STRENGTHENING OF HIGH STRENGTH REINFORCED CONCRETE …

1

STRENGTHENING OF HIGH STRENGTH REINFORCED

CONCRETE SLABS WITH CFRP LAMINATES

by

Hasan Saleh Mahmoud

A Thesis Presented to the Faculty of the

American University of Sharjah

College of Engineering

in Partial Fulfillment

of the Requirements

for the Degree of

Master of Science in

Civil Engineering

Sharjah, United Arab Emirates

May 2016

2

© 2016 Hasan Saleh Mahmoud. All rights reserved.

3

Approval Signatures

We, the undersigned, approve the Master’s Thesis of Hasan Saleh Mahmoud

Thesis Title: Strengthening of High Strength Reinforced Concrete Slabs with CFRP

Laminates

Signature Date of Signature

(dd/mm/yyyy)

___________________________ _______________

Dr. Rami Hawileh

Associate Professor, Department of Civil Engineering

Thesis Advisor

___________________________ _______________

Dr. Jamal El-Din Abdalla

Professor, Department of Civil Engineering

Thesis Co-Advisor

___________________________ _______________

Dr. Farid Hamid Abed

Associate Professor, Department of Civil Engineering

Thesis Committee Member

___________________________ _______________

Dr. Basil Darras

Associate Professor, Department of Mechanical Engineering

Thesis Committee Member

___________________________ _______________

Dr. Osman Akan

Head, Department of Civil Engineering

___________________________ _______________

Dr. Mohamed El-Tarhuni

Associate Dean, College of Engineering

___________________________ _______________

Dr. Leland Blank

Dean, College of Engineering

___________________________ _______________

Dr. Khaled Assaleh

Interim Vice Provost for Research and Graduate Studies

4

Acknowledgments

First and foremost, I thank Allah the most compassionate, the most merciful

for guiding me and helping me throughout my life as I have grown as an individual

and as an educated person.

I would like to thank my father, Saleh and my mother, Aida for supporting me

throughout my life and for being the rock that I can lean on whenever I am in need to.

I would also like to thank my sister Sara and my three brothers; Husam, Bassam, and

Yousef for bearing with me in this journey. I would like to thank my whole family for

being the greatest source of encouragement. I would also like to thank my friends

Ayham, Mohammad, and all others for extending the helping hand and being my

guide in my life.

I would also like to thank my two advisors Dr. Rami Haweeleh, and Dr. Jamal

Abdalla for helping me and guiding me. I would also like to thank Mr. Aqeel Ahmed

for being the big brother and the supporter. I would like to acknowledge the help that

was extended to me from Eng Mohammad Ansari and Eng Arshi Faridi. Many thanks

go to all my professors who sparked the love of knowledge in my heart. I would like

to thank the two companies that provided me with all the support that I needed: Rak

Precast and Structural Technologies.

At the end, I can’t thank enough my second home, the American University of

Sharjah for supporting me in every way and providing me with the chance of being a

GTA and work closely with some of the greatest minds in civil engineering.

5

Dedication

To my two superheroes; my father and my mother who bestowed on me their

unconditional love… I hope I made you proud.

6

Abstract

During the last few decades, engineers and researchers used high-strength

concrete to cast reinforced concrete (RC) structures. Accordingly, the dead weight of

buildings and structures were reduced significantly, which allowed engineers to

construct higher and larger buildings. Reinforced concrete slabs are the largest

structural members in buildings. This research aims to reduce the thickness of RC

slabs using high-strength concrete strengthened with carbon reinforced polymers

(CFRP) laminates in flexural. In this study the behavior of 100 mm thick RC slabs

with different concrete compressive strengths of 40, 70, and 100 MPa was inspected.

A total of 54 RC slab specimens were cast and tested under two-point loading until

failure. The specimens were divided into three groups having different flexural steel

reinforcement ratios of 0.45, 1.00, and 1.79%, respectively. Each group of specimens

was strengthened with one and two layers of CFRP sheets, which were externally

attached to the soffit of the RC slabs, to enhance their flexural capacity. The test

results indicated an increase in the load-carrying capacity of the strengthened slabs in

the range between 12 to 378 %. It was also observed that the highest contribution was

for those specimens with low reinforcement ratio, in which their control specimens

failed by tensile membrane action. The mid-span deflection response curves and load-

carrying capacity of the slabs were also predicted with a good level of accuracy using

the design guidelines of ACI 440-2R-08. In conclusion, strengthening of high-strength

thin RC slabs with CFRP laminates is a valid choice to enhance their flexural

behavior, with a minimal increase in their dead load, due to the lightweight of the

CFRP laminates.

Search Terms: CFRP laminates, strengthening, flexibility model, thin slabs, high

strength concrete, and reinforcement ratio.

7

Table of Contents

Abstract ........................................................................................................................... 6

Table of Contents ............................................................................................................ 7

List of Figures ............................................................................................................... 10

List of Tables ................................................................................................................ 15

Chapter 1: Introduction ................................................................................................. 16

1.1. Background ....................................................................................................... 16

1.2. Research Significance ....................................................................................... 18

1.3. Research Objectives .......................................................................................... 19

1.4. Thesis Organization ........................................................................................... 19

Chapter 2: Literature Review ........................................................................................ 21

2.1 General Overview .............................................................................................. 21

2.2 High Strength Concrete ...................................................................................... 22

2.3 CFRP Laminates for Flexure Strengthening ...................................................... 23

Chapter 3: Experimental Program ................................................................................ 25

3.1. Test Specimens Properties ................................................................................ 25

3.2. Materials ........................................................................................................... 25

3.2.1. Concrete material properties ....................................................................... 25

3.2.2. Steel material properties ............................................................................. 28

3.2.3. Epoxy V-Wrap 700 ..................................................................................... 29

3.2.4. CFRP sheets: V-Wrap C200H properties ................................................... 30

3.3 Specimens Preparation ....................................................................................... 30

3.4 Test Matrix and slab detailing ............................................................................ 33

Chapter 4: Experimental Results and Discussion ......................................................... 45

4.1. Load versus Micro-strain, and Failure Modes .................................................. 45

8

4.1.1 Group C 40 LR ............................................................................................ 46

4.1.2 Group C 40 MR ........................................................................................... 51

4.1.3 Group C 40 HR: ........................................................................................... 55

4.1.4 Group C 70 LR ............................................................................................ 59

4.1.5 Group C 70 MR ........................................................................................... 63

4.1.6 Group C 70 HR: ........................................................................................... 67

4.1.7 Group C 100 LR .......................................................................................... 71

4.1.8 Group C 100 MR ......................................................................................... 76

4.1.9 Group C 100 HR .......................................................................................... 80

4.2. Summary of the Results Obtained:.................................................................... 85

4.3. Repeatability of Results: ................................................................................... 90

4.3.1 Load versus mid-span deflection ................................................................. 91

Chapter 5: Discussion of Results .................................................................................. 98

5.1 Group (C 40) ...................................................................................................... 98

5.1.1 Load-deflection and ultimate performance .................................................. 98

5.1.2 Strain response ............................................................................................. 99

5.1.3 Ductility measures ..................................................................................... 102

5.1.4 Toughness measures .................................................................................. 103

5.2 Group (C 70) .................................................................................................... 104

5.2.1 Load-deflection and ultimate performance ................................................ 104

5.2.2 Strain response ........................................................................................... 105



5.3 Group (C 100) .................................................................................................. 109

5.3.1 Load-deflection and ultimate performance ................................................ 109

5.3.2 Strain response ........................................................................................... 110


9


5.4 Conclusions ...................................................................................................... 114

5.4.1 Effect of reinforcement ratio ..................................................................... 114

5.4.2 Effect of concrete compressive strength .................................................... 116

5.4.3 Effect of CFRP reinforcement ratio ........................................................... 119

Chapter 6: Theoretical Models.................................................................................... 123

6.1. Flexibility Model for Cracked Sections .......................................................... 123

6.2. Beams graphs and predicted curves ................................................................ 125

6.3. Ultimate Moment Capacity Prediction: ........................................................... 139

Chapter 7: Summary and Conclusion ......................................................................... 143

References ................................................................................................................... 147

Appendix ..................................................................................................................... 150

Appendix A: Load deflection graphs ..................................................................... 150

Vita .............................................................................................................................. 167

10

List of Figures

Figure 1: Stress- Strain Curve of tested Steel Rebars .................................................. 29

