STRUCTURAL BAMBOO DESIGN IN EAST AFRICA
by
EVAN T. MYERS
A REPORT
submitted in partial fulfillment of the requirements for the degree
MASTER OF SCIENCE
Department of Architectural Engineering and Construction Science
College of Engineering
KANSAS STATE UNIVERSITY
Manhattan, Kansas
2013
Approved by:
Major Professor
Kimberly Waggle Kramer, P.E., S.E.
Abstract
This document addresses East Africa‟s need for safe, sustainable, and affordable housing
and promotes use of bamboo as a structural material by providing adequate information and
resources to evaluate the strength of bamboo. East African housing is a leading issue for the
region because of the population growth, specifically in urban areas where housing resources and
infrastructure cannot match the population growth. The solution may be bamboo housing as an
alternative to urban slums.
The bamboo species Oxytenanthera abyssinica is available
throughout East Africa region and has been accepted and implemented in traditional housing
throughout the region. This document references the resources provided by the International
Code Council (ICC), International Organization for Standardizations (ISO), and International
Network for Bamboo and Rattan (INBAR) for the use of bamboo as a structural material in
buildings. This paper also discusses the mechanical strength of bamboo, and the structural
behavior of bamboo in buildings.
In addition, bamboo construction shows the tools,
connections, and preservatives used in the field. The design example, using Oxytenanthera
abyssinica, provides the traditional layout and materials for an Amhara house, and calculations
show the practicality of bamboo in structural design. This document has led to recommendations
for engineers and the bamboo industry, including the development of a codebook for bamboo
design, promoting bamboo farms and plantations, creating a uniform connection, and increasing
bamboo‟s service life. From research, bamboo is in need of further development before being
considered a viable structural material to provide for commercial use but would suffice for the
housing shortage in East Africa.
Table of Contents
List of Figures ................................................................................................................................. v
List of Tables ................................................................................................................................. vi
List of Abbreviations .................................................................................................................... vii
Glossary ....................................................................................................................................... viii
Acknowledgements ........................................................................................................................ ix
Dedication ....................................................................................................................................... x
Chapter 1 - Introduction .................................................................................................................. 1
Chapter 2 - East Africa and Bamboo .............................................................................................. 2
Need for Housing in East Africa................................................................................................. 2
Availability and Acceptance ....................................................................................................... 2
Chapter 3 - Bamboo as a Structural Material.................................................................................. 4
Design Provisions ....................................................................................................................... 4
Acceptance Criteria ................................................................................................................. 5
ISO 22156 ............................................................................................................................... 5
Empirical Design .................................................................................................................... 6
Mechanical Properties................................................................................................................. 8
Tension .................................................................................................................................... 8
Compression ........................................................................................................................... 9
Bending & Shear ................................................................................................................... 11
Modulus of Elasticity ............................................................................................................ 12
General Properties and Failures ............................................................................................ 12
Behavior .................................................................................................................................... 12
P-δ Effects ............................................................................................................................. 13
Seismic .................................................................................................................................. 14
Chapter 4 - Bamboo Construction ................................................................................................ 18
Tools ......................................................................................................................................... 18
iii
Connections .............................................................................................................................. 20
Preservatives ............................................................................................................................. 25
Traditional ............................................................................................................................. 25
Chemical ............................................................................................................................... 26
Chapter 5 - Bamboo Design Example .......................................................................................... 28
Loads ......................................................................................................................................... 29
Materials & Layout ................................................................................................................... 30
Bamboo Specification ........................................................................................................... 30
Roof....................................................................................................................................... 31
Walls ..................................................................................................................................... 32
Columns ................................................................................................................................ 33
Braces .................................................................................................................................... 33
Member Sizes........................................................................................................................ 34
Floor & Foundation............................................................................................................... 34
Connections........................................................................................................................... 34
Additional Considerations .................................................................................................... 35
Bill of Materials .................................................................................................................... 35
Drawings ............................................................................................................................... 36
Chapter 6 - Recommendations ...................................................................................................... 45
Standards ................................................................................................................................... 45
Farms & Plantations.................................................................................................................. 45
Connections .............................................................................................................................. 46
Service Life ............................................................................................................................... 46
Chapter 7 - Conclusion ................................................................................................................. 47
References ..................................................................................................................................... 49
Appendix A-Calculations.............................................................................................................. 54
Appendix B – Additional Connections ....................................................................................... 169
Appendix C - Glued-Wood Fitting Connection .......................................................................... 174
Appendix D – Source Permission ............................................................................................... 177
iv
List of Figures
Figure 3.1 Compression Failure Modes ........................................................................................ 10
Figure 3.2 Governing Failure Mode ............................................................................................. 11
Figure 3.3 Modified Mercalli Scale for Seismic Activity in East Africa ..................................... 15
Figure 3.4 Undamaged Bamboo Structure.................................................................................... 16
Figure 4.1 Tools for Bamboo Construction .................................................................................. 19
Figure 4.2 Lashing Connections ................................................................................................... 21
Figure 4.3 Glued-Wood Fitting Connection ................................................................................. 23
Figure 4.4 Grout-Filled Connection with Steel Rebar .................................................................. 24
Figure 5.1 Similar Housing in East Africa.................................................................................... 28
Figure 5.2 Traditional Amhara House in East Africa ................................................................... 29
Figure 5.3 Measurement of Oxytenanthera abyssinica ................................................................ 31
Figure 5.4 Half-fink Truss Dimensions from Design Example .................................................... 32
Figure B.1 PVC Type Fittings .................................................................................................... 169
Figure B.2 Combination Connections with Pins and Lashing .................................................... 169
Figure B.3 Threaded Bolt Connections ...................................................................................... 170
Figure B.4 Cable Tie Mount Connection .................................................................................... 170
Figure B.5 Adhesive Connection ................................................................................................ 170
Figure B.6 Clamping Connections .............................................................................................. 171
Figure B.7 Steel Wire and Clamping Connection ...................................................................... 171
Figure B.8 Double Post Connection ........................................................................................... 171
Figure B.9 Drilled Hole Lashing Connection ............................................................................. 172
Figure B.10 Further Bamboo Lashing Connections ................................................................... 172
Figure B.11 Bolt and Pin Connections ....................................................................................... 173
Figure C.1 Glued-Wood Fitting with Steel Plate Connection .................................................... 174
Figure C.2 Steel Plates Welded to Steel Ring Connection ......................................................... 174
Figure C.3 Glued-Wood Fitting with Steel Plates, Welded Connection .................................... 175
Figure C.4 Glued-Wood Fitting with Steel Plates Connected to the Foundation ....................... 175
Figure C.5 Glued-Wood Fitting with Steel Plate and Pin Bundle .............................................. 176
Figure C.6 Wood Fitting with Steel Plate and Pin Bundle ......................................................... 176
v
List of Tables
Table 5.1 Loads ............................................................................................................................. 30
Table 5.2 Member Sizes ............................................................................................................... 34
Table 5.3 Bill of Materials List ..................................................................................................... 35
vi
List of Abbreviations
Bending ........................................................................................................................................... B
Compression ................................................................................................................................... C
Density ............................................................................................................................................ ρ
Effective Length Factor ................................................................................................................. K
Length of Member .......................................................................................................................... l
Radius of Gyration .......................................................................................................................... r
Shear ............................................................................................................................................... V
Slenderness (Kl/r) ........................................................................................................................... λ
Allowable Stress Design ........................................................................................................... ASD
American Society for Testing and Materials ........................................................................ ASTM
American Society of Civil Engineers .................................................................................... ASCE
International Building Code ....................................................................................................... IBC
International Code Council ........................................................................................................ ICC
International Network for Bamboo and Rattan ..................................................................... INBAR
International Organization for Standardizations ........................................................................ ISO
Pascal ............................................................................................................................... Pa (N/m2)
Peak Ground Acceleration ........................................................................................................ PGA
United States Geological Survey ........................................................................................... USGS
vii
Glossary
Bernoulli‟s Theorem (n.):
flat cross-sections remain flat
Buckling (n.):
instability in a slender column under axial loads
Culm (n.):
main portion of bamboo member
Drawing Details (n.):
an illustration used to describe construction components
and assembly
Hectare (n.):
one thousand square meters
Joint (n.):
connection between two or more structural elements
Mega (prefix):
one million (106)
Node (n.):
region in bamboo culm where branches sprout and a
diaphragm forms inside the culm
Ultimate Limit States (n.):
associated with collapse or other forms of structural failure,
which may endanger the safety of people such as
deformations
Serviceability Limit States (n.):
associated with states beyond which the specified
service criteria such as deflections are no longer met
Service Life (n.):
length of time the building is used for its intended purpose
viii
Acknowledgements
I want to recognize Professor Kimberly Kramer for her guidance, inspiration, and care.
For this, I owe Kimberly a great deal; she is the epitome of a great professor. Kimberly, thank
you for your hard work and dedication to students and structural engineering.
ix
Dedication
I dedicate this to my Lord and Savior, Jesus Christ, who has given me the strength to
finish well. The verse below has continued to resound in my life.
Whatever you do, work at it with all your heart, as working for the Lord, not for men,
since you know that you will receive an inheritance from the Lord, as a reward. It is the
Lord Christ you are serving.
Colossians 3:23-24
I also dedicate this to my parents, Kevin and Cheryl Myers, who have continually supported my
endeavors. I love you and it is an honor to be your son. As the Lord has allowed me to stand,
you have allowed me to walk.
x
Chapter 1 - Introduction
This report addresses East Africa‟s need for safe, sustainable, and affordable housing and
aims to increase awareness of bamboo as a structural material. East African housing is a
regional issue because of the population growth, specifically in urban areas where housing
resources and infrastructure cannot match the population growth. Bamboo housing may provide
an alternative to urban slums, and the bamboo species Oxytenanthera abyssinica is available
throughout East Africa and along with other species, has been accepted and implemented in
traditional, rural housing throughout the region.
This report investigates bamboo manuals and technical information, mechanical
properties, and behavior to determine and promote bamboo feasibility as a structural material.
Manuals for bamboo include the International Code Council‟s (ICC) Acceptance Criteria and
International Organization for Standardizations (ISO) 22156, which provide information on
testing, equations, and general considerations for the use of bamboo as a structural material.
Empirical design provides an introduction to basic guidelines and equations for preliminary
guidance in design of bamboo structures. Bamboo‟s mechanical properties show quantitative
strength and qualitative behavior of the material, in general and for the species Oxytenanthera
abyssinica, used for the design example in this report. For bamboo, P-δ effects and seismic
activity have an impact on the structural design and are discussed in order to develop an
understanding of bamboo structural behavior and performance. Thus, technical information,
mechanical properties, and behavior indicate bamboo's ability as a structural material to
adequately support a building.
Bamboo construction, the bamboo design example, and recommendations develop
bamboo‟s feasibility for structural design and construction. Bamboo requires an understanding
of its physical make-up and construction in order to safely design a structure. The bamboo
design example reveals difficulties and capabilities of bamboo structural design.
aforementioned items are used to evaluate bamboo‟s feasibility as a structural material.
1
The
Chapter 2 - East Africa and Bamboo
This chapter discusses the need for housing in East Africa and the availability and
acceptance of bamboo in that region. This section also explains the goal of this document, to
promote bamboo as a structural material. East Africa‟s need for housing continues to rise
because of an exploding population and little means to provide housing. The availability and
acceptance of bamboo in East Africa is discussed in order to determine the feasibility of
structural bamboo design.
