BOND BEHAVIOR OF GROUTED SPIRAL AND SPLICE...
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BOND BEHAVIOR OF GROUTED SPIRAL AND SPLICE CONNECTION UNDER DIRECT AXIAL AND FLEXURAL PULLOUT LOAD SEYED JAMAL ALDIN HOSSEINI UNIVERSITI TEKNOLOGI MALAYSIA
Transcript of BOND BEHAVIOR OF GROUTED SPIRAL AND SPLICE...
BOND BEHAVIOR OF GROUTED SPIRAL AND SPLICE CONNECTION
UNDER DIRECT AXIAL AND FLEXURAL PULLOUT LOAD
SEYED JAMAL ALDIN HOSSEINI
UNIVERSITI TEKNOLOGI MALAYSIA
BOND BEHAVIOR OF GROUTED SPIRAL AND SPLICE CONNECTION
UNDER DIRECT AXIAL AND FLEXURAL PULLOUT LOAD
SEYED JAMAL ALDIN HOSSEINI
A thesis submitted in fulfilment of the
requirements for the award of the degree of
Doctor of Philosophy (Civil Engineering)
Faculty of Civil Engineering
Universiti Teknologi of Malaysia
AUGUST 2015
iii
“To my beloved parents and my lovely wife, for their encouragement and support”
iv
ACKNOWLEDGEMENT
First of all, gratefulness of thanks to our creator, “ALLAH” for his
continuous blessing, which make this work neither the first nor the last.
Special thanks to Assoc. Prof. Dr. Ahmad Baharuddin Abd Rahman for
giving this opportunity to work under his supervision and for sharing his great
knowledge and experience with me.
I would like to convey my deepest gratitude to Mrs. Zeinab Deriss for her
support and encouragement. Appreciation is also extended to all people who gave me
heartfelt corporation and shared their knowledge.
Finally, I would like to send my deep appreciations to my family who
brought me up with love.
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ABSTRACT
The conventional grouted connections with corrugated aluminium sleeves
have been used widely in precast concrete construction. The main problem of the
conventional grouted sleeve connections is the need for long embedded lengths
reinforcement rebars to achieve full continuity. There is a tendency for the long
rebars to touch the sleeve wall and subsequently preventing penetration of grout
around the rebar. Since the grout inside the sleeve cannot be inspected after
installation, there is doubt that the main rebar is fully bonded. This study proposed a
grouted spiral connection which can overcome the use of long embedded length of
connected rebars. The main objective of this study was to investigate the effect of
spiral confinement on the bond stress-slip relationship. The experimental program
was carried out in two phases, Phase I and Phase II. In Phase I, a total of thirty-six
spiral connections were subjected to increasing direct axial pullout loads. Then, in
Phase II, a total of twelve beams comprising spiral connections were subjected to
flexural pullout loads. Parameters considered in this study were pitch distance and
diameter of spiral connections. The experimental results showed that the use of
smaller pitch distance and spiral diameter resulted in higher bond strength. However,
the spiral diameter had more dominant confinement effect such that it increased the
bond strength of direct and flexural pullout tests very dramatically by 34.5% and
40%, respectively. In addition, lower bond strength from the beam tests was reported
as compared to the axial pullout tests. The bond strengths obtained from the flexural
pullout tests were within the range of 0.74 to 0.79 times the bond strengths of the
axial pullout tests. Finally, analytical equations were proposed to express the bond
stress-slip relationship and bond strength of the grouted spiral connection.
.
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ABSTRAK
Penggunaan sambungan grout konvensional dengan salur aluminium telah
digunakan secara meluas dalam pembinaan konkrit pratuang. Masalah utama
daripada sambungan grout konvensional adalah keperluan panjang tambatan untuk
mencapai kekuatan penuh. Terdapat kecenderungan untuk tetulang bar yang panjang
menyentuh dinding salur dan seterusnya menghalang penembusan grout di sekitar
bar. Oleh kerana grout di dalam salur tidak boleh diperiksa selepas pemasangan,
terdapat keraguan tetulang utama tidak terikat sepenuhnya. Kajian ini mencadangkan
satu sambungan gegelung grout yang boleh mengatasi masalah penggunaan tambatan
tetulang keluli yang terlalu panjang. Objektif utama kajian ini adalah untuk
menyiasat kesan kurungan gegelung ke atas hubungan tegasan ikatan-gelinciran.
