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PSZ 19:16 (Pind. 1/07)
√
DECLARATION OF THESIS / UNDERGRADUATE PROJECT PAPER AND COPYRIGHT
Author’s full name : Oh Teck Yee Date of birth : 09 April 1982 Title : The Effect of Surface Roughness and Curing Condition on The Ultimate Shear Capacity of Composite Slab 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
(NEW IC NO. /PASSPORT NO.) NAME OF SUPERVISOR
Date : 04 November 2009 Date :
NOTES : * If the thesis is CONFIDENTAL or RESTRICTED, please attach with the letter from the organization 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
organization where research was done)*
OPEN ACCESS I agree that my thesis to be published as online open access
(full text)
√
820409-05-5212 Dr. Izni Syahrizal Ibrahim
“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 : DR. IZNI SYAHRIZAL IBRAHIM
Date : _______________________
THE EFFECT OF SURFACE ROUGHNESS AND CURING CONDITION ON THE ULTIMATE SHEAR CAPACITY OF COMPOSITE SLAB
OH TECK YEE
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
ii
I declare that this project report entitled “The Effect of Surface Roughness and Curing Condition on The Ultimate Shear Capacity of Composite Slab” 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 degree.
Signature : _______________________
Name : OH TECK YEE
Date : 04th NOVEMBER 2009
iii
Specially dedicated to my beloved parents and husband.
iv
ACK�OWLEDGEME�T
I have a host of people to thank for their involvement in this major work. The
order in which they are mentioned does not necessarily represent the amount of work
they did.
Major thanks to my supervisor, Dr. Izni Syahrizal Ibrahim, who always there
to provide me guidance and honest feedback on my project. His patience and
immeasurable contribution is the key to generate this project, I would have not
completing my thesis without him.
Huge thanks to Mr. Lee Sid Hwa, Mr. Oh Teck Huat, Mr. Teo, Ms.Teo Mei
Choo, Alex and all the technicians of civil engineering laboratory for their assistance
in the casting and set up of the test frame and instrumentation.
I would also like to express my deepest gratitude to the Universiti of
Teknologi Malaysia (UTM) for providing the necessary experimental facilities and
materials.
Deep appreciation to my dear husband, Kian Wei, my parents and siblings, I
would not get very far without their support and love. They are my QA teams and my
brainstorming teams who always provide inspiring ideas on my work done.
Last, thanks are due to the people that I do not mention their name for their
assistance and encouragement.
v
ABSTRACT
This thesis presents the effect of surface roughness and curing condition on
the horizontal shear capacity of precast slabs with in-situ concrete toppings. When
the composite member is loaded and bent in flexure, they will tend to slide relatively
to each other. In the case where mechanical shear key in the form of reinforcement is
not provided at the interface of the precast units, the texture at the interface becomes
a major parameter to ensure the horizontal shear strength of the contact surfaces is
achieved. Furthermore, the effect of concrete toppings under air cured and water
cured conditions were investigated due to the practical difficulties in achieving even
the minimum specified curing on-site. The experimental results of eight (8) precast
units with different surface roughness (smooth, roughened and exposed aggregates)
under four point bending test is presented. Interface slip was also measured
throughout the test to examine the composite behavior of the composite slabs. Based
on the findings, smooth surface produced the highest ultimate shear capacity in water
cured condition i.e. 19% - 34% higher than the others. However, rough surface in
transverse direction yielded the highest ultimate shear capacity under air cured
condition. The tests had clearly shown the effect of difference surface roughness and
curing condition to the ultimate shear capacity. Large slip of between 1.0 and 1.3 mm
was also observed for the specimen under air cured condition, indicating water cured
produce better interface bond. Furthermore, comparison of the experimental shear
strength with BS 8110 and Eurocode 2 shows that even the as-cast surface can
develop adequate shear resistance. Thus, shear reinforcement is not an essential
requirement and the production of precast slabs can be simplified.
