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Sri Lanka Institute of Information Technology

Buckling and compressive strength of concrete filled bamboo columns

Research proposal

Name : Nishan Obeysekera   

Reg. No : EN  13 5225 20

Abstract

Usually steel is used for  reinforcement in concrete structures. But replacement of steel with other suitable materials as reinforcement because of  the disadvantages like cost ,corrosion and heaviness has become a major concern. Construction industry has become  the main consumer of energy and materials in most countries. So it is important to identify natural sustainable materials like bamboo for construction industry.  Bamboo has been used as a construction material since ancient times. Bamboo is still using as a construction material ,  especially in developing countries. But using bamboo as a construction material has limited due to some uncertainties. Bamboo is a natural,high strength, cheap and also readily available material and bamboo has a rapid growth cycle. These unique characteristics make bamboo a suitable material for constructions. In this research bamboo will be subjected to investigation of using as a reinforcement material to replace steel in columns. Bamboo will be investigated as concrete filled bamboo columns. Mainly, study will be carried out to test compressive and buckling strength of concrete filled bamboo. Bamboo species called Bambusa vulgaris  which is one of the most common bamboo species in Sri Lanka will be subjected into tests. Methods to drill or break membranes at nodes inside bamboo also will be experimented. Purpose of the reseach on concrete filled bamboo columns is to compare properties of bamboo with existing reinforcement materials to check the suitability of concrete filled bamboo as reinforcements in columns.

Content

1. Introduction 1

1.1. Background 1

1.2. Aim of the research 1

1.3. Objective 2

1.4. Scope of the project 2

1.5. Thesis layout 2

1.6. Gantt chart 3

2. Literature review 4

2.1. Application of bamboo as a reinforcing material. 4

2.2. Application of concrete/grout filled bamboo as a reinforcing material. 6

2.3. Structures that have been constructed using bamboo 7

3. Methodology 9

3.1. Bamboo selection for specimens 9

3.2. Experiment overview 10

3.2.1. Shrinkage 10

3.2.2. Compressive strength test 12

3.2.3. Buckling test 14

3.2.4. Moisture content 16

3.3. Concrete for filling material 17

3.3.1. Mix design 17

3.3.2. Cube test 17

4. References 18

Acknowledgment

It is always a pleasure to remind the people who supported me for their sincere guidance I received to conduct final year research. Firstly I would like to thank my research supervisor Dr. Gobithas Tharmaraja for the supervision ,guidance and help to conduct my research up to this point. And I would like to thank all my friends and my family for their support given to continue my research in a successful manner.

List of figures

Figure 1.1- Ghantt chart 3

Figure 3.1– Bambusa vulgaris 10

Figure 3.2-Micrometer 11

Figure 3.3-Electric oven 11

Figure 3.4- Universal testing machine 13

Figure 3.5-WP 120 buckling tester 14

List of notations

I =I nitial reading

F = Final reading

σ ult  = ultimate compressive stress, in MPa (or N/mm2)

Fult = maximum load at which the specimen fails, in N,

A = Cross-sectional area

λ = Slenderness ratio

lk = Buckling length

i = Initial diameter.

F = Critical buckling force

E = Modulus of elasticity

Iy = Geometric moment of inertia

lk = Buckling length

m = Mass of specimen before drying

mo = Mass of specimen after drying

1. Introduction

1.1. Background

Bamboo is not a tree. It is a giant grass .Bamboo is the plant that has the highest growing rate in the world. There are 1000 to 1500 bamboo species in the world. Bamboo grows almost anywhere in the world. About 40 million hectares from earth are covered with Bamboo. Bamboo grows three times faster than most other species. Usually bamboo can grow completely within a short time duration like 5 years. Higher growth rate of bamboo is the reason for covering that much area from earth. Bamboo is a renewable and versatile resource and can be identified as a material with higher strength with lower weight. It requires large quantity of CO2 for its growth. So cultivation of bamboo will be ecofriendly. Species, moisture content, diameter, wall thickness, distance to node, height and age are some of the factors that affecting bamboo strength. Most common bamboo species which are using in Asia for construction industry are Bamboosa vulgaris, Dendrocalamus strictus, Dendrocalamus giganteus, Ochlandra stridula, Dendrocalamus asper and Bamboosa blumena.When it comes to Sri Lanka, most common bamboo species are Bamboosa vulgaris and Ochlandra stridula.

Bamboo is a material which used for construction purposes from ancient times and still it is a popular material for constructions. Because of unique characteristics, construction industry is always interested in bamboo as a construction material.  So, in this research bamboo will be subjected into investigations of using as a reinforcement material concrete columns.