Program eksperimen telah dijalankan dalam dua fasa, Fasa I dan Fasa II. Dalam Fasa
I, sejumlah tiga puluh enam sambungan gegelung dikenakan tindakan beban
tegangan paksi. Di dalam Fasa II, sebanyak dua belas rasuk dengan sambungan
gegelung dikenakan beban lenturan. Parameter yang dikaji adalah jarak antara
gegelung dan diameter gegelung penyambung. Keputusan eksperimen menunjukkan
bahawa penggunaan jarak antara gegelung dan diameter gegelung yang kecil dapat
meningkatkan kekuatan ikatan. Bagaimanapun, kesan diameter adalah lebih
dominan dalam meningkatkan kekuatan ikatan dengan peningkatan sebanyak 34.5%
dan 40% masing-masing bagi ujikaji beban paksi dan lenturan. Di samping itu,
kekuatan ikatan yang lebih rendah didapati berlaku pada ujian rasuk berbanding
dengan ujian tegangan paksi. Kekuatan ikatan yang diperolehi daripada ujian
lenturan adalah dalam julat 0.74-0.79 kali ganda kekuatan ikatan tegangan paksi.
Akhirnya, persamaan analitik telah dicadangkan untuk menyatakan hubungan
tegasan ikatan- gelinciran dan kekuatan ikatan bagi sambungan gegelung grout.
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TABLE OF CONTENTS
CHAPTER TITLE PAGE
DECLARATION ii
DEDICATION iii
AKNOWLEDGMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES xii
LIST OF FIGURES xiv
LIST OF SYMBOLS xx
LIST OF APPENDICES xxii
1 INTRODUCTION 1
1.1 Introduction 1
1.2 Background of Study 5
1.3 Problem Statements 8
1.4 Objective 10
1.5 Scope of Research 11
1.6 Thesis Organization 13
2 LITERATURE REVIEW 14
2.1 Introduction 14
2.2 Bond Mechanisms 15
2.3 Bond of Steel Reinforcement Bars 17
2.3.1 Mechanical Interlocking 18
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2.3.2 Friction 19
2.3.3 Chemical Adhesion 19
2.4 Factors Influencing Bond Behavior 19
2.4.1 Confinement 20
2.4.1.1 Previous Research on the
Confinement
21
2.4.1.2 Effect of Confinement on the
Bond Failure
27
2.4.2 Strength of Bonding Material 29
2.5 Previous Research Studies on Grouted
Connections
30
2.6 Experimental Investigation on the Bond Force
of Splice Bars
35
2.6.1 Comparison with ACI 38
2.7 Bond Stress-Slip 40
2.7.1 Analytical Model of Bond Stress-Slip 40
2.7.1.1 BPE Model 41
2.7.1.2 Haskett et al.’s Model 43
2.7.1.3 Soroushian’s Model 44
2.7.2 Equation od Bond Stress-Slip 46
2.8 Standard Bond Tests 48
2.8.1 Review of Experimental Setups of
Direct Pullout Test
49
2.8.1.1 Single Pullout Test 49
2.8.1.2 Double Pullout Test 50
2.8.2 Review of Experimental Setups of Beam
Tests (Flexural Pullout Test)
51
2.9 Summary 53
3 RESEARCH METHODOLOGY 55
3.1 Introduction 55
3.2 Preliminary Study 58
3.3 Direct Pullout Tests 61
3.3.1 Details of Specimens 61
3.3.1.1 Trial Specimens 61
3.3.1.2 Grouted Spiral Connections 63
3.3.2 Preparations of Specimens
65
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3.3.3 Experimental Setup of Direct Pullout
Load Test
67
3.3.4 Data Acquisition System 68
3.4 Experimental Setups of Flexural Pullout Tests 69
3.4.1 Details of Specimens 70
3.4.2 Preparations of Specimens 73
3.4.3 Specifications of Material for the Beam
Specimens
81
3.4.4 Specifications of Material for the
Grouted Spiral Connections
82
3.4.5 Instrumentations 85
3.4.5.1 Measurement of Load 85
3.4.5.2 Measurement of Slip 86
3.4.5.3 Measurement of Steel Strain 87
3.4.6 Data Acquisition System 88
3.4.7 Load Control 89
3.5 Summary 90
4
PHASE I: BEHAVIOR OF GROUTED SPIRAL
CONNECTIONS SUBJECTED TO DIRECT
AXIAL PULLOUT
92
4.1 Introduction 92
4.2 Tensile Test Results of Grouted Spiral
Connections
93
4.2.1 Mechanism of Tensile Force Transfer in
Trial Specimens
96
4.2.2 Mechanism of Tensile Force Transfer in
others Series
102
4.2.2.1 Failure Modes of the Grouted
Spirals
104
4.2.2.2 Behavior of Tensile Strain in the
Connected Main Bars
107
4.3 Structural Behavior 109
4.3.1 Interlocking Mechanism of Grouted
Spiral Connections
111
4.3.2 Splitting Cracks and Effects 113
4.3.3 Confinement Effects 115
4.4 Performance of Grouted Spiral Connections 116
x
4.4.1 Performance of Bond Stiffness and Slip 116
4.4.1.1 Effects of Spiral Configuration
on the Slip
118
4.4.1.2 Behavior of Connection Stiffness 121
