 : G r a p h i c a l vi vi e w o f t e s t 3 .

Significantly lower force was needed to bend the base plate in planar direction, see Figure 43. The ultimate bending force when yield occurred was 650N, 20 times lower than test 1 and 2. The moderate gradient after the yield point I, Figure 43, can be explained as movement of the dislocations in the ferrite crystals. The process is called plastic strengthening for instance used for improving mechanical properties of Ultra Fine Grained materials.

F i gu gu r e 4 2 : B a s e p l a t e a f t e r t e s t 3 .

Cont ontrr ol of t he ult imat imate e st st r es ess s of t es estt 2 & 3

2 =

σ

M b I b

=

L ⋅ F W ⋅ H

2

=

100 mm ⋅ 10 kN 2

3mm ⋅ 60 mm

6 3 =

σ

M b I b

=

L ⋅ F W ⋅ H

6

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2

=

550 MPa

=

670 MPa

6

100 mm ⋅ 600 N 2

60 mm ⋅ 3 mm

=

6

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Bending test B Displacement [mm] -25

-20

-15

-10

-5

0 0 -100 -200 -300 -400

I

] N [ d a o L

-500 -600 -700

F i gu gu r e 4 3 : R e s u l t s o f t h e t h i r d b e n d i n g t e s t

F i gu gu r e 4 4 : P l a s t ic ic d e f o r m a t i o n o f t h e b a s e p l a t e s h o u l d e r a f t e r t h e t h i r d d e s t r u c t i ve ve t e s t .

F i gu g u r e 4 5 : Y ie ie l d l o c a t i o n o f t e s t 3 .

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11.. 11

Fai l ur e Mode Mode Ef Ef f ect Analys nalysii s

Failure Mode and Effect Analysis (FMEA) is a methodology which is used to evaluate a design for potential failures. The identified failures are also prioritised relative to how severe the consequences of the failures are and the likelihood of the failures occurring [11]. The identification and prioritisation of potential failures enables the designers to concentrate on reducing or eliminating the potential failures that have a high magnitude of risk. The FMEA also provides details on what actions can be taken to overcome the identified problem areas. An FMEA was carried out for the final design of the bamboo house. T he full analysis of the design can be seen in the folio on page 13 of the folio. For each part ratings are given for severity, occurrence and detection of the potential failure modes. These ratings are then multiplied together to produce a Risk Priority Number (RPN). RPN = S x O x D The RPN figure enables the designer to easily distinguish problem areas with a high magnitude of risk. Problems areas with a high RPN should be addressed or the part should be redesigned to decrease the RPN. The FMEA revealed that maintenance checks of the structure are imperative, particularly for the bamboo culms and the connection strapping as they were identified as parts that could degrade overtime and the degradation could be difficult to detect. It is known that the bamboo culms degrade over time as they are very susceptible to degradation from environmental exposure. It was also identified that the connection strapping should be highly resistant to environmental exposure. Both parts would be difficult to visually check as they are likely to be fully covered by cladding. This gave the potential failures of the bamboo culms and connection strapping a RPN of 240 and 200 respectively. The aforementioned problems can be addressed with the suggested 'actions' from the FMEA. The bamboo culms that are selected should be treated for weather resistance and the cladding should fully protect the culms from environmental exposure. Instruction should be given to the consumer on how to check the bamboo culms for degradation. This could be done at the point of purchase by showing the consumer examples of 'good' and 'bad' bamboo. The material for the connection strapping should be highly resistant to environmental exposure as well has having sufficient strength, this should eliminate the need for regular maintenance checks of the strapping. The selection of the bamboo was also a very important matter. The bamboo culms that are used within the structure should have a very high structural integrity. Detailed instructions should be given to the consumer at the point of purchase on how to select appropriate bamboo culms. The culms should be treated for weather resistance and should not have any cracks or rotting areas. The bamboo culms should also be of a specific diameter to ensure for strength. The diameter of the culms will be addressed in the detail design stage. The FMEA also highlighted problems with the ability of the consumer to create a secure connection. The strapping should be tight enough to provide a secure connection and the clip for the strapping should be 'crimped' firmly. To ensure that the consumer consumer knows how to create a secure connection a demonstration should be given at the point of purchase. An

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installation tool should also be used to apply the connection strapping, this will ensure for consistently strong connections. The FMEA was a successful activity that identified a number of problems with the final concept design of the bamboo house. Addressing these problems will ensure that the final design is structurally sound and safe. The problems identified will be tackled at the detailed design stage and the implementation stage.

