Jul 19, 2011 - sehingga tiang mengalami kegagalan. Kajian tingkah laku tiang konkrit berkekuatan tinggi ini dinilai dengan menggunakan lengkung liputan, ...
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UNIVERSITI TEKNOLOGI MALAYSIA DECLARATION OF THESIS / POSTGRADUATE PROJECT PAPER AND COPYRIGHT
LEE HOONG PIN___________________________________ 02 JUNE 1986________________________________________ BEHAVIOUR OF EXTERNALLY-CONFINED_______ HIGH-STRENGTH CONCRETE COLUMN UNDER__ UNIAXIAL CYCLIC COMPRESSION________________ Academic Session : 2010/2011-3__________________________________________
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Date : 19 JULY 2011
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ABDULLAH ZAWAWI BIN AWANG NAME OF SUPERVISOR
Date : 19 JULY 2011
If the thesis is CONFIDENTAL or RESTRICTED, please attach with the letter from the organization with period and reasons for confidentiality or restriction.
Date: 19 JULY 2011 Librarian Perpustakaan Sultanah Zanariah UTM, Skudai Johor
Sir,
CLASSIFICATION OF PROJECT REPORT AS RESTRICTED “BEHAVIOUR OF EXTERNALLY-CONFINED HIGH-STRENGTH CONCRETE COLUMN UNDER UNIAXIAL CYCLIC COMPRESSION” By LEE HOONG PIN
Please be informed that the above mentioned project report entitled “BEHAVIOUR OF EXTERNALLY-CONFINED HIGH-STRENGTH CONCRETE COLUMN UNDER UNIAXIAL CYCLIC COMPRESSION” be classified as RESTRICTED for a period of three (3) years from the date of this letter. The reasons for this classification is (i)
This report contains confidential material that is in the process of filing for pattern before considering open access.
Thank you. Sincerely yours,
___________________ Abdullah Zawawi Bin Awang Faculti of Civil Engineering, Universiti Teknologi Malaysia, 81300, Skudai, Johor. Tel: 019-7107185
“We hereby declare that we have read this project report and in our opinion this report is sufficient in terms of scope and quality for the award of the degree of Master of Engineering (Civil – Structure).”
Signature
: ………………………………..
Name of Supervisor
: ABDULLAH ZAWAWI BIN AWANG
Date
: 19 JULY 2011
Signature
: ………………………………..
Name of Supervisor
: PROF. IR. DR. WAHID BIN OMAR
Date
: 19 JULY 2011
BEHAVIOUR OF EXTERNALLY-CONFINED HIGH-STRENGTH CONCRETE COLUMN UNDER UNIAXIAL CYCLIC COMPRESSION
LEE HOONG PIN
A project report submitted in partial fulfillment of the requirements for the award of the degree of Master of Engineering (Civil – Structure)
Faculty of Civil Engineering Universiti Teknologi Malaysia
JULY 2011
ii
“I declare that this project report entitled “Behaviour of Externally-Confined HighStrength Concrete Column under Uniaxial Cyclic Compression” 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
: LEE HOONG PIN
Date
: 19 JULY 2011
iii
To my beloved mother and father
iv
ACKNOWLEDGEMENTS
“No man is an island”, it’s a hard task for me to complete this report without the assistance from the people around me. Without them, I am sure it’s a doubt for me to complete this report on time.
First and foremost, I would like to express my heartfelt gratitude to my supervisor, Prof. Ir. Dr. Wahid bin Omar and Abdullah Zawawi bin Awang for their support, encouragement, guidance, critics and friendship. They had taken a lot of efforts and time to go through all my report, answering all my conundrum and doubt during conducting this project and sharing their priceless experience with me. They also had taken a lot of effort to dot the I’s and cross the t’s by going through my report and came out with helpful suggestion. Without their help, surely it’s a deep problem in completing this report.