1.2. Aim of the research

Aim of this research is to introduce and promote new methods of using bamboo as a locally available sustainable materials for construction industry.

1.3. Objective

The objective of this research is to investigate the possibility of using bamboo as a reinforcing material to replace steel in columns. The study will investigate compressive characteristics, confinement effect, hoop strength and strength enhancement of bamboo and concrete filled bamboo.

1.4. Scope of the project

Bamboo is a locally available common material which has unique characteristics when comparing with other timber. Bamboo has ideal properties to use as a construction material. In this research bamboo will be investigated on using as a reinforcement material to replace steel in columns. The uniqueness of this research from most other researches is, using concrete filled bamboo as reinforcements. Filling concrete will provide a better bond between bamboo and concrete. This will be a solution for swelling and shrinking of bamboo by absorption of moisture. Mainly in this research , compressive and buckling characteristics of bamboo will be studied and experiments will be carried on concrete filling methods inside bamboo. This study is expecting to be a important step towards using locally available sustainable materials for construction

1.5. Thesis layout

1.6. Gantt chart

Activity Month

May-16 Jun-16 Jul-16 Aug-16 Sep-16 Oct-16 Nov-16 Dec-16 Jan-17

1. Literature review

2. Methodology and test setup

3. Establishing compressive strength of bamboo

4 .Flexural test on bamboo under compression

5. Analysis of test results and nonlinear finite element analysis of the tested elements

6. Final report on study

7. Submission of the final report to the faculty of Graduate studies and Research

Figure 1.1- Ghantt chart

2. Literature review

Application of bamboo for constructions is a topic that subjected to investigations in numerous times throughout the history of Civil Engineering and construction industry. Many researches were done related to bamboo applications for constructions in many ways. When considering the construction with bamboo, some structures were built completely only using bamboo. But some occasions studies were done on application of bamboo with other materials in constructions. Most common application of bamboo is using as a reinforcing material.

2.1. Application of bamboo as a reinforcing material.

Bamboo was subjected into investigations as a reinforcing material in many occasions because of its unique characteristics to replace steel in reinforced concrete.

A study on behaviour of Bamboo as reinforcement with coconut shell as aggregate concrete in compression member with different Lengths was done by Avula Ganesh Reddy and A. Joshua Daniel of  SRM University,Chennai, India. OPC of grade 53 was used in this study. River sand passing through 2.36mm sieve was used as fine aggregate. Crushed Coconut shell passing through 12.5mm sieve size was used. Bamboo type of SP-dera was used for this study. Specimens were casted with three varying lengths of 1m, 1.15m and 1.3m and tests were carried out for three different types of columns. They are columns with conventional coarse aggregate and steel reinforcement, columns with coconut shell aggregate and steel reinforcement, columns with coconut shell aggregate and bamboo reinforcement. All the specimens were cured for 28 days and tested in a column testing machine with 40T capacity. The ultimate load carrying capacity of the columns of 1m length with steel reinforced conventional concrete was 220kN while the column with coconut shell aggregate and steel reinforcement was around 190kN and column with coconut shell aggregate and bamboo reinforced concrete was about 140kN. Columns with 1.15m length with conventional concrete and steel reinforcement were provided an ultimate load carrying capacity of 205kN while the column with coconut shell aggregate and steel reinforcement was around 165kN and coconut shell aggregate and bamboo reinforcemened column was a 140kN. The ultimate load carrying capacity of columns with length of 1.30m with  steel reinforced  conventional concrete  was 200kN while the column with coconut shell aggregate and steel reinforcement was around 155kN and column with coconut shell aggregate with bamboo reinforcement was about 135kN.From the results obtained researchers have come to the conclusions of Stiffness of the column decreased by replacing coarse aggregate, olumn with bamboo reinforcement stiffness was less than the column with coconut shell aggregate and steel reinforcement. By increasing the length the ultimate load carrying capacity of the columns were decreased.