12.. 12

Bamboo Prototyping

To enable a realistic prototype to be constructed the team chose to build the prototype in half size with real bamboo culms. This would help the team validate if the design was effective when used with bamboo culms of varying diameter and straightness. For the connection plates the team approach sheet metal fabricators for quotes for material, cutting and forming. However, the prices proved to outwith the resources of the project. Instead 6mm acrylic plastic was used and the bends were formed using a strip wire heater. It must be noted that the acrylic plastic is very brittle and therefore does not represent the accurate strength of the final mild steel connection plates. However, the acrylic connection plates proved to be sufficient for the prototype. The bamboo prototype was assembled in less than two hours and was very simple to assemble. The cable tie connection system was extremely fast and secure and proved that the design of the connection system was very effective; strong and user friendly. The structure itself was also very stable even though only two diagonal support beams were unavailable. It must be noted that the diagonal support beams, roof overhangs and floor beams could not be included due to a shortage of bamboo culms A key problem that was highlighted was the splitting of the th e bamboo after construction of the house. It is suggested that this is due to the bamboo culms being indoors in an air conditioned room, which caused the bamboo culms to dry out and thus split. It is also understood that the culms being used are much smaller than the culms that would be used for a full sized structure. Larger culms would be less likely to split due to their larger wall thickness and would they be situated outdoor thus keeping them reasonably moist. Building the prototype not only helped validate the structure and connection system concepts but also helped produce assembly instructions which could be used for the implementation of the full sized structures. The assembly instructions can be seen in section below of the report. With the aid of the assembly instructions i nstructions and with two team members, m embers, it is believed that the prototyped prototyped could be be built within thirty minutes. A time-lapse video of the prototype construction can be seen in the accompanying CD.

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13.. 13

Buil d Inst Inst r uct uctii ons

Par artt s Li Lis st

Bamboo Culms Species: Local to Pabal Minimum Diameter: 3 Inches, 76mm Maximum Diameter: 6 Inches, 152mm

Check to ensure that bamboo culms are not rotten, cracked or splitting. Part

Specification

Length: 2.7m C1 (Yellow) Diagonal Support Struts

Quantity: 5 Length: 2.3m

C2 (Red) Roof Beams

Quantity: 4 Length: 2m

C3 (Green) Beams & Columns

Quantity: 20 Length: 1.7m

C4 (Blue) Floor Beams (Large) & Roof Support Struts

Quantity: 6 Length: 1m

C5 (Purple) Floor Beams (Small)

Quantity: 2 Total Quantity of Culms: 37 Total Quantity of Bamboo: 74.9m

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Connection Plates

R1

T1

R1

T T2

T2

T1

T B2

B1 B

B3

F1

B2

B1 F1

Total: 16 Connection Plates Material: Mild Steel Thickness: 3mm

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Connect onnection ion St r apping

Manufacturer: Hellermann Tyton Product: Stainless Steel Cable Tie Type: MBT14XH (Metal Ball bearing Ties) Material: Stainless Steel Type SS316 Length:362mm, Width:12.3mm, Thickness:0.3mm Min. Tensile Strength: 715, 3200lbs Quantity: 148

Manufacturer: Hellermann Tyton Product: Cable Tie Installation Gun Model: MK9SST (Installation tool will be made available to rent from bamboo housing supplier)

A similar connection strapping system will be sourced in India to ensure cost effective construction of the bamboo house. The system should be validated to guarantee strength and usability.

Creating a Connection At the point of purchase, a demonstration will be given detailing, how to select appropriate a ppropriate bamboo, how to use the installation gun and how h ow to check that the connection is secure.

Key Notes: • • •

• • •

Keep the bamboo culms to the outside of the connection plate, apart from the floor beams. When attaching the 'side' bamboo culms, leave enough space for the central bamboo culm. Ensure that the cable tie is tightly wrapped around both the bamboo culm and c onnection plate. Ensure that the cable tie is not twisted. Do not over tighten the cable tie; this may cause the bamboo culm to crack Ensure that the cable tie is properly and firmly crimped.

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Step 1 - Bottom Hexagon Construction Step: 1.A B1

C3

C3

B3

B2

C3

C3

B2

B3

C3

C3

B1

Step: 1.B B1

C3

C3 C5

B3

B2 C4

F1

C4

C3

C3

C3

F1 C4

C4 B2

B3

C5 C3

C3

B1

Position the bottom hexagon on suitable ground. Lift the bottom hexagon and position plinths under each connection point. Bolt the connection plates onto the plinths.