Figure 2: CFRP location marking ................................................................................ 31

Figure 3: Surface preparation....................................................................................... 31

Figure 4: Mixing, painting of the epoxy, and the soaking of the CFRP sheets in

epoxy. ........................................................................................................................... 32

Figure 5: Rolling and leveling of the CFRP sheets on the concrete surface. .............. 32

Figure 6: Testing method and elevation view of the tested slabs. ............................... 37

Figure 7: Front view of the slab specimens. ................................................................ 37

Figure 8: Cross-section a-a of the slab specimens. ...................................................... 37

Figure 9: Strain Gauge locations.................................................................................. 42

Figure 10: Strain Gauge locations................................................................................ 43

Figure 11: General Test Arrangement ......................................................................... 44

Figure 12: Load (kN) versus mid-span deflection (mm) schematic ............................ 45

Figure 13: Load versus microstrain for slab specimen (C 40 LR C) ........................... 47

Figure 14: Failed slab specimen (C 40 LR C) ............................................................. 48

Figure 15: Load versus microstrain slab specimen (C 40 LR 1L) ............................... 49

Figure 16: Failed slab specimen (C 40 LR 1L)............................................................ 49

Figure 17: Load versus microstrain slab specimen (C 40 LR 2L) ............................... 50


Figure 19: Load versus microstrain for slab specimen (C 40 MR C) .......................... 51

Figure 20: Failed slab specimen (C 40 MR C) ............................................................ 52

Figure 21: Load versus microstrain slab specimen (C 40 MR 1L) .............................. 53

Figure 22: Failed slab specimen (C 40 MR 1L) .......................................................... 53

Figure 23: Load versus microstrain for slab specimen (C 40 MR 2L) ........................ 54


Figure 25: Load (kN) versus micro strain .................................................................... 56

Figure 26: Concrete crushing and final failure ............................................................ 56

Figure 27: Load versus microstrain for slab specimen (C 40 HR 1L) ......................... 57

Figure 28: Failed slab specimen (C 40 HR 1L) ........................................................... 57



Figure 31: Load versus microstrain for slab specimen (C 70 LR C) ........................... 59

11

Figure 32: Slab Steel Rupture and beam failure .......................................................... 60

Figure 33: Load versus microstrain for slab specimen (C 70 LR 1L) ......................... 61


Figure 35: Load versus microstrain for slab specimen (C 70 LR 2L) ......................... 62


Figure 37: Load versus microstrain for slab specimen (C 70 MR C) .......................... 63

Figure 38: Failed slab specimen (C 70 MR C) ............................................................ 64





Figure 43: Load versus microstrain for slab specimen (C 70 HR C)........................... 68

Figure 44: Failed slab specimen (C 70 HR C) ............................................................. 68



Figure 47: Load versus microstrain slab specimen (C 70 HR 2L) .............................. 71


Figure 49: Load versus microstrain for slab specimen (C 100 LR C) ......................... 72

Figure 50: Failed slab specimen (C 100 LR C) ........................................................... 73

Figure 51: Load versus microstrain for slab specimen (C 100 LR 1L) ....................... 74

Figure 52: Failed slab specimen (C 100 LR 1L).......................................................... 74

Figure 53: Load versus microstrain for slab specimen (C 100 LR 2L) ....................... 75

Figure 54: Failed slab specimen (C 100 LR 2L).......................................................... 75

Figure 55: Load versus microstrain for slab specimen (C 100 MR C) ........................ 76

Figure 56: Failed slab specimen (C 100 MR C) .......................................................... 77

Figure 57: Load versus microstrain for slab specimen (C 100 MR 1L) ...................... 78

Figure 58: Failed slab specimen (C 100 MR 1L) ........................................................ 78

Figure 59: Load versus microstrain for slab specimen (C 100 MR 2L) ...................... 79

Figure 60: Failed slab specimen (C 100 MR 2L) ........................................................ 80

Figure 61: Load versus microstrain for slab specimen (C 100 HR C)......................... 81

Figure 62: Failed slab specimen (C 100 HR C) ........................................................... 81

Figure 63: Load versus microstrain slab specimen (C 100 HR 1L) ............................ 82

Figure 64: Failed slab specimen (C 100 HR 1L) ......................................................... 83

12

Figure 65: Load versus microstrain for slab specimen (C 100 HR 2L) ....................... 84

Figure 66: Failed slab specimen (C 100 HR 2L) ......................................................... 84

Figure 67: Load versus Mid-span Deflection for (C 40 LR 1L) slabs ......................... 91

Figure 68: Load versus Mid-span Deflection for (C 40 LR 2L) slabs ......................... 91

Figure 69: Load versus Mid-span Deflection (C 70 HR C) slabs ................................ 92

Figure 70: Load versus Mid-span Deflection for (C 70 HR 1L) slabs ........................ 92

Figure 71: Load versus Mid-span Deflection for (C 70 HR 2L) slabs ........................ 93

Figure 72: Load versus Mid-span Deflection for (C 100 MR 1L) slabs ...................... 93

Figure 73: Load versus Mid-span Deflection for (C 100 HR 1L) ............................... 94

Figure 74: Group C 40 - load (kN) versus deflection (mm) ........................................ 98

Figure 75: Steel strain response for Group C 40........................................................ 100

Figure 76: FRP strain response for Group C 40 ........................................................ 101

Figure 77: Concrete strain response for Group C 40 ................................................. 102

Figure 78: Ductility comparison ................................................................................ 103

Figure 79: Toughness comparison (UT/UTCB) ............................................................ 103

Figure 80: Group C 70 - load (kN) versus deflection (mm) ...................................... 104

Figure 81: Group C 70 – Steel strain response .......................................................... 105

Figure 82: Group C 70 –FRP strain response ............................................................ 106

Figure 83: Group C 70 –Concrete strain response ..................................................... 107



Figure 86: Group C100 - load (kN) versus deflection (mm) ..................................... 109

Figure 87: Steel strain response for Group C100....................................................... 111

Figure 88: FRP strain response for Group C 100 ...................................................... 111

Figure 89: Concrete strain response for Group C 100 ............................................... 112



Figure 92: Reinforcement ratio effect on C40 ........................................................... 114

Figure 93: Reinforcement ratio effect on C70 ........................................................... 115

Figure 94: Reinforcement ratio effect on C100 ......................................................... 116

Figure 95: Concrete compressive strength effect on LR ........................................... 117

Figure 96: Concrete compressive strength effect on MR .......................................... 118

Figure 97: Concrete compressive strength effect on HR ........................................... 119

13

Figure 98: CFRP ratio effect on LR ........................................................................... 120

Figure 99: CFRP ratio effect on MR ......................................................................... 121

Figure 100: CFRP ratio effect on HR ........................................................................ 122

Figure 101: Load versus Mid-span Deflection of C 40 LR C.................................... 125

Figure 102: Load versus Mid-span Deflection of C 40 LR 1L .................................. 125


Figure 104: Load versus Mid-span Deflection of C 40 MR C .................................. 126

Figure 105: Load versus Mid-span Deflection of C 40 MR 1L ................................. 127


Figure 107: Load versus Mid-span Deflection of C 40 HR C ................................... 128

Figure 108: Load versus Mid-span Deflection of C 40 HR 1L ................................. 128


Figure 110: Load versus Mid-span Deflection of C 70 LR C.................................... 129



Figure 113: Load versus Mid-span Deflection of C 70 MR C .................................. 131



Figure 116: Load versus Mid-span Deflection of C 70 HR C ................................... 132



Figure 119: Load versus Mid-span Deflection of C 100 LR C.................................. 134

Figure 120: Load versus Mid-span Deflection of C 100 LR 1L ................................ 134



Figure 123: Load versus Mid-span Deflection of C 100 MR 1L ............................... 136

Figure 124: Load versus Mid-span Deflection of C 100 MR 2L ............................... 136

Figure 125: Load versus Mid-span Deflection of C 100 HR C ................................. 137

Figure 126: Load versus Mid-span Deflection of C 100 HR 1L ............................... 137

Figure 127: Load versus Mid-span Deflection of C 100 HR 2L ............................... 138

Figure 128: Section behavior under loading .............................................................. 139

Figure 129: Experimental versus predicted ultimate load capacities......................... 142

Figure 130: Load versus Mid-span Deflection for C40 LR C specimens.................. 150

14

Figure 131: Load versus Mid-span Deflection for C40 LR 1L specimens ................ 150