Arpit Sethia (M.Tech Scholar) and Vijay Baradiya (Associate professor) have done a research on  “Experimental investigation on behavior of bamboo reinforced concrete member” to determine the practicability of bamboo reinforcement for concrete beams. Tests conducted were Compression Strength Testing, tension testing and beam bending test. Preparation of test specimens and testings were done using stirring concrete compression machine with a capacity of 2 ton to test the compressive strength of concrete, Universal Testing Machine (UTM) 2 ton capacity used for tension testing of bamboo.For compressive tests ,bamboo cylinders were prepared of 10 cm length  and 25mm to 30 mm diameter and about 30 of such samples were created. For beam tests, three types of  150 X 150 X 750 beams were prepared. They were plain beams, doubly bamboo reinforced beams and steel reinforced beams. IS mix design method used for concrete and slump were made lower. According to the test results mean compressive strength was obtained as 56.7 Mpa to 87.7 Mpa and mean tensile strength was obtained as 114.56 Mpa. The moment of beam specimens were obtained as  3.2 x106 kNmm to 6.1x106 kNmm. This research was concluded that it is possible to use bamboo as a reinforcement for masonry structures. The tensile strength was about 1/3rd that of steel. But it was sufficient for masonry structure and it would provide a  more economical and eco-friendly alternative.

2.2. Application of concrete/grout filled bamboo as a reinforcing material.

 “The use of bamboo as reinforcement in concrete” is a research which was done by Dr. M.M Amarathunga Bsc.(Eng) , Cey , Phd C.Eng (Department of Civil Engineering , University of Ceylon , Peradeniya) in 1970 . The research was done to investigate the feasibility of concrete filled bamboo as a reinforcement material to replace steel in concrete. Concrete was used as a filling material as a solution to swelling and shrinking. Because of shrinkage of bamboo is much higher than the shrinkage of concrete, filling concrete inside bamboo would provide a good bond between 2 materials. First the tests were conducted to check the properties of plain bamboo using species of  Dendrocalamus  stricutus and Dendrocalumus giganteus.The tensile strength between nodes was between 96.53 Mpa and 151.70 Mpa ,tensile strength at nodes was between 82.74 Mpa and 137.90 Mpa and the compressive strength was 68.95 Mpa. Then the tests were carried out to test concrete filled bamboo columns, bamboo reinforced beams and T-beams. Concrete filled bamboo columns  were subjected into compressive strength test and bamboo reinforced beams and T-beams were subjected into tensile strength test, beam bending test and deflection test. Membranes at nodes were broken by a rod and used maximum aggregate size of 3/8 inch for concrete which were using as the filling material. Shear connectors consisting 12 gauge galvanized steel wire stirrups were embedded when preparing bamboo reinforcement for beams. From the results obtained, researchers were come to the conclusions of using Bamboo as a reinforcement material has provided a high margin of safety against failure and at the design loads, the deflections were well within accepted limits.

Derek Randal Mitch (Bachelor of Science in Engineering, University of Pittsburgh, 2009) has done a research on “Structural behavior of grouted-bar bamboo column bases”. This research study on understanding the behavior of multi- and single-culm foundation connections called ‘grouted-bar column bases’. These connections consist of a reinforcing bar embedded in a concrete foundation and grout filled bamboo column. The objective of this study is to understand the behavior of these column bases in the setting of the behavior of a prototype bamboo framing system. Compression test and shear test were conducted according to ISO 22157-1 .Four pullout tests were conducted using by providing embedment lengths of 12 and 24 inches .The grout used in all of the connections was SikaGrout 212 (Sika 2003). This is a non-shrink grout .So it has permitted friction between the grout and the bamboo wall to develop. To facilitate flow into the culms, the grout was properly mixed with more water than would be normally required. Tests were carried out for single culm bases and four culm bases.The behavior of the four culm column bases was similar to the single culm columns, although the four culm specimens have shown a degree of composite action between the culms and experienced more sudden failures. For the different culm sizes used in the single and four culm tests, the capacity of the four culm bases was approximately five to ten times greater than a single culm bases. The experimentally observed value of the effective moment of inertia also showed composite action as it was twice the sum of the individual culms or twenty percent of a fully effective cross-section.

2.3. Structures that have been constructed using bamboo

Solomon K. A. (Building and Road Research Institute ) has done a research on constructing an experimental bamboo classroom building at Fumesua, Kumasi. Mechanical properties that make bamboo a good substitute for timber in some forms of construction have been highlighted and the possible use of bamboo in Ghana have been indicated. And they have mentioned that the competitive cost of materials and construction could be reduced more if labor costs and time are reduced and also by improving construction methods  . This would come with plantation bamboo, with skilled labors and the encouragement of using bamboo as a construction material.

