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DECLARATION OF THESIS / UNDERGRADUATE PROJECT PAPER AND COPYRIGHT Author’s full name : NOOR NABILAH BINTI SARBINI Date of birth : 27 OCTOBER 1985

Title : THE EFFECTIVENESS OF INDEPENDENT BENT-UP BARS

WITH INSUFFICIENT ANCHORAGE AND INCLINED LINKS AS

SHEAR REINFORCEMENT

Academic Session : 2009-2010 I declare that this thesis is classified as : I acknowledged that Universiti Teknologi Malaysia reserves the right as follows :

1. The thesis is the property of Universiti Teknologi Malaysia. 2. The Library of Universiti Teknologi Malaysia has the right to make copies for the purpose

of research only. 3. The Library has the right to make copies of the thesis for academic exchange.

Certified by :

(SIGNATURE) (SIGNATURE OF SUPERVISOR)

851027-01-6148 ASSOC. PROF. DR. RAMLI BIN ABDULLAH (NEW IC NO.) (NAME OF SUPERVISOR)

Date : NOVEMBER 2009 Date : NOVEMBER 2009

NOTES : *If the thesis is CONFIDENTIAL or RESTRICTED, please attach with the letter from the organisation with period and reasons for confidentiality or restriction.

UNIVERSITI TEKNOLOGI MALAYSIA

√

CONFIDENTIAL (Contains confidential information under the Official Secret Act 1972)*

RESTRICTED (Contains restricted information as specified by the

organisation where research was done)* OPEN ACCESS I agree that my thesis to be published as online open access

(full text)

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“I declare that I have read through this project report and to my opinion this

report is adequate in term of scope and quality for the purpose of awarding the

degree of Master of Engineering (Civil-Structure)”

Signature : ………………………….

Name of Supervisor : ASSOC. PROF. DR. RAMLI BIN ABDULLAH

Date : NOVEMBER 2009

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THE EFFECTIVENESS OF INDEPENDENT BENT-UP BARS WITH

INSUFFICIENT ANCHORAGE AND INCLINED LINKS AS SHEAR

REINFORCEMENT

NOOR NABILAH BINTI SARBINI

A project report submitted in partial fulfillment of the

requirement for the award of the degree of

Master of Engineering (Civil-Structure)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

November, 2009

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I declare that this project report entitled “The Effectiveness of Independent

Bent-Up Bars with Insufficient Anchorage and Inclined Links as Shear

Reinforcement” is the result of my own research except as cited in the

references. The report has not been accepted for any degree and is not

concurrently submitted in candidature of any other degree.

Signature : ……………………………………….

Name : NOOR NABILAH BINTI SARBINI

Date : NOVEMBER 2009

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Dearest,

Thank you for mama, papa, siblings & friends…

Special to,

Azman Hafiidz Aji…

Thank you for always be there.

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ACKNOWLEDGEMENT

I would like to take this opportunity to dedicate a special thanks to my

supervisor, Assoc. Prof. Dr. Ramli bin Abdullah, for all his guidance, advices,

critics and knowledge given. It is so excitable and challenges in exploring

Reinforced Concrete field as it provides evidences for beauty of knowledge.

Next, my sincere gratitude goes to all fellow friends who always

provided me with support and encouragement at all times. It is nice to have

friends in all several of occasions, where many ideas will be generates.

Last but not least, I indebted my appreciation towards all technicians in

Structural Laboratory FKA UTM, family, colleagues and everybody who

involved directly or indirectly in completing this research.

Thank you.

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ABSTRACT

Shear failure in beams is caused by diagonal cracks near the supports.