Figure 133: Load versus Mid-span Deflection for C40 MR C specimens ................ 151

Figure 134: Load versus Mid-span Deflection for C40 MR 1L specimens ............... 152


Figure 136: Load versus Mid-span Deflection for C40 HR C specimens ................. 153

Figure 137: Load versus Mid-span Deflection for C40 HR 1L specimens ............... 153


Figure 139: Load versus Mid-span Deflection for C70 LR C specimens.................. 154



Figure 142: Load versus Mid-span Deflection for C70 MR C specimens ................ 156



Figure 145: Load versus Mid-span Deflection for C70 HR C specimens ................. 157



Figure 148: Load versus Mid-span Deflection for C100 LR C specimens................ 159

Figure 149: Load versus Mid-span Deflection for C100 LR 1L specimens .............. 159

Figure 150: Load versus Mid-span Deflection for C100 LR 2L specimens .............. 160

Figure 151: Load versus Mid-span Deflection for C100 MR C specimens .............. 160

Figure 152: Load versus Mid-span Deflection for C100 MR 1L specimens ............. 161

Figure 153: Load versus Mid-span Deflection for C100 MR 2L specimens ............. 161

Figure 154: Load versus Mid-span Deflection for C100 HR C specimens ............... 162

Figure 155: Load versus Mid-span Deflection for C100 HR 1L specimens ............. 162

Figure 156: Load versus Mid-span Deflection for C100 HR 2L specimens ............. 163

15

List of Tables

Table 1: Properties of different types of FRP fibers [18] ............................................ 17

Table 2 : Comparison between FRP and other materials [21] .................................... 22

Table 3: C 40/20 OPC Mix Design .............................................................................. 26

Table 4: C 70/20 OPC + MS mix Design .................................................................... 26

Table 5: C 100/20 OPC + MS mix Design .................................................................. 27

Table 6: Compressive strength for the concrete cylinders ........................................... 28

Table 7: Steel Dimensions ........................................................................................... 28

Table 8: Coupon test results of steel ............................................................................ 29

Table 9: Mechanical properties of the epoxy ............................................................... 30

Table 10: Mechanical properties of the cured CFRP laminate .................................... 30

Table 11: C 40 group organization .............................................................................. 34

Table 12: C 70 group organization .............................................................................. 35

Table 13: C 100 group organization ............................................................................ 36

Table 14: Test Matrix................................................................................................... 38

Table 15: Summary of the average load data ............................................................... 85

Table 16: Summary of deflection data ......................................................................... 87

Table 17: Summary of deflection data ......................................................................... 89

Table 18: Summary of all tested specimens ................................................................ 95

Table 19: Load predictions and error estimations. ..................................................... 141

Table 20: Repeatability comparison .......................................................................... 164

16

Chapter 1: Introduction

1.1. Background

Throughout the advancement of the human race, new technologies have been

innovated and improved to keep up with the needs of today’s world. One of these

technologies is constructing buildings. Humans have always used structures as

homes, theaters, libraries, and other purposes. However, home and shelter use is the

most critical one. In the stone ages, people used to live in tents, caves, and other made

shelters that were of no strength or permanent use. Thus, when the technology of

building structures out of the known building materials started, it was of a great

benefit to the human race. Since the development of those structures, civil engineers

are trying to continue experimenting and evolving those structures and materials to

keep up with the huge demand of the modern world. As the populations of the world

continue skyrocketing, high-rise building technology was invented to keep people in

shelters while not using huge spaces of land.

In the modern days, the construction materials field had grown in complexity

and applications, so there are materials invented for almost all modern uses. One of

the most critical technologies developed in the construction materials field is fiber-

reinforced polymer (FRP) composite material that is used to repair, strengthen and

rehabilitate structures. There are many materials that can be used for these purposes.

They vary with the type and the extent of damage to structural members.

Structural damage can occur due to many reasons, such as fires, earthquakes,

terrorist’s attacks, wear and tear, and change of occupancy. Each type of damage

should be analyzed and studied to assess the repairing material and strengthening

method that should be used. One of the most commonly and widely used methods

now is the strengthening of RC structural members (slabs, beams, columns, and walls)

in shear and flexure by externally bonding FRP composite sheets and plates to

concrete surfaces [1-14]. The old method of strengthening RC slabs and beams in

flexure was done by attaching steel plates to concrete surfaces [15]. Since the

invention of FRP strengthening systems, it has proven to have enormous potential and

advantages over the steel alternative [15].

17

FRP systems also demonstrated many advantages over the old method of steel

plating [16, 17]. Those advantages can be summarized in the ease of FRP installation

and insulation, cost of materials, structural bonding, weight-to-strength ratio, and

decrease of labor forces required to install them. As this system started to grow its

range of applications, engineers and researches have conducted many research studies

on how to best optimize this technology [16, 17]. It was found from these studies that

bonding FRP sheets and plates to surfaces of RC members would increase their

flexural and shear capacities significantly.

There are many types of FRP composite materials in the construction market.

Some of the most commonly used FRP types include carbon (CFRP), glass (GFRP),

and aramid (AFRP) fibers [17]. Table 1 summarizes the different physical and

mechanical properties of the types of FRP fibers and compares them to steel and

aluminum plates [18].

Table 1: Properties of different types of FRP fibers [18]

Fiber Density

(g/cc)

Youngs

Modulus

(GPa)

Strength

(GPa)

Strain

to

Failure

(%)

Specific

Strength

Specific

Modulus

Diameter

(μm)

Upper

use

Temp

(C)

E-Glass 2.6 69-72 1.7-3.5 3.0 1.18 27.6 5-25 350

S-Glass 2.49 85 4.8 5.3 1.9 34.3 5-15 300

Carbon(HM) 1.96 517 1.86 0.38 0.95 264 7-8 600

Carbon(HS) 1.8 295 5.6 1.8 3-11 164 7-8 500

Kevlar

49(Aramid) 1.45 135 3.0 8.1 2.1 93 12 250

Steel 7.9 200 0.45 20 0.05 25 - -

Aluminum 2.7 70 0.26 17 0.1 26 - -

In summary, there are many advantages of using FRP composite materials in

strengthening RC structural elements. The main advantages are high tensile strength,

low densities, and absence of sensitivity to corrosion, which is ten times less than that

of steel, which allows possible reduction in cross-sections of structural elements. All

the mentioned advantages can be offset with the high cost of the FRP materials and

the high cost of installation [19].

In addition, it is even hard sometimes to use those materials in some structural

elements, such as the elements that are subjected to harsh environmental impact. In

18

such cases, those composites should be inserted inside the elements to protect them

from those attacks [19].

FRP systems have been primarily investigated to be used for flexural and

shear strengthening by two application methods: Externally Bonded Reinforcing

(EBR) and Near Surface Mounted (NSM) [20]. On the structural engineering side,

there are many structural elements that could use the extra capacity and reduction of

cross section that FRP can provide. One important structural element that this

research deals with is slabs. Slabs are flexural members that are used for flooring and

roofing purposes. They act like beams in transferring and reacting to loads and are

also the largest elements in any structure. The general trend of strengthening those

elements is attaching the FRP system to the soffit of the slab with epoxy resin

adhesives. In this case, the FRP system will act as secondary flexural reinforcement to

help the main longitudinal steel reinforcement in increasing the flexural capacity of

slabs.

1.2. Research Significance

Slabs are the largest elements in most reinforced concrete structural buildings.

Hence, most of the self-weight of the structure is due to the weight of slabs. The

weight of a slab is a function of its surface area and thickness. In order to reduce the

weight of slabs, one of these two parameters should be reduced. Since the surface area

of slabs is controlled by architectural plan views of each floor, the slab thickness is

the key parameter in reducing the slab weight. An important question that needs to be

asked is how could this thickness be reduced without compromising the capacity of

the slab? The answer to this question is the use of high-strength concrete instead of

normal strength concrete in casting slabs. This would reduce the total dead weight of

buildings and thus will save cost, construction materials, and ability to construct

higher and larger buildings.

The use of externally bonded CFRP composite materials to the bottom surface

of slabs would act as internal longitudinal steel reinforcement which would increase

the flexural capacity of slab. Thus, in theory, one could design externally strengthened

thin high strength slabs to provide the same flexural capacity as that of conventional

RC slabs.

19

This research aims to study the behavior of externally strengthened 100 mm

thick high-strength RC slabs with CFRP composite sheets bonded to their soffit to

improve their flexural capacity. In addition, the effect of concrete compressive

strength and flexural steel reinforcement ratio on the performance of slab specimens

will be investigated.