vi
ABSTRAK
Tesis ini membincangkan kesan kekasaran permukaan dan kaedah
pengawetan terhadap tegasan ricih mengufuk untuk papak pratuang dengan konkrit
tuang di-situ. Secara umumnya, papak rencam bergelangsar sesama sendiri di bawah
lenturan. Kekasaran permukaan unit pratuang memainkan peranan penting untuk
menjayakan tegasan ricih mengufuk di antara permukaan sentuh itu apabila tetulang
ricih tidak dipasangkan. Tambahan pula, kesan konkrit tuang di-situ di bawah
pengawetan basah dan kering juga turut dikaji memandangkan kesukaran untuk
dicapai di tapak bina. Maka, semua faktor-faktor ini akan dikaji dan pengaruh
terhadap tegasan ricih mengufuk papak rencam yang diakibatkan oleh kekasaran
permukaan berserta dengan cara pegawetan dibincangkan dalam tesis ini. Sejumlah
lapan (8) papak rencam dengan kekasaran permukaan yang berlainan (licin, dedahan
batu, kasaran melintang dan kasaran panjang) dan cara pengawetan yang berbeza
(basah dan kering) dibandingkan dalam kajian ini. Gelinciran di antara komponen
turut diukur sepanjang eksperimen dijalankan. Keputusan ujikaji menunjukkan
permukaan licin dengan pengawetan air menghasilkan kekuatan ricih yang paling
tinggi, 19% - 34% lebih tinggi berbanding dengan permukaan kasar. Manakala,
keupayaan permukaan kasar melintang adalah lebih baik berbanding dengan
permukaan licin dalam pengawetan kering. Hasilan ini membuktikan bahawa
kekasaran permukaan dan cara pengawetan yang berlainan akan menghasilkan
kekuatan ricih yang berbeza. Gelinciran di antara 1.0 dan 1.3 mm telah diperolehi
untuk spesimen di bawah pengawetan kering, menunjukkan pengawetan basah
menghasilkan ikatan antara muka yang lebih baik. Tambahan pula, tegasan ricih
mengufuk yang diperolehi dalam ujikaji eksperimen adalah lebih tinggi berbanding
dengan tegasan yang dinyatakan dalam BS 8110 dan Eurocode 2. Dengan itu, dapat
disimpulkan bahawa tetulang ricih bukanlah suatu keperluan dalam pembinaan
papak rencam.
vii
TABLE OF CO�TE�TS
CHAPTER TITLE PAGE
DECLARATIO� ii
DEDICATIO� iii
ACK�OWLEDGEME�T iv
ABSTRACT v
ABSTRAK vi
TABLE OF CO�TE�TS vii
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF �OTATIO�S xv
1 I�TRODUCTIO�
1.1 Background 1
1.2 Problem Statement 2
1.3 Objectives 4
1.4 Scopes of Study 4
1.5 Importance of Study 5
1.6 Thesis Structure 5
2 LITERATURE REVIEW
2.1 Introduction 6
2.2 Shear Capacity of the Interface 6
2.2.1 Surface Roughness 8
2.2.2 Previous Work Related to Surface 9 Roughness
2.2.3 International Codes of Practice on 13 Interface Shear Strength
viii
2.2.4 Previous Work Related to Interface 14 Shear Strength
2.3 Curing Condition versus Shrinkage Problem 17
2.3.1 Previous Work Related to Curing 19 Technique
2.4 Summary 22
3 EXPERIME�TAL METHODOLOGY
3.1 Introduction 23
3.2 Test Specimens 24
3.2.1 Surface Roughness 26
3.3 Specimens Preparation and Casting Procedure 28
3.3.1 Casting of Precast Slab Specimen 28
3.3.2 Casting of Concrete Toppings 30
3.4 Curing Techniques 31
3.4.1 Water Cured 31
3.4.2 Dry Cured 32
3.5 Combined Bending and Shear Test 32
3.5.1 Testing Procedure 34
3.6 Flow Chart of the Research Methodology 34
4 EXPERIME�TAL RESULTS
4.1 Introduction 35
4.2 Concrete Topping Properties and Interface Texture 35
4.3 Test Results 36
4.3.1 Load versus Deflection Relationship 37
4.3.1.1 Water Cured Specimens 37
4.3.1.2 Air Cured Specimens 39
4.3.2 Load versus Interface Slip Relationship 40
4.3.2.1 Water Cured Specimens 40
4.3.2.2 Air Cured Specimens 43
4.3.3 Load versus Strain Relationship 47
4.3.3.1 Water Cured Specimens 47
4.3.3.2 Air Cured Specimens 49
ix
4.3.4 Cracking Pattern 52
5 A�ALYSIS & DISCUSSIO�
5.1 Introduction 55
5.2 Shear Force and Deflection Relationship 55