Need for Housing in East Africa
International Network for Bamboo and Rattan (INBAR) has developed several
documents that address the housing problem in East Africa. Housing issues in East Africa are a
result of the population explosion, unaffordable housing, and inability of the housing supply to
(Kibwage, Frith, and Paudel, 2011). Shyam Paudel, author of several INBAR documents, has
determined slums are an issue due to the current rate of urbanization and the population growth
rate (Paudel, 2011). These slums are dangerous for the people living in the area because of
overcrowding, inadequate care, and underdevelopment. Ethiopia is the model country in East
Africa for the current housing crisis where approximately 85% of the urban population lives in
unsatisfactory conditions. These poor living conditions need addressed or will worsen as the
expected rate of population growth and urbanization increase in Ethiopia (Kibwage et al., 2011).
The issue with housing in East Africa requires a solution; bamboo could provide a safe,
sustainable, and cost-effective option as a structural material for housing. East Africa must
decrease the housing deficit and provide housing that promotes care and cleanliness.
Availability and Acceptance
A region‟s availability and acceptance of a material dictates usage in that region.
Availability is the measure of how easily accessible the commodity is in the region; acceptance,
in this case, is the willingness to use the material. An available and accepted resource can
minimize transportation costs that otherwise negate benefits of an alternative material over other
local materials. Availability and acceptance of bamboo must be identified in order to determine
the feasibility of bamboo as a structural material in East Africa.
2
As previously determined by researchers, three percent of the world‟s bamboo grows in
Africa (van der Lugt, Dobbelsteen, & Janssen, 2006; Adams, 1997). Bamboo grows in the
highlands and lowlands of the East African region, and the country of Ethiopia has 850,000
hectares of the lowland bamboo species Oxytenanthera abyssinica. A hectare is one thousand
square meters and equal to 2.47 acres. Therefore, Ethiopia has a resource of Oxytenanthera
abyssinica that would cover 10% of the state of Kansas (Kansas, 2010).
Oxytenanthera
abyssinica is available throughout eastern and western Africa, in a variety of environments
(United Nations Industrial Development Organization [UNIDO],2009). Oxytenanthera
abyssinica thrives in East Africa from Ethiopia to Malawi, Zambia, and Zimbabwe (UNIDO,
2009).
Although bamboo is widely available in East Africa, overuse has become an issue in the
regional bamboo industry for several years. Overuse of bamboo has caused the establishment of
organizations, such as the East African Bamboo Project (EABP) and INBAR, in the region in
order to facilitate growth in the bamboo population after years of depletion (Ababa, 2012).
Availability of bamboo will continue with programs and farms to encourage its growth in East
Africa.
The acceptance of bamboo as a structural material in East Africa is evident through its
use in indigenous and low-income housing. Bamboo housing in East Africa is not engineered,
but highly refined due to the tradition of building with bamboo in the region (Kibwage et al.,
2011). Thus, the acceptance of bamboo in the East African culture has been established through
tradition but has not infiltrated the middle and upper-class because of the negative connotation
towards bamboo, known as the “poor man‟s” material. The ability to integrate engineering and
traditional practices will beneficially remove the cultural stigma towards bamboo and allow for
the design of safe, affordable, and sustainable bamboo structures in East Africa.
3
Chapter 3 - Bamboo as a Structural Material
In this section, design provisions, mechanical properties, and bamboo behavior are
discussed in order to develop the feasibility of bamboo as a structural material. These topics
provide a brief overview of structural bamboo design.
Bamboo is used in a variety of
applications for structural purposes, ranging from indigenous housing to commercial buildings.
A summary of the design provisions is included, providing guidance for structural engineers
guidance while working with bamboo. Bamboo‟s mechanical properties discussed are based on
testing of a variety of species and specifically, the species Oxytenanthera abyssinica.
In
addition, general failure modes of bamboo are discussed, and bamboo structural behavior is
analyzed to determine bamboo performance during extreme load cases.
Design Provisions
Technical documents describe the benefits, uses, and equations for structural materials.
A structural codebook for bamboo does not exist, but the first manual for bamboo design was
published in 2000 with the ICC‟s technical document titled Acceptance Criteria for Structural
Bamboo, and the second in 2001 with the ISO‟s document Bamboo Structural Design (ISO
22156). The ICC‟s document defines codes and references to use during structural bamboo
design and procedures for testing. The ISO document, referred to as ISO 22156, was created to
centralize the suggestions of researchers. ISO 22156 is not an international standard, but a step
in the recognition of bamboo by other agencies as a structural material and creation of a
codebook for design. ISO 22156 has suggestions for design and drawing details to provide
adequate guidance essential for proper bamboo structural design. ISO 22156 is summarized to
increase understanding of requirements for designing bamboo structures.
Traditional knowledge can provide adequate design of bamboo structures, but structural
engineering occurs when the engineer verifies the loads on a building and executes a safe,
affordable, and sustainable design. Generally, a material has a codebook governing the structural
design, which has information regarding equations, detail guidelines, and construction practices.
Bamboo has a manual of guidelines, ISO 22156, and empirical design criteria to accommodate
quality design practice but requires the development of a codebook to become a relevant
structural material.
4
Acceptance Criteria
The ICC document Acceptance Criteria for Structural Bamboo provides codes and
references to use while designing bamboo structures, including the International Building Code
(IBC), INBAR, and several American Society for Testing and Materials (ASTM) documents.
The document primarily discusses bamboo testing and how to accurately perform tests. The ICC
document also provides equations to determine allowable stresses considering factors in design
such as the Load Duration and Adjustment Factors and Safety Factor in Allowable Stress Design
(ASD) (International Code Council [ICC], 2012). These equations were not used in the design
example because they are less conservative than the INBAR equations.
ISO 22156
ISO 22156 is based on limit state design and bamboo structural performance. It includes
requirements for mechanical resistance, serviceability, and durability of structures (International
Organization for Standardization [ISO], 2001). The ISO document does not develop specific
requirements for bamboo structural design but introduces generalities to promote safe and quality
design.
A bamboo structure must serve the intended purpose of the building with regard to
service life, cost, and durability. Damage incurred by events such as explosions, impacts,
extreme weather, or consequences of human error must be proportional to the event and not
greater. Potential damage from the aforementioned events must be mitigated by one of the
following strategies in the structural design:
Decreasing the likelihood of hazards.
Transferring forces when accidental removal of an element occurs.
Providing a form with a high degree of resistance to hazards.
Retaining continuity.
Bamboo construction concepts are based on calculations, knowledge from previous
generations, and reports. General calculations are discussed in the empirical design section and
further calculations are shown in Appendix A. ISO 22156 defines standard requirements as,
“Experience from previous generations, well preserved in a local tradition, and carefully
transmitted to people living today. This expertise can be considered as an informal, non-codified
„standard.‟” Design and construction practices must be generally known, accepted, and viewed
5
as wisdom by the local authority. ISO 22156 defines applicable cases as those in which, “The
community shall be characterized by an undisturbed social structure, with a well-recognized
social pattern.” These practices are not valid after the community migrates, unless applied in
comparable conditions.
Disaster reports of quantitative magnitude that analyze successful bamboo structures with
full details and information may be applied to similar instances in the future. ISO 22156 requires
the disaster report receive recognition from engineers with experience in bamboo structural
design and the international technical community in order to verify the report‟s accuracy and
reliability.
Design requirements include checking all limit states and load cases. An accurate design
model must be created to perform calculations, and the limit states and load cases must comply
with national standards. For design purposes, bamboo culms are tapered, hollow tubes with
differing thickness and minimal eccentricity. In bamboo design, the structural engineer should
treat joints or supports as hinges, use conventional structural analysis, use Bernoulli‟s theorem,
and use Euler‟s buckling.
Air-dried bamboo must be used for construction with the structure designed and detailed
in such a way as to keep the bamboo dry and allow wet bamboo to dry. This measure protects
bamboo from deteriorating and developing structural inadequacies in-situ. The construction
process shall be monitored to verify assumptions made during the design phase and validate the
design as sufficient.
All bamboo projects must meet these requirements with adequate
specifications, detailing, production, construction, and compliance with ISO 22156 (ISO, 2001).
This description of ISO 22156 refers to key points for design and construction of
structural bamboo. The document is purely descriptive, not prescriptive in the guidelines and
does not provide values or equations for the design process.
Empirical Design
Several empirical design criteria and guidelines for bamboo structures have been
developed in order to use bamboo in structural design. The empirical design criteria for bamboo
strength require the density of the species analyzed (Janssen, 2000). The equations below pertain
to air-dried bamboo in compression (C), bending (B), shear (V), modulus of elasticity (E),
slenderness (λ), and deflection (δ). These equations relate to the density (ρ in kg/m3) and safety
6
factor (Ω) for allowable stresses (MPa=N/mm2). These equations are used when the mechanical
properties are unknown.
C=0.094ρ
(1)
CALLOWABLE=0.094ρ/Ω
(2)
B=0.14ρ
(3)
BALLOWABLE=0.14ρ/Ω
(4)
V=0.021ρ
(5)
VALLOWABLE=0.021ρ/Ω
(6)
E=24ρ
(7)
λ=Kl/r ≤ 50
(8)
δmax=l/300
(9)
The determined compression, bending, and shear stresses are the primary stresses a
bamboo member experiences in application. Tension stresses must also be considered in design;
thus, an equation is necessary to determine allowable tension stresses for structural bamboo
design. The modulus of elasticity, slenderness, and deflection also contribute to the structural
design and can be attributed to the limit states involved.
Allowable stresses are the calculated stresses divided by the safety factor. Research by
Dr. Jules Janssen‟s indicates that the safety factor varies based upon testing quality and loadcases in order to account for the variance in bamboo culm diameter, thickness, degradation, and
eccentricity (Janssen, 2000). The safety factor provides a conservative design approach for
structural bamboo applications, and the equation presented by Dr. Janssen directly mirrors the
ICC‟s
allowable
stress
equation
but
has
more
conservative
coefficients.
The deflection guideline defined by Janssen in The Fundamentals of Bamboo is δmax=l/300,
consequently preventing the designed members from experiencing extreme deformation and
bending and allowing for continued serviceability of bamboo structures and their components
(Janssen, 2000).
The empirical design criteria provide a baseline for structural engineers to begin
designing bamboo structures. These calculations allow engineers to produce a proposal before
conducting formal testing on the specified bamboo species. The empirical design criteria do not
replace or neglect the significance of quantitative mechanical properties determined from testing
because without these properties, the engineer cannot accurately design a structure. However,
these empirical design criteria provide further documentation of design parameters and
7
equations. Again, the next step for the bamboo industry is to provide a codebook or reference
manual for structural design.
Mechanical Properties
Mechanical properties of bamboo vary depending on the analyzed species, therefore this
section considers bamboo‟s mechanical properties, specifically Oxytenanthera abyssinica’s
mechanical properties. Properties required for structural design and applications include tension,
compression, bending, shear, and the modulus of elasticity. These mechanical properties provide
the framework for bamboo‟s implementation in structural design.
Mechanical properties,
general properties, and failures are discussed in order to more fully understand bamboo behavior.
Oxytenanthera abyssinica has a density of 778 kg/m3, a height ranging from five to
fifteen meters, a diameter of three to ten centimeters, and intermodal lengths of fifteen to forty
centimeters (Didier, Ngapgue, Mpessa, & Tatietse, 2012; Inada & Hall, 2008). Oxytenanthera
abyssinica is defined as a solid bamboo with a completely solid base and nearly solid above the
base (Kitil Farm, UNIDO, 2009). Since mechanical properties are dependent on the crosssectional area of the culm, the average diameter and wall thickness are required for design and
will be discussed for the design example.