1.3. Research Objectives

This research aims to study the behavior of high-strength RC slabs bonded

externally with CFRP composite sheets to improve their flexural capacity. A total of

fifty-four slabs have been cast and tested to prove the theory and the objective of the

proposed study. The slabs were tested in a two-point loading arrangement until

failure. The variables of the experimental program were the concrete compressive

strength, longitudinal steel reinforcement ratio, and number of layers of CFRP

composite sheets. The results of these tests were compared together to conclude the

range of the enhancement of the CFRP and the effect of the mentioned variables on

the performance of high-strength RC slabs. The main objectives of this study are to:

1. study the effect of the concrete compressive strength variation on the flexural

performance of un-strengthened and externally strengthened 100 mm thick RC

slabs.

2. examine the effect of flexural steel reinforcement ratio on the flexural

performance of the tested slab specimens.

3. investigate the effect of the number of CFRP layers when externally bonded to

the slab’s soffit on the flexural performance of high-strength composite slabs.

4. compare the load-carrying capacity; load verses mid-span deflection curves,

and ductility of the tested specimens.

5. predict the flexural capacity of the tested slab specimens using the ACI318-11

and ACI 440.2R-08 guidelines.

6. develop analytical models to predict the mid-span deflection response of the

tested slab specimens.

1.4. Thesis Organization

This thesis is divided into a total of 7 chapters. The first chapter introduces the

thesis topic in general; it is also subdivided into subchapters that explain the general

idea of the study, significance of the research, and the objectives of the research. The

20

second chapter presents the literature review that spots light on the papers and studies

that are associated with either the field of FRP strengthening of flexural members or

the use of high strength concrete. The third chapter deals with the experimental

program. This chapter is organized in subchapters to explain the materials used in the

study, the test setup, cross sectional detailing of the tested specimens, and the test

matrix. The fourth chapter in this study deals with the results of the experimental

program of the study. It also discusses the load verses mid-span deflections, and load

verses strains diagrams in an elaborate manner. The fifth chapter has technical

discussions on the data and observations of different comparisons within the groups of

specimens. It also compares the differences between the capacities of the tested

specimens. The sixth chapter in this thesis has analytical predictions according to ACI

440-08.2R of the load carrying capacity, and load verses mid-span deflections

compared to the actual tested data. The final chapter has an overall conclusion on the

results, discussion, and technical outcomes of the study.

21

Chapter 2: Literature Review

2.1 General Overview

There are many research studies on the effect of CFRP composite sheets and

plates in strengthening RC structural members [1-15]. These studies paved the way

for the use of such composite materials in repair and strengthening of structural RC

members nowadays. The main feature that allowed this wide range of applications is

material properties of the carbon fibers themselves.

Carbon fibers are made from carbon atoms consolidated together to create

long stands, which eventually creates thin sheet that is used in strengthening

applications. The low weight-to-volume ratio of the carbon atoms is the main reason

that allows the CFRP system to have a high strength-to-weight ratio [19]. Those

carbon fibers can never be used alone; they have to be consolidated with different

resins to allow the bond between the atoms to grow strong. This is what differentiates

the different CFRP types that are available in the construction market. Some of the

amazing properties that carbon fibers have are [21]:

High tensile strength

Low density

High modulus of elasticity

Low thermal conductivity

Thus, there are many benefits of using FRP composite over the conventional

steel material.

Table 2 compares the physical and mechanical properties of FRP materials to

other metals used in the field of construction [21]. The superior properties landed the

FRP composites many applications, not only in the field of construction but also in

the fields of aerospace, oil and gas, automobiles, and many others.

22

Table 2 : Comparison between FRP and other materials [21]

2.2 High Strength Concrete

The main aspect of this research study is the use of high strength concrete in

casting thin RC slabs. In principle, high strength concrete (HSC) is a concrete mix

that has the ability to reach a compressive strength above 50 MPa [22]. The use of this

type of concrete mix is very obvious, with the increase in strength; HSC can provide a

stretched range of durability.

The production of HSC can be simplified in the process of increasing the

compactness of the mix by increasing the aggregates and cement materials, and by

decreasing the water to cement (w/c) ratio in order to obtain a denser mix that has

more of the stronger elements [23].

The use of HSC increased during the last decade due to many reasons. The

high strength and durability it provides, makes it an impeccable option for clients

opting for a highly conservative structure, with low maintenance costs in the long run.

Engineers have used HSC to repair parts of pre-existent structure that have suffered

from fatigue and cracking. The on-site application makes its use easier and workable.

Common HSC applications are:

Property

FRP Carbon

Steel

Stainless

Steel Hastelloy Aluminum Titanium

With Glass

Mat Roving

All Glass

Mat

AISI

1020 316L C 1050-O Grade 12

Density, Kg/m3 1799.2 1383.995 7861.1 7916.45 8968.28 2712.63 4511.82

Tensile Strength, MPa x103 0.082-0.138 0.07-0.138 0.38 0.55 0.55 0.076 0.61

Yield Strength, MPa x103 0.07-0.138 0.062-0.1 0.227 0.234 0.351 0.027 0.475

Modulus of Elasticity, MPa

x106 0.005-0.01 0.048-0.007 0.206 0.206 0.18 0.07 0.097

23

Nuclear Waste Containment

High Rise Structures

Long Span Bridges & Walkways

Maintenance

2.3 CFRP Laminates for Flexure Strengthening

The use of CFRP composite sheets and plates in strengthening RC flexural

members (slabs and beams) has been increased dramatically over the last few years.

Numerous experimental and numerical research studies have also been conducted

which shows the use of CFRP flexural strengthening in increasing the flexural

capacity of beams and slabs.

Al-Rousan et al. [24] tested eight slabs that were strengthened with different

layers and configurations of CFRP system. They also developed a nonlinear finite

element model to correlate the behavior of the test specimens with the actual test

results. They found that the results of the models were comparable with that of the

actual test specimens. Their main finding from both the tested specimens and models

is that the strengthening of under reinforced concrete slabs using CFRP laminates

could substantially improve the flexural capacity on the compromise of the ductility

of the strengthened member. Moreover, the increase in flexural strength and

corresponding reduction in ductility had been increased with the increase in the

number of CFRP layers. Their final conclusion was that strengthening RC slabs with

CFRP laminates is effective, economical, and applicable, if the increase of flexural

capacity would not change the failure mode into a shear failure mode.

Toutanji et al. [25] also tested seven strengthened RC beams in flexure in

addition to a control un-strengthened specimen. The strengthened specimens were

varied with three to six layers of CFRP sheets bonded externally to the bottom beams’

surface with the use of inorganic epoxy. They have found that the load carrying

capacity was directly proportional to the number of CFRP layers, up to almost 170%

of the strength of the control beam specimen. The failure mode also varied with the

number of CFRP layers. It was found that the specimens that had three and four layers

failed by rupture of the CFRP sheets, while specimens that had five and six layers of

24

CFRP failed by delamination of CFRP sheets. Another main finding is the reduction

of the strengthened member’s ductility compared to the control beam. The deflection

was recorded until failure, and the results showed that the deflection didn’t vary with

the increase in the number of CFRP layers, which is consistent with the findings of

other research studies [24].

Al Zaid et al. [26] developed a simple numerical model based on a cross-

sectional analysis that satisfied strain compatibility and equilibrium conditions. They

generated moment-curvature relationship with an incremental strain technique. They

also calibrated their model with experimental data published in the literature. The

results of the developed models were in close agreement with the obtained

experimental data. They concluded that their developed model could be used in the

design and analysis of FRP-strengthened RC members. The developed model can also

predict the load-deflection response curves and failure mode of the strengthened

member.

Floruţ et al. [27] discussed the effect of FRP-strengthening two-way slabs with

and without cutouts. They tested eight slabs; four with cut outs and four without

cutouts. The results of this experimental program revealed that the FRP system could

only be fitted on the edges of the cut out. In areas of high demand, the FRP composite

system must be placed in most of the soffit to enhance the load carrying capacity and

decrease the maximum deflection of the strengthened member in flexure. In fact, the

load carrying capacity has been increased in all the control samples by 121% and 57

%, for slabs with and without cut outs, respectively.