Never forgot too, I would like to give my heartily and thousand thank to Mr Khor Chu Kiat and laboratory technical staff, Mr. Razale Mohammad and Mr Zulkifly Abdul Wahid for their help and support along the period. With their present and help, my master project becomes more meaningful.
Finally, I would like to thank my parents and family for their support and encouragement. Their support is invaluable and means to me. Last but not least, thanks for all my friends who willing to help me, thank you very much.
v
ABSTRACT
The behaviour of confined high-strength concrete under uniaxial cyclic compression is of vital important for the study either for seismic retrofitting technique of concrete columns or for the structure designs in seismic regions. Hence, the effectiveness of external wrapping with steel straps in reducing the brittleness and enhancing the strength and ductility of HSC column under uniaxial cyclic compression are to be properly understood. Twenty four high-strength concrete columns with diameter of 150 mm and 300 mm in height were cast, wrapped with pre-tensioned steel strap at spacing of 15 mm and tested to failure under both uniaxial monotonic and uniaxial cyclic compression load test. Test results obtained from steel strap-confined high-strength concrete cylinders are presented and examined, which allows a number of significant conclusions to be drawn, including the existence of an envelope curve, dependency of plastic strain to the number of layers of confinement, the cumulative effect of loading cycles, mode of failure under external confinement, etc. The present results are also compared with several results from previous study for various types of confined-concrete. The present study indicates that the column pre-tensioned with steel straps, performed better than the unconfined high-strength concrete columns. It is proved that externally confinement using steel straps do help to control the brittleness and at the same time, enhancing the ductility up to 56.2% and compressive strength up to 108.5% . The envelope curve of uniaxial cyclic loading almost coincides with the corresponding monotonic loading test, with a dependent plastic strain to the amount of layers of confinement.
vi
ABSTRAK
Kelakuan konkrit berkekuatan tinggi terkurung di bawah beban mampatan paksi cyclic adalah sangat penting untuk kajian sama ada untuk baik pulih tiang konkrit atau reka bentuk struktur di kawasan yang mengalami gempa bumi. Oleh itu, keberkesanan kurungan dengan lilitan keluli dalam mengurangkan kerapuhan dan meningkatkan kekuatan dan kemuluran tiang konkrit berkekuatan tinggi di bawah beban mampatan paksi cyclic hendaklah dibuat kajian. Dua puluh empat tiang konkrit berkekuatan tinggi berdiameter 150 mm dan berketinggian 300 mm disediakan, dipra-tegangkan dengan lilitan keluli pada jarak 15 mm dan diujikaji dengan beban mampatan paksi monotonic dan beban mampatan paksi cyclic sehingga tiang mengalami kegagalan. Kajian tingkah laku tiang konkrit berkekuatan tinggi ini dinilai dengan menggunakan lengkung liputan, perhubungan terikan plastik dengan bilangan lapisan lilitan keluli kurungan, kesan kumulatif beban mampatan cyclic, mod kegagalan dan lain-lain lagi. Keputusan kajian ini juga dibandingkan dengan beberapa keputusan kajian lepas. Kajian ini menunjukkan tiang ditegangkan dengan lilitan keluli mempunyai prestasi yang lebih baik berbanding dengan tiang konkrit berkekuatan tinggi yang tidak ditegang dengan jalur keluli. Kajian ini membuktikan bahawa tiang ditegangkan dengan lilitan keluli mampu mengawal kerapuhan konkrit dan pada masa yang sama, meningkatkan kemuluran sehingga 56.2% dan kekuatan mampatan sehingga 108,5%. Di samping itu, lengkung liputan bagi beban mampatan paksi cyclic berlaku pada lengkung yang dengan graf tegasanterikan bagi beban mampatan paksi monotonic. Kajian ini juga membuktikan bahawa nilai terikan plastik bergantung kepada bilangan lapisan lilitan kurungan keluli.
vii
TABLE OF CONTENT
CHAPTER
1.
2.