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St ep 2 - At t ach Upr Upr i ght Columns B1 C3

B3

C3

C3

B2

B2

C3

C3

B3

C3

B1

Attach upright bamboo culms (C3) to each of the outer connection points of the bottom hexagon.

(Floor beams not shown)

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Step 3 - Construct Top Hexagon Step: 3.A Attach the appropriate connection plates to the top of the upright bamboo culms. T1

C3

C3

T2

T3

C3

C3

T3

T2

C3

C3

T1

Step: 3.B Attach bamboo culms (C3) to each of the connection points to form the top hexagon.

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Step 4 - Attach Diagonal Support Beams Attach diagonal support beams (C1) to the walls of the bamboo house. A minimum of three walls (every second wall) must be supported.

T

T

C1

B

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Step 5 - Construct the Roof Step: 5.A Assemble roof as one separate unit.

C2 C

R1

C2 C

C2

R1

C

C2

Step: 5.B Lift the roof and position it on top of the top hexagon. Attach the roof at each of the connection points on the top hexagon. Ensure that an overhang of 0.3m is left over each connection point.

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14.. 14

Modul odular ar Bamboo Hous House e Cons Constt r uct i on

The bamboo house structure is modular in design thus allowing multiple structures to be attached together creating a much larger structure. Attaching the bamboo houses together also makes the overall structure more stable as they support each other. The bamboo houses can be attached together with cable ties or with standard construction strapping as seen in the image below. Product: Construction Strapping Material: Stainless Steel (Grade 304) Width: 10-20mm Thickness: 0.3-0.5mm

The bamboo houses can be clad with various different materials depending on the local resources.

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15.. 15

Costing and Manufacturing

There are several aspects to consider in order to estimating a reasonable cost for a single hexagonal unit. The obvious starting place is with the bamboo beams, connections and strapping. As detailed in the build steps above the amount of bamboo required is approximately 75m that is to be cut into combinations that total 37 beams. From discussion with Vigyan Ashram it is suggested that th at the suitable bamboo can be as cheap as 13 Indian Rupees or £0.20 per meter. These beams will be attached to sheet metal connection plates with two straps at each end and of length 0.6m, totalling 148 straps at just under 90m. In order to allow further strapping of cladding, walls and floors this was increased to 150m and at a cost of £0.10 per square meter is minimal influence.

A sheet metal manufacturer [13] was contacted to find out the manufacturing cost of the e f e r e n c e so so u r c e connection plate. The first three quotes in the diagram Figure 46 E r r o r ! R ef n o t fo f o u n d . were offered for manufacturing of 1, 12 and 100 pieces as £67, £11.50 and £7 respectively. The final figure approximating £2.50 is cost of the material only. Mitallsteel [16] sells 1x2m wide and 3mm thick mild steel for £45 and there is a possibility to manufacture 18 pieces of the connection plates from one sheet. Therefore the mass production cost of one piece would approximate cost of the material at £2.80. Figure 46 also suggests manufacturing processes that can be used for different number of pieces which is also associated with different manufacturing costs [iii]. For 16 of these blanked and formed connections using stamping manufacture this could be as low as £45 for a single hex unit. These primary materials give the following calculation and a cost of £75, inside our target cost.

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Secondary to these and while implementation and testing of is not fully covered for this project, the roofing, flooring, cladding and insulation are also required and can add significant cost to the project. Using a range of typical UK building suppliers including B&Q, Wickes, Screwfix, etc. rough estimates were w ere made for the following materials:

While the roof and flooring are taken as simple single layers of th e respective materials, the walls require several layers from inside to out of: • • • • •

Internal plasterboard Diffusion foil Wool insulation Diffusion foil Locally available and inexpensive material (not costed) for outer protection

Combining these secondary materials with our main structure the following calculations give and a total cost of £375 for our bamboo hex unit.

This now far exceeds our target cost, however in India many substitutes could be made for the UK products of wall insulation and plasterboard, chipboard flooring and corrugated steel roofing we selected with locally sourced cheap alternatives.