Any form of effectively anchored reinforcement which intersect these cracks

will be able to resist the shear stress to a certain extend. This thesis presents the

results of an experimental investigation on six reinforced concrete beams in

which their structural behaviour in shear was studied. All the beams were cast

with the same grade of concrete and provided with identical amount of main

reinforcement. In order to investigate the contribution of the independent bent-

up bars with insufficient anchorage and varying amount as well as the inclined

links to the shear carrying capacity of the beam. Four of the beams were

provided with independent bent-up bars of different amount and anchorage,

and one with inclined links. The performances of the beams were measured in

terms of deflection, strain, diagonal cracks loads and ultimate loads. The results

show that the shear capacities of the beam with inclined links and independent

bent-up bars (4T16) of 150 mm anchorage length are higher than that of the

conventional designed beam. At the same time, independent bent-up bars of

9T16 with 50 mm anchorage length also give higher shear capacities due to its

larger shear reinforcement to cross-sectional ratio of 1.2%. Meanwhile,

independent bent-up bars of 4T16 with 50 mm anchorage length to cross-

sectional ratio of 0.8% give low shear capacities. It may therefore be suggested

that independent bent-up bars of 150 mm anchorage length be used to replace

the conventional vertical links as shear reinforcement.

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ABSTRAK

Kegagalan ricih di dalam rasuk adalah disebabkan oleh keretakan

condong yang wujud berdekatan penyokong. Apa sahaja bentuk tetulang yang

merintangi keretakan ini, akan dapat menahan tegasan ricih sehingga sampai

had yang tertentu. Kajian ini memaparkan keputusan ujikaji yang telah

dijalankan ke atas enam sampel rasuk konkrit bertetulang, yang mana

struktur kelakunannya dikaji. Semua rasuk dibina dengan kekuatan gred

konkrit yang sama, dan menggunakan bilangan dan jenis tetulang utama yang

sama. Bagi mengkaji sumbangan bar condong bebas dengan panjang tambatan

yang tidak mencukupi dan kuantiti yang pelbagai, juga perangkai condong

terhadap keupayaan rasuk menanggung ricih, empat rasuk telah disediakan

dengan kuantiti bar condong bebas serta panjang tambatan yang berbeza,

serta satu rasuk dengan perangkai condong. Kelakunan rasuk dalam

menghalang ricih dikaji berdasarkan nilai pesongan rasuk, keterikan bar

condong bebas, beban ketika keretakan condong berlaku serta bebn

muktamad. Keputusan ujikaji menunjukkan bahawa rasuk yang

menggunakan perangkai condong dan bar condong bebas (4T16) dengan

panjang tambatan 150 mm boleh menanggung keupayaan ricih lebih daripada

rasuk yang menggunakan perangkai pugak. Pada masa yang sama, bar

condong bebas dengan panjang tambatan 50 mm juga memberikan lebih

keupayaan ricih disebabkan oleh bar condong bebas yang lebih daripada 1.2 %

terhadap keratan rentas rasuk. Manakala 0.8%bar condong bebas, 4T16

dengan panjang tambatan 50 mm terhadap keratin rentas rasuk memberikan

rintangan ricih yang rendah. Justeru itu, bar condong bebas dengan panjang

tambatan 150 mm dicadangkan untuk menggantikan perangkai pugak sebagai

tetulang ricih.

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TABLE OF CONTENTS

TITLE iii

DECLARATION iv

DEDICATION v

ACKNOWLEDGEMENT vi

ABSTRACT vii

ABSTRAK viii

TABLE OF CONTENTS ix

LIST OF FIGURES xii

LIST OF TABLES xv

LIST OF SYMBOLS xvi

LIST OF APPENDICES xx

CHAPTER 1 INTRODUCTION

1.1 Background of Study 1

1.2 Problem Statement 3

1.3 Research Objectives 4

1.4 Scope of the Research 4

CHAPTER 2 LITERATURE REVIEW

2.1 Overview of Shear 6

2.2 Shear Stress in Reinforced Concrete Beams 7

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2.3 Types of Shear Failure 8