TITLE
PAGES
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENTS
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENT
vii
LIST OF FIGURES
xii
LIST OF TABLES
xvii
LIST OF SYMBOLS
xix
INTRODUCTION
1
1.1. Introduction
1
1.2. Problem statement
2
1.3. Research significance
3
1.4. Scope of study
3
1.5. Objective
4
LITERATURE REVIEW
5
2.1. Introduction to high-strength concrete
5
2.1.1. High-strength concrete
5
2.1.2. Factors that govern the strength
7
of high-strength concrete
viii
2.1.2.1. Paste properties
7
2.1.2.2. Transition zone properties
7
2.1.2.3. Aggregate properties
7
2.1.3. Advantages and disadvantages
8
of high-strength concrete 2.2. Confinement
9
2.2.1. Lateral confinement
9
2.2.2. External confinement
10
2.2.3. Confine concrete as seismic
12
retrofiting method 2.3. Advantages in using metal / steel strap 2.3.1. Effect of strap spacing 2.4. Compression test
12 13 13
2.4.1. Monotonic compression load test
13
2.4.2. Uniaxial cyclic compression load test
14
2.4.2.1. Envelope curve
15
2.4.2.2. Plastic strain
17
2.4.2.3. Effect of loading history
19
2.5. Existing model equation 2.5.1. Theoritical stress-strain model
24 24
for confined concrete by Mander, Priestley and Park (1988) 2.5.1.1. The basic model equation
24
for monotonic compression loading for confined concrete 2.5.1.2. Stress-strain relation for cyclic
27
loading at slow strain rates 2.5.2. Behaviour of laterally confined high-
30
strength concrete under axial loads by Yong, Malakah and Edward (1988) 2.5.2.1. Parameter of stress-strain
30
relationship 2.5.2.2. Empirical model for rectilinearly confined high-strength concrete
32
ix
2.6. Previous study
33
2.6.1. Effects of external confinement on
33
concrete columns by Tan and Kong (1992) 2.6.2. Cyclic loading of laterally confined
36
concrete columns by Cheong and Perry (1993)
3.
4.
METHODOLOGY
39
3.1. Introduction
39
3.2. Preparation procedures
39
3.2.1. The mixing materials
39
3.2.2. Cement
40
3.2.3. Coarse aggregates
40
3.2.4. Fine aggregates
41
3.2.5. Chemical admixtures – superplasticizer
42
3.2.6. Water
42
3.2.7. Concrete cube
42
3.2.8. The concrete steel mould formwork
43
3.2.9. Steel strap
44
3.3. Trial mix design
45
3.4. Specimen preparation and testing method
46
RESULTS AND ANALYSIS
51
4.1. Introduction
51
4.2. Control columns’ observation and discussion
53
4.2.1. Mode of failure
53
4.2.2. Cracking pattern
55
4.2.3. Stress-strain relationship
57
4.2.3.1. Stress-strain relationship in
57
longitudinal direction 4.2.3.2. Stress-strain relationship in
60
x
transverse direction 4.3. Columns strengthened with two layers
63
of steel straps’ observation and discussion 4.3.1. Mode of failure
63
4.3.2. Cracking pattern
66
4.3.3. Stress-strain relationship
68
4.3.3.1. Stress-strain relationship in
68
longitudinal direction 4.3.3.2. Stress-strain relationship in
74
transverse direction 4.3.3.3. Stress-strain relationship
78
of steel strap 4.4. Column strengthened with four layers
83
of steel straps’ observation and discussion 4.4.1. Mode of failure
83
4.4.2. Cracking pattern
86
4.4.3. Stress-strain relationship
87
4.4.3.1. Stress-strain relationship in
87
longitudinal direction 4.4.3.2. Stress-strain relationship in
94
transverse direction 4.4.3.3. Stress-strain relationship
98
of steel strap 4.5. Comparison
103
4.5.1. Analysis of test result
103
4.5.2. Stress-strain relationship of uniaxial
105
monotonic and cyclic compression 4.5.3. Envelope curve
108
4.5.4. Effect of loading history
108
4.5.5. Plastic strain
109
4.5.6. Stress-strain relationship for steel strap
110
4.5.7. Comparison with previous study
111
xi
5.