4.4.2 Evaluation of Bond Strength 123
4.4.2.1 Effects of Spiral Configuration
on the Bond Strength
124
4.5 Summary 130
5
PHASE II: BEHAVIOR OF GROUTED SPIRAL
CONNECTIONS SUBJECTED TO INCREASING
FLEXURAL PULLOUT
131
5.1 Introduction 131
5.2 Flexural Test Results of Grouted Spiral
Connections
132
5.2.1 Mechanism of Force Transfer in Trial
Specimens
135
5.2.2 Flexural Test Results of other Series 137
5.2.2.1 Failure Modes of the Grouted
Spiral Connections
140
5.2.2.2 Behavior of Tensile Strain in
Connected Main Bars
143
5.3 Comparison of Results between Direct Axial
and Flexural Pullout Loads
144
5.4 Design Recommendation 149
5.5 Summary 151
6 ANALYTICAL BEHAVIOR OF GROUTED
SPIRAL CONNECTION UNDER AXIAL AND
FLEXURAL PULLOUT
153
6.1 Introduction 153
6.2 Bond Stress-Slip Behavior of Grouted Spiral
Connections
155
6.2.1 Analysis of Bond-Slip Relationship by
Curve Fitting
155
6.2.2 Modelling of the Bond Stress-Slip
Relationship
158
6.3 Evaluating the Confinement Effect by Bond
Energy
163
6.4 Prediction of Bond Strength of Spiral
Connections in Deformed Steel Bars
168
6.5 Comparison with Orangun’s Equation 172
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6.6 Limitations 179
6.7 Summary 180
7 CONCLUSIONS 181
7.1 Summary 181
7.2 Conclusion 182
7.3 Recommendations for Future Research 185
REFERENCES 187
Appendices A-C 193-210
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LIST OF TABLES
TABLE NO. TITLE PAGE
1.1 Comparisons of the commercial and proposed connections
of this research
3
2.1 Application of NMB splice sleeve and Lenton Interlok 32
2.2 Test-prediction ratios for bars confined by transverse
reinforcement [45]
39
2.3 The value of pitch distance studied by other researchers 45
2.4 Assessment of the performance of the prediction models 48
3.1 Preliminary feasibility evaluation of specimens in
preliminary study
60
3.2 Details of trial specimens 62
3.3 Dimension of all series in Phase I 64
3.4 Details of grouted spiral connection in Phase II 73
3.5 Mix proportion of concrete in grade 40 81
3.6 Description of concrete in grade 40 82
3.7 Average specifications of Sika Grout-215 84
3.8 Properties for the rib parameters 84
3.9 Tensile test results of steel reinforcement bars 84
3.10 Specifications of strain gauges for deformed steel main bar 87
3.11 The measured data and accuracies 89
4.1 Summary of test results of grouted spiral connection 94
4.2 Average of test results in trial specimens 96
4.3 Average of test results in Series 𝐷𝑠 25, 𝐷𝑠 35 and 𝐷𝑠 45 103
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4.4 Bond stiffness of the grouted spiral connections, MPa/mm 120
4.5 Strength ratio of specimens 128
4.6 Bond strength, (MPa) with respect to different spiral
diameters
129
4.7 Bond strength, (MPa) with respect to different pitch
distance
129
5.1 Test results of flexural pullout loads 134
5.2 Bond strength, (MPa) with respect to different spiral
diameter
139
5.3 Bond strength, (MPa) with respect to different pitch
distance
140
5.4 Comparison of bond strength between axial and flexural
pullout tests
148
5.5 Calculation of required embedded length 151
6.1 Curve-fitting parameter of α and β 161
6.2 Bond energy of grouted spiral connections tested in
Phase I
167
6.3 Bond energy of grouted spiral connections tested in
Phase II
168
6.4 Comparison between test results in Phase I and proposed
Equation 6.6
171
6.5 Comparison between test results in Phase II and proposed
Equation 6.7
172
6.6 Values of parameters used for Equation 6.8 175
6.7 Comparison between test results in Phase I and Equation
6.9
178
6.8 Comparison between test results in Phase II and Equation
6.9
179
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LIST OF FIGURES
FIGURE NO. TITLE PAGE
1.1 Grouted splice connection in precast concrete components
[13]
4
1.2 Mechanism of load transfer [17] 5
1.3 Spiral confinement in splice connections [29] 8
1.4 Projecting the long embedded length in conventional
grouted sleeve [30]
9
1.5 Cross section through grouted sleeve column splice [31] 10
2.1 Grouted sleeve connection and connecting elements [33] 15
