ICE Emerging Engineers Paper 2017

© LafargeHolcim Foundation (2012)

Bamboo, an alternate structural material for The Corps of Royal Engineers

Capt J Murrow RE

ContentsBamboo, an alternate structural material for The Corps of Royal Engineers.....................................4

1. Introduction.................................................................................................................................41.1 Aim...................................................................................................................................4

1.2 Recommendations and findings.......................................................................................42. The need to consider alternate materials...................................................................................5

2.1 Requirement.....................................................................................................................52.2 Availability........................................................................................................................5

2.3 Economic benefits............................................................................................................62.4 Sustainability....................................................................................................................7

3. Comparison of characteristics and properties............................................................................73.1 Industrial drivers...............................................................................................................7

3.2 Material properties...........................................................................................................73.2 Standardisation................................................................................................................8

3.4 Comparison with known materials...................................................................................94. Practical application..................................................................................................................10

4.1 Corps skills.....................................................................................................................104.2 Member connections......................................................................................................10

4.3 Example structures........................................................................................................125. Conclusion................................................................................................................................12

Annexes:..........................................................................................................................................13Annex A - Calculation sheets.......................................................................................................14

Annex B – ME Vol. 2 Tables.........................................................................................................16References.......................................................................................................................................17

Table of figures................................................................................................................................18

Bamboo, an alternate structural material for The Corps of Royal Engineers.

1. Introduction.

1.1 Aim. Show that bamboo is a credible construction material for Royal Engineers to use in the absence of structural timber.

The Corps may be required to build structures where there is a shortage in supply of structural timber. In many of these regions, bamboo is a popular construction material due to its abundance and strength characteristics. It does not currently feature in any military engineering publication but with some guidance could have practical applications, particularly in disaster relief operations.

This paper has been inspired by the current strides in industry to create a functional set of design codes for structural bamboo. The five-part series compiled by the IStructE builds upon generations of construction experience as well as comprehensive material testing and experimentation.

The evaluation of bamboo will explore the need for alternate options to timber, bamboo’s availability and its sustainable benefits. Bamboo members perform well when subject to axial loading and for this reason, the material is a popular choice for scaffolding in Asia. This paper will not evaluate bamboo scaffolding but instead focus on the factors which have led industry to consider it as a credible option in permanent construction. It will look at the performance of bamboo in testing and how it compares to the RE material catalogue. Finally, the paper will consider the practical implications for RE tradesmen building with bamboo and review case studies of real-world designs.

1.2 Recommendations and findings.

1.2.1 Bamboo has a long history of being a credible structural material and now has the industry guidance to support safe design and construction.

1.2.2 Professional Engineering Wing (PEW) should consider a further review of the complete IStructE ‘Structural use of bamboo’ series and evaluate its findings for incorporation of bamboo into Military Engineer Design Volumes (ME Vol.).

1.2.3 RE to consider introducing Military Engineer (Carpenter & Joiner) trade (ME (C&J)) to bamboo familiarisation in training or the creation of bespoke Mission Specific Training (MST) packages.

1.2.4 RE to exploit all opportunities to be at the forefront of the emerging profile of bamboo in construction, particularly in support of humanitarian relief operations.

2. The need to consider alternate materials.

2.1 Requirement. The Corps may be required to conduct hasty or temporary construction projects, such as on natural disaster relief operations, where bamboo is a more viable material selection than timber. South East Asia has an abundance of bamboo but it is not limited to this region alone. The Corps also has a societal responsibility to use renewable resources where possible and the low-cost, high yield of bamboo could contribute towards this.

Why should Royal Engineers seek alternate construction materials?

Building materials are commonly selected through functional, technical and financial requirements and this section will evaluate the use of bamboo by considering its cost, availability and sustainability benefits.

The specifications of materials approved in Royal Engineer design guides are discussed later but those featured in this paper are limited to steel and timber only. Bamboo is a material currently not included in these guides but is economical, has environmental benefits and is readily available across the temperate, tropical and sub-tropical world as shown in Figure 1 Bamboo geographical zones – Green Pot Enterprises.

