Technical Note Series: Structural Use of Bamboo
Technical Note 1: Introduction to Bamboo
Sebastian Kaminski, MEng (Hons) ACGI CEng MIStructE, Senior Structural Engineer at
Arup Advanced Technology & Research, London, UK; Member of INBAR Task Force –
Andrew Lawrence, MA (Cantab) CEng MICE MIStructE, Associate Director at Arup
Advanced Technology & Research London; Member of INBAR Task Force – Bamboo
David Trujillo, MSc DIC CEng MIStructE, Senior Lecturer at Coventry University; Member
of INBAR Task Force – Bamboo Construction
Bamboo is a strong, fast growing and very sustainable material, having been used structurally
for thousands of years in many parts of the world. In modern times it has the potential to be
an aesthetically-pleasing and low-cost alternative to more conventional materials such as
timber, as demonstrated by some visually impressive recent structures.
This Technical Note Series brings together current knowledge and best practice on the
structural use of bamboo, covering:
1. Introduction to bamboo
2. Durability and preservation
3. Design values
4. Element design equations
The series is aimed at both developed and developing world contexts. This first Technical
Note 1 provides an introduction to bamboo and the physical characteristics that are relevant
to structural design. Basic properties along with a selection of suitable structural species are
presented, and fire resistance and specification of bamboo are discussed, along with other
considerations as to whether bamboo is suitable for a particular project.
Bamboo is widely used across the world for everything from food and medicine to furniture
and scaffolding. It tends to grow in a “belt” running through tropical, subtropical and
temperate climates around the globe, and up to 3500m altitude. There are more than 1000
species of bamboo in total, broken into two “groups”: herbaceous and woody. The former
tend to be very small-diameter and resemble grasses, while the latter are the more familiar
large diameter ones that can be used for construction and will be the focus of this Technical
Note Series. Woody bamboos can be broadly divided into two groups: clumping and
Clumping species sprout their new shoots close to the base of the existing culm,
while running species may send their shoots as far out as 30m from an existing culm. Woody
bamboo diameters vary from 10mm to 200mm, wall thicknesses from <10% of the external
diameter to completely solid, and culm heights can exceed 30m
Bamboo is a form of grass and can grow up to 25m in six months
. Each culm emerges from
the ground at its final diameter (i.e. its girth does not expand during its life), tapering as it
increases in height, and growing vertically through cell-division “telescopically” between the
nodes (i.e., the distance between nodes increases as it grows). Once fully grown, culms
typically take three to five years to mature to full strength, during which they experience
silification and lignification. After a period of five to six years, the culm’s strength begins to
Worldwide there are around 100 so-called “woody” species suitable for construction. Clumps
(a group of culms growing together) of the larger woody species normally reach peak
production after about seven years and can maintain regular cropping of around 20-25%
throughout their productive lifecycle. Figure 1 shows a bamboo plantation in Ecuador.
Figure 1: Dendrocalamus asper plantation in Ecuador
The stem, or culm, is segmented by nodes, the bands at regular intervals. The node manifests
as a diaphragm to the interior of the culm which helps to prevent buckling of the walls. The
space between nodes is known as the internode (Figure 2); the internodal spacing varies along
the culm and between species. Within the internodes, cellulose fibres and vascular bundles
run parallel to the length of the culm
, while at the nodes they intersect, with some of them
crossing into the nodal diaphragm
. For natural efficiency, these fibres are roughly six times
more numerous on the outside of the culm compared to the inside (Figure 3) making it both
denser and stronger towards the outside
. As in timber, a weak matrix called parenchyma
(which is primarily made of lignin) holds these strong fibres transversely together
, and it is
this material which normally governs the strength of a bamboo culm, especially in tension
perpendicular to the fibres and in shear. Providing a protective shell around the cellulose is a
tough silica layer about 0.25mm thick, which is relatively impermeable
. The dry density of
bamboo is typically about 500-800kg/m
, although this can vary both along the length of the
culm and as noted through the thickness of the wall.
Figure 2: Structure of a bamboo culm
Figure 3: Section through the culm wall showing variation in fibre density
Amongst non-engineers, it is a common misconception that bamboo is “as strong as steel”
(see Technical Note 3). In fact, some of the stronger bamboo species possess strength
properties similar to high grade (e.g. D40) hardwood, except in tension perpendicular to fibre
where it is weaker. Bamboo generally has very good parallel-to-fibre structural properties,
with allowable stresses in bending, tension and compression all around 15N/mm
for one of
the main species of bamboo used structurally called Guadua angustifolia Kunth
, and a wider
range of between 10-20 for most species of bamboo
. Allowable shear stresses are relatively
low at around 1.2N/mm
, which is further accentuated by bamboo’s tendency to split
the weak parenchyma matrix and the typically thin section walls – suggested characteristic
tensile strengths perpendicular to the fibre are as low as 0.46N/mm
. Because of these
properties and the hollow nature of bamboo, joints are normally the most difficult aspect to
design and also likely to be the weakest elements in the structure.
Beams should generally be limited to lightly loaded roofs and floors, heavily loaded beams
should be avoided, as the hollow cross-section risks crushing or shear failure at the supports.
It is therefore most efficient to use bamboo structural members mainly in axial tension or
compression, however, for tension members connections will be the weakest link. Figures 4-8
show a few examples of buildings where bamboo is the primary structural material.
Starch content varies between different bamboos, making some more susceptible than others
to insect attack
; however, bamboo still has less natural durability than most woods, owing to
a shortage of some naturally occurring chemicals present in wood that enhance durability
In addition, the hollow nature of bamboo means that any insect or fungal damage that does
occur is likely to reduce the total section by a larger proportion than when compared to a
solid section of timber. Therefore, permanent structures in countries at risk of termites and/or
beetles should always be chemically treated.