Oxytenanthera abyssinica test results provide
quantitative data for the mechanical properties. From Inada and Hall‟s technical document, the
mechanical properties for Oxytenanthera abyssinica were determined at 47% moisture content,
which is high for structural applications (Inada & Hall, 2008). Additional test results were used
from Markos Alitos‟ research on Oxytenanthera abyssinica; thus, the most conservative value
was taken for each mechanical property.
Tension
Tension forces are experienced in a variety of structural members, beams, truss-members,
and others. All species of bamboo have high tensile strength, but bamboo has an advantage over
other structural materials because of its dual strength in tension and compression (Trujillo,
2009). Thus, structural bamboo design must utilize the tensile strength of bamboo. The general
tensile strength range is 35-230 MPa, and Oxytenanthera abyssinica‟s tensile strength is 127
MPa (Arce-Villalobos, 1993; Bhalla, 2008; Janssen, 2000; Kassa, 2009; Yu, Chung, & Chan,
2003; Alito, 2005).
8
Many parameters affect the tensile strength, including node placement, age, and moisture
content. Based on Arce-Villalobos‟ research, tensile strength at the nodes is 80% of the tensile
strength at the internodes (Arce-Villalobos, 1993). Peak tensile strength occurs from age three to
four of the culm (Arce-Villalobos, 1993).
The moisture content of the bamboo culm can
dramatically impact the tensile strength of the bamboo, decreasing it by half in extreme cases
(Yu & Chung, 2002). A brittle failure occurs in bamboo under tension, affecting design because
engineers prefer members and systems to fail in a ductile manner (Arce-Villalobos, 1993).
Compression
The compressive strength of bamboo allows structural engineers to design columns,
truss-members, and other compression members in bamboo structures. The general compressive
strength parallel to bamboo‟s grain ranges from 27-176 MPa, with a majority of species‟ testing
around 60 MPa (Arce-Villalobos, 1993; Bhalla, 2008; Sharma, 2011; Yu, Chung, & Chan,
2003).
The compression strength of Oxytenanthera abyssinica is 40 MPa (Alito, 2005).
Bamboo compressive strength increases with age, while nodes and moisture content do not affect
compressive strength (Arce-Villalobos, 1993). Although Oxytenanthera abyssinica has a lower
compressive strength, P-δ effects generally govern the structural design of bamboo compression
members.
Failure modes for compression are splitting and end bearing. Figure 3.1 shows splitting
in a test specimen (Yu & Chung, 2002). Splitting is the primary failure mode for bamboo in a
majority of load cases. In Chung and Yu‟s testing of the species Bambusa pervariabilis and
Phyllostachys pubescens, most specimen‟s failed in end bearing resulting in crushing. This plays
a key role in connection design, as discussed in Chapter 4.
9
Figure 3.1 Compression Failure Modes
(Reproduced from K.F. Chung and W.K. Yu‟s Mechanical properties of structural bamboo for
bamboo scaffoldings)
Splitting occurs in bamboo because of tangential stresses induced by the circular shape of
the bamboo culm (Arce-Villalobos, 1993). These stresses govern a majority of failures in
bamboo, especially in compression members because bamboo is weak in perpendicular
compression and tension (Trujillo, 2009). When maximum tangential stress is reached within
the culm fibers, longitudinal splitting of the culm occurs. Maximum tangential strength is
determined by bamboo‟s tangential modulus of elasticity, which is approximately one-eighth of
the longitudinal modulus; for Oxytenanthera abyssinica the tangential strength is 1827 MPa
(Arce-Villalobos, 1993; Didier et al., 2012).
Arce-Villalobos found a majority axial stresses in bamboo culms are distributed to the
outermost rings due to axial stiffness increasing from the inside to outside of the culm, as shown
in Detail A of Figure 3.2. The distribution of axial stresses creates radial bending moments in
the culm, as the outermost layers are in compression and the innermost layers are in tension as
shown in Detail B of Figure 3.2. Compression on the outermost rings will force the culm to
expand to the failure as shown in Detail C of Figure 3.2; when longitudinal cracking
commences.
Cracking may occur around the ring of the culm because of movement and
interaction of the outermost and innermost rings (Arce-Villalobos, 1993). Yet, Oxytenanthera
abyssinica is less susceptible to these stress concentrations because of its solid form, assuming
minimal eccentricity (UNIDO, 2009).
10
Figure 3.2 Governing Failure Mode
(Reproduced based upon figure in Arce-Villalobos‟ Fundamentals of the Design of Bamboo
Structures)
Bending & Shear
Bamboo bending strength is critical to determine member size and span length. Bending
strength of a bamboo member can be determined by the span. Shear governs for short members,
and pure bending governs for long members, generally depending on load intensity, strength of
the species, and span. Bending strength can be compromised because of stresses producing
strain, which have a critical value of 1.1x10-3 for bamboo. The average tested bending strength of
bamboo is 62 MPa (Janssen, 2000). The modulus of rupture indicates the ultimate strength of
the a bamboo culm in bending, and Oxytenanthera abyssinica’s modulus of rupture is 82 MPa
and shear strength is 11 MPa (Inada & Hall, 2008; Ahmad, 2000; Sharma, 2011).
Bamboo failure modes for bending are local crushing and splitting (Yu & Chung, 2002;
Janssen, 2000). For Chung and Yu‟s research, local crushing was a failure mode because the
researchers carried out a single-point load bending test at the mid-point, instead of a three or four
point bending test. Although the worst-case scenario, a single-point load will not occur often in
application unless prescribed by the engineer. The typical failure mode for bending is splitting
with the culm separating into four quarters, similar to Figure 3.1 (Janssen, 2000).
11
Modulus of Elasticity
The modulus of elasticity of bamboo is significant because it indicates bamboo‟s
flexibility and behavior. The modulus of elasticity helps predict the culm‟s change in length
based on axial loading in tension or compression, and the modulus of elasticity is used to
determine member deflection. The modulus of elasticity for tested bamboo species ranges from
2113-22000 MPa (Sharma, 2011; Yu, Chung, & Chan, 2003). INBAR conducted a study which
found that the modulus of elasticity for air-dried bamboo can be estimated as twenty-four times
the bamboo density, E=24ρ (Janssen, 2000). Therefore, Oxytenanthera abyssinica‟s modulus of
elasticity could be taken as 18672 MPa (ρ=778 kg/m3), but the tested modulus of elasticity for
Oxytenanthera abyssinica is 14617 MPa (Didier et al., 2012). Thus, structural engineers should
use the latter value in design because the value is determined from testing and more
conservative. 14617 MPa for the modulus of elasticity indicates Oxytenanthera abyssinica has a
high resistance to deflection compared to other bamboo species yet provides flexibility (Ahmad,
2000).
General Properties and Failures
General properties and failures of bamboo in design include the inherent variation of
culms and buckling. Culm variation contributes to the difficulty of designing bamboo structures
and obtaining accurate quantitative data. Bamboo is weak because of variation in the crosssection, which can substantially impact the bending and axial stiffness of the culm (ArceVillalobos, 1993). Buckling occurs in bamboo culms because of bamboo culm‟s slenderness and
curvature (Yu et al., 2003). Both qualities are avoidable through quality control and design
checks throughout the design and construction process.
Behavior
Bamboo behavior depends on mechanical properties discussed in the previous section.
P-δ effects and seismic behavior provide insight into the mechanical properties and performance
of bamboo. These two behaviors can initiate complete failures of a structure if not accounted for
in the design process. Thus, behavior of bamboo through P-δ effects and seismic events are
paramount to understanding and safely designing bamboo structures.
12
P-δ Effects
P-δ effects are secondary forces induced by initial eccentricity of a structural member and
increase with increased axial loading. These secondary forces create additional bending stresses
within the structural member experiencing the effects, thus creating instabilities leading to
failure. Member slenderness contributes to P-δ effects because slenderness correlates with the
member‟s ability to resist P-δ effects. The approach for resisting P-δ effects differs based on the
structural material used by the engineer because mechanical properties influence material
behavior during P-δ effects (Kramer, 2011).
P-δ effects create bending stresses and can negate the compressive strength of bamboo
(Arce-Villalobos, 1993). P-δ effects occur in bamboo because of initial eccentricity of the culm,
and P-δ effects can detrimentally impact the integrity of bamboo structural members because of
bamboo‟s flexibility. Bamboo has a tendency to buckle during P-δ effects due to the slenderness
of the culms. Thus, bamboo member‟s maximum slenderness ratio is 50 or less (λ≤50) to avoid
significant P-δ effects. Nodes within the culms weaken the structural integrity of the member in
bending, but decrease the effect of buckling (Arce-Villalobos, 1993). Since creep is negligible in
bamboo, initial P-δ effects of a member are not magnified (Janssen, 2000). Bamboo‟s flexibility
and strength combination make initial deflection critical in design, but proper bracing design and
details can decrease the impact of P-δ effects.
Buckling, due to P-δ effects, is a significant consideration in structural bamboo design.
The Euler buckling equation can be used for structural bamboo, which is similar to the Euler
buckling equation for materials such as steel and wood. (Janssen, 2000).
Arce-Villalobos
determined the following assumptions to be adequate for buckling analysis of bamboo (ArceVillalobos, 1993):
1. The cross-section of the culm is a circular ring with a constant diameter and wall
thickness.
2. The modulus of elasticity in the x-direction along the element is constant.
3. The angular modulus of elasticity is constant.
4. Deformations in bamboo are small.
5. Material is perfectly elastic.
13
These assumptions provide a basis for determining the stability of bamboo structural members
and simplify the culm‟s complexity, and these assumptions are appropriate with the use of
conservative design values.
Seismic
Seismic performance of structures in East Africa warrants consideration because of the
high degree of seismic activity in the region. Figure 3.3 shows East African seismic activity and
the intensity of this activity ranging from minimal to destructive, based on the Modified Mercalli
Scale (The Modified Mercalli Intensity Scale). This section explains two seismic measuring
systems and then briefly two seismic events in which bamboo structures performed in a pristine
manner. The attributes contributing to bamboo‟s success during seismic events are listed in
order to encourage the consideration of bamboo as a structural material.
The Modified Mercalli Scale shown in Figure 3.3 is defined as a scale measuring
magnitude of seismic events in relation to event effects. For example, few people at rest feel a
Degree II seismic event, but during a Degree VIII seismic event, ordinarily designed structures
experience extensive damage and seismically designed structures experience slight damage or
partially collapse, in addition to overturning of heavy furniture (The Modified Mercalli Intensity
Scale). Degree VIII governs for East Africa and was considered in the design example because
as engineers, we must design for the worst-case scenario for the location.
14
Figure 3.3 Modified Mercalli Scale for Seismic Activity in East Africa
(Reproduced from the United Nations Office for the Coordination of Humanitarian Affairs‟
[OCHA] Earthquake Risk in Africa: Modified Mercalli Scale)
15
The Richter Scale is another technique to substantiate a seismic event through
quantitative results.
The Richter Scale logarithmically measures the size of an earthquake
comparatively to past earthquakes based on seismograph readings taken during the earthquake
and translated to a Richter Scale magnitude. The Richter Scale determines magnitude based on
seismograph readings, not damage (The Richter Magnitude Scale).
In design, structural engineers use the spectral response acceleration to determine the
forces experienced by a structure. The spectral response acceleration is derived from ASCE 7-10
based on data taken from past events at the project location. In the United States, ASCE 7-10
provides spectral response acceleration and equations for seismic design with a 2% probability of
being exceeded in fifty years. Thus, a severe earthquake‟s maximum peak ground acceleration
(PGA) will exceed the design capacity for the structure and may produce localized failures
within a structure.