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Plasma, flame cutting

Abrasive water jet cutting

Connection plate manufacturing manufacturing cost co st 80

] £ [ 70 t s 60 o c g 50 n i r 40 u t c 30 a f u n 20 a M10 0 1

10

100

1000

10000

100000

1000000

Number Number of pieces pi eces [ ]

CNC punching Punching

F i gu gu r e 4 6 : Sh Sh e e t M a n u f a c t u r i n g

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16.. 16

Implementation

Just as Vigyan Ashram produces the geodesic domes as a do-it-yourself kit [22] for the lower-middle class of rural and urban populations of India, this project aims to pro vide bamboo housing as a kit, it too will target those in need of fast and cheap shelter. The package will include sheet metal connections, strapping, tools and instructions as a kit so that the user can purchase bamboo locally at more suitable prices although the suitable species will need to be clearly identified. The instructions are included above as a step-by-step guide that are typical of flat-pack purchases; if the steps are followed it is likely a suitable hexagonal hut can be build by two unskilled workers within one day. It is unlikely the sheet connections could be used for many other configurations but it is very possible for other suitably trained engineers could adapt this concept of bamboo, strapping and sheet connection for other arrangements. Using locally sourced alternatives for flooring, roofing and walls the price for this structure could be under £180/12,000 INR for a 10m 2 structure, a reasonable price to pay for a shelter in poor areas of India that retains the key features of box-shaped buildings so avoiding the cultural problems of domes and tents. With the modular configuration, additional rooms and structures can be easily added once further funds are available to the purchaser/family.

17.. 17

Future Work

Cultivation While these structures are going to be widely used the h igh demand for bamboo will likely increase its cost. The local people would be in the same situation as at the beginning when they could not afford the house. Therefore, systematic grooving of the appropriate species of bamboo in controlled quality would mitigate potential issued with its increasing price. If simple and efficient strategy for the bamboo cultivation is developed, Pabal people would be able to grow the bamboo on their own which would significantly reduce the house cost. Further, having the joints made of weather resistant material, the locals can even fix or rebuild the house every 5 years when the new crop of bamboo is ready.

Bamboo treatment Bamboo is locally treated to improve its mechanical properties. Boric acid and sulphur solutions may lead to health complications of the house inhabitants. Therefore, it would be appropriate to investigate health and safety impact of the bamboo treatment. Another, more efficient methods of the bamboo treatment should be investigated in order to improve its structural performance.

Floor ing and and cla cl adding Focus of this project was on design of low cost joining mechanism and design of house structure. However, there are still other factors influencing the final cost of the house such as the roof, wall and floor covering materials and their attachments. Hence, the future work should focus on selection of non-expensive covering materials and their attachment to the

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bamboo structure with respect to the local weather conditions, mechanical performanc e and availability in Pabal.

Real scale model and testing Half scale model was built in the DMEM department to demonstrate functionality of the hexagonal structure. However, full scale model should be built before mass deployment in order to empirically test endurance of the structure and its mechanical properties. This should be carried out in local, Pabal, environment to experience skills of the local people, quality of local material and readiness of the structure.

18.. 18

Conclusion

This project started with research of previous bamboo investigations by EWB students and the academic literature available on bamboo properties, connection systems and bamboo usage. It was found that much academic work has been done on mechanical properties testing and the use of bamboo as structural re-enforcing. Meanwhile it seems little effort has been made into a complete implementation study or design project for dev eloping nations. Once a good understanding of bamboo and related literature was attained, the connection system options were investigated and explored with a research and concept development phase. There are several types of bamboo connection; with lashing as the most common but least structured option, it was decided a new method to standardise and improve upon the lashing process would be worthwhile. Concurrently research was performed into architectural usage of bamboo and found despite the long history of usage; bamboo has fallen out of favour in modern structures except for a few pioneering architects and organisations in Colombia or the Far East such as Simón Vélez and Guadua Tech. Concept modelling was used to investigate and develop a structural system that could be implemented as small but cheap structures in Pabal, India. After a divergent phase that included options of geodesic domes or large roof coverings, the concept selected was based on a hexagonal plan. This configuration has structural advantages and utilises some of the best features of bamboo such as shear beam loading and load distribution down multiple columns. This concept was also preferred due to the closeness with typical box-shaped buildings that residents prefer and the distance from strange concepts that are clearly bamboo and highlight the bamboo use and so would become associated wi th ownership by poor. With this hexagonal structure selected the connections were r eviewed and the concept of sheet metal plates with strapping to attach to bamboo were identified as simple and cheap yet advantageous over the simple and ad-hoc lashing that is comm onplace with bamboo. Virtual prototyping was performed with a number of fin ite element analysis and optimisations performed on the connections and the general structural configuration in order to quickly and cheaply identify the connection and structure problems. With the output of these, changes were made and then followed two paths: •

Mechanical testing of a full scale prototype connection to find how the sheet metal will perform in real world and extreme loading conditions.