5.3 Interface Shear Stress and Interface Slip 58
Relationship
6 CO�CLUSIO� A�D RECOMME�DATIO�
6.1 Conclusion 63
6.2 Recommendation 64
LIST OF REFERE�CES 65
APPE�DIX A – Determination of Pult 67
APPE�DIX B – Calculation of Vu 68
APPE�DIX C – Calculation of Vco 69
APPE�DIX D – Concrete Mix Design 70
APPE�DIX E – Calculation of Shear Strength, ���� 72
x
LIST OF TABLES
TABLE �O. TITLE PAGE
2.1 Investigated Test Parameters 11
2.2 Surface Treatment of the Composite Beam 12
2.3
c and � Factors Depending on the Roughness at the Interface
14
3.1 Mix Proportions Design for Specimens 25
3.2 Specimen Details and Test Parameters 27
4.1 Specimen Description and Concrete Properties at Test Day
36
4.2 Water Cured Specimen Shear Test Result 38
4.3 Air Cured Specimen Shear Test Result 40
5.1 Comparisons of Test Results with Vco and Vu 58
5.2 Interface Shear Strength Result 61
xi
LIST OF FIGURES
FIGURE �O. TITLE PAGE
1.1 Interface Shear Stress of Composite Member 2
1.2 Precast Slab with Extruded Shear Key 2
2.1
Measuring Device for Measuring Surface Roughness
8
2.2 Arithmetical Mean Deviation of the Profile, Ra
8
2.3 Specimen Details 10
2.4 Schematic Diagram of Experimental Setup 10
2.5 Test Specimens 12
2.6 Intended Construction Joint 13
2.7 Transformed Uncracked Section 15
2.8 Transformed Cracked Section 15
2.9
Typical Shear Pattern in Test Beams Bent in Flexure
16
2.10 Schematic Diagram of “Push-off” Method 16
2.11 Schematic Diagram of Ideal Curing of Concrete
18
2.12 Concrete Strength with Moisture Present for Curing
18
2.13 Substrate bodies with sandblasted interfaces (S1-S4)
20
2.14 Smooth Interfaces 21
2.15 Notched Interfaces 21
xii
3.1 Dimension of Precast Slabs 24
3.2 BRC Installed in Concrete Topping 25
3.3 Air Hammer Hand Tool 26
3.4 Difference Surface Roughness of the Precast Slab
27
3.5 Concrete Drum Mixer with 0.3m3/cast 29
3.6 Fresh Precast Slab after Casting 29
3.7 Optimum Wet Surface prior to Placement of Topping
30
3.8 Cross Section of the Specimen with Concrete Topping
30
3.9 Specimen Water Cured with Burlap 31
3.10 Combined Bending and Shear Test Setup 32
3.11 Position of Demec Pips attached to Specimens
33
3.12 Demec Gauge 33
3.13 Flow Chart of the Research Methodology 34
4.1 Load vs. Deflection Relationship for Water Cured Specimens
38
4.2 Load vs. Deflection Relationship for Air Cured Specimens
39
4.3(a) Load vs. Interface Slip for Specimen Smooth-A up to 1mm
41
4.3(b) Load vs. Interface Slip for Specimen Exposed-A up to 1 mm
41
4.3(c) Load vs. Interface Slip for Specimen Rough-LD-A up to 1 mm
42
4.3(d) Load vs. Interface Slip for Specimen Rough-TD-A up to 1 mm
43
4.4(a) Load vs. Interface Slip for Specimen Smooth-B up to 1 mm
44
xiii
4.4(b) Load vs. Interface Slip for Specimen Exposed-B up to 1 mm
44
4.4(c) Load vs. Interface Slip for Specimen Rough-LD-B up to 1 mm
45
4.4(d) Load vs. Interface Slip for Specimen Rough-TD-B up to1 mm
46
4.5(a) Load vs. Strain Relationship for Specimen Smooth-A
47
4.5(b) Load vs. Strain Relationship for Specimen Exposed-A
47
4.5(c) Load vs. Strain Relationship for Specimen Rough-LD-A
48
4.5(d) Load vs. Strain Relationship for Specimen Rough-TD-A
48
4.6(a) Load vs. Strain Relationship for Specimen Smooth-B
49
4.6(b) Load vs. Strain Relationship for Specimen Exposed-B
50
4.6(c) Load vs. Strain Relationship for Specimen Rough-LD-B
50
4.6(d) Load vs. Strain Relationship for Specimen Rough-TD-B
51
4.7(a) Shear Cracking Pattern at Failure for Specimen Smooth-A
52
4.7(b) Shear Cracking Pattern at Failure for Specimen Exposed-A
52
4.7(c) Shear Cracking Pattern at Failure for Specimen Rough-LD-A
52