2.2 Distribution of bond stress at different levels of pulling
force [36]
16
2.3 (a) Bond force transfer mechanisms [45], (b) typical bond
stress-slip relationship [46]
18
2.4 (a) Plain round bar, (b) lateral pressure parallel to the
transverse rib, (c) lateral pressure perpendicular to the
transverse rib [54]
22
2.5 Typical failure pattern (a) without spiral, (b)with spiral
[56]
23
2.6 Grouted spiral connection (a) four splice bars inside the
spiral [61], (b) four splice bars outside the spiral
24
2.7 Anchorage of beam reinforcement at exterior joints [55] 25
2.8 Stress-slip responses under confinement of transverse
reinforcement [55]
26
2.9 Effect of confinement on the bond failure (a) by splitting
in an embedded bar without any confinement, (b) by
pullout with present of confinement [66]
28
2.10 Relationships of bond stress versus displacement [72] 30
xv
2.11 Proprietary products tested by Jansson [73] 31
2.12 Fatigue test setup by Jansson [73] 32
2.13 Details of test specimens [7] 33
2.14 Proposed bar splice sleeve [33] 34
2.15 Configuration of test specimens given by Ling et al. [59] 34
2.16 Test-prediction ratios for descriptive equations with
confinement provided by transverse reinforcement [45]
39
2.17 Schematic representation of Eligehausen’s tests [42] 41
2.18 BPE model [42] 42
2.19 Haskett et al.’s model [84] 43
2.20 Typical types of pullout tests [91] 50
2.21 Direct Tension Pullout Bond Test (DTP-BT) [91, 92] 50
2.22 Experimental setup of tensile load test by Einea et al [7] 51
2.23 Diagram and reinforcement of RILEM beam test, test
pattern for 𝑑𝑏 ≥16 mm [95]
52
2.24 Modification of RILEM beam tests by other researchers
[97]
53
3.1 Flow chart of the research carried out 57
3.2 Labelling of the specimens 58
3.3 Series of grouted splices tested in preliminary study [98] 59
3.4 Configuration of trial specimens T1, T2 and T3 62
3.5 Configuration spiral with four splice bars in trial specimen
T3
63
3.6 Details of all specimens comprising main bars, spiral, and
splice bars
64
3.7 The arrangement of connections in the PVC before
casting
65
3.8 Preparation of specimens 66
3.9 Installation of strain gauge 67
3.10 Experimental setup of tensile load test 68
3.11 Data acquisition system of tensile load test 68
3.12 Grouted spiral connections in flexural pullout test 70
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3.13 Details of specimen in Phase II 72
3.14 Preparation of formwork 74
3.15 Preparation of reinforcement cage 75
3.16 Preparing the beam specimen 77
3.17 Casting of ready-mix concrete 79
3.18 Compacting of concrete with a hand-held vibrator 80
3.19 Smoothing the surface of beam specimens 80
3.20 Demoulding and preparing the specimens in final step 81
3.21 Position of grouted spiral connection in beam specimen 83
3.22 The rib geometry of deformed steel bar 83
3.23 Position of load cell 86
3.24 Arrangement of LVDTs 87
3.25 Location of strain gauge attached to the main bar 88
3.26 Data acquisition system for flexural pullout tests 89
3.27 Setup of loading frame for flexural pullout tests 90
4.1 Specimen A-T1-S (a) failure mode, (b) force transfer
mechanism
97
4.2 Specimen A-T2-S (a) failure mode, (b) force transfer
mechanism
98
4.3 Comparison of slip between A-T1-S and A-T2-S 99
4.4 Confinement effects contributed by the splice bars in
A-T3-S
100
4.5 Comparison of bond strength between A-T2-S and
A-T3-S
101
4.6 Failure mode of specimen A-T3-S 102
4.7 Pullout failure mode 104
4.8 Mechanism of bar bond-slip failure 106
4.9 Bond stress distribution (modified from Ferguson model)
[36]
107
4.10 Stress-strain in the main connected bar 108
4.11 Failure mode (a) without radial crack, (b) with radial
crack
110
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4.12 Mechanical interlocking mechanism of bond [108] 112
4.13 Componential stresses of resultant stress [108] 112
4.14 Componential stress 112
4.15 Propagation of splitting cracks and effects [111] 113
4.16 Componential derivation of resultant bearing stress [108] 114
4.17 Reduction of shear area due to splitting cracks [108] 115