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•

Functional prototyping of the structure with bamboo and PMMA connections at half scale to determine the how the build process would work and get a sense of success.

These prototypes have given a fairly good review of our proposed structure for Pabal and further full scale testing is necessary in the real world conditions of India. The costing shows that the structural elements come within the budget of £100 and when combined with construction material typically available in the UK such as cladding, corrugated roofing, flooring and insulation, the total would be under £400. This price should be reduced when components more readily available in Pabal are used. Th e speed at which this structure was prototyped also suggests that two unskilled workers following the instructions could build one hexagonal unit within a day.

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References 1. Chung, K.F., Chan, S.L. (2003), “Design of Bamboo Bamboo Scaffolds”, INBAR INBAR Technical Report No.23, The Hong Kong Polytechnic University, China 2. Davies, A., (2009), "Investigation of Bamboo Reinforced Concrete for Potential Use in Developing Countries", University of Brighton, May 2009 (MEng Final Year Project Dissertation) 3. Davies, C., (2009), "Bamboo Connections", University of Bath, April 2009 (MEng Final Year Project Dissertation) 4. Grewal, J., (2009), "Bamboo Housing in Pabal", EWB-UK Research Conference 2009 at the RAEng. London, February February 2009. 5. Liang, C.B. (2009), "Bamboo as a permanent Structural Component", Imperial College London, April 2009 (BEng Final Year Project Dissertation) 6. Amada, S., Ichikawa, Y., Munekata, T. (1995), “Fibre texture and mechanical graded structure of bamboo”, Department of Mechanical Engineering, Gunma University, p. 13-20 7. Nogata, F. (1995), “Intelligent functionally graded material: Bamboo”, Composites Engineering, Vol.5 No.7 pp.743-751 8. Ashby, M. F. (1991), “Materials Selection in Mechanical Design”, p.35. Pergamon Press, Oxford 9. Albermania, F., Goha, G.Y. G.Y. , Chan, S.L. (2007), “Lightweight bamboo bamboo double layer grid system”, Engineering Structures Vol.29 pp.1499–1506 10. Bambus- RWTH Aachen. Public report: “Construction with Bamboo: Modern Bamboo Architecture”. 2002, Institute for Structural Design at RWTH Aachen University. [accessed 19th Jan 2010: http://bambus.rwth-aachen.de/eng/reports/modern_architecture/referat.html http://bambus.rwth-aachen.de/eng/reports/modern_architecture/referat.html]] 11. Ming Lu (2002), “Reliability analysis for mechanical properties of structural bamboo” 12. Stamatis, D. H. (1995). Failure Mode and Effect Analysis: FMEA from Theory to Execution . Amer Society for Quality. 13. ZOT Enginnering Ltd. , http://www.zot.co.uk/ 14. http://www.envirometrics.com/abstracts/CFDwindloading.pdf http://www.envirometrics.com/abstracts/CFDwindloading.pdf [accessed [accessed April 2010] 15. http://www.seismicsafety.com/drainage.htm [accessed April 2010] 16. http://www.arcelormittal.com/ [Accessed April 2010] 17. Bc. Ašot Babadjanjan,2010, http://www.smeral.cz (blanking/punching tool manufacturer) 18. Boothroyd, G., Dewhurst, P., Knight, W., (2002), “Product design for manufacture and assembly”, Edition: 2nd ed., rev. and expanded. Publication Details: New York : Marcel Dekker 19. Singh, U. P., (1992), “Design study of the geometry of a punching/blanking tool”, Journal of Materials Processing Technology, Volume 33 20. http://rooflandia.ca/ruukki/roofing_sheets.htm 21. Lesko, Jim (1999) Industrial design : materials and manufacturing guide, New York: Wiley Gratani, Loretta; Maria Fiore Crescente, Laura Varone, Giuseppe Fabrini, and Eleonora Digiulio (2008). "Growth pattern and photosynthetic activity of different bamboo species growing in the Botanical Garden of Rome". Flora 203: 77–84. 22. Kubik, M., (2009) “Structural Analysis of Geodesic Domes”, School of Engineering, Durham University (Final Year Project)