4.7(d) Shear Cracking Pattern at Failure for Specimen Rough-TD-A
52
4.7(e) Shear Cracking Pattern at Failure for Specimen Smooth-B
53
4.7(f) Shear Cracking Pattern at Failure for Specimen Exposed-B
53
xiv
4.7(g) Shear Cracking Pattern at Failure for Specimen Rough-LD-B
53
4.7(h) Shear Cracking Pattern at Failure for Specimen Rough-TD-B
53
5.1(a) Shear Force vs. Deflection Relationship for Water Cured Specimens
56
5.1(b) Shear Force vs. Deflection Relationship for Air Cured Specimens
57
5.2(a) Interface Shear Stress vs. Interface Slip Relationship for Water Cured Specimens up to 1 mm
59
5.2(b) Interface Shear Stress vs. Interface Slip Relationship for Air Cured Specimens up to 1 mm
60
xv
LIST OF �OTATIO�S
Icomp Second moment are of the composite section
bi Width of the interface
bw , bv Width of the concrete topping
beff Effective width
Scomp First moment of area above and about the centroidal axis
ft Concrete splitting tensile strength
fcp Concrete compressive stress at the centroidal axis due to prestressing
fy Characteristic strength of reinforcement
fck Cylinder compressive strength of concrete = 0.8fcu
fcu , fcc Cube compressive strength of concrete
p Ratio of tensile reinforcement
w Uniform load distribution
d Effective depth of the tension reinforcement
L Effective span length
a Shear span
x Neutral axis
z Lever arm of composite action
yt Distance from the neutral axis of the composite section to half of concrete topping depth
ht Concrete topping depth
ys Distance from the neutral axis of the composite section to the steel centroid
As Area of tension reinforcement
xvi
As’ Area of compression reinforcement
A Compression zone being considered
A’ Effective area under normal compressive stress
Mur Design ultimate bending moment
Vu , Vult Ultimate shear capacity
Vds Transverse shear force
Vco Design ultimate shear capacity of a uncracked flexure section
�� Normal compressive stress
�� Stress per unit area
sn Imposed slip displacement during the cycle
su Shear slip corresponding to maximum mobilized shear stress
�,� Frictional stress response to the nth cycle
�� Design shear stress at the interface
�� Design shear resistance at the interface
���� Experimental shear stress
CHAPTER 1
I�TRODUCTIO�
1.1 Background
Reinforced concrete is concrete in which steel reinforcement bars have been
incorporated to give it extra tensile strength. It can be further classified into cast in-
situ concrete or precast concrete. Precast concrete is cast and cured in a controlled
environment. It is then transported to the construction site and lifted into position. In
contrast, precast concrete is having higher standard compare to cast in-situ concrete.
Apart from the quality, precast concrete system offers faster erection speed when
compared to normal reinforced concrete construction. Erection is carried out with the
aid of lifting equipments.
There are many different types of precast concrete forming systems
including slabs, walls, beams, columns, foundations, etc. However, main focus is
given to floor systems as this is the key to creating optimal building structures.
Difference in floor systems may have significant impact on construction schedule
and materials cost. Precast concrete flooring offers an economic and multitalented
solution to ground and suspended floors in any types of building construction. In
order to enhance the structural performance, cast in-situ toppings are added to the
precast slab. This composite member is designed to act monolithically. Hence,
understanding the behavior of monolithic action of composite member has become a
topic of particular challenge to researchers throughout the world recently.
