BEHAVIOUR OF FIBRE REINFORCED CONCRETE UNDER CYCLIC AND
FATIGUE LOADING
by
VINOD KUMAR JAIN
DEPARTMENT OF CIVIL ENGINEERING
Submitted in fulfillment of the requirements of the degree of
DOCTOR OF PHILOSOPHY
to the
INDIAN INSTITUTE OF TECHNOLOGY, DELHI
DECEMBER, 2005
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CERTIFICATE
This is to certify that the thesis entitled "Behaviour of Fibre Reinforced Concrete Under Cyclic and Fatigue Loading" being submitted by Mr. Vinod Kumar Jain to the Indian Institute of Technology, Delhi for the award of the degree of Doctor of Philosophy in Civil Engineering, is a record of bonafide research work carried out by him. Mr. Vinod Kumar Jain has worked under my guidance and supervision and has fulfilled the requirements for the submission of this thesis, which to my knowledge, has reached the requisite standard.
The matter embodied in this thesis has not been submitted to any other University or Institute for the award of any degree or diploma.
Dr. S. N. Sinha Professor
Department of Civil Engineering Indian Institute of Technology, Delhi
New Delhi, India
ACKNOWLEDGEMENTS
It is with a sense of deep gratitude and a feeling of immense pleasure that I extend my thanks to Dr. S. N. Sinha, Professor, Department of Civil Engineering for his invaluable guidance, encouragement and constructive discussions at every stage of this investigation. The cooperation and assistance of the staff of the Department of Civil Engineering, Structural Engineering Laboratory and Civil Engineering Workshop is gratefully acknowledged.
I am thankful to my wife and children for bearing with me and moral support provided by my parents during this research work.
(Vinod Ku ar Jain)
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ABSTRACT
In this study, an experimental investigation was conducted to study the behaviour of Steel Fibre Reinforced Concrete (SFRC) under cyclic: compressive, fatigue compressive and cyclic flexural loading. Six grades of SFRC consisting of two aspect ratios of 60 and 100, three percentages (0.5, 1, 1.5) of fibres with diameter 0.5mm and length 30 and 50mm were used. The study conducted in three phases. A brief review is described as follows :
In phase I of the study, 72 SFRC cylinder specimens having 150mm diameter and 300mm height were tested to investigate the behaviour under cyclic compressive loading. Three types of tests were conducted for each grade of SFRC: (i) Monotonic tests where load was increased to failure; (ii) Repeated loading — unloading in which the peak of each loading cycle approximately coincided with the monotonic curve. The stress-strain hysteresis obtained in this test possessed a locus of common points, which is a point of intersection of reloading curve with the previous unloading curve; (iii) Tests consisting repeated loading-unloading in which the repeated load was applied as in the second type of test except that in each cycle, loading and unloading were repeated several times, each time the load was released when the reloading curve intersects the initial unloading curve. This point of intersection gradually descended and stabilised at a lower bound point. Such lower bound/ points are termed as stability points s and the further cycling led to the formation of a closed hysteresis loop.
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A single general mathematical expression is proposed for the envelope stress-strain curve, the locus of common points and the locus of stability points for all six grades of SFRC. It was observed that the addition of fibres has little effect (5 to 7 percent) on the compressive strength of concrete but the ductility of concrete increases significantly. The stability point curve may be used to define the permissible stress level, when reduction in strength due to effect of repeated loading has to be considered. The maximum permissible stress obtained in this investigation is based on maximum permissible plastic deformation capacity.
The energy dissipation characteristics of SFRC cylinders under cyclic compressive loading were determined. The stress-strain hysteresis obtained by performing cyclic loading was used to study the energy dissipation capicity of SFRC. The relation between energy dissipation ratio and plastic strain in the material was used to identify the point in the load history at which the process of strength deterioration begins. The stress at this stage is close in value to the peak stress of the stability point curve.
A mathematical model is proposed to obtain the stress-strain reloading and unloading curves for SFRC cylinders under cyclic compressive loading. Both reloading and unloading curves were found to depend on the plastic strain.
In phase II of tl'ie study, 54 SFRC cylinder specimens having 150mm diameter and 300mm height were tested to investigate its behaviour under
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repeated uniaxial compressive loading between three minimum stress and various ma:.:imum stress levels, until the strains accumulated to produce failure.
The fatigue study presented in this investigation was limited to approximately upto 13500 cycles. It was found that the effect of repeated compressive loading can cause reduction in the compressive strength of SFRC as high as 28 percent of the ultimate compressive strength.
Finally in phase Ill of the study, 72 SFRC beam specimens having a cross section of 100mmx100mm and length of 500mm were tested under cyclic flexural loading. Three types of tests as done in phase I of the study were c;onducted. The envelope, common point and stability point load deflection curves were established for SFRC beams. The energy dissipation characteristics SFRC beams were also determined. The relation between energy dissipation ratio and plastic: deflection was used to identify the point in the load history at which cif strength deterioration begins.