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Appendix Design Specification 1. Patents 1.1. Product should avoid utilization of any patents in order to avoid paying for licences. 1.2. No patents can be found that would infringe with the bamboo structure in future. 2. Quality & Reliability 2.1. Quality of connections should be carefully controlled and checked before distribution. 2.2. Any 2.2. Any failures should be at interfaces not internally to components or bamboo. 2.3. Interface between connection and bamboo should be strong enough to hold structure together safely. 2.4. Bamboo types and species should be documented with suitable recommendations. 2.5. Unsuitable types of bamboo must be clearly identified and documented. (there will be a list of suitable/non-suitable types of bamboo) 3. Packing 3.1. The kit components excluding bamboo must be able to be packaged onto a standard pallet (ISO Standard 6780) (1100mm × 1100mm). 4. Competition 4.1. Commonly timber frame reinforced concrete walls and corrugated iron roof. 4.2. 1-3 Rooms. 4.3. Single or Double Story. 4.4. Average 4.4. Average room measures 3m × 4m. 4.5. Sloping roofs are common and the height of the roof ranges from 3m to 4m. 4.6. Rs.250 (£3.40) per square foot to build (Rs.21,000/£286). 4.7. http://sites.google.com/a/engindia.net/main/pabal-information/housing---buildings 5. Maintenance 5.1. Any changes to bamboo or components should be possible in a working day. 5.2. Connections should disassemble and reassemble with minimal waste. 5.3. Any fixes should be possible with minimal disassembly. 5.4. Minor changes to structure configuration should be possible as trial and error may be used by consumers. 6. Weight 6.1. Weight of all connections that are to be used for complete house should not exceed maximum transportable weight of small lorry (3.5 tonnes). 6.2. Weight 6.2. Weight of one connection has to be optimized so that assembler would be able to hold the connection mechanism at least 5m above head during the structure assembly. 7. Market constraints 7.1. Market for low cost bamboo building already exist if the price is reasonable (<£500). 7.2. The product to be sold as long term family-house. 7.3. Introduction time of the house structure solution is not critical. 7.4. Customers (Pabal inhabitants) prefer traditional, colonial, rectangular house shapes that would not point out their low social status. Therefore traditional shapes will be preferred. 8. Politics 8.1. Main client is Vigyan Ashram. 8.2. Location is Pabal near Pune, Maharashtra, India. 8.3. Pabal has approximate population of 7,000 to 15,000. 8.4. Vigyan 8.4. Vigyan Ashram has around 50 full time students each year and serv es 5,000 across Maharashtra. 8.5. Supervisory organisation are Engineers Without Borders United Kingdom (EWB-UK) based in Cambridge. 9. Manufacturing facility

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10.

11.

12.

13.

14.

15.

16.

17. 18.

9.1. Manufacturing should ideally be possible at Vigyan Ashram using the resources available locally, a FabLab with advanced CNC machines are available, without the need of new machinery purchase or non-standard materials - this excludes basic construction items needed for drilling, joining, etc. 9.2. There are two Roland CAMM-1 sign cutters, two Roland MDX-1 3 axis mills (limited by the material's thickness). There is an Epilog laser cutter. 9.3. There is an out of action Torchmate so welding is not possible at VA but the IIT does have capability if necessary. 9.4. Outsourcing connection manufacture may be possible with investment if necessary. 9.5. Any treatments and preparations to bamboo must be possible on site. Disposal 10.1. Disassembly of structure should be simple and easy after life in service. 10.2. Any disassembly of connections should be possible by skilled worker. 10.3. For disposable parts, organic materials should quickly degrade once disposed; for non-degradable items such as metal connections should be recovered for recycling or remanufacture. 10.4. Remanufacture of connection components should be possible on site. 10.5. Recycling of materials should be possible in Maharashtra. Company constraints 11.1. Consider technical abilities of Vigyan Ashram and manufacturing personnel. 11.2. Vigyan Vigyan Ashram are a centre of Indian Institute Of Education (IIE) for Pune and have a FabLab. 11.3.History 11.3.History of small scale building construction projects. Mechanical, electrical and mechatronic projects are also common. Shipping 12.1.Finished 12.1.Finished product to be transported either by private cars if modified for a safe transport of goods, or by lorries over short distances (up to 200km). 12.2. Finished product should be easy to fit onto a pallet (ISO) for fork lift truck manipulation. In case of additional components they should fit into a pasteboard box for simple private transportation. Size 13.1.Bamboo 13.1.Bamboo culms are available up to 3m lengths. 13.2. Modular with one room as standard. 13.3. Floor should be raised, minimum of 100mm. Processes 14.1.Preparation of bamboo should take no more than one working day by lone worker. 14.2. Assembly should be possible by single worker in 5 working days or team of thre e workers in single working day. Customer 15.1.The 15.1. The customer is Vigyan Ashram with influence and input from EWB-UK and engIndia. 15.2. The consumer will be the poor communities and families in the localities surrounding Vigyan Ashram partners. 15.3. The consumer must be able to assemble the kit without expert assistance. Time Scale 16.1. Milestone 1: 16th Dec 2009 16.2. Milestone 2: 24th Feb 2010 16.3. Final Submission: 12th May 2010 16.4. (See Project Gantt Charts) Product Cost 17.1.Preferably 17.1. Preferably under Rs.8,000/£100 but at most Rs.32,000/£400 Performance 18.1. Structure must resist the local environmental conditions namely long lasting monsoon rains and strong winds.