Several studies reveal the impact of seismic loading on bamboo structures.
The
performance of a bamboo structure under seismic loading contributes to the degree of safety of
the occupants, sustainability, and economics of the structure.
Figures 3.4 shows bamboo
performance during the 2006 Sikkim earthquake in India, which was a 5.7 magnitude event on
the Richter Scale with a maximum peak ground acceleration of 0.036g. As noted in the caption,
this bamboo structure was undamaged from the earthquake (Sharma, 2011; Shakemap
usjdae_06: Peak Ground Acceleration, 2006). Figure 3.4 provides an example of bamboo‟s
stability and strength during seismic loading (Janssen, 2000).
Figure 3.4 Undamaged Bamboo Structure
(Reproduced from Bhavna Sharma‟s Doctoral Dissertation, Seismic Performance of Bamboo
Structures)
During a 1991 Costa Rican earthquake of 7.5 magnitude on the Richter Scale (maximum
PGA of 0.27g), twenty houses made of bamboo located near the epicenter of the earthquake were
16
undamaged, testifying to bamboo‟s flexibility and ductility as a structural system (Janssen, 2000;
National Commission for Risk Prevention and Response [CNE]).
These two examples
demonstrate bamboo performance in seismic activity and encourage further exploration of
bamboo as a structural material. Further data and testing performed on bamboo shows that it has
the ability to safely dissipate seismic forces without damage to the structure (Janssen, 2000).
Bamboo has many mechanical properties allowing it to dissipate forces from seismic
activity. Bamboo strength, stiffness, and flexibility allow for safe structural performance during
seismic events, as seen in Figure 3.4 (Janssen, 2000). The low-weight of bamboo contributes to
its success because of the contribution of building weight to forces accruing in the structure
during seismic activity, thus reinforcing the process in ASCE 7-10 to calculate forces from a
seismic event on a structure. Continued use of bamboo structures is advantageous after seismic
events because they do not require extensive repairs compared to other structural materials. This
provides long-term cost savings for bamboo houses in regions of the world, such as East Africa,
where poverty-stricken people cannot afford to replace their homes after natural disasters.
17
Chapter 4 - Bamboo Construction
This chapter briefly examines the tools, connections, and preservatives used in bamboo
construction. Construction of structural bamboo houses influences design of bamboo structures.
Thus, the construction process must be understood in order to design an effective structure.
Tools and connections to execute construction and stabilize structures are essential for bamboo
construction because both of these items impact construction with their influence on efficiency,
time, and capabilities of the construction crew. Tools used for construction indicate complexity
of construction and skill needed for labor. Connections contribute to the structural integrity of
the building, making them pertinent to the structural engineer. Preservatives extend the service
life of bamboo; the various preservatives for treating bamboo are discussed in this section.
Although construction entails many facets, this section focuses on contributors to structural
bamboo design, tools, connections, and preservatives. Construction practices would require a
separate document due to the variance in construction practices across the globe. Therefore,
specific construction practices are not covered in this research.
Tools
Construction begins and ends with tools used throughout the process. Effective use of
tools during construction determines the timeline and cost of a project. The difficulty of working
with round culms of bamboo has limited the types of tools used during bamboo construction.
Tools used for construction of bamboo housing are shown in Figure 4.1. A variety of hand tools
and power tools are used in bamboo construction and suffice in completing the needed tasks.
However, tools used in bamboo construction are the most rudimentary of all building materials
because of the simple techniques of bamboo construction and traditions of bamboo structures.
18
Figure 4.1 Tools for Bamboo Construction
(Reproduced from the United Nations Industrial Development Organization Cottage
Industry Manuals: Raw Materials and Tools for Bamboo Applications)
Tools shown in Figure 4.1 and presented by the United Nations Industrial Development
Organization (UNIDO) and Kassa include the following hand and power tools:
Carving Tool
Chopping Knife
Drill Bits
Planer
Rotary Saw
Chisel
Drill
Nail Gun
Pliers
Saw
Hacksaw
Handsaw
Ladder
Scissors
Shaping Knife
Hand Drill
Jig Saw
Saw Horses and Jigs
Scraping Knife
Torch
(UNIDO, 2008; Kassa, 2009)
19
Although not an exhaustive list, the tools shown are examples of common tools used for
bamboo construction. These tools require limited training, thus enlarging the market of available
workers and allowing for a swift transfer of knowledge between parties in the construction
process. The simplicity of these tools also provides high constructability because they do not
require a high skill level in order to be utilized.
New tools will eventually be used in bamboo construction, but the market for bamboo
construction has determined the type of tools used. Since bamboo is largely used in poor, rural
regions of East Africa, the tools associated with bamboo construction are simple, inexpensive,
and readily accessible. New technology will become a part of bamboo construction if bamboo
becomes a widely-used material in all cultures, climates, and classes.
Connections
Structural connections strive to create continuity between bamboo culms and verify that
failure of the structure occurs in bamboo members and not in connections (Arce-Villalobos,
1993). The inherent variance of bamboo creates a multiplicity of connections for structural
bamboo design. Many bamboo connections provide a way to transfer loads out of the culm and
into another element, and connections used are lashings, steel wires, nails, bolts, pins, clamps,
glued-wood fittings, grout fills, and proprietary connections (Janssen, 2000; Arce-Villalobos,
1993; Construction with Bamboo-Bamboo Connection). The number of connections allows
flexibility for structural engineers to implement a connection for a project that effectively
supplements the rest of the bamboo structure.
A successful connection affects the economy, rigidity, and structural continuity; thus,
these items must influence structural design. Many connections discussed in this section have a
practical niche, but in order for bamboo to become an internationally recognized material,
several quality connections must be developed. Research has shown that two connections, the
glued-wood fitting and grout-filled with rebar connection, are practical for most conceivable
situations. Common connections in bamboo design are presented in this section with a brief
overview of alternatives in bamboo connections including lashings, nails, bolts, and pins. The
glued-wood fitting and grout fill with rebar connections are also examined.
Lashings are traditional connections in bamboo design and demonstrate a natural beauty
and flexibility. Natural materials used in lashings include cain, coir, vines, sisal fiber, bark,
20
bamboo strips, and rattan (Socrates; Janssen, 2000). In general, lashings are made from wet,
green strips of bamboo because as strips dry, they shrink and tighten the connection, increasing
strength (Socrates). The versatility of lashings allows them to be used in numerous situations
because of the free-flowing nature of the connection. However, lashings cannot be checked
quantitatively due to their variance in craftsmanship and strength (Janssen, 2000). The two
pictures in Figure 4.2 indicate the vast difference in lashing quality, reinforcing why lashings are
not practical as a stand-alone connection. Additional lashing connections can be viewed in
Appendix B.
Figure 4.2 Lashing Connections
(Reproduced from Nicholas Socrates‟ Bamboo Construction)
Steel wire is a newer development in lashing connection for bamboo, but steel wire has
difficulty fitting tightly to bamboo and transferring forces through tension. Thus, a wire-lacing
tool has been invented to assist in wrapping wire around the bamboo, but this method and
product have not been widely used in bamboo design (Arce-Villalobos, 1993; Janssen, 2000).
Other materials used as lashing include plastic tape and rope.
Although lashing is a popular connection, it does not provide adequate stiffness for
structural bamboo design.
Lashing connections allow significant displacement because the
lashing does not adequately hold the culm, and if green bamboo is used, the culm shrinks and
moves (Arce-Villalobos, 1993). In addition, the variability of lashing connections diminishes the
ability to verify the strength and adequacy of the field connection. Thus, lashing connections are
not feasible for structural bamboo design (Janssen, 2000).
Nail, bolt, and pin connections are frequently used in structural bamboo because they
provide a simple means to connect the culms. These connections are not preferred in bamboo
21
structures because they induce splitting in the culm and are not versatile (Socrates). Bamboo
culms are damaged and cracked from drilling, causing early splitting that leads to failure. Predrilling holes in order to place the bolts and pins can prevent splitting, but nails, bolts, and pins
are not versatile connections because they only suffice for situations with two culms and do not
provide adequate transfer of forces (Janssen, 2000). Appendix B provides examples of nail,
bolt, and pin connections.
Additional connections are not discussed due to the limitations of this section, but
Appendix B has information on additional connections. Connections range from PVC fittings,
combination connections with pins and lashings, threaded bolts, cable-tie mounts, adhesives, and
clamps. These connections cannot be considered in structural bamboo applications because of
expense, labor costs, load transfer, or durability.
The glued-wood fitting and grout-filled connection with steel rebar were chosen based on
several parameters, including Arce-Villalobos keys to a successful connection (Arce- Villalobos,
1993):
1. Avoid penetration by nails, screws, or bolts.
2. Avoid open ends.
3. Solve the problem of size variability.
4. Transfer forces by axially distributing them to the fiber of the culm.
The glued-wood fitting and grout-filled with steel rebar connection satisfy these
suggestions and may increase bamboo‟s viability as an internationally recognized structural
material. Although bamboo varies in shape, size, and thickness, the glued-wood fitting and
grout-filled with steel rebar connection have the flexibility to accommodate changing
characteristics.
The glued-wood fitting connection could improve uniformity of structural bamboo design
and has gained popularity due to its success, as it is placed within the cavity of the culm to create
a structural continuous connection (Arce-Villalobos, 1993; Janssen, 2000).
Glue testing has
shown that “normal” glue provides a higher strength than the bamboo culm due to the culm‟s
weakness in the tangential direction (Socrates). Thus, the glued-wood fitting is adequate and
should not incite failure of the bamboo structure. Figure 4.3 illustrates a glued-wood fitting,
which is a wood fitting cut to fit within the interior cavity of the culm. Two slits are cut into the
22
culm to control cracking while the wood fitting is placed (Arce-Villalobos, 1993). Advantages
of this connection include low cost, use of accessible materials, versatility, simplicity, extension,
and increase of area (Socrates; Arce-Villalobos, 1993). A disadvantage would be splitting
induced by the slits created to place the connection.
For a structural engineer, the glued-wood fitting connection has several viable qualities.
The connection transfers forces tracking through the culm into a larger cylindrical wood fitting,
and this fitting distributes forces into the next member or element.
The glued-wood fitting
provides protection for the culm by closing off the end and reinforcing the hollow interior of the
culm. This additional strength decreases likelihood of splitting or crushing and redistributes
shear stresses, and decreases bending stresses in the connection area. Capping the end of the
culm prevents insects from entering and destroying it from the interior (Arce-Villalobos, 1993).
Therefore, the glued-wood fitting meets all Arce-Villalobos‟ suggestions and demonstrates
superior performance compared to other bamboo connections. Discussion of the versatility of
this connection continues in Appendix C.
Figure 4.3 Glued-Wood Fitting Connection
(Reproduced based upon figure from Antonio Arce-Villalobos‟ Fundamentals of the Design of
Bamboo Structures)
Another simple, successful connection mentioned by researchers is the grout-filled
connection with steel rebar. Figure 4.4 depicts a grout-filled connection with steel rebar, a
preferred connection in practice because of its reliability and ease of placing (Janssen, 2000).
Grout supports the culm similarly to the glued-wood fitting and transfers compression forces,
23
while steel rebar transfers tension forces. This connection is successful in truss design because
of the aforementioned characteristics.
The primary disadvantage of the grout-filled connection with steel rebar is its practicality
and interaction with bamboo. This connection may not be practical in most situations except
trusses and at the foundation of the structure. When placing grout, moisture produces swelling
and splitting of the bamboo culm, and bamboo tends to shrink when it loses moisture. In this
case, though, the culm cannot shrink due to the grout, producing splitting (Janssen, 2000).