Figure 1 Bamboo geographical zones – Green Pot Enterprises

2.2 Availability. In two recent cases1, the Corps has been required to construct hasty structures where reliable materials were scarce. In 2013, elements of 24 Cdo Engr Regt deployed to the Philippines to conduct damage repairs following Typhoon Haiyan and in 2014, the outbreak of Ebola in Sierra Leone prompted the design of a field hospital by a STRE from 170 (Infra Sp) Engr Gp. Similar projects will be typical as the Army transitions into a period where deployments will be short notice and most likely in support of disaster relief or humanitarian operations. If bamboo had been available as a material option for 24 and 170, there could have been significantly less resourcing issues.

1 At the time of writing, elements from the Corps deployed to the Caribbean to provide support to relief operations following Hurricane Irma. Details of their remit had not yet emerged.

Across the world, the largest stock of bamboo still grows in natural forests. Increasingly, bamboo is being grown in plantations that feed a demand in its pulp for paper production and as a structural material. These plantations are very effective at producing large crops and exploit the speed at which it grows. Bamboo is the family name for more than 1000 different species of which the varieties used for construction are capable of producing mature culms in 4-6 years. This is a significant replenishment rate given that the fastest growing softwoods cannot be harvested in less than 20 years.

2.3 Economic benefits. The abundance of bamboo means it can be a very cost effective material for construction. When compared to conventional timber, concrete and steel products, it performs well across all five Life-Cycle cost energy consumption criteria;

2.3.1 Manufacturing. Bamboo is a fast replenishing crop requiring far lighter scaled equipment to harvest than timber. Other than drying and pest treatment, there is minimal refinement required before it can be used as a structural member.

2.3.2 Transportation. The main factor that increases the cost to move material is self-weight. Not only is bamboo lightweight but if sourced locally, there is no need to ship the material great distances. In war torn states, or those ravaged by humanitarian crisis, it can be assumed that conventional material supply will be severely restricted and funding limited.

2.3.3 Construction. Structural bamboo member connections will be evaluated later but they rely upon similar techniques and products to timber. The real benefit of using bamboo is linked to its low self-weight. The material is much easier to handle and, as with transportation criteria, this ease in construction mean less energy is consumed.

2.3.4 Operation. The durability of bamboo can be considered its weakest quality. It does not have the resilience of steel but given the lifespan requirement of structures produced by Royal Engineers, this is no grounds for dismissal. Kaminski (Kaminski S. , 2013) observed houses in Costa Rica that were 25 years old and in a fair condition. A similar design life would be suitable for operations where untreated bamboo could expect to achieve a service life of 10-15 years (Kaminski, Lawrence, Trujillo, & King, 2016).

2.3.5 Recycling. Bamboo is a naturally occurring material and therefore far simpler to recycle than concrete or steel. As in construction, bamboo framed buildings are typically fast to dismantle and can be done without the need of large equipment.

Figure 2 Energy Requirement of Construction

2.4 Sustainability. As set out in its ‘Sustainable Strategy’, the MOD seeks to reduce its environmental footprint without compromising on operational deliverables. In the last two decades, vast swaths of expeditionary infrastructure have been produced with functionality as the key driver. The consequence of this has been little consideration to the end of life for these structures, or for seeking a sustainable source. Producing a robust asset and being environmentally conscious do not need to be mutually exclusive. In bamboo, there is a material that offers credible structural properties for minimal environmental impact. Its rapid regeneration produces usable crops more frequently than a timber equivalent and so reduces the need for deforestation. No factories are required for its processing and there are no harmful industrial by-products as with concrete and steel. Bamboo has the ability to absorb carbon from the atmosphere and lock it within its structure. Studies have shown that bamboo actually grows more efficiently in areas of high carbon levels (Ghavami & García, 2017).