4.18 Passive confinement generated by spiral 116
4.19 Best-fit straight lines to calculate the bond stiffness of
connection
117
4.20 Comparison of average bond stiffness in all series 119
4.21 Effect of spiral diameter on the average bond stiffness 119
4.22 Bar slips due to micro-space and compressive
deformations of grout [35]
122
4.23 Bar slips due to micro-space and compressive
deformations of grout
122
4.24 Development of inclined cracks [55] 123
4.25 Bond strength versus pitch distance 125
4.26 Stress transfer mechanism 126
5.1 Flexural pullout experimental (a) beam details showing
the spiral connection, unbonded length of rebar, loads and
LVDTs positions, (b) actual beam tested in the laboratory
133
5.2 Grout fracture initiating the bar pullout 135
5.3 Comparison of bond strength between specimens F-T3-S
with splice bars and F-T2-S without splice bars
136
5.4 Bond strength versus spiral diameter under flexural
pullout
138
5.5 Comparison of confined surface area 138
5.6 Bond strength versus pitch distance 139
5.7 The location of the failure in the left side of the beam in
connector
141
5.8 Failure mode (a)-(b) flexural pullout with the grouted
connection located inside the left beam, (c) pullout of the
main rebar
141
xviii
5.9 Stress-strain of specimens under flexural pullout test (a)
F-P15-D25-S, (b) F-P35-D25-S
143
5.10 Comparion of bond strength between direct axial and
flexural pullout (a) bond strength versus spiral diameter,
(b) bond strength versus pitch distance
145
5.11 Stress-strain in the main steel bar (a) specimen A-P15-
D25-S under direct axial pullout test, (b) specimen
F-P15-D25-S under flexural pullout test
146
5.12 Bond stress-slip relationship (a) specimen A-P15-D25-S
under direct axial pullout test, (b) specimen F-P15-D25-S
under flexural pullout test
147
5.13 Level of bond strength of specimens for different series 150
6.1 Analytical behavior of grouted spiral connection 155
6.2 Curve fitting of experimental bond stress-slip of grouted
spiral connection (a) under direct axial pullout, (b) under
flexural pullout
157
6.3 Comparison of bond stress-slip relationships between
experimental results and curve fitting equation of (a)
specimen A-P25-D35-S direct axial pullout test, (b)
specimen F-P25-D35-S under flexural pullout test
158
6.4 (a) Configuration of specimen in research of Soroushian
model [55], (b) equivalent Soroushian model used in the
spiral connections
159
6.5 Comparison between predicted bond stress-slip
relationships with experimental results (a) A-P15-D25-S
(I), (b) A-P25-D25-S (I), (c) F-P15-D25-S, (d) F-P25-
D25-S
161
6.6 Bond energy (a) A-P15-D25-S, (b) A-P15-D35-S and
(c) A-P15-D35-S in direct axial pullout in Phase I
164
6.7 Bond energy (a) F-P15-D25-S (b) F-P15-D35-S and
(c) F-P15-D35-S in flexural pullout in Phase II
165
6.8 Statistical approach- logarithmic regression method for
predicting parametric response (a) direct axial pullout, (b)
flexural pullout
169
6.9 Grout confined area in grouted spiral connections 174
6.10 Comparison between direct axial pullout and Equation 6.9 177
6.11 Comparison between flexural pullout and Equation 6.9 177
xx
LIST OF SYMBOLS
P - Applied load
𝑑𝑏 - Diameter of main bar
𝑙𝑑 - Embedded length
𝜏 - Average bond stress
U - Bond strength of concrete
ƒ𝑛 - Lateral confining pressure
𝑓𝑐𝑢 - Concrete compressive strength
ƒ𝑏𝑡 - Bond stress
𝑇𝑏 - Bond force
𝐴𝑏 - cross sectional area of spliced bars
𝐴𝑡𝑟 - Area of transverse reinforcement normal to the plane of
splitting through the anchored bars
𝐶𝑚𝑖𝑛 - Smaller of minimum concrete cover or ½ of clear spacing
between bars
𝑓𝑦𝑡 - Yield strength of transverse reinforcement
s - Spacing of transverse reinforcement
n - Number of bars developed or splice at the same location
CSo - Side cover
CSi - 1/2 of the bar clear spacing
CS - Minimum (CSo , CSi + 6.4m)
Cb - Bottom cover
Cmax - Maximum (Cb, CS)
𝜏𝑚𝑎𝑥 - Maximum bond strength
𝑆 - Slip
𝑠1 - Slip at maximum bond strength of 𝜏1
α - a curve-fitting parameter
xxi
𝑓𝑐′ - Tensile strength of concrete
𝑓𝑠 - Steel stress
X - Distance from loaded face pullout bond specimen.