However, this connection provides structural continuity and increases the area in order to
decrease stresses transferred from connection to connection.
Figure 4.4 Grout-Filled Connection with Steel Rebar
(Reproduced from the INBAR‟s Designing and Building with Bamboo)
A variety of connections are used in bamboo projects because of bamboo variability.
Many of these connections are case-specific, and connections used include lashings, steel wires,
nails, bolts, pins, clamps, glued-wood fittings, grout-filled, and proprietary connections. With
economy, rigidity, and structural continuity, however, a majority of these connections do not
suffice.
Only two simple, versatile connections, the glued-wood fitting and grout-filled
connection with steel rebar, fulfill the goals and suggestions of Arce-Villalobos that a structural
engineer must consider. The glued-wood fitting and grout-fill with steel rebar connections,
provide minimal adjustment and construction issues and avoid the lead-time of proprietary
connections, but the variance in design and construction may force the implementation of several
different connections. The design example utilizes the glued-wood fitting coupled with lashing
because the combination provides flexibility and adequate strength and rigidity to succeed in a
variety of circumstances. Lashings transfer and develop forces from lateral loads into adjacent
members.
24
Preservatives
Preservatives are essential for increasing structural bamboo service life. Bamboo service
life may be limited to one to three years when outside in contact with soil and up to ten to fifteen
years under very good conditions, including positioning bamboo off the ground away from other
organic matter in a dry environment (Janssen, 2000). Preservation begins with consideration of
the harvesting process. The time of year and where the bamboo culm is cut has proven to
increase the durability and longevity of the culm‟s service life; culms cut in the dry season have
higher durability than culms cut in the rainy season. After flowering, bamboo has lower starch
content, decreasing likelihood of insect attacks. Insects are attracted to starch in the culms; thus,
lowering the starch content will help protect and preserve the culms. The lower portion and
outer layer of culms have higher durability than the rest of the culm; thus, the lower part of the
culm should not be cut off during harvesting in order to take advantage of its durability.
Culm characteristics provide various advantages and difficulties for preservation. The
exterior layer of the culm is made of a water repellent film, which prevents insects and other
organic material from entering from outside the culm.
As an organic compound, bamboo
requires a preservative to protect it from deterioration. Bamboo has two types of standard
preservatives, traditional and chemical (Janssen, 2000). Janssen developed a list of fundamental
rules to assist in bamboo durability and preservation:
1. Harvest bamboo when the starch content is low.
2. Select species that locals have determined suitable for the project‟s purpose.
3. Keep bamboo dry and free from soil.
4. Store culms:
Under cover.
Away from water.
In horizontal layers with room for airflow.
5. Keep bamboo in adequate storage during transportation. (Janssen, 2000)
Traditional
Traditional methods for placing preservatives on or in bamboo culms include curing,
smoking, soaking and seasoning, and lime-washing. These methods involve minimal cost and
low skill levels. For curing, bamboo is left completely intact outside to air-dry after harvesting.
25
Transpiration occurs through clumping or air-drying culms, causing starch content to decrease in
the culms (Janssen, 2000). Clump-curing, placing newly cut culms against uncut culms, is one
of the most economical ways to preserve bamboo. Then, culms are left outside to dry for four to
eight days, decreasing the starch level (Kassa, 2009).
Air-drying involves storing culms
horizontally for three to four weeks in a clean, well-ventilated warehouse or covered yard where
culms are protected from direct sunlight and humidity fluctuations (Kassa, 2009). Smoke and
ash-type solutions act as preservatives when placed on culms. Smoking involves placing culms
over a fire to allow smoke to encompass the culms, deterring fungi and insects from infesting the
culms (Janssen, 2000). Soaking and seasoning consist of completely submerging the culms in
stationary or moving water for a few weeks, extracting starches. After soaking is complete, the
bamboo is air-dried in the shade. Lime-washing protects culms from fungi by washing the culms
with limewater (Janssen, 2000). Traditional methods are proven and simple to implement; thus,
depending on material availability and application, traditional methods may be appropriate.
Chemical
All safe, cost effective, and applicable chemical methods contain boron.
Several
chemical preservative mixtures are copper-chrome-boron, boron-based fertilizer (Disodium
Octoborate Tetrahydrate with sixty-six percent active boron content) and a borax-boric acid
(Adams, 1997; Janssen, 2000). Similar to the exterior layer, bamboo culm interior layers have a
waxy film cover; thus, chemicals must enter through the end of the culm to move through and
absorb into the culm‟s fibers. Preservatives must enter through conducting vessels that comprise
only 10% of the culm‟s cross-section. Chemical preservation must occur within twenty-four
hours after cutting because conducting vessels close after twenty-four hours.
Boron-based
fertilizer has provided “good preservation” in extensive use in Costa Rica. Two methods are
used to pass these chemicals through culms, modified boucherie and dip-diffusion (Janssen,
2000).
Modified boucherie is used for whole green culms by pushing the mixture through the
culms using pressure. This process must occur within twenty-four hours after cutting to allow
the preservative to move through the entire culm. A storage drum filled with preservative is
connected to one end of the culm with rubber tubes and sleeves clamped around the culm. For
the modified boucherie process, an air pump is used to push preservative through conducting
26
vessels of the culm. The process is finished when the concentration exiting the opposite end of
the culm matches the preservative concentration in the drum. Another technique to execute this
process is to cut the inner wall of the bottom portion of the culm, hang it vertically, and infuse it
with the preservative (Janssen, 2000).
Dip-diffusion is used for sawn or split culms where the culm is placed fully in the
mixture to allow infiltration into culm vessels. The process lasts ten minutes; then culms are
removed from the preservative, wrapped in plastic sheets and left to dry. After a week, the
sheets are removed and culms vertically placed to season for one week (Janssen, 2000).
The use of chemical preservation for bamboo culms has ramifications. First, adequate
preservation relies on mixture accuracy.
Second, culms impregnated with chemical
preservatives should not be burnt. Third, overall cost of bamboo increases 30%. Fourth,
disposal of toxic waste in chemical preservatives contributes to environmental issues. But for
boron-based fertilizer, waste is considered negligible because the preservative can be mixed with
starch and sugar from culms and reused as fertilizer. Fifth, the service life of the bamboo
increases to fifteen years in the open and twenty-five years under very good conditions (Janssen,
2000).
Bamboo structures have structurally supported buildings longer than twenty-five years,
but the previous estimate considers structural integrity and serviceability of bamboo.
The
increase in bamboo service life overrides the increase in cost to purchase preservatives. Thus,
chemical preservation of bamboo is a viable option with various financial setbacks due to the
process and transportation.
27
Chapter 5 - Bamboo Design Example
This section explains the basis behind the calculations, including loads, materials, and
layout of the traditional East African, Amhara house. The bamboo design example was executed
to provide an example of a structurally engineered bamboo house. The structure is a traditional,
lowland, East African house, known as an Amhara bamboo house, which is circular with an
eight-meter diameter (Kibwage et al., 2011). The primary difference between the house in the
design example and a typical Amhara bamboo house is that the interior column is made of four
bamboo culms, not one solid timber column and columns are on a concrete pedestal or curb
connected to the foundation, not rammed earth, as shown in Figure 5.2. The structure was
designed based on the bamboo species Oxytenanthera abyssinica (Kibwage et al., 2011).
The designed structure utilizes a similar quantity of bamboo culms, approximately 320,
as provided by the INBAR document for the Amhara bamboo house.
An INBAR study
estimated the cost of a similar structure used for lodging and hotels in East Africa at
approximately $12,000. Figure 5.1 shows the house examined in the INBAR study. This house
has more material for the exterior, walls, and foundation; therefore, the design example may
have a lower cost associated with its design and construction than the house in Figure 5.1.
Figure 5.2 provides an example of a traditional Amhara house (Kibwage et al., 2011).
Figure 5.1 Similar Housing in East Africa
(Reproduced from the INBAR‟s Bamboo as a building material for meeting East Africa’s
housing needs: a value chain study from Ethiopia)
28
Figure 5.2 Traditional Amhara House in East Africa
(Reproduced from the INBAR‟s Bamboo as a building material for meeting East Africa’s
housing needs: a value chain study from Ethiopia)
Loads
Loads considered for this structure include dead, roof-live, wind, and seismic loads.
Dead loads always reside on the structure, but due to bamboo‟s lightweight nature, dead load did
not significantly impact the structure compared to wind loads except at the roof where grass
thatch adds significantly to the dead load. Roof-live loads could be neglected because of the
single story nature of the structure and ability to erect the structure without placing workers on
the roof. However, this design considered a roof-live load to account for unforeseen loading and
maintenance on the roof.
Wind loads governed over seismic loads in design of the structure,
and all of the loads were calculated based on the ASCE 7-10, which provides a basis for
designing structures. Table 5.1 and Appendix A contain further information regarding the
loads.
29
Loads
Roof Dead
Wall Dead
Roof-Live
Seismic
Wind
Force
2.16 kPa (45 PSF)
1.00 kPa (20 PSF)
1.0 kPa (20 PSF)
Ss=0.82g & S1=0.33g
150 mph
Table 5.1 Loads
Materials & Layout
Materials and layout of the traditional East African structure significantly impact the
structural design. Materials used for the roof, walls, and floors influence the member sizes
because of the dead loads introduced by various materials. Layout of architectural features
influence where the structure can reside and placement of the structure. Items discussed in this
section include bamboo specifications, roof, walls, columns, braces, floor and foundation, and
connections. Further information and drawings of the example structure are at the end of this
chapter. Drawings provide an in-depth look at the layout briefly described in this section.
Bamboo Specification
Oxytenanthera abyssinica, as discussed in Chapter 3, is the bamboo species used for the
design example of a traditional Amhara bamboo house. Bamboo will be purchased from a
supplier such as Kitil Farms and preserved by boron-based fertilizer. All of the Oxytenanthera
abyssinica bamboo members in this design are six or ten centimeters in diameter with 1.5 or 3.5
centimeter thick culm walls, respectively and harvested at three to six years of age (Kitil Farm).
These values were extracted from research determining the average diameter of Oxytenanthera
abyssinica to range from three to ten centimeters with the thickness deduced from pictures
provided by sources similar to Figure 5.3 (Kitil Farm; & UNIDO 2009).
30
Figure 5.3 Measurement of Oxytenanthera abyssinica
(Reproduced from Kitil Farm‟s Oxytenanthera Abyssinica (Solid bamboo))
Roof
The roof of the structure consists of architectural and structural elements integral to the
service life of the house. The roof is made of a grass thatch exterior, corrugated sheet metal, an
air cavity with structural elements and burlap bags of hay, and a woven layer of bamboo on the
inside for the ceiling. Grass thatch provides the house with a traditional East African look and
acts as a temperature control by absorbing the sun‟s rays, preventing the corrugated sheet metal
from directly heating the entire structure, but also adds significantly to the roof-dead load (1.2
kPa or 25 PSF). Hay-filled burlap sacks insulate the structure. In addition, the roof forms a cone
to tie to the structure with an overhang that extends out from the house 0.6 meters. This
overhang extends the bamboo wall weaving‟s service life.
Trusses supplement the structural capacity of the roof. Sixteen trusses will originate from
the center of the structure at the interior column and rest on the exterior columns at equal
spacing. The trusses are four meters long and two and one half meters high. The top chord of
the truss supports loads from the roof overhang and intermediate roof members. These trusses
could be constructed on site in an effort to minimize transportation costs or in a factory for
quality control.