3. Comparison of characteristics and properties.

3.1 Industrial drivers. Industry is seeking to codify the performance of bamboo for use in design guides. Extensive property testing now provides the data to compare its characteristics with similar materials featured in ME Vol. 2.

This section will analyse the material properties of bamboo and then evaluate its performance in; Compression / Tension / Bending / Shear / Durability / Density. These results will be used to grade bamboo alongside the recognised RE material catalogue.

The practise of using bamboo in construction has been around for hundreds of years. Despite the lack of codified guidance, it has been highly effective as well as economical. An increasing social demand for sustainable construction materials has fuelled industry to create recognised standards to enable architects and designers to work with bamboo. Below, the physical properties of bamboo will be evaluated to show how it achieves a beneficial strength to weight ratio.

3.2 Material properties. Of the 1000+ types of bamboo, approximately 100 are classed as ‘woody’ and widespread across Africa, Asia and South America. With diameters ranging between 50-200mm and long stems commonly reaching 30m, these woody bamboos have a plethora of uses in construction. The physical properties are the key to its superior strength. The naturally occurring grass stems, known as culms, grow to form hollow tube structures.

3.2.1 Columns. Round hollow tubes, or circular hollow sections (CHS), are capable of outperforming solid members of similar width under axial loading due to a much larger radius of gyration. This reduces slenderness and, in turn, allows for a member of greater height to be used as a column (Annex A). Regular banding, known as nodes, provide multidirectional resistance to buckling, increasing the usable length of structural members that subsequently require minimal modification prior to use; (Kaminski, Lawrence, & and Trujillo, Structural use of bamboo. Part 1:, 2016)Figure 3 Structure of bamboo culm (Kaminski, Lawrence, & and Trujillo, Structural use of bamboo. Part 1:, 2016).

Figure 3 Structure of bamboo culm (Kaminski, Lawrence, & and Trujillo, Structural use of bamboo. Part 1:,2016)

3.2.2 Beams. CHS are often disregarded as beams by designers but upon inspection, the cross sectional area shares similar qualities to an I-section (Janssen, 2000). Tests upon steel CHS with external fabricated loading plates returned significantly higher resistance to bending than those without. These plates simulated the effect of a bamboo culm’s nodes and although bamboo does not compare in strength to steel, it does demonstrate where it achieves greater structural properties over smooth CHS (Guo,2013). The potential limiting factor for bamboo as a flexural member is the amount of deflection that occurs under loading – an example calculation is shown in Appendix A. Deflection varies depending on dimensions selected and can be best calculated by using standard elastic engineering formulae (Kaminski, Lawrence, D, I, & López, 2016). Considerations must therefore be given to the serviceability conditions for the intended use.

3.2 Standardisation. The vernacular of bamboo buildings has long prompted codification of the material. Design codes allow replications of structures, seen mainly in tropical regions, to be designed and erected around the wider world. With many clear benefits associated with building in bamboo, the challenge became how to modify existing test methods that would allow bamboo to be compared with timbers and steel.

The first official standards published for bamboo construction were in 2004 by the International Organisation for Standardisation. They sought to fuse existing traditional knowledge with adapted timber testing procedures. China, Columbia, Ecuador, India and Peru have all since released guidance for bamboo use in construction based on analysis of its physical and mechanic properties(Harries, Sharma, & Richard, 2012). More recently, the IStructE has launched a 5-part technical series with a view to codify bamboo for safe design within the UK (Kaminski, Lawrence, & and Trujillo, 2016). It is from this data that Royal Engineers could justify the production of safe designs utilising bamboo.

(Harries, Sharma, & Richard, 2012)Figure 6 Bamboo testing (Harries, Sharma, & Richard, 2012)- gives a pictorial indication of how testing was conducted where all results can be related to the culm dimensions; the external diameter (D), the wall thickness (t) and the section length (L). This allows for rapid field classification of bamboo and could allow Royal Engineers to conduct simple quality assurance checks on this building material. In the absence of refined construction materials, or where a Military Construction Force (MCF) require an optimal solution, bamboo members may provide the solution.