As can be seen from the literature review above, it is clear that the literature is

missing adequate information of strengthening high-strength RC slabs in flexure with

CFRP composite sheets. In this research different concrete strengths, reinforcement

ratios, and number of layers of CFRP composite sheets will be examined, to study

their effect on the performance of thin slabs. This topic was chosen due to the

importance of slabs as structural elements and to investigate the behavior of thin (100

mm) slabs when externally strengthened with CFRP laminates. The trend will be

attaching the CFRP to the soffit of the slabs to observe the change in the load carrying

capacity, load-deflection response curves, failure modes, and ductility at specified

locations within the slab specimens.

25

Chapter 3: Experimental Program

3.1. Test Specimens Properties

To accomplish the objectives of this project, a total of 54 reinforced concrete

slab specimens were cast and tested in the structures lab of the American University

of Sharjah (AUS). The slabs were cast in three batches; each with a different

compressive strength of 40, 70, and 100 MPa, respectively. In addition, the variables

within each group are the flexural steel reinforcement ratio (ρs), and the number of

CFRP layers. In particular, the specimens were strengthened with one and two layers

of CFRP sheets bonded to the bottom surface of the slab with epoxy adhesive. In

addition, each group of specimens was reinforced with three reinforcement ratios; low

= 0.45%, medium = 1.0%, and high = 1.79%.

It should be noted that for each set of specimen, two identical slabs were

tested to ensure repeatability and credibility of the obtained experimental data. The

mechanical properties of the used materials, slab detailing, testing matrix,

instrumentation, and test setup will be discussed in the subsequent sections of this

chapter.

3.2. Materials

All the materials used in this research study will be obtained from local

suppliers and are readily available in the market. The materials used are described in

the following subsection.

3.2.1. Concrete material properties

The three groups of concrete compressive strengths that were used to cast the

100mm thick slabs are:

1. 40/20 Ordinary Portland Cement (OPC)

This concrete mix has a compressive strength of 40 MPa.

Table 3 below shows the mix design of the C 40/20 OPC mix.

26

Table 3: C 40/20 OPC Mix Design

2. 70/20 OPC+Microsilica (MS)


Table 4 below shows the mix design of the C 70/20 OPC + MS mix.

Table 4: C 70/20 OPC + MS mix Design

CONCRETE MIX DESIGN 70/20 OPC + MS

Batch weight per m3

Material Description S.G (SSD) Water Absorption

% Weights (S.S.D) Kg

Cement OPC - - 470

Microsilica - - 30.00

20 mm Aggregate 2.88 0.6 610

10 mm Aggregate 2.86 0.7 430

0-5 mm Washed Crushed

Sand 2.67 1.2 570

Dune Sand 2.64 0.8 260

Free Water - - 140

Admixture Glenium 110 1.1 - 7 - 9

Total (Kg) 2515

REMARKS

Wet Density: 2515 Kg / m3

Max size of aggregate 20 mm

Slump / Flow 550 -650 mm

W/C Ratio 0.28 -

CONCRETE MIX DESIGN 40/20 OPC

Batch weight per m3

Material Description S.G. (SSD) Water

Absorption %

Weights (S.S.D)

Kg

Cement OPC - - 400

20 mm Aggregate 2.86 0.5 650

10 mm Aggregate 2.85 0.6 380

0-5 mm Washed Crushed Sand 2.68 1.1 590

Dune Sand 2.67 0.8 285

Free Water - - 160

Admixture ADVA XR 1.1 - 8

Total (Kg) 2473

REMARKS



Slump / Flow 175 + 25 mm

W/C Ratio 0.4 -

27

3. 100/20 OPC+Microsilica(MS)


Table 5 below shows the mix design of the C 100/20 OPC + MS mix.

Table 5: C 100/20 OPC + MS mix Design

CONCRETE MIX DESIGN 100/20 OPC + MS

Batch weight per m3

Material Description S.G. (SSD) Water Absorption % Weights (S.S.D)

Kg

Cement OPC - - 500

Microsilica - - 50

20 mm Aggregate 2.70 0.6 580

10 mm Aggregate 2.69 0.7 350

0-5 mm Washed Crushed

Sand 2.66 1.3 550

Dune Sand 2.63 0.9 250

Free Water - - 149

Admixture Glenium 110 1.1 - 8 - 11

Total (Kg) 2430

REMARKS



Slump / Flow 550 -650 mm

W/C Ratio 0.27 -

All specimens were cast in RAK Precast Company. The compressive strength

of the cubes and cylinders were tested at AUS labs and facilities.

Table 6 provides the obtained results of the cylinder’s compressive strength

that was tested at the same time of the slab testing.

28

Table 6: Compressive strength for the concrete cylinders

Design

Strength

(MPa)

Cylinder Comp. Strength Average

Ref. (MPa) (MPa)

40

1 43

42

2 41

70

3 72.6

72.8

4 73.2

100

5 103.5

102.85

6 102.2

3.2.2. Steel material properties

All the reinforcement steel that were used in this study are hot rolled deformed

bars manufactured in accordance to BS EN 10080; B500A [28]. This high grade of

steel was chosen due to its availability in the United Arab Emirates market.

Properties and dimensions of the reinforcing steel are presented in Table 7.

Table 7: Steel Dimensions

Metric Bar

size

Linear Mass

Density(kg/m)

Nominal

diameter(mm)

Cross-sectional

Area (mm²)

8 0.395 8 50.3

12 0.888 12 113.1

16 1.579 16 201.1

29

The yield stress of the steel that was used in this study is determined through a

tensile coupon test in accordance with BS 4449: 2005 grade B500B using a universal

testing machine that has a capacity of 100 kN. The obtained results in terms of stress-

strain curves, yield and tensile strength are shown in Figure 1and Table 8.

Figure 1: Stress- Strain Curve of tested Steel Rebars

Table 8: Coupon test results of steel

Specimen Rebar 1 Rebar 2 Rebar 3 Average

Yield Strength

(MPa) 553.9 546.2 550.3 550.13

Tensile Strength

(MPa) 666.4 671.3 664.5 667.4

Modulus of

Elasticity (GPa) 200.02 200.00 199.97 199.99

3.2.3. Epoxy V-Wrap 700

In this study Epoxy Adhesive V-Wrap 700 was used to attach the CFRP sheets

to the soffits of the slabs strips. The properties of the adhesive are summarized in

table 9 below.

0

100

200

300

400

500

600

700

800

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

Str

ess

(Mp

a)

Strain (mm/mm)

Rebar 1

Rebar 2

Rebar 3

30

Table 9: Mechanical properties of the epoxy

Property Value

Tensile Strength (MPa) 72.4

Tensile Modulus(MPa) 3180

Flexural Strength(MPa) 123.4

Flexural Modulus(MPa) 3120

Elongation at Break(%) 5

Glass Transition Temperature (Tg) (° C) 82

Density (Kg/L) 1.11

3.2.4. CFRP sheets: V-Wrap C200H properties

In this study CFRP V-Wrap C200H supplied from Structural Technologies

Company is used. Table 10 below shows the properties of the cured CFRP laminates

embedded between two layers of epoxy adhesives, as reported by the manufacturer.

They were used in this study, as provided by the manufacturer.

Table 10: Mechanical properties of the cured CFRP laminate

3.3 Specimens Preparation

All specimens were cast in RAK Precast Company and brought to AUS

construction laboratory for strengthening and testing. The materials and application of

the strengthening of the specimens were done with the help of Structural Company

that is a specialist in this field.

The first step in the strengthening process is the marking of the location of the

CFRP external reinforcement. Figure 2 shows the marking process.

Mechanical Properties Average Value Design Value

Tensile Strength (MPa) 1,240 1,034

Modulus of Elasticity (GPa) 73.77 73.77

Elongation at Break (%) 1.7 1.4

Thickness (mm) 1.02 1.02

Strength Per Unit Width

(kN/mm) 1.26 1.05

31

Figure 2: CFRP location marking

The second step is the sample preparation. This step is done to scrub the

finished cover of the specimen. The surface preparation is done with the use of an

electric grinder to remove the dirt and chemicals from the release molds. The other

reason is to expose the micro cracks for the bonding of the epoxy resin with the

concrete surface. Figure 3 shows the process of surface preparation.

Figure 3: Surface preparation

The third step is the mixing of the epoxy mix, and the painting of the surface

on the pre-specified area. The fourth step is to soak CFRP laminates in the epoxy mix

to allow full bonding. The third and fourth steps of the strengthening process are done

32

together, since the epoxy mix should not be exposed to air after mixing. Figure

4shows the third and fourth steps in the strengthening process.