31
The half-fink truss is produced from eight bamboo members of varying lengths. Figure
5.4 accurately depicts the half-fink truss used for the design example. Truss members largely
experience tension forces, which utilize the strongest bamboo mechanical property, tension. The
previously considered truss produced compression in the majority of the members, which made
the truss members larger and less efficient. Sixteen half-fink trusses complete the roof structure
with sixteen intermediate roof members at the two joints of the top chord. The roof requires
approximately 180 Oxytenanthera abyssinica culms. Calculations for the truss are in Appendix
A.
Figure 5.4 Half-fink Truss Dimensions from Design Example
(Reproduced from Author‟s Drawings)
Walls
The wall materials and layout of the structure provide bamboo and occupants protection
from the exterior environment. Wall materials from the outside to inside include a woven layer
of bamboo, corrugated sheet metal, an air cavity with structural elements and burlap bags of hay,
and a woven layer of bamboo on the inside of the wall. The majority of these materials,
including corrugated sheet metal, burlap sacks, and hay are materials available in most of East
32
Africa (Kassa, 2009). The woven layer of bamboo on the outside of the wall continues the
traditional use of bamboo weavings to cover the house and acts as a temperature regulator by
absorbing and reflecting the sun‟s rays to avoid heating the layer of corrugated sheet metal
underneath. Corrugated sheet metal provides an attachable surface for the bamboo weavings and
burlap bags and becomes a barrier between the exterior and interior environment. Burlap sacks
of hay create a layer of insulation to protect the house from the elements. The structure resides
within the layer of burlap sacks and is concealed from view.
The final layer of bamboo
weavings encloses the insulation and structure from view. The layout consists of a continuous,
circular wall around the perimeter of the traditional housing unit. Architectural elements found
in the exterior wall include one door and multiple windows. Major structural elements are
concealed in the exterior wall, including the columns and diagonal bracing. Traditionally,
interior walls are included in Amhara houses, and the interior wall is similar to the exterior wall
but without hay-filled burlap sacks for insulation. The interior wall is not shown in the drawings
shown at the end of this chapter.
Columns
Columns of this structure reside at the center of the structure and at the exterior wall.
Exterior columns are spaced equally around the perimeter of the structure at 3.05 meters and
intermediate columns spaced at 0.78 meters. The exterior columns carry truss loads, brace loads,
and experience lateral wind loads. The interior column is comprised of four culms carrying
loads from the trusses including vertical and lateral loads. The interior column allows the sixteen
trusses to bear on it through connection to a steel plate. All of the columns are 2.85 meters in
height, and the exterior columns generally contain bracing halfway up the member to decrease
the slenderness ratio (λ=KL/r per Janssen, 2000).
Braces
Diagonal braces providing lateral support to the structure are located in the exterior walls
of the structure. This layout allows for an open floor plan for the rooms within the structure.
Diagonal braces are located in each column to column space, with the exception of the entrance.
This placement provides adequate lateral resistance to the governing wind loads and flexibility
for architectural features within the walls, such as windows and doors. The diagonal braces are
4.15 meters long and extend into the space approximately thirty centimeters at all locations.
33
Member Sizes
Member
Roof Intermediate 1
Roof Intermediate 2
Top Chord of Truss
Truss Members
Braces
Columns
Wall Member-Intermediate Girt
Intermediate Column-Above Door
Door Frame Beams
Door Frame Columns
Window Frame Beams
Window Frame Columns
Diameter (cm) Wall Thickness (cm)
6
1.5
10
3.5
10
3.5
6
1.5
10
3.5
10
3.5
6
1.5
6
1.5
10
3.5
10
3.5
6
1.5
10
3.5
Table 5.2 Member Sizes
Floor & Foundation
The concrete floor slab for this project is optional based on the Amhara bamboo house
from INBAR. If the concrete floor slab is chosen, it will be cast on the site. The concrete slab
will be poured last to decrease the amount of necessary formwork because the curb acts as
formwork for the slab.
The foundation for the structure is concrete, and the curb, column cap, continuous
footing, and spread footings are cast-in-place concrete. A modular foundation was considered
until the need of forming the curb arose, and since curb must be cast-in place, the rest of the
foundation is cast-in-place. The curb and piers provide a pedestal for the columns to rest on in
order to assure that bamboo culms do not easily absorb water.
The curb extends fifteen
centimeters above the foundation wall. A foundation wall is used to prevent the curb from
cracking or experiencing differential settlement.
Connections
The glued-wood fitting connection is used for all structural connections in the traditional
Amhara bamboo house. Lashing acts as additional connection support to strengthen trusses and
lateral supporting members. In all lateral load-transferring elements, lashing provides additional
strength, stability, and flexibility to the connection and develops and transfers lateral forces to
34
adjacent members including the entire roof and columns where braces and columns connect.
Thus, this combination connection may be practical to use for the entire structure.
For design, the assumption is made that the connections are adequate for the loads
encountered. Thus, only members were analyzed for failure. Engineers desire failure to occur in
individual members to prevent total collapse.
Additional Considerations
Additional considerations not mentioned previously include providing roof vents,
lighting, and a tension ring. The best option for providing roof vents and lighting is to create a
central vent system that adds to the façade architecture by elevating the center portion of the roof
to allow for smoke to leave and light to infiltrate the space. A tension ring is a structural option
for this example but due to time limitations, was not considered in the calculations. The tension
ring would rid the need for the interior column, which provides additional floor space but
complicates construction. These additional considerations would add functionality to the design
example if implemented.
Bill of Materials
Material
Use
Wood
Fasteners
Steel
Adhesive
Steel Rebar
Concrete
Corrugated Metal
Hay
Burlap Sacks
Bamboo
Tools
Connection
Connection
Connection
Connection
Foundation
Floor Slab & Foundation
Wall & Roof
Wall & Roof
Wall & Roof
Structure
Construction
Table 5.3 Bill of Materials List
35
Drawings
This section provides the building layout and drawings. These drawings show member
sizes and design determined through calculations, shown in Appendix A. Drawings are meant to
provide a brief introduction to the structure and preliminary design and do not provide
information required to carry this design to construction.
36
37
38
39
40
41
42
43
44
Chapter 6 - Recommendations
Recommendations in this section refer to areas the bamboo industry should develop and
standardize in order to create an environment of consistency and growth allowing for frequent
use of bamboo as a structural material. Items discussed in this section include standards, farms
and plantations, connections, and service life. The bamboo industry needs to address these
issues before allowing commercial use of bamboo as a structural material.
Standards
Research has shown that bamboo‟s hindrance in structural applications is due to its lack
of a technical document that provides adequate explanation of bamboo and equations pertaining
to its implementation in structural design. Current technical documents generalize bamboo
design and construction to cover all situations, creating difficulties for structural design.
Technical documents require specific and relevant information regarding design and construction
of bamboo structures.
For bamboo to become a prominent structural material, development and publishing of a
codebook must occur, similar to the AISC or NDS. A codebook would allow direct use of
bamboo in a variety of applications.
Research has been conducted for a variety of bamboo
species, but all of this research must be centralized and used to formulate an explanation of
bamboo behavior and quantitative mechanical properties of prominent species. INBAR could
advance the bamboo industry forward by specifying bamboo species used for structures and
placing those species in a technical document to begin development of a codebook.
Farms & Plantations
Investment in farms and plantations must be developed in countries where bamboo
naturally thrives. Oxytenanthera abyssinica has the capability of growing the bamboo industry
because of its solid nature and mechanical properties; thus, a commercial plantation could grow
and supply Oxytenanthera abyssinica to East Africa. If the bamboo industry unifies from
INBAR to the farms and plantations, public awareness of bamboo and its capabilities as a
structural material will increase.
Support of farms and plantations by organizations such as INBAR and EABP must
continue to bring farms and plantations to a standard for quality control. Kitil Farms is currently
45
working in Ethiopia to promote Oxytenanthera abyssinica and build awareness of this bamboo
species, but farms and plantations need financial support and information on manufacturing
practices in order to thrive. As bamboo production becomes commercialized, the industry may
begin to receive support from additional structural and sustainability organizations.
Connections
Currently, connections pose a problem for structural bamboo design.
Variance in
connections and bamboo culms cause difficulties in understanding which connection will
perform appropriately in a given circumstance.
Thus, a connection that has high variability in
use and high strength must be developed to provide bamboo with an economical and consistent
connection. Development of a common connection would decrease design problems structural
engineers have with using bamboo as a structural material. An increase in consistency for
bamboo connections would increase the likelihood of structural engineers using bamboo as a
structural material.
Service Life
Service life of bamboo must be considered before structural use of bamboo commences.
Lack of long-term service life negates any benefit or sustainable aspect to using bamboo as a
structural material for commercial purposes. Thus, the expected service life of bamboo must be
extended longer than twenty-five years in order to encourage its use as a structural material.
Without this development, the use of bamboo as a structural material is not feasible for
commercial use.
46
Chapter 7 - Conclusion
This report responds to the need in East Africa for safe, sustainable, and affordable
housing and promotes bamboo as a structural material. East African housing needs continue to
increase because of the growing population and inability for the region to provide housing and
infrastructure at a corresponding rate. Bamboo housing provides an alternative to urban slums
and could solve the housing sector differential. The bamboo species Oxytenanthera abyssinica is
available throughout the region and is accepted and used in traditional houses in the culture.
The primary purpose of this report is to promote bamboo as a structural material.
Technical documents support use and guide design of bamboo structures, and mechanical
properties and behavior promote the advantages of bamboo as a structural material. Bamboo
technical documents include the ICC‟s Acceptance Criteria and ISO 22156, which provide
information on testing, equations, and general considerations for bamboo use as a structural
material.
Empirical design introduces various suggestions and equations that provide
preliminary knowledge on bamboo structural design.
The mechanical properties indicate
strength and behavior of bamboo, in general and the specific species Oxytenanthera abyssinica.
Bamboo behavior impacts structural design and the structure‟s ability to dissipate loads; for
bamboo, the behavior due to P-δ effects and seismic activity successfully convey the flexibility
and strength of bamboo as a structural material. Thus, the technical information, mechanical
properties, and behavior adequately support the implementation of bamboo as a structural
material.
Bamboo construction and the design example indicate bamboo‟s practicality in
construction and design. Bamboo construction utilizes simple tools but has complex connections
and preservation techniques. The design example showcases difficulty for bamboo in spanning
distances for bending and bamboo‟s parallelism to wood in layout.
Throughout this report, bamboo demonstrated its practical capabilities for construction
and design. Thus, bamboo may have the ability in the future to become recognized as a
structural material in commercial design and construction with further development of the items
in the Recommendations section. Currently, bamboo would suffice as a structural material for
the housing crisis in East Africa.
However, bamboo needs further development before
47
commercial use commences. The use of bamboo in commercial structural design may begin
when the recommendations suggested are fully developed.
48
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www.networkearth.org/naturalbuilding/bamboo.html
Ahmad, Mansur. (2000) Analysis of Calcutta bamboo for structural composite materials
(Doctoral dissertation). Retrieved from Virginia Tech University website:
http://scholar.lib.vt.edu/theses/available/etd-08212000-10440027/
Alito, Markos (2005). Bamboo Reinforcement as Structural Material for the Construction of
Low-Cost Houses in Ethiopia (Master’s Thesis). Addis Ababa University.
American Concrete Institute (ACI). (2011). ACI 318-11: Building Code Requirements for
Structural Concrete and Commentary. Farmington Hills, MI: Author.
American Institute of Steel Construction (AISC). (2011). Steel Construction Manual (14th Ed.).