2.4 Shear in Beams without Shear Reinforcement 9

2.4.1 Mechanisms of Shear Transfer 9

2.4.2 Factors Affecting the Shear Capacity 10

2.4.3 Design Formula for Shear Stress 11

2.5 Shear in Beams with Shear Reinforcement 12

2.5.1 Function of Shear Reinforcement 12

2.5.2 Shear Resistance of a Beam with Vertical Links 13

2.5.3 Shear Resistance of a Beam with Bent-up Bars 15

2.5.4 Shear Resistance of a Beam with Horizontal 16

Web Steel

2.6 Summary 17

CHAPTER 3 EXPERIMENTAL INVESTIGATION

3.1 Introduction 26

3.2 Design of Experiment 26

3.3 Details of Specimens 27

3.4 The Materials 29

3.4.1 Concrete 29

3.4.2 Steel Reinforcement 30

3.4.3 The Mould 30

3.5 Casting and Curing 31

3.6 Test Procedures 31

CHAPTER 4 TEST RESULTS

4.1 Beam B1 44

4.1.1 Specimen Behaviour 44

4.1.2 Test Results 45

4.2 Beam B2 45

4.2.1 Specimen Behaviour 45

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4.2.2 Test Results 46

4.3 Beam B3 46

4.3.1 Specimen Behaviour 46

4.3.2 Test Results 47

4.4 Beam B4 47

4.4.1 Specimen Behaviour 47

4.4.2 Test Results 48

4.5 Beam B5 48

4.5.1 Specimen Behaviour 48

4.5.2 Test Results 49

4.6 Beam B6 49

4.6.1 Specimen Behaviour 49

4.6.2 Test Results 50

CHAPTER 5 ANALYSIS AND DISCUSSION

5.1 Influence of the Amount of Independent Bent-Up Bars 69

5.2 Influence of the Anchorage Length in Independent 71

Bent-Up Bars

5.3 Influence of the Inclined Links 72

CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS

6.1 Conclusions 77

6.2 Recommendations 78

REFERENCES 79

BIBLIOGRAPYH 81

APPENDICES 82

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LIST OF FIGURES

Figure No. Description Page

Figure 2.1 Simply supported beam 19

Figure 2.2 Shear stresses in a segment 19

Figure 2.3 Shear stresses in each sides of the segment 19

Figure 2.4 Resolved forces due the shear stress in the segment 20

Figure 2.5 Principal stresses 20

Figure 2.6 Stress path 20

Figure 2.7 Beam subjected to two point loads 21

Figure 2.8 Bending moment diagram 21

Figure 2.9 Shear failure type I 21

Figure 2.10 Shear failure type II 22

Figure 2.11 Shear failure type III 22

Figure 2.12 Shear failure type IV 22

Figure 2.13 Beam with longitudinal reinforcement 23

Figure 2.14 Dowel action of the reinforcement 23

Figure 2.15 Aggregate interlock in the concrete 23

Figure 2.16 Free-body diagram for the beam between support 24

and first inclined crack

Figure 2.17 Vertical stirrups/links as shear reinforcements 24

Figure 2.18 Vertical links are assumed to resist the crack in 24

concrete at 45° from the horizontal axis of the beam

Figure 2.19 Bent-up bars considered as members in tension and 25

concrete as members in compression

Figure 2.20 Ultimate force in bent-up bars 25

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Figure 3.1 General Illustration of specimen 34

Figure 3.2 Beam B1 35

Figure 3.3 Closed view of steel reinforcement in beam B1 35

Figure 3.4 Beam B2 36

Figure 3.5 Closed view of steel reinforcement in beam B2 36

Figure 3.6 Beam B3 37

Figure 3.7 Closed view of steel reinforcement in beam B3 37

Figure 3.8 Beam B4 38

Figure 3.9 Closed view of steel reinforcement in beam B4 38

Figure 3.10 Beam B5 39

Figure 3.11 Closed view of steel reinforcement in beam B5 39

Figure 3.12 Beam B6 40

Figure 3.13 Closed view of steel reinforcement in beam B6 40

Figure 3.14 T16 as independent bent-up bar with 150 mm 41

anchorage length

Figure 3.15 T16 as independent bent-up bar with 50 mm 41

anchorage length

Figure 3.16 T10 as independent bent-up bar with 50 mm 41

anchorage length

Figure 3.17 Machine for steel bending 42

Figure 3.18 The Mould 42

Figure 3.19 Data logger 42

Figure 3.20 Hydraulic jack 43

Figure 3.21 Arrangement of testing apparatus 43

Figure 4.1 Propagation of crack with load increment 52

Figure 4.2 Diagonal crack at 85 kN 52

Figure 4.3 Diagonal crack restrain by vertical shear links 52

Figure 4.4 Load-deflection relationships for specimen B1 53

Figure 4.5 Shear crack development in specimen B1 54

Figure 4.6 First crack in specimen B2 54

Figure 4.7 Crack in constant moment region 54

Figure 4.8 Diagonal crack in specimen B2 at 85 kN 55

Figure 4.9 Flexural failures in specimen B2 55

Figure 4.10 Diagonal crack pattern at ultimate load 55

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Figure 4.11 Load-deflection relationship for specimen B2 56