Suitable Structural Species
The bamboo species that have traditionally been used for construction tend to have the
• grow locally in abundance
• stronger than other local species
• large diameter (50mm–200mm)
• grow relatively straight.
• mature quickly (three to five years)
• slightly more resistant to insects and fungi (lower starch content).
• less susceptible to splitting
Table 1 presents a list of some commonly used structural species around the world.
Table 1. List of commonly used structural bamboo species around the world
Scientific name (local name) Areas found Diameter
Guadua angustifolia Kunth South America 120–160 Hollow
Dendrocalamus strictus (Calcutta) Asia 25–80 Hollow
Bambusa vulgaris Africa, Asia, South
Phyllostachys edulis (Moso) Asia 120–180 Hollow
Dendrocalamus asper (Petung) Asia, South America 80–200 Hollow
Bambusa blumeana (Spiny/Thorny Bamboo) Asia, Asia-Pacific 60-150 Hollow
Gigantochloa apus Asia 40–100 Hollow
Basic properties of bamboos used structurally are as follows
• dry density: 500kg/m
• culm heights: 6m–25m
• nodal spacing 250mm–500mm
• diameters 50mm–200mm
• elastic modulus E ~7000N/mm
• wall thickness = 10% external diameter.
Some typical design capacities of various bamboo diameters are provided in Table 2, based
on the strengths and design equations proposed in the forthcoming papers. Its variability and
the lack of proper grading methods mean that testing of members and connections will
always be needed for all but the most modest structures.
Table 2. Typical indicative design capacities of different bamboo culm diameters in different
failure modes based on a limit state approach using Technical Note 3 and 4, for Service Class
2 and Permanent loading.
∅, 5mm wall
∅, 10mm wall
∅, 15mm wall
Flexure (kNm) 0.1 0.7 2.4
Shear (kN) 0.3 1.0 2.4
Axial (kN) 10 45 100
Bamboo behaves in a similar way to timber in fire in that it chars at a slow and predictable
rate and is also a poor conductor of heat, so that the bamboo behind the charred layer remains
virtually undamaged. Though limited fire tests have been conducted
, it is possible to
assume charring rates similar to those for timber (e.g. 0.6mm/minute), and because the culm
walls are so thin it is possible to conclude that after burning for only a few minutes the thin
walls will start to lose strength rapidly. . This implies that a visually exposed bamboo
structure would only be suitable for situations where there is no fire resistance requirement
such as roofs and possibly the walls of single-storey buildings. It has occasionally been used
for two-storey dwellings
but only in locations where fire regulations are not rigorously
applied or where the bamboo is adequately protected by e.g. cement render.
Behaviour in earthquakes
It is a common misconception that bamboo as a material is somehow ‘miraculously’ good in
earthquakes. In fact as an individual element it possess several brittle failure modes which
could affect its seismic performance. Bamboo buildings have historically performed well in
earthquakes primarily because of their lightweight nature (high strength-to-weight ratio), and
secondarily because of their ability to absorb energy at connections, especially if using nails.
This has been seen after earthquakes in vernacular buildings such as bahareque
normally uses nailed connections. The flexible nature of some traditional bamboo
constructions may also be favourable in earthquakes, but this is not a characteristic that can
be easily exploited in modern constructions which tend to be heavier, have smaller movement
tolerances and require a greater certainty of resistance to earthquakes than traditional
Modern bamboo structures generally require higher strength bolted connections with mortar,
which are unfortunately relatively brittle. However, where good practice seismic design
principles are applied in conjunction with more locally ductile connections such as nails,
greater earthquake resistance and overall building ductility can be achieved
Specification of bamboo
When specifying bamboo, it is important to ensure that it comes from a sustainable source
and is harvested, procured and visually graded by a reputable and experienced organisation
(note current visual grading is very limited in detail, mostly comes from experience, and has
not yet been correlated with strength data). The following criteria should be included in a
• exact species and origin (eg guadua is the name for many different sub-species, each
with different properties, so, for example, Guadua angustifolia Kunth should be
• acceptable age range (note that this is difficult to control for, and requires using
reputable and trustworthy suppliers)
• culm length, minimum external diameter and minimum wall thickness
• straightness (1% out-of-straightness limit recommended)
• splitting (no splitting is acceptable) (this should be checked after the material has been
• no insect and fungal damage
• treatment, fumigation and seasoning.
• moisture content (recommend it is delivered dry).
Culms which are split should not be used as they are significantly weaker (in shear, bending,
axial and at the connections).
Considerations for whether bamboo is suitable for a project
Bamboo used in the round is a strong, lightweight, fast-growing material which also has a
very low embodied energy
. The following questions will help decide if bamboo, used in the
round, is a suitable material for a particular project:
• Does bamboo satisfy the architectural aesthetic?
• Is there any risk of exposure to rain or other sources of water?
• Is a suitable size and species of bamboo available locally?
• How demanding are the loads on the members and connections?
The next paper in this Technical Note Series will cover durability and preservation methods
of bamboo, which is an essential consideration when designing with this material.
Figure 4: Prototype of ZERI bamboo pavilion used in the EXPO 2000 in Hannover,
Colombia, by Simon Velez. Bamboo is Guadua
Figure 5 and 6: Jenny Garzon Bridge, Colombia, by Simon Velez. Bamboo is guadua
Figures 7 and 8: Low-cost bamboo housing in Costa Rica, part of the National Bamboo
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