Chicago, IL: Author.
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Buildings and Other Structures. Reston, VA: Author.
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Washington, DC: Author.
Arce-Villalobos, O.A. (1993). Fundamentals of the Design of Bamboo Structures (Doctoral
dissertation). Retrieved from Eindhoven University of Technology website:
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Bhalla, Suresh. (2008). Scientific design of bamboo structures. [PowerPoint slides]. Retrieved
from Bamboo Technologies website:
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Corrugated Metal, Inc (CMI). Precision Cut, High Quality Metal Roofing and Siding for
Industrial, Commercial and Architectural Projects. Retrieved upon request from
Corrugated Metals website: http://www.corrugated-metals.com/.
Didier, F., Ngapgue, F., Mpessa, M.,& Tatietse T.T. (2012). Physical characterization of two
Cameroon bamboo species: Arundinaria alpina and oxytenantera abyssinica.
International Journal of Engineering and Technology (IJET) 4(2), 82-92. Retrieved from
Engineering Journals website: http://www.enggjournals.com/ijet/docs/IJET12-04-02053.pdf
Drysdale, Robert, & Hamid, Ahmad. (2008) Masonry Structures Behavior and Design (3rd ed.).
Boulder, Colorado: The Masonry Society (TMS).
Inada, T. & Hall, J.B., 2008. Oxytenanthera abyssinica (A.Rich.) Munro. In: Louppe, D., OtengAmoako, A.A. & Brink, M. (Editors). Prota 7(1): Timbers/Bois d‟œuvre 1. [CD-Rom].
PROTA, Wageningen, Netherlands.
International Code Council (ICC). (2012). Acceptance Criteria for Structural Bamboo. Retrieved
from International Code Council website: www.icc-es.org.
International Organization for Standardization (ISO). (2001). Bamboo Structural Design (ISO
22156). Technical Committee 165.
Janssen, J.J.A (2000). Designing and Building with Bamboo (Technical Report No. 20).
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Kansas (2010). City-Data. http://www.city-data.com/states/Kansas.html.
Kassa, B.Z. (April 2009). Bamboo: An Alternative Building Material for Urban Ethiopia (M.S.
Report). Retrieved from California Polytechnic State University website:
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Kibwage, J., Frith, O.B., & Paudel, S.K. (2011). Bamboo as a building material for meeting East
Africa’s housing needs: a value chain case study from Ethiopia. Retrieved from The
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Kitil Farm. Oxytenanthera Abyssinica (Solid bamboo) [Brochure]. Nairobi, Kenya: Author.
Kramer, Kimberly (2011). Columns & Eccentricity. Lecture presented at Kansas State
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Paudel, Shyam (2011). Development and Promotion of Bamboo Housing Technology in East
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Schroeder, J.W. (July 2013). Quality Forage: Storage, Sampling, and Measuring. Retrieved
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Sharma, Bhavna (2011). Seismic Performance of Bamboo Structures (Doctoral dissertation).
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Socrates, Nicholas. Bamboo Construction. Retrieved from Academia website:
http://www.academia.edu/1586984/Bamboo_Construction.
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Masonry Structures (MSJC 2011). Boulder, CO: Author.
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http://earthquake.usgs.gov/learn/topics/mercalli.php.
The Richter Magnitude Scale. Retrieved from U.S. Geological Survey (USGS) website:
http://earthquake.usgs.gov/learn/topics/richter.php.
Trujillo, David. (2009). Axially Loaded Connections in Guadua Bamboo. In NOCMAT 2009:
11TH International Conference on Non-conventional Materials and Technologies. Bath,
UK: NOCMAT.
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Manuals: Raw Materials and Tools for Bamboo Applications. Eastern Africa Bamboo
Project: Chen, Brias, Fu, Hierold. Retrieved from website: http://www.pfmpfarmsos.org/Docs/bamboomanual_raw%20materials_eng.pdf.
United Nations Industrial Development Organization (UNIDO). (2009). Bamboo Cultivation
Manual: Guidelines for Cultivating Ethiopian Lowland Bamboo. Eastern Africa Bamboo
Project: Brias, Tesfaye, Hunde, Hierold. Retrieved from UNIDO website:
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http://www.unido.org/fileadmin/user_media/Publications/Pub_free/Guidelines_for_cultiv
ating_Ethiopian_lowland_bamboo.pdf.
United Nations Office for the Coordination of Humanitarian Affairs (OCHA). (2007).
Earthquake Risk in Africa: Modified Mercalli Scale. Retrieved from Prevention Web
website:
http://www.preventionweb.net/files/7483_OCHAROCEAEarthquakesv2071219.pdf
van der Lugt, P., van den Dobbelsteen, A.A.J.F., & Janssen, J.J.A. (2006). An environmental,
economic, and practical assessment of bamboo as a building material for supporting
structures. Retrieved from ScienceDirect website:
http://www.sciencedirect.com/science/article/pii/S0950061805001157.
Wald, D.J., Quitoriano V., Heaton T.H., & Kanamori, H. Relationships between Peak Ground
Acceleration, Peak Ground Velocity, and Modified Mercalli Intensity in California
(Earthquake Spectra, August 1999). Retrieved from Purdue University website:
ftp://ftp.ecn.purdue.edu/ayhan/Aditya/Papers/Wald%20Quitoriano%20Heaton%20Kana
mori_1999.pdf.
Worldwide Seismic Design Values (January 2011). Retrieved from U.S. Geological Survey
(USGS) website: http://earthquake.usgs.gov/hazards/designmaps/wwdesign.php.
Yu, W.K., Chung, K.F., & Chan, S.L. (2003). Column buckling of structural bamboo. Retrieved
from ScienceDirect website:
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scaffoldings. Retrieved from Bambu Brasileiro website: http://bambubrasileiro.com/.
53
Appendix A-Calculations
The load calculations were all based upon the ASCE 7-10 and the processes indicated
within the code. The calculations can be seen in the following pages. Seismic and wind were
the governing lateral loads and had some interesting occurrences regarding calculations. Wind
governed in design because of the large surface area of the structure and low-weight of bamboo.
Seismic
The seismic forces were determined using several different sources. The Modified
Mercalli Scale was used for the East African region. The maximum occurrence provided a PGA
of 0.65g (OCHA, 2007; Wald, D.J., Quitoriano V., Heaton T.H., & Kanamori, H, 1999). The
USGS‟s beta program for East Africa spectral responses provided a higher value. The highest
spectral response came from Djibouti where the Ss=0.82g and the S1=0.33g. Thus, the USGS
values were used in calculating the seismic force within the structure (Worldwide Seismic Design
Values, 2011).
Wind
The wind calculations used the ASCE 7-10 and assumed the worst-case for the structure,
which is along the coast. So the velocity of the wind taken from the ASCE 7-10 equaled 150
mph. The calculation used in design was miscalculated based upon the pressures going towards
or away from the structure. But determining the actual loads revealed that the initial,
miscalculated loads were slightly more conservative. Thus, the initial calculations were used for
the design, as is noted on one of the calculation sheets.
Design Calculations
All of the calculations for the structure are included in this section, including the
mechanical properties, roof and trusses, braces, columns, irregular members, and foundation.
These calculations largely use statics to determine the member sizes along with RISA to provide
deflections and compare the bending moments, shear forces, and axial forces within members for
the roof and trusses, braces, and columns.
54
55
Seismic
56
57
Wind
58
Wind: Updated
59
Wind: Old Calcs for MWFRS (Kd=0.85)
Conservative, thus used for calculations.
60
61
62
Wind: Circular Surface (Kd=0.95)
63
64
Wind: New Calcs MWFRS (Kd=0.85)
65
66
67
Mechanical Properties
68
69
70
RISA Custom Member
71
Roof & Truss
72
73
74
75
76
77
78
79
80
81
82
83
Forces from RISA, after comparing calculations from original truss geometry.
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
Braces
99
100
101
102
103
104
105
106
107
108
Brace Load Reversal
109
110
111
112
113
114
115
116
117
118
Columns
Exterior Column
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
Interior Column
152
153
Irregular Members
154
155
156
157
158
159
160
161
Foundation
162
163
164
Exterior Footing
165
166
Interior Footing
167
Continuous Footing
168
Appendix B – Additional Connections
This appendix provides pictures of additional connections for bamboo as indicated in
Chapter 3, including PVC type fittings, combination connections with pins and lashings,
threaded bolts, cable-tie mounts, adhesives, clamps, and others. These connections are casespecific and generally have disadvantages that cannot be overcome in design or detailing. They
have a niche but may not have the strength or flexibility to be used in other situations.
Figure B.1 PVC Type Fittings
(Reproduced from Nicholas Socrates‟ Bamboo Construction)
Figure B.2 Combination Connections with Pins and Lashing
(Reproduced from INBAR‟s Designing and Building with Bamboo)
169
Figure B.3 Threaded Bolt Connections
(Reproduced from Nicholas Socrates‟ Bamboo Construction)
Figure B.4 Cable Tie Mount Connection
(Reproduced from Nicholas Socrates‟ Bamboo Construction)
Figure B.5 Adhesive Connection
(Reproduced from INBAR‟s Designing and Building with Bamboo)
170
Figure B.6 Clamping Connections
(Reproduced from INBAR‟s Designing and Building with Bamboo)
Figure B.7 Steel Wire and Clamping Connection
(Reproduced from INBAR‟s Designing and Building with Bamboo)
Figure B.8 Double Post Connection
(Reproduced from Nicholas Socrates‟ Bamboo Construction)
171
Figure B.9 Drilled Hole Lashing Connection
(Reproduced from Nicholas Socrates‟ Bamboo Construction)
Lashing connections are captured in Figure B.10, starting from left to right. The first
connection is lashing that supports both culms but only in one direction. This is not practical due
to its high displacement and ability to only resist shear once displacement has occurred. The
second example is widely used in trusses because truss forces enable the connection to succeed.
Compressive force in the vertical culm keeps the diagonal culm in place, while lashings keep the
vertical culm relatively stable. The third connection is only used for fencing in Asia but has
simplicity that may provide practicality in other situations. The vertical culm has a tongue
portion that is wrapped around the horizontal culm and tied on the backside with lashing. The
fourth connection is another example of a traditional lashing bamboo connection (Janssen, 2000).
Figure B.10 Further Bamboo Lashing Connections
(Reproduced from the INBAR‟s Designing and Building with Bamboo)
172
Figure B.11 Bolt and Pin Connections
(Reproduced from the INBAR‟s Designing and Building with Bamboo)
173
Appendix C - Glued-Wood Fitting Connection
The glued-wood fitting connection‟s high versatility provides the bamboo industry with
an option that should improve bamboo‟s feasibility as a structural material. Figures C.1 through
C.6 give examples of this connections uses. In Figure C.1, A is the culm, B the wood fitting,
and C-E are the different type of steel plates used for this conneciton.
Figure C.1 Glued-Wood Fitting with Steel Plate Connection
(Reproduced based upon a figure from Antonio Arce-Villalobos‟ Fundamentals of the Design of
Bamboo Structures)
Figure C.2 Steel Plates Welded to Steel Ring Connection
(Reproduced based upon a figure from Antonio Arce-Villalobos‟ Fundamentals of the Design of
Bamboo Structures)
174
Figure C.3 Glued-Wood Fitting with Steel Plates, Welded Connection
(Reproduced from Nicholas Socrates‟ Bamboo Construction)
Figure C.4 Glued-Wood Fitting with Steel Plates Connected to the Foundation
(Reproduced based upon a figure from Antonio Arce-Villalobos‟ Fundamentals of the Design of
Bamboo Structures)
175
Figure C.5 Glued-Wood Fitting with Steel Plate and Pin Bundle
(Reproduced from Nicholas Socrates‟ Bamboo Construction)
Figure C.6 Wood Fitting with Steel Plate and Pin Bundle
(Reproduced from INBAR‟s Designing and Building with Bamboo)
The connection in Figure C.6 is a slight variation from the glued-wood fitting because it
uses an aluminum or steel ring to keep the plug in place and a bolt to extend the connection.