1.2 Problem Statement
The principle of composite construction can be demonstrated by comparing
the action of two joists placed one on top of the other. When the precast
concrete toppings is bent in flexure, the composite members tend to slide to e
other as shown in Figure 1.1.
Figure 1.1: Interface Shear Stress of Composite Member
If these composite
key, the bending strength and stiffness will be significantly improved. Nevertheless,
reliance has to be made on the shear strength and bond between the contact surfaces
without any mechanical
Figure
Problem Statement
The principle of composite construction can be demonstrated by comparing
the action of two joists placed one on top of the other. When the precast
bent in flexure, the composite members tend to slide to e
Figure 1.1.
: Interface Shear Stress of Composite Member
these composite members are physically connected using mechanical shear
key, the bending strength and stiffness will be significantly improved. Nevertheless,
made on the shear strength and bond between the contact surfaces
shear key.
Figure 1.2: Precast Slab with Extruded Shear Key
2
The principle of composite construction can be demonstrated by comparing
the action of two joists placed one on top of the other. When the precast unit with
bent in flexure, the composite members tend to slide to each
: Interface Shear Stress of Composite Member
mechanical shear
key, the bending strength and stiffness will be significantly improved. Nevertheless,
made on the shear strength and bond between the contact surfaces
3
Normally, the need for reinforcement across the interface will depend upon several
factors: type of surface texture, the loading or geometry of the construction [6]. In the
case where joint surface area is having the same area as the topping, it is referred as
low shear area at the interface, where the force can be transmitted without shear key
as long as adequate interlocking effects are available.
In designing the interface to ensure composite action, several Codes of
Practice [2,5,6] have considered surface roughness as the major factor contributing to
limiting stresses for different roughness categories. Some attempts to enumerate
surface texture are given in the FIP document [6]. The general types of surface texture
are smooth and rough. Within the FIP Commission itself, they believe smooth
interfaces have better bonding effects compared to the roughened. The design
guidance is still lack of congruency especially at the serviceability limit state.
Other than surface texture, surface preparations may cause problems and
affect the monolithic behaviour of the composite member. According to the research
work carried out by Walraven [16], the precast slab surface preparation will affect the
capacity of the interface shear strength. This includes reductions to the interface
shear strength and lead to occurrence of interface slip.
The other common problem associated with concrete industry is cracking
problem. The most common causes of cracks in concrete are: stress due to applied
loads or stress due to drying shrinkage or temperature changes. Stress cracks can be
easily eliminated by having proper concrete design for the load. However, drying
shrinkage is an inescapable and inherent property of the concrete. To minimize these
cracks, proper curing to hold the moisture is obligatory. As long as the moisture in
concrete is trapped for certain period, and that adequate tensile strength is allowed to
gain in concrete for this particular period, the concrete is unlikely to shrink [1].
Two major parameters will be focused in this study i.e. surface texture of the
precast slab and the curing technique applied for the concrete topping. The effect of
these parameters on the interface shear strength shall be examined.
4
1.3 Objectives
The objectives of this study are as follows:
(i) To study the structural performance of composite slab with different surface roughness
(ii) To evaluate the interface shear strength of the composite slab for different curing condition
(iii) To compare the experimental shear stress result with the minimum horizontal shear stress provided in BS 8110 and Eurocode 2
1.4 Scopes of Study
The endeavor of this project is to study the interface shear strength between
the 100 mm thickness precast solid slab and 75 mm thickness concrete toppings with
different surface roughness and curing conditions. A total number of eight precast
units will be prepared in this study. The performance of these specimens will be
assessed through the shear capacity and load-deflection relationships of the
composite slabs under the combined bending and shear test.
Since the precast concrete slab surface is not provided with any shear
mechanical key, the texture of the interface of the precast units becomes the key
parameter for determining the interface shear strength of the composite members. It
is vital to study what kind of surface can produce better bond at the interface.
Therefore, eight composite slabs with four different types of surface roughness
(smooth as-cast, roughened in both the longitudinal and transverse direction, and
surface with exposed aggregate) were prepared.
