Haritha IITD Bamcrete Technology
A paper published in an International Magazine
Key Engineering Materials Vol. 517 (2012) pp 203-207
Online available since 2012/Jun/26 at www.scientific.net
© (2012) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/KEM.517.203
Experimental Study of Twin Bamboo Concrete Composite Column
Under Laterally Restrained Pure Axial Loading
Korde Chaaruchandra1,a*, Ashok Gupta2,b and P. Sudhakar3,c
1Centre for Rural Development & Technology, IITD, India
2Department of Civil Engineering, IITD, India
3Haritha Ecological Institute, Andhra Pradesh, India
a chaarukorde27@gmail.com, b ashokg@civil.iitd.ac.in, c sudhakar.puttagunta@gmail.com
Keywords: bamboo concrete composite column, laterally restrained, pure axial loading
Abstract. Bamboo has a huge potential to be used under affordable housing. The beauty about
bamboo is that it has an inherent negative carbon foot print in its natural round form. This ability
can aid in developing a nearly zero carbon foot print construction using round bamboo. Also, it has
been observed in India that the traditional constructions of houses are with bamboo used as a load
distributor and not as a main load bearing element. The key to achieve higher bending strength,
required for main load bearing elements, is through enhancing the second moment of area to
achieve desired bending strength. This is achieved using a new innovative jointing technology i.e.
“Haritha IITD Bamcrete Technology (HIB)” for developing twin bamboo columns as main load
bearing elements to develop bamcrete columns (bamboo concrete composite columns). The present
study reports the performance of a twin bamboo column developed using HIB technology & tested
to 32 kN load under pure axial loading, with lateral restrains, developing compressive stress of 14
MPa in bamboo (Dendrocalamus strictus).
Introduction
A “miracle plant'' or `an ordinary plant' with `extraordinary qualities, "a
green gold", “a timber of the poor”, “a minor forest product”, “a wonder
grass” etc, are the few names earned by a grass called Bamboo. Bamboo
plant is unique in the entire plant kingdom in two ways: 1) The timber of
an individual culm matures in 3-5 years and 2) A mature bamboo bush can
yield culms with high quality timber in the form of functionally graded
light weight composite which can be harvested all through the dry season
of every year for several decades without effecting the leaf index of the
plant (bush) substantially. It is a sturdy plant that can survive and thrive
even in resource constrained marginal / degraded / wastelands.
Fig.1. Bamboo
Bamboo offers multiple utility: food through shoots, fodder through
leaves, slats and silvers for 100's of traditional house-hold (Dendro-calamus strictus)
appliances including handicrafts and energy through biomass. Thus,
bamboo being a holistic material, offers a unique challenge to be explored as a modern green
structural engineering material. This challenge, if achieved, can be directed towards developing
affordable housing & green constructions. The beauty about bamboo is that it has an inherent
negative carbon foot print in its natural round form. This ability can aid in developing a nearly zero
carbon foot print construction using round bamboo.
A single bamboo culm as a column element is used by the tribal communities across almost all
the countries, where potentially bamboo grows. In order to improve the strength of the bamboo
column, two or more bamboo is integrated together by various kinds of innovative fabrication
methods of joints (Hidalgo – Lopez, 2003 and Jayaniti, L. 1998) by traditional artisans. To enhance
the strength of the joint a composite of bamboo-concrete column (Janssen, 1995) is developed for
single culm bamboo to integrate as a linear joint or with foundation. Simon Velez, a renowned
architect of bamboo (DeBoer, 2007) has used bamboo culms as column element for construction of
pavilion, cathedrals, bus stops, houses, etc. Also, extensive study is conducted for the use of
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Novel and Non-Conventional Materials and Technologies for Sustainability
bamboo in the construction industry of South Asia as scaffolding columns (Yu W., 2003) for
building construction. However to use bamboo for structural purpose, it is required to have a higher
second moment of area for a given cross section. In order to achieve this bamboo culms are
clubbed, nailed or bolted. But this result into an inefficient design as the spacing between two
bamboos required for achieving the second moment of area plays a very important role, which
cannot be achieved by the above mentioned means. An innovative form of integrating two
bamboos is demonstrated which engages two or more bamboos together using a steel dowel
(Sudhakar 2006). This form of joint enables the bamboos to be engaged at a required spacing in
order to generate the designed moment of cross section.
Figure 1 shows a bamboo bush of Dendrocalamus strictus genera. This species is found to deliver
minimum compressive strength of 35 MPa (NBC, 2005). This species if abundantly available in
India and constitutes around 45 % of the Indian bamboo. Hence it becomes more meaningful to
explore the potential of this species in structural/ constructional applications. It is towards these
efforts that an investigations program on developing bamboo as a green engineering material for
rural housing and agricultural infrastructure is initiated. Under this program research is undertaken
on developing applications of bamboo as a main structural load bearing element. The possibilities
of developing columns with bamboo are explored and new designs of columns are developed. The
present study brings out one such effort of developing Bamcrete column as a main structural load
bearing element, the concept developed at Haritha Ecological Institute and in process of validation
at IIT Delhi. Here, only two culms of bamboo from this kind of bush of Dendrocalamus strictus are
used for developing a column of 2.7m height. An experimental investigation is undertaken on this
column to find out the strength of the column under laterally restrained pure axial loading.