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18.2. Considering relatively low temperature during winters (10°C) and high temperature during summer (45°C), the house must provide appropriate features – insulation, vent system, sealed doors/windows. 18.3. Due to multi-purpose use of the house, cooking and/or lavatory facilities should be considered. 19. Installation 19.1. Usage and construction of connections should be easy to explain and understand. 19.2. Multiple configurations of structure should be proposed and rules for construction will be strongly advised. 20. Aesthetics 20. Aesthetics 20.1. Must look like a professionally designed and assembled building, not a kit or a temporary structure (e.g. tent). 20.2. Should appear similar to other structures not made of bamboo and fit in the socio-cultural scenery of India. 20.3. Must consider cultural barrier of materials and form. Bamboo structures and dome shaped buildings are considered for the poor while the upper classes use concrete and steel box-shaped homes. 21. Ergonomics 21.1. Assembly: Assembly: Individual parts must be easy to handle. 21.2. Assembly: Individual parts must be able to be lifted by one person. 21.3. Door Size Recommendation: 0.8m × 2m. 22. Materials 22.1. Bamboo culms are to be used as the beam construction material. 22.2. The connections are to be made of material that local FabLab facility can handle namely plastic subtractive manufacture, steel welding, steel subtractive manufacture. 22.3. For a large scale deployment additive or formative manufacturing methods to be considered. Then the material range would extend by injection-mould-able plastics and cast iron. 23. Quantity 23.1. A small community (40 families) with two modules e ach. 23.2. Production should be easily scaled up. 24. Documentation 24.1. Minimal documentation should be necessary for usage of connections. 24.2. Guidelines and instructions should be completely visual due to language barrier and low level of education. 24.3. Any written material should be translated to all significant languages of the region/users and provided alongside the English output. 24.4. Disclaimers of responsibility and liability of designers should be included. 25. Legal 25.1. The house design has to be in consonance with Indian building and planning legislation. 25.2. The structure to provide an adequate strength so that it can be granted final building approval. 26. Safety 26.1. Should not pose a risk to any inhabitants during construction or in final form. 26.2. Any advised configuration should be tested virtually and with physical scale models. 26.3. High factor of safety of 3 will be employed as this is a living environment. 26.4. Extreme weather conditions and maximum residents possible should be considered for worst case. 27. Testing 27.1. The structure to be tested by simulation and then empirically tested before wide scale deployment. 28. Life in Service 28.1. A structure that can survive 50 years is desirable or multiple decades is desir able. Team L

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29. Environm Environment ent 29.1. http://sites.google.com/a/engindia.net/main/pabal-information/climate-- weather 29.2. Low temperature during winters (10°C) and high temperature during summer (45°C). 29.3. It is estimated that there are approximately 25-45 rainy days each year. Temp erature ranges during day-tim e and night-time night-time

Nov-Jan (Winter): 25-35°C, 10-15°C Feb-Jun (Summer): 30-45°C, 28-35°C Jul-Oct (Monsoon): 10-20°C, 10-20°C An n u a l Ra R a in fa ll

1983: 570mm 1984: 717mm 1985: 308mm 1986: 402mm 2005-2006: 800mm 2006-2007: 1000mm

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Bamboo as a Structural Material

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