This connection has a quantitative strength of twenty-seven kilo-Newton for a 6.4 cm diameter
culm of no specific bamboo species (Janssen, 2000). This connection is viable but more labor
intensive, more expensive, and not versatile outside the culm, where the glued-wood fitting has
flexibility in use of the wood platform or steel plates.
176
Appendix D – Source Permission
SENT:
Date: Tue, 9 Jul 2013 20:39:15 -0700
Subject: Citing Master's Report
From: emyers89@gmail.com
To: nicholassocrates@live.com
Dear Nicholas Socrates,
My name is Evan Myers, and I am a graduate student in Architectural Engineering at Kansas
State University. I am currently researching for my master‟s report on Structural Bamboo Design
in East Africa.
Through my research, I have found some of your work that I would like to include in my
report. I am seeking your permission to use your work directly or as a reference for the original
composition of my report. I would like to include the following materials:
1. Text and images from your document Bamboo Construction (2012).
Additionally, I welcome any other information you would like to provide on bamboo as a
structural material. I appreciate your consideration and assistance, and look forward to your
reply. Thank you.
Evan Myers
emyers89@gmail.com
(785)819-3106
177
REPLY:
Dear Evan,
Feel free to use the material, but please do reference it as in any academic work.
Feel free to use my images also.
Please do reference and if you like I will be interested to read your work after you complete it.
Thank you for being in touch.
Best Wishes,
Nicholas
Nicholas Socrates
BA (Hons), BA (Hons), MA, MArch
w. www.nicholassocrates.com - architecture & urban design
p. www.nicholassocrates.com/portfolio
w. www.nicksocrates.com - art
l. uk.linkedin.com/in/nicksocrates/
t. @nick_socrates
e. nicholassocrates@live.com
m. 07842825312 / 07821646183
178
SENT:
From: Evan Myers [mailto:emyers89@gmail.com]
Sent: 10 July 2013 05:23
To: UNIDO-OFFICIAL-MAILBOX
Subject: Cottage Industry Manuals
UNIDO,
My name is Evan Myers, and I am a graduate student in Architectural Engineering at Kansas
State University. I am currently researching for my master‟s report on Structural Bamboo
Design in East Africa.
Through my research, I have found some of your work that I would like to include in my
report. I am seeking your permission to use your work directly or as a reference for the original
composition of my report. I would like to include the following materials:
1. Text and images from Cottage Industry Manuals: Raw materials and tools for bamboo
applications. Joint venture with CFC and INBAR. (Copyright 2008).
Additionally, I welcome any other information you would like to provide on bamboo as a
structural material. I appreciate your consideration and assistance, and look forward to your
reply. Thank you.
Evan Myers
emyers89@gmail.com
(785)819-3106
179
REPLY:
Dear Evan Myers,
Good day!
You are welcome to use the information with due credit to UNIDO.
Best wishes
Ravindra Wickremasinghe (Mr.)
Advocacy and External Relations Assistant
Room D2116
Vienna International Centre
Wagramerstrasse. 5
A-1400, Vienna
Austria
www.unido.org
180
SENT:
On Jul 10, 2013, at 4:14 AM, "Evan Myers" <emyers89@gmail.com> wrote:
Dr. Bhavna Sharma,
My name is Evan Myers, and I am a graduate student in Architectural Engineering at Kansas
State University. I am currently researching for my master‟s report on Structural Bamboo
Design in East Africa.
Through my research, I have found some of your work that I would like to include in my
report. I am seeking your permission to use your work directly or as a reference for the original
composition of my report. I would like to include the following materials:
1.Text and images from your 2010 University of Pittsburgh Dissertation: Seismic
Performance of Bamboo Structures.
Additionally, I welcome any other information you would like to provide on bamboo as a
structural material. I appreciate your consideration and assistance, and look forward to your
reply. Thank you.
Evan Myers
emyers89@gmail.com
(785)819-3106
REPLY:
Evan,
Thank you for your email. If I understand correctly, you would like to reference my dissertation? It is fine
to reference the dissertation using the appropriate citations. I suggest you speak with your reasearch or
academic advisor regarding this.
Bhavna
181
SENT:
From: Evan Myers [mailto:emyers89@gmail.com]
Sent: Friday, July 12, 2013 9:21 AM
To: Chung, Kwok-fai [CEE]
Subject: Citing Source
Professor Chung,
My name is Evan Myers, and I am a graduate student in Architectural Engineering at Kansas
State University in the United States. I am currently working on my master‟s report
on Structural Bamboo Design in East Africa.
Through my research, I have found some of your work that I would like to include in my
report. I am seeking your permission to use your work directly or as a reference for the original
composition of my report. Any sources authorized will be cited in the report based on APA
formatting. I would like to include the following materials:
1. Text and images from your work with W.K. Yu in Mechanical properties of structural
bamboo for bamboo scaffoldings (2001).
Additionally, I welcome any other information you would like to provide on bamboo as a
structural material. I appreciate your consideration and assistance, and look forward to your
reply. Thank you.
Evan Myers
emyers89@gmail.com
(785)819-3106
182
REPLY:
Thanks for your e-mail, and I have no objection to your request. I have copied your e-mail to r H C Ho,
and he will provide your further information shortly.
Regards.
183
SENT:
-------- Original Message -------Subject: Citing Source
From: Evan Myers <emyers89@gmail.com>
Date: Wed, July 10, 2013 4:47 am
To: info@kitilfarm.com
Hi,
My name is Evan Myers, and I am a graduate student in Architectural Engineering at Kansas
State University. I am currently researching for my master‟s report on Structural Bamboo
Design in East Africa.
Through my research, I have found some of your work that I would like to include in my
report. I am seeking your permission to use your work directly or as a reference for the original
composition of my report. I would like to include the following materials:
1. Text and images from your brochure, Oxytenanthera Abyssinica (Solid Bamboo).
2. Text and images from Bamboo as an alternative source of energy.
Additionally, I welcome any other information you would like to provide on bamboo as a
structural material. I appreciate your consideration and assistance, and look forward to your
reply. Thank you.
Evan Myers
emyers89@gmail.com
(785)819-3106
184
REPLY:
Dear Evan,
Your request to use material in www.kitilfarm.com for research in a master’s report
on Structural Bamboo Design in East Africa, is approved.
Please provide us with a copy of the report or its location on the internet once finalised.
Regards,
J. M. Njuguna
CEO, Kitil farm.
A solid solution to a solid problem, with the SOLID BAMBOO!!
Please come and discuss with us your bamboo investment needs.
--------------------------------------------Kitil Farm HQ, Isinya, Kajiando District
P.O.Box 762 00606 Sarit Centre, Nairobi, Kenya
Tel: +254 787456156, +254 753683129, +254 722729630, Fax: +254 2 02701803
E-mail: info@kitilfarm.com;
---------------------------------------------------------We have over 2 million bamboo seedlings, 30-60 cm tall and planted on internationally
accepted media. Ready for local, regional and international markets.
Facebook
https://twitter.com/kitilfarm
185
SENT:
From: Evan Myers [mailto:emyers89@gmail.com]
Sent: Friday, August 16, 2013 10:40 AM
To: Megan Sappenfield
Subject: Fwd: Sources
Hi,
My name is Evan Myers, and I recently contacted you(August 1, my original email was sent to
an incorrect address). I am a graduate student in Architectural Engineering at Kansas State
University. I am currently working on my master‟s report on Structural Bamboo Design in East
Africa.
Through my research, I have found some of INBAR‟s work that I would like to include in my
report. I am seeking INBAR‟s permission to use the work directly or as a reference for the
original composition of my report. Any sources authorized will be cited in the report based on
APA formatting. I would like to include the following materials:
1. Text and images from the INBAR Technical Report 20 (Copyright 2000)
2. Text and images from Bamboo as a building material for meeting East Africa’s
housing needs: a value chain study from Ethiopia (2011).
Additionally, I welcome any other information you would like to provide on bamboo. I am also
trying to contact Dr. Jules Janssen and Dr. Oscar Antonio Arce-Villalobos in order to receive
their permission as sources if they have any affiliation with INBAR. I appreciate your
consideration and assistance, and look forward to your reply.
Attached are the images I would like to include in my report from INBAR Technical Report 20
and Bamboo as a building material for meeting East Africa’s housing needs: a value chain study
from Ethiopia (2011). The images titled Cement Grout and Amhara-Traditional East African
186
House would be used in the body of the report, while the others would be placed in the
appendices for reference. Thank you for your help and have a great day.
Evan Myers
emyers89@gmail.com
(785)819-3106
REPLY:
Hi Evan,
I spoke with Oliver Frith, one of our staff members who does bamboo construction, and he said he
already told you to use any material necessary as long as you cite it properly. Please go ahead as
planned.
Thanks,
Megan
187
SENT:
Hi,
My name is Evan Myers, and I am a graduate student in Architectural Engineering at Kansas State University. I am
currently
finish
ing my master’s report on Structural Bamboo Design in East Africa.
Through my research, I have found your work that I would like to include in my report. I am seeking your
permission to use your work directly or as a reference for the original composition of my report. Any reference used
will receive proper APA citation.
I would like to include the following materials:
1. Image from Earthquake Risk in Africa: Modified Mercalli Scale.
Additionally, I welcome any other information you would like to provide on bamboo as a structural material. I
appreciate your consideration and assistance, and look forward to your reply. Thank you.
Evan Myers
emyers89@gmail.com
(785)819-3106
REPLY:
Dear Evan,
Thank you for your inquiry.
OCHA is hereby granted non-exclusive rights subject to the conditions below to republish in master report
entitled Structural Bamboo Design in East Africa the following OCHA map:
Earthquake Risk in Africa: Modified Mercalli Scale, December 2007
http://reliefweb.int/map/ethiopia/earthquake-risk-africa-modified-mercalli-scale-december-2007
The following conditions apply:
188
1. OCHA maps must be republished in their original form and cannot be modified without the express
permission of OCHA. Modification includes, without limitation, removing, resizing, or otherwise altering a
map's title, contents, legend, symbology, acknowledgements, attributions, or disclaimers. An OCHA map
may be reduced in size at the discretion of the Requestor provided the original spatial proportions are
maintained.
2. The following attribution ("Attribution") must accompany OCHA maps: "Map provided courtesy of the
UN Office for the Coordination of Humanitarian Affairs". The Attribution must be clearly readable. The
Attribution may appear alongside the map or elsewhere in the publication, so long as a link to the
Attribution on pages where a ReliefWeb map appears is provided.
3. The following disclaimer ("Disclaimer") is clearly readable on each page where a ReliefWeb map
appears: "The boundaries and names shown and the designations used on this map do not imply official
endorsement or acceptance by the United Nations". Should the Requestor reduce the size of the map so
that the Disclaimer appearing in the map is no longer clearly readable, the text of the Disclaimer must be
reproduced and appear alongside the map.
If you have any questions, please do not hesitate to contact us at maps@reliefweb.int.
Kind regards,
Dita Anggraeni
ReliefWeb Map Centre
maps@reliefweb.int
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189
Evan Myers