Experimental Investigation
General. Figure 2 shows the schematic view of the bamcrete column which is fabricated from the
two bamboos of the Dendrocalamus strictus. This species of bamboo is slender; gradually change
from solid to hollow across diameter from bottom to top respectively with tapering in cross section
form base to top. The two bamboos of Dendrocalamus strictus having a geographical origin form
Nagpur, Maharashtra, India are rigidly connected and separated to required clear spacing ‘S’ using a
ferro-cement band of depth ‘d’ and breath ‘b’. The specimen column has length = 2700 mm, depth
d = 400 mm, breath = 300 mm, width w = 70 mm and clear band to band spacing h = 500 mm.
w
d
s
(a) Dimensions of column
Section A - A
(b) Cross sectional details
Section B - B
Fig.2. Line Diagram of the HIB column
Material Test. The bamboo sample is from the same bulk of bamboo, of which the column is
fabricated, is taken for material testing. Since the column is fabricated from the middle section of
the culm, two samples of L/d ratio 2 are taken for strength determinations of the bamboo, one each
from middle non-nodal specimen and one from middle nodal specimen. The stress Vs end plate
deformation is as shown in the figure 3.
Key Engineering Materials Vol. 517
205
Fig.3. Stress Vs End Plate Displacement of Dendrocalamus strictus (middle specimen)
Fabrication. The fabrication of the column is done in four stages. The process of fabrications is as
explained in the fig. 4. Here two bamboos are put at a required spacing. A U – stirrup is made out of
6 mm diameter mild steel rod to the required dimensions as per the spacing of the two bamboos and
the required overlapping. The stirrup is protruded inside the two bamboos & finally wrapped with
thin wire mesh to develop the connection between the two bamboos as shown in the figure 4. The
column is then casted with concrete and cured for 28 days. The final form of the column after
fabrications is as shown in figure 5.
Fig.4. Stage wise fabrication of twin
bamboo HIB column joints
Setup & Instrumentation. A new experimental test setup is developed for testing of life size
bamboo column. This equipment has an adjustable cross head for engaging a variety of lengths of
columns and enabling them to be testes under lateral restrains. This experimental column test setup
is as shown in figure 6.
Fig.5. Twin Bamboo HIB column after
fabrication & casting
Fig.6. Test Setup for axial compression of bamcrete column under laterally restrained conditions
The bamcrete column is engaged in the test setup as shown in the figure 6. The support conditions
of the column are pin – pin. The pinned support condition is developed by placing steel rod along
the centerline of the column for the bottom and then using a plumb bob line the bottom line support
is adjusted to ensure centre line pin supports for the column. Thus this ensures the pure axial
loading of the column. The column is compressed using a hydraulic jack from the bottom & in
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plane deformations are measured using 3 dial gauges. Dial gauge 2 is placed at exact centre of the
column, DG 1 & 3 are placed at the centre of the 2nd & 3rd band for measuring the in plane
deformations. A load cell is engaged between the jack and column at the bottom for measuring the
load.
Bamcrete column test
Initial explorations with short bamboo columns with four bamboo shows the maximum load of 7.5
tons by bamboo of diameter 3-4 cm with average compressive stress of 23 MPa (Supratic Gupta et
al 2007), however this makes the column too heavy. Also, some more alternatives of four bamboo
columns with steel clamps, with steel dowels & concrete composite are demonstrated & tested
which establishes the rigid band behavior of the concrete band (Korde et al, 2010). The new form of
hydraulic load applications system is developed for testing column which can be seen at the back
side of the column test setup. The column fails at an ultimate load of 32 kN. The failure is in the
concrete band at the bottom.
Fig.7. A typical load deformation curve for pure axial compression test of HIB column No. 2
Result & Discussion
The bamboo column is found to buckle under global buckling. There was no damage observed in
bamboo. The above form of failure is caused primarily because of the pin – pin conditions of
loading, wherein concentrated point load is acting on the concrete band. The concentrated point
load is acting at the bottom, where button load cell is directly engaged and at the top where a line
support is provided. The failure of the band is primarily a shear failure which can be addressed
using a steel plate before engaging the column. However, the applications of this column will
engage the connection on the band and hence this form of failure resembles the actual behavior of
the composite column. The maximum stress generated at the ultimate load of 32 kN on a twin
bamboo column of average cross sectional area of column as 2350 mm2 is 14 N/mm2.
Conclusion
The Haritha – IIT D Bamcrete Technology of developing twin bamboo columns has shown a good
potential for applications of slender bamboo (Dendrocalamus strictus) in columns. This can be
extended to other species as well for developing prefabricated bamboo columns for structural main
load bearing applications. The failure of the column at stress levels of 14 MPa shows that this
column has further potential to carry higher loads if it is able to engage the concrete and bamboo
both in the band region. Thus, the bamcrete column opens up a new possibility of developing green
columns using bamboo for structural main load bearing applications.
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Acknowledgement
This research was supported by the National Agricultural Innovation Project (NAIP), Indian
Council of Agricultural Research (ICAR) through its sub-project entitled “Bamboo as a Green
Engineering Material in Rural Housing and Agricultural Structures for Sustainable Economic
Growth” code number “NAIP/ Comp – 4/ C-2009/ 2008-2009. Also, the authors would like to
acknowledge Dr. Supratic Gupta for the mix design of concrete & M/s Bamboo Technocraft for
providing the fabrication support.
References
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Novel and Non-Conventional Materials and Technologies for Sustainability
10.4028/www.scientific.net/KEM.517
Experimental Study of Twin Bamboo Concrete Composite Column under Laterally
Restrained Pure Axial Loading
10.4028/www.scientific.net/KEM.517.203
