TH-1074

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F L E X U R L B E H V I O U R O F R E I N F O R C E D C O N C R E T E B E M S

M D E W I T H C O I R O R S T E E L F I B R E C O N C R E T E

VISHAL CHAND JAIN

Submitted in fulfilment of the

requirements of the Degree of

DO TOR OF PHILOSOPHY

to the

Indian Institute of Technology Delhi

DEPARTMENT OF CIVIL ENGINEERING

INDIAN INSTITUTE OF TECHNOLOGY DELHI

NEW DELHI 11 16

SEPTEMBER 1983

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CERTIF ICATE

This is to certify that the

t h4s, entitled tFLE XUR A L

BEHAVI OUR OF REI NF ORCED CONCRETE BEAMS MADE W TH COI R OR

STE E L FIBR E C ONC R E TE being submitted by Mr. Vishal C hand

Jain to the Indian Institute of Technology Delhi in ful-

filment of the requirements of the Degree of Doctor of

Philosophy, is a record of bonafide research work c ar r i ed

out by him under our guidance and supervision.

To the best of our knowledge, the thesis has reached the

requisite standard. The material presented in this thesis

has not been submitted in part or full to any other

University or Institution for award of a degree or

diploma.

( 0 . P J J a i n )

Ibrmerly Director,

Indian Institute of Technology,

Del hi .

Ahuja)

Professor of Civil Engineering

Indian InstitUte of Technology

Delhi.

New Delhi,

(S.,Krishnamoorthy)

16th Sep ,

1

983.

Professor of Civil Engineering

4

ndian Institute of Technology

Delhi.

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A C K N O W L E D G E M E N T S

I have the privilege of working under the guidance of

Prof. O.P. Jain on several important projects dtring the

last twenty five years. I would like to express my sincere

gratitude to him for his inspiration and guidance at all

stages of this work.

I am thankful to Prof*B.M.Ahuja and Prof.,S.Krishnamoorthy

for suggesting an interesting and useful problem for research.

I

am

grateful to them for their guidance and encouragement at

all times. I am especially thankful to Prof.S.Krishnamoorthy

for carefully checking the manuscript.

I am thankful to the staff of Concrete and Structures

Laboratory, Strength of Materials Laboratory, Fibre Testing

Laboratory, and Civil Engineering DepaiLnient Workshop of

Delhi, for their cooperation and help. Special thanks

are due to Messers Shiv Lal Sachdeva, Shree Chand, Badan Singh,

Badle Ram, C.L.yerma and G.K. Mehta for their assistance in

experimen tal w ork.,

I am extremely grateful to my brother Ashok for preparing

t he t r ac i ngs ,

and for his help in compiling the thesis. He

also assisted me in cutting the coir fibres.

I em thankful to the Head of Civil Engineering Department

and the Vice Chancellor

;

University of Roorkee, for

granting me study leave to work at

Delhi I am also

thankful to Mr.R.C.Sharma for typing the thesis neatly

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iii

A B S T R A C T

The work relates, principally,to the flexural behaviour

of R.C. beams made with fibre concrete. The relationship

between fibre content and workability of fibre concrete

m x es ha s al s o be en s t udi e d, s o t h at wor k abl e m x es o f

specified fibre contents

c a n be ma de . T he wo r k , f ur t he r ,

includes study of the stress-strain

be ha vi o ur of pl a i n and

fibre concretes in compression, as this directly influences

the

be ha vi o ur o f a

R . C . me mb e r .

Two

types of fibres, namely steel and coir, have been used.

Steel fibres have been mostly favoured for structural use.

Coir fibres have been chosen because these are relatively

i nex pe ns i ve, ar e abunda nt l y avai l abl e i n I ndi a , a nd ha ve

adequate durability in a cement concrete matrix.

The Expe r i me nt a l P r o gr a mme i nc l uded V* - 1 3 t e s t s o f p l a i n and

fibre concrete mixes,

t e s t s f or c ompr e s s i v e s t r e ngt h

and

modulus of rupture, tests to obtain

c ompl et e s t r es s - s t r a i n

c ur v es of c onc r e t e i n c ompr e s s i on, a nd t e s t s of r e i n f or c e d

fibre concrete beams in flexure under a mo onic loading

upt o f a i l ur e .

A method has been developed to

d e t e r m ne t h e max i mu m

volume fraction of fibres, which can be included in a given

mix for desired workability.

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iv

A performance index for fibre concrete, called Ductility

Factor, has been postulated. This factor is a measure of

the ductility in compression achieved with the addition of

fibres. A relation between ductility factor and volume

fraction of fibres has been obtained.

The idealised stress-strain curve of fibre concrete has

been related to that of

pl a i n conc r et e by a s i ngl e

parameter,

namely, the ductility factor of fibre concrete.

Tests on reinforced fibre concrete beams show that, in the

range of service loads, addition of steel fibres results

in reduced deflections and crack widths, whereas coir

fibres produce little influence at this stage. At ultimate

l oad, t he beams exhi bi t i nc r eas ed duc t i l i t y i f t he f i br e

c ont ent i s l e s s t han

a critical fibre content whose

value depends on percentage of tension steel.

A

method has been developed to determine the stiffening

effect of fibres in the tension zone of a R.C. beam,

which is an extension of the method adopted by British

Code, CP110:1972, to estimate curvature of a cracked

section.

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C O N T E N T S

Chapter

Page

CERTIFICATE

A C K N O W L E D G E M E N T S

A B S T R A C T

LIST OF SYMBOLS

1-

D i 7 R O D U C T I O N

1.1 General

1 2 Fibre Concrete

MOO

2

1.3 Need for the S t u dy

3

1.4 Scope of Study

/Oa 4

1.5 Brief Outline of E :Terimental Programm e

4

2 -

L I T E R A T U R E R E V I E W

2.1 Introduction

24,2 Fibre Concrete

2 3

C oncrete M atrix

2 4

Fibres

2 . 4 0 .