It is obvious that curing method affect significantly the performance expected
from specified water/cement ratio and cement content. In reality, it is always difficult
to cure concrete satisfactorily due to some practical problems especially when the
surface area is large. Hence, the concrete toppings of these eight specimens shall be
5
further categorized into two curing conditions i.e. air cured and water cured. Air
cured represents the actual poor curing practice at construction site and the effect on
the shear strength in lieu to this condition will be studied. Meanwhile, all the precast
slab units will be water cured as practiced by the manufacturer.
In the combined bending and shear test, a pair of point loads was applied at
1.5H from the support at both ends, where H is the overall depth of the composite
slab. The interface slip of the longitudinal joints will be monitored throughout test.
1.5 Importance of Study
The study is intended to determine the most suitable casting method
according to different surface characteristic and curing conditions. Appropriate
casting method may reduce the remedial work due to delamination, loss of
serviceability or curvature problem associated with concrete toppings. By improving
the composite performance, the overall construction cost and maintenance cost can
be reduced.
1.6 Thesis Structure
The structure of this thesis is as shown below: (a) Chapter 2 describes a review of the literature on the subject of this project
(b) Chapter 3 presents the preparation work for the specimens and the experimental
setup for combined bending and shear test
(c) Chapter 4 interpret the experimental results
(d) Chapter 5 presents the analysis and discussion of the results
(e) Chapter 6 presents the conclusions and the recommendations for further
investigation
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
For full composite action of the precast slab with concrete topping, the shear
and bond strength of the interface between the two elements are critical. Various
international codes of practice recommend different allowable interface shear
strengths depending on the surface characteristics. Whereas, the relationship between
shear, surface roughness and bond strengths of interfaces in different composite
concrete structures have been investigated by many researchers in the previous
studies. The results and findings shall be discussed in detail in the following sections.
2.2 Shear Capacity of the Interface
To retain the continuity and efficiency of monolithic construction, composite
construction is the most cost-effective way of combining precast and cast in-situ
concrete. The monolithic behavior is possible only if the horizontal shear is
effectively transferred between the topping and precast slab at their interface. When
the composite member is bent in flexure, they tend to slide with each other
respectively. For ensuring the horizontal strength is achieved, shear connector is
provided at the interface to transfer the force and act as an interlocking device. In the
case where no mechanical key is provided, reliance has to be made on the bond and
shear strength between the contact surfaces.
7
In 1991, Ueda and Stitmannaithum [15] conducted an experimental program to
investigate the shear-carrying capacity of precast prestressed hollow core slabs
(HCU) with concrete topping. Ten specimens were prepared and the study parameter
includes pre-stressing force, tension reinforcement ratio, shear span-to-effective-
depth ratio and the concrete topping depth. In their experimental investigation, two
types of shear cracking were observed; web shear cracking and flexural shear
cracking. In the prediction of ultimate shear capacity, reference was made to the
formula proposed by Niwa [11] for ordinary reinforced concrete beams (a/d < 2.5) and
the modified formula proposed by Okamura et. al. [12] for ordinary reinforced
concrete slender beams (a/d > 2.5) without shear reinforcement. These formulas are
given as:
�� = 0.244������1 + !" #1 + 3.33 %
� & ''(#)
*&� +%, if (a/d < 2.5) (2.1)
�� = 0.20���-�(100!)
-�(1000/,)
-1(0.75 + '.4
)*
)+%, if (a/d > 2.5) (2.2)
They observed in their tests complete composite action although only rough
surface finishing was provided. Small slips were measured between the precast and
topping concrete elements, and there was no evidence that the interface was an
initiator of ultimate failure. For both the thick and thin concrete topping, web shear
cracking always took place in the precast element at the level of the hollow where the
narrowest web width was found. Because of the circular hollow, the highest principle
tensile stress – resulting from the combination of shear stress and flexural stress due
to the external applied load, as well as the compressive stress due to the effective
prestressing force – can be found at the narrowest web instead of that of the
centroidal axis depth. The comparison between the calculated and experimental
results shows good agreement. Ueda [15] suggested that the equations used to
calculate the ultimate shear capacity for ordinary reinforced concrete beams without
shear reinforcement can also be applied to the HCU with concrete toppings by using
the strength of the concrete toppings and its width in the prediction.