TABLE OF CONTENTS
TABLE OF CONTENTS Page No.
LIST OF FIGURES
LIST OF TABLES xxii
NOTATIONS xxiv
Chapter 1 INTRODUCTION
1.1 General 1
1.2 Objectives and Scope of Present Investigation 3 1.2.1 Tests Under Uniaxial Cyclic Compression 4 1.2.2 Tests Under Fatigue Compression 7
1.2.3 Tests Under Cyclic Flexure 8
1.3 Summary 9
Chapter 2 LITERATURE REVIEW
2.1 Introduction 10
2.2 Types of Fibres Used in Concrete 14 2.3 Properties of Freshly-Mixed SFRC 14 2.4 Properties of the Hardened SFRC
2.4.1 Behaviour Under Static Loading 19 2.4.2 Behaviour Under Impact Loading 24 2.4.3 Behaviour Under Fatigue Loading 25
2.4.4 Creep and Shrinkage 26
2.4.5 Modulus of Elasticity and Poisson's Ratio 26
2.4.6 Toughness 27
2.4.7 Thermal Conductivity 29
2.4.8 Abrasion Resistance 29
2.4.9 Friction and Skid Resistance 29 2.5 Durability
2.5.1 Freezing and Thawing 30
2.5.2 Corrosion of Fibres-Cracks — Free Concrete 30 2.5 3 Corrosion of Fibres-Cracked Concrete 31
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2.6 Shrinkage Cracking ,... •-,,
2.7 -7 t Behaviour of Fibre Reinforced Concrete under
Cyclic Compression 33
2.8 Behaviour of Fibre Reinforced Concrete under Flexure 39
2.9 Summary 41
Chapter 3 BEHAVIOUR OF FIBRE REINFORCED CONCRETE UNDER CYCLIC COMPRESSION
3.1 Introduction 43
3.2 Properties and Composition of SFRC Mix 45
3.2.1 Design Stipulation 46
3.2.2 Preparation of Mix 46
3.3 Experimental Program 49
3.3.1 Test Specimens 49
3.3.2 Loading Arrangements 49
3.3.3 Instrumentation 49
3.3.4 Test Procedure 53
3.4 Test Results and Evaluation 54
3.4.1 Failure Mode 54
3.4.2 Stress Strain Envelope Curve 57 3.4.3 Common Point and Stability Point Curves 64
3.4.4 Analytical Curves 75
3.4.5 Concept of Cyclic Permissible Stress 77
3.4.6 Plastic Strain 82
3.5 Summary 102
Chapter 4 ENERGY DISSIPATION CHARACTERISTICS OF FIBRE REINFORCED CONCRETE UNDER CYCLIC COMPRESSIVE LOADING
4.1 Introduction 104
4.2 Energy Dissipation Capacity 105
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Chapter
4.3 5
Summary 117
CYCLIC COMPRESSIVE LOADING-UNLOADING CURVES
5.1 Introduction 119
5.2 Stress — Strain Coordinate System 120 5.3 Unloading And Reloading Stress-Strain Curves 121
5.3.1 Unloading Curves 121
5.3.2 Reloading Curves 133
5.4 Summary 146
Chapter 6 BEHAVIOUR OF FIBRE REINFORCED CONCRETE UNDER FATIGUE COMPRESSION
6.1 Introduction 148
6.2 Experimental Program 149
6.2.1 Test Specimens 149
6:7'.'1 Loading Arrangement 149
6.2.3 Instrumentation 153
6.2.4 Test Procedure 153
6.3 Test Result 157
6.3.1 Failure Characteristics 157
6.3.2 Plastic Strain 170
6.4 Summary 178
Chapter 7 BEHAVIOUR OF FIBRE REINFORCEMENT CONCRETE UNDER CYCLIC FLEXURE
7.1 Introduction 179
7.2 Experimental Program 180
7.2.1 Test Specimens 180
7.2.2 Loading Arrangement 180
7.2.3 Instrumentation 184
7.2.4 Test Procedure 184
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7.3 Test Results And Evaluation 186
7.3.1 Failure Mode 186
7.3.2 Load Deflection Envelope Curve 186 7.3.3 Common Point and Stability Point Curves 192 7.3.4 Average Experimental Curves 201 7.3.5 Concept of Cyclic Permissible Load 201
7.3.6 Plastic Deflection 206
7.4 Energy Dissipation Capacity 219
7.5 Summary 236
Chapter 8 CONCLUSIONS AND RECOMMENDATIONS
8.1 Introduction 238
8.2 Behaviour Under Uniaxial Cyclic Compressive Loading 238 8.3 Behaviour Under Fatigue Compression 240 8.4 Behaviour Under Flexural Loading 241 8.5 Recommendation For Future Study 242
REFERENCES 243