Prasad J. et al. has done a study on cement-sand mortar panels with bamboo as reinforcing material to making low cost housing in hilly regions. Wall and roof elements were made of simple bamboo mat which do not last long due to their poor strength against static and impact loads and durability. To make bamboo mat panels, bamboo splits, made from seasoned and locally available matured bamboo, of size 10-12 mm width and 6-8 mm thickness were laid horizontally at certain distance. To limit the size of bamboo based cement-sand panels and to hold the panels vertically in position, extra timber of dimensions 75 mm x 75 mm cross-sectional sections were used horizontally  and vertically. From this study they have come to conclusion of construction of houses in hilly region using locally available material with bamboo as an economical alternative..

3. Methodology

For the tests and experiment purposes most common bamboo species in Sri Lanka expected to use. As the statistics says two most common bamboo species is Bambusa vulgaris Bambusa vulgaris is the yellow giant bamboo which can find easily around Sri Lanka.

Tests will be done to analyze the compressive strength and buckling resistance of bamboo. Both concrete filled bamboo specimens and plain bamboo specimens will be prepared for the tests. Specimen preparation, apparatus selection, performing tests, calculations, analysis and results obtaining of compressive strength test, shrinkage and moisture content will be done according to the ISO 22157-1:2004 which is the standard for determining the physical and mechanical properties of bamboo. Specimen tests of buckling test will done according to the Experiment Instructions of WP 120 Buckling test device.

According to the experimental results and background overview, properties of concrete filled bamboo columns will be compared with the plain bamboo and steel which are using for reinforcements of concrete. And the possibility of using concrete filled bamboo columns as a reinforcing material to replace steel in columns will be discussed.

3.1. Bamboo selection for specimens

Experiments will be performed using bamboo species of Bambusa vulgaris. Bambusa vulgaris is one of the most common bamboos in Sri Lanka. It is an open-clump type bamboo species. This is an endemic plant to Indochina and to the province of Yunnan in southern China, but it has been extensively cultivated in many other places and due to that it has become naturalized in several. This is one of the largest and most easily recognized bamboo species.

Figure 3.1– Bambusa vulgaris

Selection of the longest, large diameter, straight bamboos without any deformations and cracks will be done. Bamboos should be free of any decay, fungus growth or holes. Bamboo specimens will be seasoned before using.

3.2. Experiment overview

3.2.1. Shrinkage

All the specimen preparations, specimen tests, Calculation and expression of results will be done according to the ISO 22157-1 standard.

• Specimen preparation

Specimens will be prepared from internode sections of bamboo culm .Specimen height will be

100 mm and specimens will be taken from the lowest section of the culm.

,

• Specimen testing

Shrinkage will be observed in the outer diameter D, wall thickness t and length L of the specimen. Firstly on each specimen, diameter, wall thickness will be measured from 4 places. And also 2 lengths will be measured.The specimen will be allowed to dry  under  decreasing humidity with increasing temperature. Masses and dimensions will be recorded regularly, until the dimensions become constant .Then the specimens will be put into an oven at a temperature of about 103°C, until the specimens  become completely dry. Finally dimensions will be measured.

• Apparatus

Micrometer will be used  for measurements

Figure 3.2-Micrometer

Electric oven will be used to dry bamboo specimens

Figure 3.3-Electric oven

• Calculation and expression of results

Shrinkage will be calculated by the following formula

(I-F)/ I   X 100

I  =initial reading

F  = final reading

3.2.2. Compressive strength test

All the specimen preparations, specimen tests, Calculation and expression of results will be done according to the ISO 22157-1 standard.

• Specimen preparation

Specimens for compressive strength test will be extracted from the bottom part, middle part and top part of each culm. These specimens will be marked as B, M and T respectively. Four specimens will be prepared from each bottom, middle and top part of the culm. specimens will be prepared without nodes, and the length of the specimen will be  equal to the outer diameter . if the diameter  is 20 mm or less, the height should be twice the outer diameter.

Two specimens from each bottom, middle and top part of the culm will be filled with concrete and 2 specimens from each part of the culm will be kept plain. Concrete of grade 10 will be used as the filling material. Grade 20 concrete will be used because of the purpose to make bamboo reinforcements lighter in weight. Concrete filled bamboo specimens will be cured 28 days before testing.

• Specimen testing

The specimen will be placed in the testing machine and the center of the movable head should be vertically above the center of the cross-section of the specimen, and a load of 1 kN will be initially applied to set the specimen. The load will be applied continuously during the test .Movable head of the testing machine will be allowed to travel at a constant rate of 0,01 mm/s. The final reading of the maximum load will be recorded when the specimen is failing.

• Apparatus

Universal testing machine (UTM) will be used for the specimen tests to test compressive strength.