Figure 4 Bamboo cross section (Janssen, 2000)

Figure 5 CHS Loading plates (Guo, 2013)

Figure 6 Bamboo testing (Harries, Sharma, & Richard, 2012)

3.4 Comparison with known materials. Royal Engineers may be required to identify materials in field conditions and assess the suitability of those materials as a structural element. To assist with this, ME Vol. 2 (MOD, 1996) features a series of tables to aid in obtaining the strength classification of types of timber.

Scots Pine is classified as Strength Class 3 (SC3) (Table 2-2 Annex B) and is common to the UK with a variety of uses in structural joinery. The design properties of SC3 timbers are then listed in (Table A-1 Annex B). For comparison the properties of bamboo determined by IStructE research have been added to a similar table (Table 1 Characteristic strengths) where the following observations should be considered;

Bamboo outperforms all structural timber classifications listed in ME Vol. 2 in tension, compression, bending and shear. Only the Young’s Modulus is less, where bamboo is closely matched by a SC5 timber. At the time of writing, no data exists to assess bamboo’s performance in compression, perpendicular to the grain. Given that it achieves in excess of three-times the resistance to both bending and tension, at only half the density of a SC9 timber, when utilised correctly, it performs very well.

Ser.Strength

Class

Bending parallel to grain

Tension parallel to grain

Compression Shear Young's ModulusApprox Density

Parallel to grain

Perp to grain

Parallel to grain Mean Minimum

  N/mm2 N/mm2 N/mm2 N/mm2 N/mm2 N/mm2 N/mm2 N/mm2 kg/m3

1Guadua (Columbia) 50 40 20 - 5 15000 7500 533

2

For scheme design (all species) 30 40 20 - 2 12000 6700 447

3 SC3 4.2 2.6 4.1 1 0.6 7040 4640 5404 SC9 16.4 9.8 11.7 2.8 2.03 17280 14400 1200

Table 1 Characteristic strengths

4. Practical application.

4.1 Corps skills. The fundamentals of structural design in bamboo are similar to those skills taught within the Corps. This section will explore the limitations of bamboo as a construction material and consider ways to overcome the nuances associated with assembly that may make building with bamboo a risk for RE tradesmen. Particular consideration will be given to the methods of jointing bamboo structural members.

4.2 Member connections. The previous section listed the credible strength characteristics of bamboo elements but without a means to transfer loads throughout a structure the performance of a single member has limited use. Several studies have been conducted to assess methods of forming joints in bamboo but the IStructE is yet to publish its technical guidance note, Structural use of bamboo: Part 5 - Connections. In order to form a connection between two or more bamboo culms, there are three main options; lashing, bolts and plugs.

4.2.1 Lashing. Similar to the methods taught on all ME Cbt2 courses, fixing multiple members together with cordage has its roots in traditional bamboo frame construction. The integrity of the culm is preserved thus reducing the chance of splitting failure within a member however, a far higher skill level is required to ensure effective quality joints are formed as seen in (Janssen, 2000) Figure 8 Lashing (Janssen, 2000). It does allow multiple culms to be lashed together to form larger members with a combined higher load bearing capacity shown by (Patil & Mutkekar, 2014)Figure 7 Bamboo frame (Patil & Mutkekar, 2014).

Figure 8 Lashing (Janssen, 2000)

2 Military Engineering (Combat) Class 1-3 – 3 RSME

Figure 7 Bamboo frame (Patil & Mutkekar,2014)

4.2.2 Bolts. Direct fixings into bamboo can be achieved with timber or metal pins but rely upon puncturing the tube. It is possible to combine bolts with splice plates to join multiple members at a single connection. The advantage of these types of connection are in the simplicity. Existing methods used by RE for timber (Figure 10) are applicable and can also be used in conjunction with lashing to reduce damage (Figure 9).