6.
CONCLUSION AND RECOMMENDATION
113
5.1. Summary of study
113
5.2. Recommendations for future study
115
REFERENCES
116
xii
LIST OF FIGURES
FIGURE NO.
TITLE
PAGES
2.1
Typical concrete and steel strain-strain curve
6
2.2
Stress-strain curves for confined and unconfined concrete
11
2.3
Effectively confined core for rectangular hoop
11
reinforcement 2.4
Typical stress-strain curve for concrete under axial cyclic
14
compression 2.5
Envelope curve proposed by Sinha et al. (1964)
16
2.6 (a)
Experimental envelope curve of Cheong H. K. and
16
Perry S. H. (1993) 2.6 (b)
Experimental envelope curve of L. Lam et al. (2006)
16
2.7
Plastic strain versus envelope unloading strain
18
2.8
Relationship between residual strain ratio and strain
19
ratio attained in the preceding cycle, Curve C: ungrouted columns; curve d: grouted columns. 2.9
Experimental result of effect of tie reinforcement ratio
19
2.10
The uniqueness concept suggested by Sinha et al. (1964)
20
2.11
The proposed stability point
21
2.12
Cyclic stress-strain curve of concrete confined
22
with one ply of CFRP 2.13
Cyclic stress-strain curve of concrete confined with
22
two plies of CFRP 2.14 (a)
Stress-strain relation under unloading and reloading
23
for 3 times each 2.14 (b)
Stress-strain relation under unloading and reloading for 10 times each
23
xiii
2.15
Stress-strain model proposed for monotonic loading
25
of confined and unconfined concrete 2.16
Stress-strain curve for unloading/reloading branches
30
in the model of Mander J. B. et. al. (1988) 2.17
Stress-strain curve and parameter in Yong Y. K.
31
et. al. (1988) empirical model 2.18
Reinforcement detail for columns
34
2.19
Detail of a strap and arrangement of straps on columns
35
2.20
Geometry and bolt reinforcement of a typical
37
column (left), column after cyclic test (right) 2.21
Graph of test result from Cheong H. K. and Perry S. H.
38
(1993) 3.1
Coarse aggregate of 12 mm maximum size
41
3.2
Fine aggregate
41
3.3
100mm x 100mm x 100mm cube mould
43
3.4
150 mm in diameter and 300 mm in height of
44
concrete steel mould 3.5
Stress-strain relationship for steel strap
45
3.6
Cement mix in specimens
47
3.7
Curing process of concrete specimens
47
3.8
Diagram for measuring equipments (LVDTs)
48
3.9
Diagram for loading device
48
3.10
Detail of specimen size and the strain gauge position
49
(unit: mm) 3.11
Specimens series arrangement for testing method
50
4.1
Mode of failure of control specimens
54
4.2
Cracking pattern for C60-C-02
55
4.3
Cracking pattern for C60-C-1C-05
56
4.4
Graph of stress-strain relationship for longitudinal
57
direction under uniaxial monotonic compression load test 4.5
Graph of stress-strain relationship for longitudinal direction (Comparison between uniaxial monotonic compression load test and uniaxial cyclic compression load test)
59
xiv
4.6
Graph of stress-strain relationship for transverse direction
60
4.7
Graph of stress-strain relationship for transverse direction
61
(Comparison between uniaxial monotonic compression load test and uniaxial cyclic compression load test) 4.8
Failure mode of specimens which undergone uniaxial
64
monotonic compression load test 4.9
Failure mode of specimens which undergone uniaxial
66
cyclic compression load test, for single cycle (1C) and three cycles (3C) at prescribed load level 4.10
Cracking pattern for C60S15-2FT-07, C60S15-2FT-14
67
and C60S15-2FT-3C-19 4.11
Graph of stress-strain relationship for longitudinal
68
direction under uniaxial monotonic compression load test 4.12
Graph of stress-strain relationship for longitudinal
70
direction (Comparison between uniaxil monotonic compression load test and uniaxial cyclic compression load test – single cycle) 4.13