Figure 4: Mixing, painting of the epoxy, and the soaking of the CFRP sheets in epoxy.

The final step of the strengthening process is to apply the soaked CFRP sheets

on the painted area. After applying the CFRP sheets, the process of consolidating and

bonding of the CFRP sheets is initiated via roller and leveler. This process is done to

ensure the full bonding and the removal of the air bubbles and the filling of the micro

cracks that exist on the surface of the concrete. Figure 5 shows the two processes of

the rolling and the leveling of the CFRP sheets on the concrete.

Figure 5: Rolling and leveling of the CFRP sheets on the concrete surface.

33

3.4 Test Matrix and slab detailing

A total of fifty-four 100 x 300 x 2000 mm slabs were cast and divided into

three major groups. Each group consisted of a total of 18 samples under it; nine of

which are originals, and the other nine were added to ensure repeatability, which is

discussed in details in other chapters.

The concrete compressive strengths of the cast slabs were 40, 70 and 100

MPa, respectively. The slabs that were strengthened with CFRP laminates had

a100mm wide CFRP sheets attached to the slab’s soffit with epoxy adhesives. This

will prove the validity and efficiency of the proposed study of casting thin RC slabs

with internal steel bars and external CFRP composite reinforcement. Tables 11 to13

explain in details the breakdown of the groups and the properties of the slabs in each

group and illustrate relation and technical information of each subgroup.

In this study, three reinforcement ratios were used with the first one close to

the minimum, the second between the minimum and the maximum and the third one

is close to the maximum. The reason behind this is to define a trend of the behavior.

34

Table 11: C 40 group organization

Group

Designation C 40

Sub-Group

Designation 40 LR 40 MR 40 HR

Size

100 x 300 x 2000 100 x 300 x 2000 100 x 300 x 2000 (mm x mm x

mm)

( Depth x Width

x Length)

Steel

Reinforcement 2 Φ8 mm 2 Φ12 mm 2 Φ16 mm

ρ % (mm2/mm

2) 0.45% 1.00% 1.79%

ρmin% 0.29%

ρb% 2.44%

ρmax % 1.83%

CFRP 0, 1, and 2 layers 0, 1, and 2 layers 0, 1, and 2 layers

Cross-section

Detailing

f’c (MPa) 40MPa

fy (MPa) 550 MPa

Number of

specimens 9 x 9 = 18 specimens

35


Group Designation C 70

Sub-Group Designation 70 LR 70 MR 70 HR

Size

100 x 300 x 2000 100 x 300 x 2000 100 x 300 x 2000 (mm x mm x mm)

( Depth x Width x

Length)

Steel Reinforcement 2 Φ8 mm 2 Φ12 mm 2 Φ16 mm

ρ % (mm2/mm

2) 0.45% 1.00% 1.79%

ρmin% 0.38%

ρb% 3.06%

ρmax % 2.30%


Cross-section Detailing

f’c (MPa) 70MPa

fy (MPa) 550 MPa

Number of specimens 9 x 9 = 18 specimens

36


Group Designation C 100

Sub-Group

Designation 100 LR 100 MR 100 HR

Size

100 x 300 x 2000 100 x 300 x 2000 100 x 300 x 2000 (mm x mm x mm)

( Depth x Width x

Length)

Steel Reinforcement 2 Φ8 mm 2 Φ12 mm 2 Φ16 mm

ρ % (mm2/mm

2) 0.45% 1.00% 1.79%

ρmin% 0.45%

ρb% 2.65%

ρmax % 1.99%


Cross-section

Detailing

f’c (MPa) 100MPa

fy (MPa) 550 MPa

Number of

specimens 9 x 9 = 18 specimens

37

Figures 6, 7, and8 show the detailing of the cast slab specimens in terms of

dimensions and location of steel and CFRP reinforcement. Figure 6 shows the slab’s

dimensions and location of loading supports. The slabs had a total length, span length,

width, and thickness of 2000, 1700, 300, and 100 mm, respectively. The slab

thickness is 100 mm, and its effective depth is 75 mm. Figure 6 shows the loaded slab

specimen, while Figure 7 shows a longitudinal section of the slab. Figure 8 shows a

cross section of the slab.

Figure 6: Testing method and elevation view of the tested slabs.

Figure 7: Front view of the slab specimens.

Figure 8: Cross-section a-a of the slab specimens.

Table 14 summarizes the test matrix of this study. The designation and cross-

section of every tested slab specimen are presented in Table 14. Furthermore, it shows

567 mm h = 100 mm

CFRP Sheet/s (1500 mm length by 100 mm width)

a = 600 mm

150 mm

1700 mm

2000 mm

150 mm

2Φ 8 mm

2Φ12 mm

2Φ16 mm

150 mm a

a

100 mm

100 mm

300 mm

180 mm

75 mm

38

the parameters that were varied in order to show the technical validity of this study

and the importance aspect of the use of this technology.

Table 14: Test Matrix

Slab

Designation Slab Designation Slab Detail

C40 LR-C

Control Slab, low reinforcement

ratio, and concrete compressive

strength of40MPa.

C40 LR-1L

Strengthened slab with one layer

of CFRP, with low

reinforcement ratio, and

concrete compressive strength

of40MPa.

C40 LR-2L

Strengthened slab with two

layers of CFRP, with low



of40MPa.

C40 MR-C

Control Slab, medium



of40MPa.

C40 MR-1L


of CFRP, with medium



of40MPa.

100 mm

300 mm

180 mm

75 mm

2 Φ 8mm

100 mm

300 mm

180 mm

75 mm

100 mm 2 Φ 8mm

100 mm

300 mm

180 mm

75 mm

100 2 Φ 8mm

100 mm

300 mm

180 mm

75 mm

2 Φ 12mm

100 mm

300 mm

180 mm

75 mm

100 mm 2 Φ 12mm

39

C40 MR-2L


layers of CFRP, with medium



of40MPa.

C40 HR-C

Control Slab, high



of40MPa.

C40 HR-1L


of CFRP, with high



of40MPa.

C40 HR-2L


layers of CFRP, with high



of40MPa.

C70 LR-C



strength of70MPa.

C70 LR-1L


of CFRP, with low



of70MPa.

C70 LR-2L





of70MPa.

100 mm

300 mm

180 mm

75 mm

100 2 Φ 12mm

100 mm

300 mm

180 mm

75 mm

2 Φ 16mm

100 mm

300 mm

180 mm

75 mm

100 mm 2 Φ 16mm

100 mm

300 mm

180 mm

75 mm

100 2 Φ 16mm

100 mm

300 mm

180 mm

75 mm

2 Φ 8mm

100 mm

300 mm

180 mm

75 mm

100 mm 2 Φ 8mm

100 mm

300 mm

180 mm

75 mm

100 2 Φ 8mm

40

C70 MR-C




of70MPa.

C70 MR-1L





of70MPa.

C70 MR-2L





of70MPa.

C70 HR-C

Control Slab, high



of70MPa.

C70 HR-1L


of CFRP, with high



of70MPa.

C70 HR-2L





of70MPa.

C100 LR-C



strength of100MPa.

100 mm

300 mm

180 mm

75 mm

2 Φ 12mm

100 mm

300 mm

180 mm

75 mm

100 mm 2 Φ 12mm

100 mm

300 mm

180 mm

75 mm

100 2 Φ 12mm

100 mm

300 mm

180 mm

75 mm

2 Φ 16mm

100 mm

300 mm

180 mm

75 mm

100 mm 2 Φ 16mm

100 mm

300 mm

180 mm

75 mm

100 2 Φ 16mm

100 mm

300 mm

180 mm

75 mm

2 Φ 8mm

41

C100 LR-1L


of CFRP, with low



of100MPa.

C100 LR-2L





of100MPa.

C100 MR-C




of100MPa.

C100 MR-1L





of100MPa.

C100 MR-2L





of100MPa.

C100 HR-C

Control Slab, high



of100MPa.

C100 HR-1L


of CFRP, with high



of100MPa.