x - Distance from center of embedded bar
D - Diameter of cylindrical grout
𝐷𝑠 - Diameter of spiral
𝑃𝑠 - Pitch distance of spiral
𝐿𝑠 - Length of grouted spiral connection
𝐿𝑒 - Embedded length of main connected bar
𝑁𝑐 - Number of Coil
h - Rib height
c - Rib spacing
ʋ - Rib inclination
fc,g - Compressive strength of grout
σ - Stress
Ks - Stiffness
Rs - Strength ratio
fu,b - Maximum stress at failure
Pu - Load capacity
fsy,b - Specified yield strength
T - Tensile load in the main bars of beam specimen
a - Shear span
j - Distance between the resultant tensile and compressive loads
ɤ - Ratios between bond strength of axial and flexural pullout
β - A curve-fitting parameter
Ag - Confined grout, cross sectional area
𝑓spiral - Tensile stress in spiral
Aspiral - Cross sectional areas of the spiral
𝑑𝑠𝑝𝑖𝑟𝑎𝑙 - Diameter of cross sectional area of spiral
𝑑sb - Diameter of splice bar
𝑃g - Tensile strength of grout in connection
𝑃spiral - Tensile load endured by the spiral
xxii
LIST OF APPENDICES
APPENDIX TITLE PAGE
A Response of grouted spiral connection with deformed steel
bars under direct axial pullout in Phase I
193
B Response of grouted spiral connection with deformed steel
bars under flexural pullout in Phase II
199
C List of publication 210
CHAPTER 1
INTRODUCTION
1.1 Introduction
The construction industry in Malaysia has shifted from conventional
reinforced concrete system to industrialized building system (IBS) through the
application of precast concrete system. The precast concrete system has led the
building market to an extremely competitive environment. Using this system,
considerable amount of building components are fabricated in factories in a fully
controlled condition by means of proper equipment. The precast concrete system has
considerable advantages such as certainty in cost and time, enhancing occupational
health and safety, achieving higher construction productivity and quality, reliance on
manual foreign labor, and decreasing the cost of construction [1].
In 1960, Ministry of Local Government and Housing visited a number of
European countries for evaluation of their housing development program [2], which
led to initiating IBS in Malaysia. Then, the government dedicated about 22.7 acres of
land along Jalan Pekeliling, Kuala Lumpur to a great project that consisted of seven
blocks of 17 stories flat, 3000 units of low-cast flat, and 40 shop lots [3].
In 2006, the Malaysian construction industry re-introduced the IBS system
with the expectation the new technologies in precast concrete can be adopted for
innovative construction techniques. For instance, the Construction Industry Master
2
Plan (CIMP) 2006-2015 published in December 2006 was an attempt to plan the
direction for future developments of the Malaysian Construction Industry. In the
2005 Budget, the construction of 100,000 units of reasonably-priced houses using
IBS was pledged by the government. The Surat Pekeliling Perbendaharaan Bil. 7
Tahun has 2008 strongly asserted that the government’s projects must use IBS in
their construction process not less than 70% of the whole structures [1]. These efforts
demonstrate the situation of IBS in the construction industry of Malaysia.
One of the major concerns that commonly arise with regard to the use of
prefabricated precast concrete components is the needs to develop quality
connections in a way to maintain the structural integrity through the precast sections
[4]. In the precast continuous construction system, both the design and structural
details of the precast connections should have the same features of cast-in-place
connection [5]. In this regard, the America Concrete Institute (ACI) has published
different details on how to emulate cast-in-places in the precast construction sites [6].
On the other hand, still there is not enough supplementary information in the ACI
code regarding the design of precast connections in particular the knowledge related
to continuity and bond in reinforcement bars.
In order to achieve full continuity of reinforcement bars for joining precast
concrete components, grouted splice connectors are preferred and employed (see
Figure 1.1). Grouted splice connectors have shown the capability of being used as
connections in the precast concrete structures. These connectors reduced the splice
length for ensuring the continuity of steel bars considerably [7]. The splice
connectors make the installation process simpler and solve the problems of bar
congestion and detailing, especially in structures that are heavily reinforced[8]. For
the first time, in the late 1960s [9, 10], this splice method was introduced by Dr.
Alfred A. Yee upon the invention of NMB splice sleeve® [10]. From that time,
different types of mechanical couplers such as BarSplice Double Barrel Zap
Screwlok©, Lenton Interlok® [11, 12] Lenton QuickWedge©, etc. have been
developed and commercialised. Most of the splice connectors have been invented by
private individuals and are difficult to obtain the technical details due to the
proprietorship rights. Due to limited literature regarding the behavior of grouted
3
splices connections, researchers prefer to investigate the non-proprietary splice that is
inexpensive. Table 1.1 shows the differences between the commercial connections
and non-proprietary splice connections which were studied in this research. The
commercial splice connections normally required special mould to fabricate and are
made from cast iron. On the other hand, the proposed non-proprietary connectors
required steel pipe, spiral and splice bars only. Concerning the performance, an
adequate splice connector should be capable of providing high quality assurance in
bond strength even with short spliced lengths. In this splices technique, the strength
of the splice joint relies heavily on the anchorage bond.
Table 1.1: Comparisons of the commercial and proposed connections of this
research
Commercial splice connector Proposed splice connector in this research
NMB splice sleeve
Double Barrel Zap Screwlok
Lenton Interlok
Characteristics of commercial splice
connectors:
1. Need special moulds to fabricate
the thread and splice which is
expensive
2. Cast iron is used for the splice
which is brittle
3. Proprietary
Steel pipe with spiral confinement
Spiral confinement with four splice bars
Characteristics of proposed non-proprietary splice
connectors:
1. Steel pipe spiral and splice bars of
connections are easily available in the
market with inexpensive materials
2. These types of connections can be
fabricated easily without any special
mould.