Figure 4.12 Development of crack in specimen B3 57

Figure 4.13 Crack in shear region 57

Figure 4.14 Diagonal crack restrain by independent bent-up bars 57

Figure 4.15 Load-deflection relationship for specimen B3 58

Figure 4.16 Stress-strain relationship in inner pair of 59

independent bent-up bars

Figure 4.17 Stress-strain relationships in outer pair of 60

independent bent-up bars

Figure 4.18 First crack development in specimen B4 61

Figure 4.19 Diagonal crack in specimen B4 61

Figure 4.20 Early diagonal crack development in specimen B4 61

Figure 4.21 Diagonal crack in specimen B4 restrain by 62

independent bent-up bars

Figure 4.22 Load-deflection relationship for specimen B4 63

Figure 4.23 Early crack development in specimen B5 64

Figure 4.24 Early shear crack development in specimen B5 64

Figure 4.25 Diagonal crack restrain by independent bent-up bar 64

Figure 4.26 Load-deflection relationship for specimen B5 65

Figure 4.27 First crack in specimen B6 66

Figure 4.28 Shear crack in shear region 66

Figure 4.29 Load-deflection relationship for specimen B6 67

Figure 4.30 Load-deflection relationship for specimens B1, B2, B3, 68

B4, B5 & B6

Figure 5.1 Load at first diagonal crack occurred 74

Figure 5.2 Ultimate load of specimens 75

Figure 5.3 Maximum deflection of specimens in mm 76

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LIST OF TABLE

Table No. Description Page

Table 3.1 Summary of specimens 33

Table 4.1 Results for specimens B1, B2, B3, B4, B5 & B6 51

Table 5.1 Percentages different between ultimate loads of 73

specimens compared to control specimen B1

Table 5.2 Comparison of ultimate loads between design 73

calculation and test

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LIST OF SYMBOLS

Symbol Description

As - Area of reinforcement

Asb - Area of steel in bent-up bars

Asv - Total cross-sectional area of links at the neutral axis

av - Distance between zero and maximum moment(shear span)

b - Width of a section

bv - Width of the beam for shear resistance

d - Effective depth

fcu - Characteristic strength of concrete at 28 days

fs - Service stress in reinforcement

ftt - Design tensile stress in concrete at transfer

fy - Characteristic strength of steel reinforcement

fyb - Characteristic strength of inclined bars

fyv - Characteristic strength of link reinforcement

M - Moment

sb - Spacing of bent-up bars

sv - Spacing of links

V - Shear force

Vb - Design ultimate shear resistance of bent-up bars

Vc - Total capacity to resist shear force

V - Shear stress

vb - Design shear stress resistance

vc - Design ultimate shear stress resistance

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α - Angle between a bent-up bar and the axis of a beam

β - Bond coefficient

θ - Angle

Ø - Bar diameter

° - Degree

% - Percent

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LIST OF APPENDICES

Appendix No. Title Page

Appendix 1.0 Specimen analysis 82

Appendix 2.0 Concrete mix design form 87

Appendix 3.0 Experimental Results 89

Appendix 4.0 Shear Stress Analysis 96

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CHAPTER 1

INTRODUCTION

1.1 Background of Study

Shear failure in beams is caused by the diagonal cracks near the

support. These cracks start at the bottom and extend towards the compression

zone. Any form of effectively anchored reinforcement that intersects these

diagonal cracks will be able to resist the stress to a certain extend. In practice,

shear reinforcement is provided in the forms of vertical links or combination

system of vertical links and bent-up bars.