100 mm

300 mm

180 mm

75 mm

100 2 Φ 8mm

100 mm

300 mm

180 mm

75 mm

100 mm 2 Φ 8mm

100 mm

300 mm

180 mm

75 mm

2 Φ 12mm

100 mm

300 mm

180 mm

75 mm

100 mm 2 Φ 12mm

100 mm

300 mm

180 mm

75 mm

100 2 Φ 12mm

100 mm

300 mm

180 mm

75 mm

2 Φ 16mm

100 mm

300 mm

180 mm

75 mm

100 mm 2 Φ 16mm

42

3.3. Instrumentation (Strain Gauges)

Figure 9 shows the locations of the strain gauges on the slabs. Strain gauges

were installed primarily on the concrete, steel, and CFRP materials along the

horizontal axis of the slab specimen at the slab's mid-span as shown in Figure 9.

Figure 9: Strain Gauge locations.

The strain gauges used for each material is specific to the material type. The

different sizes are due to the nature of the pre-failure behavior that is developed on the

material and the sensitivity of the strain gauge.

Figure 10 shows typical slab sample instrumentation with strain gauges. All

strain gauges were monitored and the strain values were recorded using data

acquisition system with a recording capacity of 100 Hz.

C100 HR-2L





of100MPa.

100 mm

300 mm

180 mm

75 mm

100 2 Φ 16mm

PP

567 mm

Concrete Strain Gauge (50 mm long)

Steel Strain Gauge (15 mm long)

CFRP Strain Gauge (10 mm long)

43

Figure 10: Strain Gauge locations.

3.4. Accuracy of Specimens

All the testing results values in this study are with an order of accuracy of

+/-1% since all testing and recording instrument has this error percentage.

Furthermore, the accuracy of the specimens and their preparations are of the order of

+/-2% due to human errors.

3.5. Experimental Setup and Procedure

A two-point loading test arrangement was used to test all specimens as shown in

Figure 11. This testing arrangement was chosen to simulate the common loading case

on slabs, which is uniformly distributed loading. The slabs were tested under a

displacement control mode of 2 mm/min using a Universal Testing Machine (UTM)

with a capacity of 2000kN.

Steel Strain

Gauge

Concrete

Strain Gauge

CFRP Strain

Gauge

44

Figure 11: General Test Arrangement

P

567 mm h = 100 mm 550 mm 550 mm 600 mm

150 mm 150

1700 mm

45

Chapter 4: Experimental Results and Discussion

4.1. Load versus Micro-strain, and Failure Modes

In this chapter the experimental results are presented in the form of load

versus strain graphs in the concrete, steel, and CFRP respectively. In addition, the

failure mode of each specimen is discussed. All slab specimens were tested in two-

points loading arrangement with many parameters recorded such as: load versus mid-

span deflection, and load versus strain in steel, concrete, and CFRP where applicable.

The recorded data afterwards was plotted and discussed in the subsequent sections of

this chapter. The plots for load versus mid-span deflection curves are provided for

each pair of specimens in Appendix A of this study. However, a schematic analysis of

the load versus mid-span deflection curves presenting the symbols of the data

obtained is shown in Figure 12. The discussion involved the analysis of deflection and

strain data along with the different modes of failure. Moreover, photos of the failed

slab specimens are provided for each specimen to elaborate on the modes of failure.

At the end of this chapter, a summary of the obtained experimental data is provided,

which includes the ultimate load carrying capacity (Pu) and its corresponding

deflection (δu), the yield load (Py) and its corresponding deflection (δy), and the

deflection at failure (δf). The failure deflection is defined in this study as the

deflection when the ultimate attained load (Pu) is dropped by 20% (0.8 Pu) as shown

in Figure 12.

Figure 12:Load (kN) versus mid-span deflection (mm) schematic

46

4.1.1Group C 40 LR

The first group of this study is the C 40 LR. This group was cast with concrete

of compressive strength of 40 MPa and close to minimum reinforcement ratio with

two tension rebars of 8 mm diameter. The reinforcement ratio in this group is 0.45 %

which is close to minimum 0.29%. The reason behind the choice of this reinforcement

ratio is to explore the applicability of FRP strengthening over vast range of

reinforcement ratios and concrete compressive strengths. The yielding strain of the

tension steel reinforcement used is 2750 microstrain, while the debonding

microstrains (ϵfd) for this group of specimens strengthened with one layer and two

layers of CFRP reinforcement are 9687 and 6849 respectively. Hence if the strain

reaches this debonding level, brittle failure will occur. The debonding strain (ϵfd) is

computed according to the guidelines of the ACI 440. 2R-08 [17] as follows:

ϵfd = 0.41√𝑓′𝑐

𝑛 𝐸𝑓𝑡𝑓 ≤ 0.9𝑓𝑢 (Eq 1)

Where:

Ef: Tensile modulus of elasticity of FRP, (MPa).

𝑓𝑐′: Specified compressive strength of concrete, (MPa).

𝑛 : Number of plies of FRP reinforcement.

𝑡𝑓: Nominal thickness of one ply of FRP reinforcement, (mm).

In addition, the strain (ϵο) at which the concrete reaches its compressive

strength (𝑓𝑐′) is 2090 microstrain. The concrete strain (ϵο) is computed based on a

model developed by Collins and Mitchell [30] as follows:

ϵo = 𝑓′𝑐

𝐸𝑐 (

𝑛

𝑛−1) (Eq 2)

Ec = 3320√𝑓′𝑐 + 6900 (Eq 3)

n = 0.8 + (𝑓𝑐

′

17) (Eq 4)

47

where:

𝐸𝑐: Concrete modulus of elasticity, (MPa).

𝑓𝑐′: Specified compressive strength of concrete, (MPa).

𝑛 : Curve fitting factor.

4.1.1.1 Control slab (C 40 LR C)

The control slab achieved an ultimate load (Pu) of 11.63 kN with a

corresponding deflection (δu) of 21.01 mm. The deflection at which the steel yielded

(δy) was 1.93 mm and the failure deflection (δf) was 31.07 mm. The failure mode of

the slab matched the failure mode of an under-reinforced slab which was initiated

with the yielding of the steel, followed by tensile membrane action failure without

concrete crushing at the top. The tensile membrane action failure mode happens when

the reinforcement ratio is close to the minimum, at which the neutral axis of the

concrete goes up close to the top compression fibers, and the concrete becomes under

tension. This condition happens when slabs’ experiences after the flexural mechanism

fail and undergo big deformations. Figure13 shows the load versus strain response

curve in the concrete and steel reinforcement of the specimens. It is clearly indicated

that the strain in the concrete in Figure 13 below didn’t reach 2090 microstrain; hence

below the concrete crushing strain level is presented. The failed slab specimen at

failure is shown in Figure 14.

Figure 13: Load versus microstrain for slab specimen (C 40 LR C)

0

2

4

6

8

10

12

14

16

18

-2000 -1500 -1000 -500 0 500 1000 1500

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

48

Figure 14: Failed slab specimen (C 40 LR C)

4.1.1.2 Slab (C 40 LR 1L)

This slab was strengthened with one 100 mm width sheet of CFRP attached to

the center of the soffit. It was cast to see the effect of one sheet strengthening on the

increase of load carrying capacity and other properties. The slab ultimate load (Pu)

was 21.69kN with a corresponding deflection (δu) of 19.86 mm. The deflection at

which the steel yielded (δy) was 0.91 mm and the failure deflection (δf) was 23.3 mm.

The failure mode of this slab started with the steel yielding followed by the CFRP

debonding and membrane action failure. The load versus micro-strain graph is shown

in Figure 15 to illustrate the mode of failure. The maximum microstrain in the

concrete was less than 2090 which indicates that no crushing happened. On the other

hand, the microstrain in the steel reached 2750, which is the yield strain. Moreover,

the microstrain in the CFRP reached below 9687, which is the debonding strain;

hence it supports the argument on the brittle failure of the specimen. Figure 16 shows

the failed specimen.

49

Figure 15: Load versus microstrain slab specimen (C 40 LR 1L)

Figure 16: Failed slab specimen (C 40 LR 1L)

4.1.1.3 Slab (C 40 LR 2L)

This slab was strengthened with two 100 mm width sheet of CFRP attached to

the center of the soffit. This slab was cast to see the effect of two sheet strengthening

0

5

10

15

20

25

-2000 -1000 0 1000 2000 3000 4000

Lo

ad

(k

N)

Microstrain

Concrete Microstrain

Steel Microstrain

CFRP Microstrain

50

on the increase of load carrying capacity and other properties. The slab ultimate load

(Pu) was 38.5 kN with a corresponding deflection (δu) of 24.5 mm. The deflection at

which the steel yielded (δy) was 2.39 mm and the failure deflection (δf) was 25.88

mm. The failure mode of this slab started with the steel yielding followed by

membrane action failure and CFRP debonding. Figure 17, which shows load strain

response, supports this mode of failure. The strain in the concrete didn’t reach the

crushing strain of 2090 while the steel reached the yielding strain of 2750 and the

CFRP reached the debonding strain of 6849 which is the debonding strain where the

specimen experienced a brittle failure. Figure18 shows the failed specimen.