Figure 3.4- Universal testing machine

• Calculation and expression of results

The maximum compressive stress will be determined by the following formula

σ ult = Fult

A

σ ult  -ultimate compressive stress, in MPa (or N/mm2)

Fult  - maximum load at which the specimen fails, in N,

A     - Cross-sectional area

3.2.3. Buckling test

• Specimen preparation

Four specimens will be prepared for buckling test. Specimen’s slender ratio will be 60. So the length of specimen will depend on diameter of the bamboo. Two specimens will be filled with concrete and other set of specimens will be kept plane. Concrete of grade 20 will be used as the filling material.

• Specimen testing

After placing the specimen in the testing machine, the load will be applied continuously during the test. The movable head of the testing machine will be allowed to travel at a constant rate. The final reading of the maximum load, at which the specimen starts buckling, will be recorded. Specimen tests will done according to the Experiment Instructions of WP 120 Buckling test device.

• Apparatus

WP 120 buckling tester will be used for specimen tests to test buckling capacity of bamboo.

Figure 3.5-WP 120 buckling tester

• Calculation and expression of results

Length of specimens which will be used for buckling test will be obtained from slenderness ratio equation.

λ = lk/i

λ=Slenderness ratio

lk = Buckling length

i = Initial diameter.

Buckling strength will be obtained using Euler formula.

F = (π2 E Iy)/ lk 2

F = Critical buckling force

E = Modulus of elasticity

Iy = Geometric moment of inertia

lk = Buckling length

3.2.4. Moisture content

All the specimen preparations, specimen tests, Calculation and expression of results will be done according to the ISO 22157-1 standard.

• Preparation of test pieces

Test specimens for moisture content determination will be prepared immediately after each mechanical test.The number of specimens for determination of moisture content will be equal to the number of specimens for mechanical tests. The form will be 25 mm wide, 25 mm high and it will have a thickness of a wall. Specimens should be taken near to the place of failure, and should be stored under conditions where the moisture content remains constant.

• Specimen testing

The specimen weight should be measured to an accuracy of 0.01 g. Then the specimens should be dried in an oven at a temperature of 103 °C. After 24 hours, the mass of specimens will be recorded at regular intervals. Intervals should be not less than 2 hours. The drying will be completed when the difference between the successive readings  not exceeding 0.01 g.

• Apparatus

Electric oven will be used to dry bamboo specimens.

Digital scale will be used to measure weights of bamboo specimens.

• Calculation and expression of results

The moisture content MC of each specimens will be calculated using the formula below.

Moisture content = (m-m0)/m0  X100

m = Mass of specimen before drying

mo = Mass of specimen after drying

3.3. Concrete for filling material    

3.3.1. Mix design

Mix design will be done according to the IS456 standard.

In here concrete of grade 20 will be used for as the filling material. because of the purpose to make bamboo reinforcements lighter in weight and lower in cost. Maximum course aggregate size of 15mm will be used for the concrete and slump value will be made higher to achieve higher workability.

Mix propotion = 1:1.5:3

3.3.2. Cube test

Three test cubes will be prepared from the concrete which will be used as the filling material.After 28 days of curing Cube test(compressive strength test) will be done using the compression testing machine.

4. References

• Amarathunga, M.M. (1970) ‘The use of Bamboo as Reinforcement in Concrete’, Transactions of the institute of Engineers,Ceylon, vol 1, pp. 71–79.

• Mitch, D.R. (2010) Structural behavior of grouted-bar bamboo column bases

• Reddy, A.G. (2015) ‘Study on Behaviour of Bamboo as Reinforcement with Coconut Shell as Aggregate Concrete in Compression Member with Different Lengths’, Innovative Research in Engineering & Management, Volume-3, pp. 191–194.

• Sethia, A. and Baradiya, V. (2014) ‘Experimental investigation on behavior of bamboo reinforced concrete member’, International Journal of Research in Engineering and Technology, volume 3(Issue: 02), pp. 344–348.

• Solomon-Ayeh, K.A. (2010) Use of bamboo for buildings.

• Prasad, J., Pandey, B.S., Ahuja, R. and Ahuja, A.K. (2005) ‘low cost housing for hilly regions using locally available material’, Asian journal of civil Engineering, vol 6(Issue 04), pp. 257–265.

• dancilhoney (2013) Civil engineering. Available at: http://civil-resources.blogspot.com/2010/06/use-of-bamboo-as-construction-material.html (Accessed: 17 May 2016).

• ISO 22157-1 Bamboo — Determination of physical and mechanical properties — (2004)

• Gerätebau, G.U.N.T. WP 120 Buckling Test Device. .

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