3. Non-proprietary
4
Figure 1.1 Grouted splice connection in precast concrete components [13]
Usually the bond development has strong effect on the interaction between
the grout and splice bar for the grouted splice connections, that are usually used in
connecting precast concrete components. In fact, the mechanism of load transfer
between the precast concrete components depends on the quality of adequate bond
provided by the grouted splice (Figure 1.2) [14]. Investigation works on the factors
that affect the bond were studied greatly over the last 40 years and as a result,
considerable modifications have been introduced to bond clauses in design codes
worldwide [15]. Detailed evaluations of bond strength and bond behavior are
complicated, as the magnitude of bond strength is influenced by a wide range of
factors. For example, the CEB-FIP Model Code 90 [16] includes not less than 10
parameters which influence the anchorage bond behavior.
5
Figure 1.2 Mechanism of load transfer [17]
In the bond aspect, one of the key factors that can improve the value of bond
stress is the present of confinement between the steel bar and grout. The confinement
can influence the anchorage bond and reduces the required embedment length of the
spliced steel bars [7, 18-20]. The application of confinement delays early
development of the splitting cracks either by expansion resistance or bridging of
surrounding materials of the steel bars.
This study concentrates on the behavior of proposed grouted splice
connections with spiral confinement. To investigate the behavior of new splice
connections, it is very essential to know the interactions and also internal stress
distribution among the deformed steel spliced bars and its surrounding materials.
1.2 Background of Study
In reinforced concrete structures, the reinforcement bars attain continuity
through lapping full anchorage lengths of the steel bars [21]. On the other hand, the
long bar lapping lengths may be impractical in cases where there is not adequate
space for the accommodation of the required bar development lengths, especially in
structures that are heavily reinforced and in cases where larger bar sizes are used,
6
leading to impractical lapping lengths, or it may be not permissible to be lap spliced
by codes [8].
In precast concrete structures, prefabricated components such as wall to wall
and column to column need to be jointed together by ensuring the continuity of
rebars from the lower component to upper components. To join the prefabricated
elements of the precast concrete systems, the lengthy lapping system have not been
shown quite appropriate. For example, long extruding starter bars provided for
embedment in the adjoining structural elements in the installation process often cause
problems of transportation and handling. As a result, for ensuring the ease of the
installation and maximizing the speed of construction process, there is a need for
short bar anchorage length
The grouted splice offers a feasible solution to connect the prefabricated
elements during erections. During the assembly process, prior to pouring or pumping
the grout in the sleeves, the short extruding steel bars could be inserted to the pre-
embedded sleeves in the targeted elements. Using this technique, the problem of long
embedded lengths can be solved and the process of handling and installation can be
performed more easily.
In general, using grouted splices, discontinued bars can be spliced at short
embedded bar lengths. Though, the bond performance may be different because of
variations existing in the grouted splice configurations. Knowing these issues, the
grouted splices responses should be investigated, particularly regarding the bond
behavior, for identification of the major factor like confinement that has impact on
the bond mechanism in grouted splices.
The influence of confinement on the ductility and compressive strength of
compression members has been reported by many researchers [22-26]. Their work
was based on the confinement of members along their full length. The confinement
effect using spirals or ties on lap splice lengths and development of the longitudinal
7
reinforcement was investigated in their work. Based on the shape of confinement,
circular spirals provide a continuous confining pressure around their axial axis [27].
The concept of spirally confined lap splices of deformed bar comes from the
above theory to generate the strength required for connecting the reinforcement bars
together (see Figure 1.3). So, In order to employ spiral confinement in grouted
connections, more investigations are required rather than relying on speculated
predictions. Thus, it is essential to understand the responses of the grouted splices
when subjected to the load cases of direct axial and flexural pullout loads. Other
forces that may occur in the splice are axial force-moment and axial compression-
moment. the work by Kuttab and Dougill [28] has shown that most of the grouted
connections in precast column components experienced axial force–moment
interaction characteristics. Hence, multi-phases of experimental studies are carried
out to study the behavior of proposed connections caused by the bond stress-slip
relationship of individual short deformed steel by spiral reinforcement. The
confinement provided by the spirals is part of the proposed short splicing method
which increases the bond strength. The spirals characteristics and properties are
applied in Industrial Building Systems (IBS) where other types of mechanical spliced
connections could be substituted by this connection.