2.2.1 Surface Roughness
In the FIP Guide to Good Practice (FIP 1982)
surface roughness in which a precast unit may have prior to
concrete toppings. They were categorized based on the end production and there is
no clear guidance to differentiate between
Nevertheless, FIP Commission it
better overall bonding than rough surfaces. According to Swedish Standard
measuring device as shown in Figure 2.1 is use
a member. The measuring device shall be
and the gauge is read. The measurement procedure is based on procedure given in
BS1134 [3]. The roughness amplitude represented by
deviation of the profile, taking the average value of t
Figure 2.2.
Figure 2.1: Measuring Device for Measuring Surface Roughness
Figure 2.2: Arithmetical Mean Deviation of the Profile,
Surface Roughness
In the FIP Guide to Good Practice (FIP 1982) [6], there are ten categories of
in which a precast unit may have prior to the casting of the
concrete toppings. They were categorized based on the end production and there is
no clear guidance to differentiate between the rough and smooth surface.
Nevertheless, FIP Commission itself believes that smooth interface always provide
better overall bonding than rough surfaces. According to Swedish Standard
measuring device as shown in Figure 2.1 is used to measure the surface roughness of
a member. The measuring device shall be placed along one measured
and the gauge is read. The measurement procedure is based on procedure given in
. The roughness amplitude represented by Ra is the arithmetical mean
deviation of the profile, taking the average value of the surface profile shown in
Figure 2.1: Measuring Device for Measuring Surface Roughness
: Arithmetical Mean Deviation of the Profile, R
8
, there are ten categories of
the casting of the in-situ
concrete toppings. They were categorized based on the end production and there is
rough and smooth surface.
self believes that smooth interface always provide
better overall bonding than rough surfaces. According to Swedish Standard [13], a
to measure the surface roughness of
line at a time
and the gauge is read. The measurement procedure is based on procedure given in
is the arithmetical mean
he surface profile shown in
Figure 2.1: Measuring Device for Measuring Surface Roughness
Ra
9
The departure of the profile is represented by y1 to yn, where n is the number of
profile departures. The equation of Ra given by:
56 = '7 8 9:(;)<,;7
= (2.3) or approximately,
56 ≈ '� ∑ (:@
�@A' )
(2.4) In practice, the values of Ra are determined within the evaluation length which
covers several sampling lengths, l, i.e. equal to the cut-off point. In the work by
Mitchell Gohnert [7], similar roughness measurement was used to determine the
roughness for smooth and rough surfaces. The work shall be further discussed in the
following section.
2.2.2 Previous Work Related to Surface Roughness
In 1987, Theodossius & Elisabeth [14] studied the mechanism of load
transferred along unreinforced concrete interfaces by means of friction for several
surface roughnesses. The behavior of both smooth and rough interfaces of plain
concrete subjected to monotonically or cyclically impose shear displacements was
investigated through several series of tests. Unreinforced concrete blocks of 0.90 m
long x 0.30 m height x 0.15 m wide were cast in metal molds. During concreting,
two grooves with 15 mm deep and 300 mm long were provided at each face of the
specimen. Before testing, the specimens were cracked by splitting. Thus, between
adjacent concrete sub-blocks, two interfaces were formed as shown in Figure 2.3.
The three concrete sub
steel rods, 30 mm in diameter. Schematic
shown in Figure 2.4. The tests were displacement
branch of the shear stress versus shear displacement diagram is obtained. Shear
displacement was imposed by means of mechanical jacks and the re
specimen was measured by using load
experimentally investigated are summarized in Table 2.
Figure 2.4: Schematic Diagram of Experimental Setup
Figure 2.3: Specimen Details
The three concrete sub-blocks were held together by means of four external
steel rods, 30 mm in diameter. Schematic diagram of the experimental setup is as
shown in Figure 2.4. The tests were displacement-controlled so that the falling
branch of the shear stress versus shear displacement diagram is obtained. Shear
displacement was imposed by means of mechanical jacks and the re
specimen was measured by using load-cells. Test parameters
experimentally investigated are summarized in Table 2.1.
Figure 2.4: Schematic Diagram of Experimental Setup
10
blocks were held together by means of four external
experimental setup is as
controlled so that the falling
branch of the shear stress versus shear displacement diagram is obtained. Shear
displacement was imposed by means of mechanical jacks and the response of the
which were
Figure 2.4: Schematic Diagram of Experimental Setup