Figure 9 Bamboo bolts (Janssen, 2000) Figure 10 Timber bolts (MOD, 1995)

4.2.3 Plugs. Filling the hollow core with a solid material allows an axial bolt to form subsequent connections. Plugs provide solid fixings to join multiple bamboo members or connections with other structural materials. They cause little damage to the integrity of the culm and do not rely so heavily upon user expertise (as in lashing). Plugging products are not readily available and due to their bespoke nature, are likely to be more expensive than common bolts used for similar scale timber frames.

Figure 11 Bamboo plugs (Janssen, 2000)

If producing simple and economical structures quickly is the key driver for using bamboo as a structural material within the Corps, then the connections must be subject to the same critiquing factors. Test results using the bolt connections show some reduction in material performance of bamboo (Mauro, 2012) but this should be offset by the gains in practicality and availability of timber pegs or off the shelf steel bolts.

4.3 Example structures. The concept of using bamboo to support RE construction activities is based around the advantages of selecting a timber alternative. It should not be considered as a complete replacement but rather seek to enhance existing and proven designs. In Costa Rica, a large proportion of single storey homes are built around bamboo frames. (Kaminski S. , 2013)Figure 12 Bamboo structure (Kaminski S. , 2013) shows how the material can be combined successfully with a range of established materials to produce functional buildings. These buildings are typically fast in construction and also reap the benefits of bamboo’s ductility in seismic zones prone to earthquakes.

Figure 12 Bamboo structure (Kaminski S. , 2013)

5. Conclusion.

This paper has sought to introduce bamboo as a structural material for Royal Engineers. Bamboo is readily available across large regions of the world and has many benefits that include, favourable material properties as well as both energy and financial savings. As the Corps looks outwards to likely future deployments, increasing the number of material options available for construction will allow RE designers increased flexibility in their concepts.

Industry is driven by the need to reduce spending and through that desire, academics and professionals have increased their research into more cost effective solutions that also reduce environmental impacts on the planet. By starting to codify bamboo as a credible structural material, they have presented designers with the opportunity to create safe structures around the world in the absence of traditional expertise.

For an organisation that relies heavily on a complex logistic chain, bamboo may provide RE with a new locally sourced structural option that is lightweight and capable of out-performing traditional materials in many uses.

Research has identified the connection of bamboo structural members as a challenge. This also poses the greatest risk for practical implementation by RE tradesmen. Currently, industry favours similar methods to those practiced by the Corps’ joiners but the anticipated publication of ‘Structural use of bamboo: Part 5 – Connections’ will prove to be the single point of reference and industry recognised standard.

Recent case studies have suggested that, had bamboo been available for selection, it could have been used to great effect in relief operations. Bamboo is increasing its stake in the global construction market and is clearly fit for purpose. Once the design code series is complete, the risk should be low enough for RE designers to consider it as a truly viable option.

ANNEXES:

A. Annex A – Calculation sheetsB. Annex B – ME Vol. 2 Tables

Annex A - Calculation sheets.

Ref. Calculation Output

Circular Hollow Section (CHS)

d1 = 140mmt = 140 * 0.1 = 14mmd2 = 112mm

A = (π * d12 / 4) - (π * d2

2 / 4) = 5,542mm2

Ix = π * (d14 – d2

4) / 64 = 11,133,000mm4

Circular Solid Section (CSS)

d = 140mm

A = π * d2 / 4 = 15,394mm2

Ix = π * d4 / 64 = 18,857,000mm4

Square Solid Section

b = d = 150mm

A = 22,500mm2

Iyy = b*d3 / 12 = 42,187,500mm4

Slenderness

r = √ I /A λ = Le / r

rCHS = 44.82mm λCHS = 66.93

rCSS = 34.99mm λCSS = 85.72

rSQUARE = 43.30mm λSQUARE = 69.28

r = Radius Gyration

Le = 3000mm(Common column height)

λ = Slenderness

σ

λ

σ y

λCHS λCSSλSQUARE

λCHS < λSQUARE < λCSS Therefore CHS is least slender and so has the greatest load carrying capacity.