Graph of stress-strain relationship for longitudinal
72
direction (Comparison between uniaxial monotonic compression load test and uniaxial cyclic compression load test - three cycles.) 4.14
Graph of stress-strain relationship for transverse
74
direction (concrete) 4.15
Graph of stress-strain relationship for transverse
76
direction (concrete) (Comparison between uniaxial monotonic compression load test and uniaxial cyclic compression load test – single cycle.) 4.16
Graph of stress-strain relationship for transverse
77
direction (concrete) (Comparison between uniaxial monotonic compression load test and uniaxial cyclic compression load test – three cycles.) 4.17
Graph of stress-strain relationship for transverse
79
direction (steel strap) 4.18
Graph of stress-strain relationship for transverse
80
xv
direction (steel strap) (Comparison between uniaxial monotonic compression load test and uniaxial cyclic compression load test – single cycle.) 4.19
Graph of stress-strain relationship for transverse
82
direction (steel strap) (Comparison between uniaxial monotonic compression load test and uniaxial cyclic compression load test – three cycles.) 4.20
Failure mode of confined specimens which undergone
85
uniaxial monotonic (1st row) and cyclic compression load test, for single cycle (2nd row) and three cycles (3rd row) at prescribed load level respectively. 4.21
Cracking pattern for C60S15-4FT-11, C60S15-4FT-
87
1C-17 and C60S15-4FT-3C-24 4.22
Graph of stress-strain relationship for longitudinal
88
direction under uniaxial monotonic compression load test. 4.23
Graph of stress-strain relationship for longitudinal
90
direction (Comparison between uniaxial monotonic compression load test and uniaxial cyclic compression load test – single cycle.) 4.24
Graph of stress-strain relationship for longitudinal
92
direction (Comparison between uniaxial monotonic compression load test and uniaxial cyclic compression load test - three cycles.) 4.25
Graph of stress-strain relationship for transverse
94
direction (concrete) 4.26
Graph of stress-strain relationship for transverse
95
direction (concrete) (Comparison between uniaxial monotonic compression load test and uniaxial cyclic compression load test – single cycle.) 4.27
Graph of stress-strain relationship for transverse direction (concrete) (Comparison between uniaxial monotonic compression load test and uniaxial cyclic compression load test – three cycles.)
97
xvi
4.28
Graph of stress-strain relationship for transverse
98
direction (steel strap) 4.29
Graph of stress-strain relationship for transverse
100
direction (steel strap) (Comparison between uniaxial monotonic compression load test and uniaxial cyclic compression load test – single cycle.) 4.30
Graph of stress-strain relationship for transverse
101
direction (steel strap) (Comparison between uniaxial monotonic compression load test and uniaxial cyclic compression load test – three cycles.) 4.31
Uniaxial cyclic stress-strain curves of concrete
106
confined with two layers of steel straps in comparison with monotonic stress-strain curves of confined and unconfined concrete. (a) One cycle of unloading/reloading load at prescribed load value, and (b) Three cycles of unloading/reloading load at prescribed load value. 4.32
Uniaxial cyclic stress-strain curves of concrete
107
confined with four layers of steel straps in comparison with monotonic stress-strain curves of confined and unconfined concrete. (a) One cycle of unloading/reloading load at prescribed load value, and (b) Three cycles of unloading/reloading load at prescribed load value. 4.33
Plastic strain (ε ) versus envelope unloading strain (ε
4.34
,
109
)
The stress strain curve for steel strap
110
xvii
LIST OF TABLES
TABLE NO.