Steel Fibres

2 .4.2 Polypropylene

ibres

2.4.3 vegetable Fibres

2 .5 Workability and F ibre C ontent

2 6

Behaviour of Fibre Concrete in Tension,

Flexure , and C ompression

2.7 Strength of Fibre Concrete

2.7.1 Tensile Strength

2.7..2 Flexural Strength

2 7 . , 3

C ompressive Strength

2 .7.4 Im pact Strength

2 7..5 F atigue Strength

28

T heory of Fibre R einforcement

O

00

6

9

1

0

12

13

14

... 16

18

4 00

19

.

doe

19

. . . p a

. . .

2 1

... 22

... 22

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vi

Chapt er

Page

2. 8. 1 Cr ac ki ng St r engt h

. . .

2 3

2. 8. 2 Pos t - c r ac ki ng Tens i l e St r engt h

OIPO

5

2. 8. 3 Pos t - c r ac ki ng Fl exur al St r engt h

. . . 27

2. 8. 4 Cr i t i c al F i br e Cont ent f or

St r e ngt heni ng i n T ens i on or F l ex ur e

OVO

29

2. 9 Use i n Re i nf or ced o r P r es t r essed Concr e t e

Member s

OM

29

Tabl es

4. . 32

F i gur es

. . .

3 4

MATERLALS

3. 1 I nt r oduc t i on

11

6

32

Coar se Aggr egat e

6

3 . 3

F i ne Aggr egat e

440,

7

3. 4 Cement

37

3. 5 Coi r F i br es

Y

3 7

3 : 6

St eel F i br es

9

3 . 7

Rei nf or c i ng Bar s

4 0

T abl e s

Of

42

F i gur es

40

47

4 -

FI BRE CONTENT AND WORKABI L I TY


SO

1

42 V- B Test o f Concr et e Mi xes

0 2

4 . 3

Pl ot s of of ver s us l og ( t )

. . .

r7

0

4 . 4

Expr es s i on f or m

5 3

4 . 5 Det er m nat i on of n1

n2

c

a

p a n d c

f

. . .

5 5

4 . .

6

Rel at i on bet ween o

f

and t

4' 57

Tabl es

. . . 59

F i gur es

0114 65

COMPRESSI VE AND FL EXURAL STRENGTHS


000

9

5 . 2 P l ai n Conc r et e Mi x

9

5 . 3 F i br e Conc r e t e Mi x es

IWO

0

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vii

Chapter

5 . 4 Ca s t i ng and Cur i ng

Page

71

5 . 5 Co mpr e s s i v e St r e ngt h

72

5.6 modulus of Rupture

. . .

7 3

T abl e s

75

6

STRESS- STRAI N BEHAVI OUR

6.1

I nt r oduc t i on

7 7

6.2

Pr epar at i on of Tes t Cyl i nder s

7 8

6.3

Test Set-up

7 8

6.4

Test Results

30

6.5 Discussion of Test

Res ul t s

8

6.6

Stress Block Parameters and Ultimate

Compressive Strain in Flexure

82

Tabl es.

84

F i gur es

97

7

DUCTILITY FA CTOR AND IDEAL ISED

T I R E S S

STRAIN CURVE


7. . 2 Duc t i l i t y F ac t or

101

101

7. 3

Relation between D

_ and o

f

103

7.4

Idealised Stress-Strain Curve of Fibre

Concrete

104

Tables

105

F i gur es

108

8

TES TS OF REI NFORCED F I BRE CONCRETE BEAMS

I N FL EXURE


.4S

110

8. . 2 De t a i l s o f Tes t Beams

. . . 110

8.3

Casting

and Cur i ng of Beams

8.4

Handl i ng of Beams

4

4 : :

11

14

8..5 Preparation for Tcsting

O00

114

8 6

Experimental Set-up

060

115

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viii

Page

hapter

8.7

Test Procedure

8.8

Cube Strength of Concrete

8.9

Test Results

8.1

0

Discussion of Test Results

Tables

Figures

9

NALYSIS OF TE ST BEAMS

di

1

8

120

120

121

125

154

9 . 1 Introduction

190

9.2 Relevant Material Data

191

9.2.1 Compressive Strength of Concrete

4 . .

91

9.2.2

Modulus of Rupture of Concrete

192

9 . 2 . 3

Modulus of Elasticity of Concrete....

193

9 . 2 . 4

Concrete Strain and Stress

Block Parameters at Flexural

Strength

1 9 4

9.2.5 Stress Block Parameters

195

9 3

Method of Analysis

196

9.3.1 Determination of M

cr

and 0

cr

96

9.5.2

Determination of M

u

and W

u

196

9 . 3 . 3

Determination of M and W for a

given f

s

9 3

9 . 3 . 4

Determination of f

t

at a given

load stage

1 9 9

9 . 4

values of f

t 202

Tables

2 0 4

Figures

230

10-

STIFFE NING AND DUCTILITY OF R . C. SECT IONS

'WITH FIBRE CONCRET E

10.1 Introduction

231

10.2 Expression for f

t

232

10.3 Stiffening of R.C. Sections with

Fibre Concrete at Service Loads

2 3 4

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Chapter

11

10.4 Ductility of R.C. Sections with Fibre

Concrete

10.5 Critical Fibre Content for Ductility

Tables

Figures

O N L U S I O N S

PLATES

R E F E R E N E S

AUTHO R S BIO D ATA

x

Page

235

236

238

240

241

249

254

263

TH-1074

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