Ref. Calculation Output

Table A-1Annex B

Self-weight per unit length

ρBAMBOO = 533kg/m3

ρSC3 = 540kg/m3

CHSBAMBOO = 5,542 * 10-6 * 533 = 2.95kg/m

SquareSC3 = 22,500 * 10-6 * 540 = 12.15kg/m

Bamboo is considerably lighter per unit length.

Deflection

1KN

δmax = W*L3 / 48 *EI

δBAMBOO = 1000 * 30003 / 48 * 15,000 * 11,133,000 = 3.4mm

δSC3 = 1000 * 30003 / 48 * 7,040 * 42,187,500 = 1.9mm

Deflection in bamboo is greater than pine therefore serviceability checks must be considered in addition to other design calculations.

Load = 1KN(Unit load)

EBAMBOO = 15,000N/mm2

EPINE = 7,040N/mm2

Annex B – ME Vol. 2 Tables.

REFERENCES

Gatóo, Sharma, Bock, Mulligan, & Ramage. (2014). Sustainable structures: bamboo standards and building codes. Proceedings of the Institution of Civil Engineers - Engineering Sustainability, 189-196.

Ghavami, K., & García, J. J. (2017, March 30). Building with bamboo. Retrieved from Institution of Civil Engineers: https://www.ice.org.uk/news-and-insight/the-civil-engineer/march-2017/building-with-bamboo

Guo, L. (2013). Behavior of thin-walled circular hollow section tubes. Elsevier.Harries, K., Sharma, B., & Richard, M. (2012). Structural Use of Full Culm Bamboo: The Path to

Standardization. International Journal of Architecture, Engineering and Construction, 66-75.Janssen, J. (2000). Designing and Building with Bamboo. International Network for Bamboo and

Rattan.Kaminski, S. ,. (2016). Structural use of bamboo. Part 1:. The Structural Engineer, volume 94 (8),

40-43.Kaminski, S. (2013, October). Engineered bamboo houses for low income communities in Latin

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Design values. TheStructuralEngineer, 42-45.Kaminski, S., Lawrence, A., D, T., I, F., & López, L. (2017). Structural use of bamboo. Part 4:

Element design equations. TheStructuralEngineer, 24-27.Kaminski, S., Lawrence, A., Trujillo, D., & King, C. (2016). Structural use of bamboo: Part 2:

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Patil, S., & Mutkekar, S. (2014). Bamboo as a Cost Effective Building. Journal of Civil Engineering and Environmental Technology, 35-40.

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Trujillo, D. J., Ramage, M., & Chang, W.-S. (2013). Lightly modified bamboo for structural applications. Proceedings of the Institution of Civil Engineers - Construction Materials, 238-247.

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TABLE OF FIGURES

Figure 1 Bamboo geographical zones – Green Pot Enterprises........................................................5Figure 2 Energy Requirement of Construction...................................................................................6Figure 3 Structure of bamboo culm (Kaminski, Lawrence, & and Trujillo, Structural use of bamboo. Part 1:, 2016).....................................................................................................................................7Figure 4 CHS Loading plates (Guo, 2013).........................................................................................8Figure 5 Bamboo cross section (Janssen, 2000)...............................................................................8Figure 6 Bamboo testing (Harries, Sharma, & Richard, 2012)...........................................................9Figure 7 Bamboo frame (Patil & Mutkekar, 2014)............................................................................10Figure 8 Lashing (Janssen, 2000)....................................................................................................10Figure 9 Bamboo bolts (Janssen, 2000) Figure 10 Timber bolts (MOD, 1995)..........................11Figure 11 Bamboo plugs (Janssen, 2000).......................................................................................11Figure 12 Bamboo structure (Kaminski S. , 2013)...........................................................................12