TITLE
PAGES
2.1
Details of columns and cycling regimes
37
3.1
Mix proportion design for concrete grad 60 MPa
46
4.1
Cube test result
52
4.2
Ultimate load for control specimens
54
4.3
Test results of control specimens
57
4.4
Uniaxial cyclic compression load test results of
59
control specimens 4.5
Uniaxial monotonic load test result of two layers of
69
steel straps confined specimens 4.6
Uniaxial cyclic compression load test (single cycle)
70
results of two layers of steel straps confined specimens 4.7
Uniaxial cyclic compression load test (three cycles)
72
results of two layers of steel straps confined specimens 4.8
Uniaxial monotonic load test result of four layers
88
of steel straps confined specimens 4.9
Uniaxial cyclic compression load test (single cycle) results of four layers of steel straps confined specimens
90
xviii
4.10
Uniaxial cyclic compression load test (three cycles)
92
results of four layers of steel straps confined specimens 4.11
Average test results of unconfined concrete columns
103
4.12
Average test results of confined concrete columns
103
4.13
Comparison between previous studies with present study
111
xix
LIST OF SYMBOLS
′
-
Area of concrete section
-
Area of core of section enclosed by the perimeter spiral or hoop
-
Effective area of confined concrete enclosed by perimeter spiral or hoop
"
ɛun
-
Area of steel section
-
Area of effectively confined concrete core
-
Core dimensions to centerlines of perimeter hoop in x direction
-
Diameter of spiral between bar centers
-
Core dimensions to centerlines of perimeter hoop in y direction
-
Nominal diameter of lateral ties in inches
-
Nominal diameter of longitudinal steel bars in inches
-
Tangent modulus of elasticity of concrete
-
Secant modulus of confined concrete at peak stress
-
Tangent modulus at the beginning of the unloading branch
-
Tangent modulus at the returning point
-
Axial unloading strain
-
Longitudinal compressive strain of concrete
-
Strain at maximum concrete stress ′
-
Strain at maximum concrete stress
-
Spalling strain
-
Irrecoverable or inelastic strain
-
Coordinate of the strain of reloading located in an unloading branch
′
of confined concrete of unconfined concrete
or in a cracked state 85
-
The strains at 85% of the peak compression strength after the full peak compression strength
50
-
The strains at 50% of the peak compression strength after the full
xx
peak compression strength ′
-
Cylinder compressive strength of concrete
-
Yield strength of steel
"
-
Yielding stress of the lateral steel
′
-
Compressive strength of confined concrete
′
-
Unconfined concrete strength
′
-
Effective lateral confining pressure from transverse reinforcement
-
Reversal (unloading) compressive concrete stress
-
Coordinate of the load of reloading located in an unloading branch or in a cracked state
fc0
-
The peak compression strength in the unconfined specimens
fcc
-
The peak compression strength in the confined specimens
ℎ"
-
Length of one side of the rectangular ties in inches
-
Confinement effectiveness coefficient
-
Number of longitudinal steel bars
-
Load at first visible cracking
Pcr
P’max " ′
′
Maximum axial load
-
Ration of area of longitudinal reinforcement to area of core of section
-
Volumetric ratio of lateral reinforcement
-
Volumetric ratio of longitudinal reinforcement
-
Clear vertical spacing between spiral or hoop bars
-
The center-to-center spacing of the lateral ties in inches
-
The ith clear distance between adjacent longitudinal bars
1
CHAPTER 1
INTRODUCTION
1.1
Introduction Recently, wide application in high-strength concrete have been found in
construction industry due to the lower unit weight for a given strength with potential seismic advantages, reduced member dimension and reinforcing requirement, and more economical construction (Weston T. Hester, 1980). However, there is a major problem with high-strength concrete. Although high-strength concrete exhibit high compressive strength, high-strength concrete generally more brittle and less ductile than normal strength concrete. It is important to make sure that the minimum level of ductility is provided during designing the high-strength concrete (Neville A. M., 2002).