8
Figure 1.3 Spiral confinement in splice connections [29]
1.3 Problem Statements
The problems that need to be addressed in grouted splice connections are:
1. The conventional grouted sleeve connector is one of the famous methods for
joining precast concrete components (see Figure 1.4). According to the
finding of Kuttab [28], the combination of axial and flexural loads interaction
characteristics of grouted sleeve connectors has to be equal to the parent
column. Due to this axial and flexural load interaction, long embedded length
of 35 times bar diameter based on BS 8110 [21] is needed to achieve the full
continuity of reinforcement bars. The main problem in using this connection
is the installation process of the grouted sleeve connectors which is quite
difficult and it is not easy to achieve with any accuracy. The main bars in the
sleeve may not always be perfectly located at the centre of sleeve (See Figure
9
1.5). There is a tendency the long bars to touch the wall of the sleeve in the
precast component, so preventing penetration of grout around the bar and it is
not allowing the grout to fill all the voids inside of the sleeve completely.
Since the grout inside the sleeve cannot be inspected after installation, there is
doubt that the main bar is fully bonded. So, it is necessary to provide the
system which can be assembled by prefilling [8].
2. There is not much research works on the effect of spiral confinement on the
bond behavior of grouted splices. Therefore, there is a need to study the
confinement effects in the grouted splice connectors.
Figure 1.4 Projecting the long embedded length in conventional grouted
sleeve [30]
10
Figure 1.5 Cross section through grouted sleeve column splice [31]
1.4 Objectives
Owing to these important characteristics, the bond behavior of reinforcement
embedded in grout needs to be investigated accordingly. The key factor governing
the anchored-bar behavior in confined grout is the local bond stress-slip relationship.
Consequently, to develop new splice connections, it is important to understand the
internal stress and the local bond stress-slip relationship between various main
connected bars and their surrounding materials. Failure of bond leads to slippage in
reinforcement bars and consequently failure of structural members.
To achieve the task of solving the problems stated above, this research is
outlined with several main objectives as follows:
i. To investigate the performance of spiral confinement and splice bars to the
behavior of connected deformed steel bars in grouted connections under
direct axial and flexural loads.
ii. To study the effect of spiral configurations on the bond stress-slip behavior of
the deformed steel bars under direct axial and flexural loads.
11
iii. To study the comparison of direct axial and flexural pullout loads on the bond
behavior of deformed steel bars in grouted spiral connection.
iv. To propose equations for predicting the bond strength and bond stress-slip
relationship of the grouted spiral connections under direct axial and flexural
loads.
1.5 Scope of Research
The scope of the research program includes:
a. The experimental tests of grouted spiral connections with different
configurations of spiral confinement.
b. The investigation of the performance of the proposed grouted spirals when
subjected to load cases of direct axial and flexural pullout.
c. The study of responses of the grouted spirals towards tree considered parameters,
pitch distance of spiral, diameter of spiral and type of main bars.
d. The development of simplified equations for predicting the responses of the
connections under mentioned load cases
e. Additionally, two major phases of experimental tests involves
i) Testing of thirty-six grouted spiral specimens under monotonic direct axial
pullout to study the behavior of the connections under tension.
ii) Experimental testing of twelve full-scale beam specimens, connected with
grouted spirals, under flexural pullout loads to acquire the response of the
steel deformed bars in grouted spiral connections.
12
Furthermore, the scope of the test results for each phase comprises:
a. Phase I – Direct tensile axial pullout test of grouted spiral connections
i. Failure load capacity
ii. Bond strength
iii. Bond stress-slip behavior
iv. Stress-strain response
v. Failure mode
b. Phase II – Flexural pullout test of the steel deformed bars in grouted spiral
connections
i. Failure load capacity
ii. Bond strength
iii. Bond stress-slip behavior
iv. Stress-strain response
v. Failure mode
Lastly, the scope of analytical research consists of:
a. Analysing the bond stress-slip relationship of the grouted splices under direct
axial and flexural pullout loads from the experimental results in Phases I and II.
b. Deriving equations to predict the bond strength of the grouted spiral connections
under tensile and flexural pullout loads.
c. Evaluating the effect of spiral confinement on the bond stress-slip relationship by
calculating the bond energy
d. Comparison of the experimental test results to other researcher to validate the
data.
13
1.6 Thesis Organization
Chapter 2 presents a review of the available literature and the present state of
knowledge regarding grouted connections and mechanism of bond stress.
Chapter 3 describes the experimental program, including the details of test
specimens, connection configurations, material specifications, instrumentations, test
setup and procedures.
Chapter 4 presents the results and discusses the responses of grouted spiral
specimens when subjected to increasing direct axial pullout loads.
Chapter 5 displays and discusses the test results and response of full-scale
beam specimens, connected with steel deformed bars in grouted spiral connections,
under flexural pullout loads.
Chapter 6 presents the analytical derivations for predicting the bond strength
response and bond stress-slip relationship of the proposed grouted spiral connections
under direct axial and flexural pullout loads.
Chapter 7 summarizes and concludes the entire research carried out.
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