In conventional system of shear resistance, vertical links play an

important role in effectively restrains the formation of shear cracks in

reinforced concrete beams. This system is preferred due to installing and

fabricating simplicity. However, closed arrangement of shear links from

various elements at elements intersection (near the support) causes problems in

fixing.

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The use of bent-up bars along with vertical links as shear reinforcement

had been practiced before. In situations where the tensile reinforcement is

required to resist bending moment, only some of the rest was bent-up in the

region of high shear to form the inclined legs of shear reinforcement. For

example, beams which have four bars as the main tensile reinforcement at mid

span, two bars may be bent-up diagonally and act as shear reinforcement, while

the other two would be left to continue to the support.

However, its application has been less preferred nowadays. The

difficulties to form the bent-up bars and required adequate amount of main

reinforcement make it rarely used in construction. It is because, in beams with

small number of main bars provided, the bent-up system is not suitable because

insufficient amount of reinforcement would be left to continue to the support as

required by the code of practice.

In this study, an alternative to overcome those problems is using

independent bent-up bars. The application of independent bent up bars give

strong resistant to the shear cracks due to better redistribution of internal

forces across the cracks. In addition, this phenomenon leads to restrict the

growth of the inclined cracks and maintain the interface of shear transfer

effectively compared to conventional shear resistance system.

The selection of the amount of independent bent-up bars to be used is

important. If the amount is too little, those bars will yield at the formation of

inclined cracks and cause the beams to fail. This situation is dangerous to the

structures. However, too much amount of independent bent-up bars caused a

shear-compression failure without the yielding of independent bent-up bars. It

meaning that, the beams element will fail in flexure. This situation is not

suitable if the objectives of the study are to determine the shear characteristic

and contribution of independent bent-up bars to the shear resistance. Besides,

in real situation, excessive amount of independent bent-up bars cannot give

3

profits to the project. Thus, an adequate amount of independent bent-up bars

should be obtained sufficiently.

The anchorage length plays an important aspect of independent bent-up

bars. If the anchorage length is too long, the position of the successive

independent bent-up bars will be apart from the first layer. The question is

that; can the inclined cracks passing the second layer and if it is not, it is such a

waste to install those independent bent-up bars at the second layer. In this

study, specimens are prepared with different anchorage length to study the

anchorage length contribution to the shear resistance. The anchorage length is

decided based on experience and engineering sense.

1.2 Problem Statement

The congestion near the support due to closed arrangement of shear

links causes problems in fixing the reinforcements. For the application of bent-

up bars, it has been less preferred nowadays. The difficulties to form as bent-up

bars and required adequate amount of main reinforcement make it rarely used

in construction. In beams with small number of bars provided, the bent-up

system is not suitable because insufficient amount of reinforcement would be

left to continue to the support as required by the code of practice. Due to this

problems as well as the conventional shear reinforcement, the use of

independent bent-up bars and inclined links arranged in the high shear region

have been studied.

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1.3 Research Objectives

The objectives of this research are :

i) To study the effectiveness of independent bent-up bars as shear

reinforcement compared to conventional system.

ii) To study the effectiveness of inclined links as shear reinforcement

compared to conventional system.

iii) To compare the shear resistance of independent bent-up bars plus

nominal links with inclined links.

iv) To study on the effectiveness of independent bent-up bars with different

anchorage length.

v) To study the effects of different amount of independent bent-up bars as

shear reinforcement.

1.4 Scope of the Research

This study is based on experimental investigation within the scopes listed

below:

i) The test were carried out on six specimens of reinforced concrete beams

of identical size of 2300 mm length, 200 mm width and 250 mm of

overall depth.

ii) All specimens were provided with identical amount of main

reinforcements that is 3T16 with 2T10 as hanger bars.

iii) All specimens were tested to failure with two point load at distance 650

mm from beam edges.

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iv) The concrete compressive strength for all specimens is in the ranges of

35±0.5 N/mm2.

v) The inclination of independent bent-up bars and inclined links are 45° to

the longitudinal axis of the beam.

vi) The variables in the specimens are the amount of independent bent-up

bars, anchorage length of independent bent-up bars, arrangement of

independent bent-up bars and the inclined links as shear reinforcement.