In Malaysia, most of the concrete structures are not designed using earthquake specification. Although Malaysia is free from earthquake intrusion, there still have some collateral impact when earthquake happened on neighbouring country. The earthquake impact will cause severe damages to the structures due to inadequate confinement of concrete, leading to shear anchorage and splice failures of concrete members. It is expensive and almost impossible to demolish and rebuilt the existing vulnerable structures, therefore innovative rehabilitation and strengthening techniques are needed to ensure the life expectancy of many existing building can be extended (Hasan M. et. al., 2008).
2
This report presents the results of an experimental study on the behaviour of externally confined high-strength concrete using steel strap under uniaxial cyclic compression. Twenty four high-strength concrete column specimens with different layers of steel strap wrapping are tested in order to investigate the external lateral confinement effect on the strength and ductility properties of high-strength concrete under uniaxial cyclic compression load. The effect of external confinement was performed by pre-tensioning steel straps in discontinuous rings with proposed width and thickness around the column specimens. Test results obtained are assessed and presented in this report.
1.2
Problem statement
Although there are many successful applications and researches conducted on high-strength concrete over the years, there is still a lack of confidence in the use of high-strength concrete among the code drafting committees, civil engineering, consultants, designers and clients in most countries. The main key points for the limited usage of high-strength concrete are its high brittleness and low ductility which are the primary emphasis in the assessment of safety (Mazen, S. Z., 2005). Many of the researches conducted only emphasized on short-term based and laboratory mix only. However, when deal with the long term based and commercial mix, issues concerned with the properties, such as strength and ductility will arise.
In the past decade, many studies have examined the monotonic stress-strain behaviour of unconfined and confined concrete (Hasan M. et. al., 2008, Saadtamanesh H. et. al., 1994, Weena P. L., et. al., 2005, and Yong Y. K., et al., 1988). Besides, extensive researches have been conducted on the stress-strain behaviour of unconfined and confined concrete under cyclic compression (Cheong H. K. and Perry S. H., 1993 and Lam L. et al., 2006), there were limited studies concerned of confined high-strength concrete under cyclic compression (Weena, P. L., et al., 2004). There exist many uncertainties in several issues concerning the high-strength concrete, including the validity of envelope curve for the concrete, the effect of loading history on the stress-strain response, and ultimate condition of
3
confined concrete using steel strap under uniaxial cyclic compression in comparison with those of uniaxial monotonic compression.
Therefore, the study of high-strength concrete column confined with the steel-straps subjected to uniaxial cyclic compression load is very important and will enhance the knowledge on the composite material. It can be applied to retrofit the existing building in potential seismic region and at the same time, to increase the confidence in the use of the high-strength concrete.
1.3
Research significance This report presents the test results of a study on the externally-confined
high-strength concrete columns with steel strap subjected to uniaxial cyclic compression load. The study also investigated on the effect of confinement using steel straps on the compressive strength and ductility of the externally-confined highstrength concrete column in fundamental simulation of earthquake loading (i.e. uniaxial cyclic compression load). At the same time, the effect of confinement ratio to the externally-confined high-strength concrete column will also be investigated.
1.4
Scope of study This study focused on the stress-strain relationship, compressive strength and
ductility of the externally-confined high-strength concrete column under uniaxial cyclic compression load. The interested parameters to be investigated are confinement ratio (volumetric ratio of steel strap), method of testing for hardened concrete (uniaxial monotonic compression load and uniaxial cyclic compression load), compressive strength and ductility of the high-strength concrete specimens. Due to time constraint, only the column specimens with designed compressive strength of 60 MPa will be cast and investigated in this study.
4
1.5
Objectives
The objectives of this study are as follows: i)
To study the stress-strain relationship of externally-confined highstrength concrete column specimen under uniaxial cyclic compression load.
ii)
To study the dependency of deformation of externally-confined highstrength concrete column specimen to the volumetric ratio.
iii)
To compare the test results between present and previous studies.