Figure 17: Load versus microstrain slab specimen (C 40 LR 2L)


0

5

10

15

20

25

30

35

40

45

-2000 0 2000 4000 6000 8000 10000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

CFRP

Microstrain

51

4.1.2 Group C 40 MR

The second group of this study is the C 40 MR. This group was cast with

concrete of compressive strength of 40 MPa and a reinforcement ratio between the

minimum and the maximum reinforcement ratio with two tension rebars of 12 mm

diameter. The reinforcement ratio in this group is 1.0 %. The reason behind the choice

of this reinforcement ratio is to explore the applicability of FRP strengthening over

vast range of reinforcement ratios and concrete compressive strengths. The yielding

strain for the tension steel used is 2750 microstrain, while the debonding microstrains

of this group of one layer and two layers strengthened are 9687 and 6849 respectively;

hence if the strain reaches this level, a brittle failure is bound to happen. In addition,

the strain (ϵο) at which the concrete reaches its compressive strength (𝑓𝑐′) is 2090

microstrain.

4.1.2.1 Control slab (C 40 MR C)

The slab ultimate load (Pu) was 22.6 kN with a corresponding deflection (δu)

of 28.4 mm. The deflection at which the steel yielded (δy) was 1.3 mm and the failure

deflection (δf) was 29.2 mm. The failure mode of the slab started with the yielding of

the steel, followed by concrete crushing at the top with the neutral axis shifting up.

The load versus micro-strain graph is shown in Figure 19. Figure 20 shows the failed

specimen. The strain in the concrete almost reached the crushing strain of 2090, while

the strain in the steel reached the yielding strain of 2750.

Figure 19: Load versus microstrain for slab specimen (C 40 MR C)

0

5

10

15

20

25

30

-4000 -2000 0 2000 4000 6000 8000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrai

n

52

Figure 20: Failed slab specimen (C 40 MR C)

4.1.2.3 Slab (C 40 MR 1L)


the center of the soffit. The load versus micro-strain graph is shown in Figure 21. This

slab was cast to see the effect of strengthening on the increase of load carrying

capacity and other properties. The slab ultimate load (Pu) is 36.9kN with a



this slab started with the steel yielding followed by concrete crushing at the top

shifting the neutral axis up, at the end CFRP debonding. The strain in the concrete

reached near the crushing strain of 2090 while the steel reached the yielding strain of

2750 and the CFRP almost reached the debonding strain of 9687 which is the

debonding strain where the specimen experienced a brittle failure. Figure 22 shows


53

Figure 21: Load versus microstrain slab specimen (C 40 MR 1L)

Figure 22: Failed slab specimen (C 40 MR 1L)

0

5

10

15

20

25

30

35

40

-4000 -2000 0 2000 4000 6000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

CFRP

Microstrain

54

4.1.2.2 Slab (C 40 MR 2L)


the center of the soffit. This slab was cast to see the effect of double sheet

strengthening on the increase of load carrying capacity and other properties. The load

versus micro-strain graph is shown in Figure 23. The slab ultimate load (Pu) was

50.53 kN with a corresponding deflection (δu) of 24.48 mm. The deflection at which

the steel yielded (δy) was 5.03 mm and the failure deflection (δf) was 26 mm. The

failure mode of this slab started with the steel yielding followed by concrete crushing

at the top shifting the neutral axis up, at the end CFRP debonding. The maximum

microstrain in the concrete was near 2090 which indicates that crushing happened at

the top. On the other hand, the microstrain in the steel reached 2750 which is the yield

strain. Moreover, the microstrain in the CFRP reached a little below 6849 which is the

debonding strain; hence it supports the argument about the brittle failure of the

specimen. Figure 24 shows the failed specimen.

Figure 23: Load versus microstrain for slab specimen (C 40 MR 2L)

0

10

20

30

40

50

60

-4000 -2000 0 2000 4000 6000 8000 10000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

CFRP

Microstrain

55


4.1.3 Group C 40 HR:

The third group of this study is the C 40 HR. This group was cast with

concrete of compressive strength of 40 MPa and a reinforcement ratio close to the

maximum reinforcement ratio which is 1.83 %, with two tension rebars of 16 mm

diameter. The reinforcement ratio in this group is 1.79 %. The reason behind the

choice of this reinforcement ratio is to explore the applicability of FRP strengthening

over vast range of reinforcement ratios and concrete compressive strengths. The

yielding strain for the tension steel used is 2750 microstrain, while the debonding

microstrains of this group of one layer and two layers strengthened are 9687 and 6849

respectively. Hence, if the strain reaches this level, a brittle failure is bound to happen.

In addition, the strain (ϵο) at which the concrete reaches its compressive strength (𝑓𝑐′)

is 2090 microstrain.

4.1.3.1 Control slab (C 40 HR C)

The slab ultimate load (Pu) was 44.88 kN with a corresponding deflection (δu)

of 21.5 mm. The deflection at which the steel yielded (δy) was 5.37 mm and the

failure deflection (δf) was 22.3 mm. The failure mode of the slab started with the

yielding of the steel, followed by concrete crushing at the top with the neutral axis

shifting up. The strain in the concrete almost reached the crushing strain of 2090,

while the strain in the steel reached the yielding strain of 2750. Figure 25 shows the

load strain response and Figure 26 shows the failed specimen, both of which support

the argument on the mode of failure.

56

Figure 25: Load (kN) versus micro strain

Figure 26: Concrete crushing and final failure

4.1.3.2 Slab (C 40 HR 1L)


the center of the soffit. This slab was cast to see the effect of single sheet

strengthening on the increase of load carrying capacity and other properties. The slab

ultimate load (Pu) was 52.25 kN with a corresponding deflection (δu) of 30.22 mm.

The deflection at which the steel yielded (δy) was 2.1 mm and the failure deflection

(δf) was 45.0 mm. Figure 27 shows the load strain response. The failure mode of this

slab started with the steel yielding followed by the CFRP debonding. The maximum

microstrain in the concrete was less than 2090 which indicates that no crushing

0

10

20

30

40

50

60

-4000 -2000 0 2000 4000 6000 8000 10000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

57

happened. On the other hand, the microstrain in the steel reached 2750 which is the

yield strain. Moreover, the microstrain in the CFRP reached a little below 9687 which

is the debonding strain; hence it supports the argument about the brittle failure of the

specimen. Figure 28 shows the failed specimen.

Figure 27: Load versus microstrain for slab specimen (C 40 HR 1L)

Figure 28: Failed slab specimen (C 40 HR 1L)

0

5

10

15

20

25

30

35

40

45

50

-4000 -2000 0 2000 4000 6000 8000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

CFRP

Microstrain

58

4.1.3.3 Slab (C 40 HR 2L)


the center of the soffit. This slab was cast to see the effect of two sheet strengthening

on the increase of load carrying capacity and other properties. The slab ultimate load

(Pu) was 53.85 kN with a corresponding deflection (δu) of 20.38 mm. The deflection

at which the steel yielded (δy) was 1.10 mm and the failure deflection (δf) was 21.7

mm. The failure mode of this slab started with the steel yielding followed by CFRP

debonding. As shown in Figure 29, the strain in the concrete didn’t reach the crushing

strain of 2090, while the steel reached the yielding strain of 2750 and the CFRP

almost reached the debonding strain of 6849 which is the debonding strain where the

specimen experienced a brittle failure. Figure 30shows the failed specimen.



0

10

20

30

40

50

60

-4000 -2000 0 2000 4000 6000

Lo

ad

(k

N)

Microstrain

Concrete

MicrostrainSteel

MicrostrainCFRP

Microstrain

59

4.1.4 Group C 70 LR

The fourth group of this study is the C 70 LR. This group was cast with

concrete of compressive strength of 70 MPa and close to minimum reinforcement

ratio with two tension rebars of 8 mm diameter. The reinforcement ratio in this group

is 0.45 % which is close to minimum 0.38%. The reason behind the choice of this

reinforcement ratio is to explore the applicability of FRP strengthening over vast

range of reinforcement ratios and concrete compressive strengths. The yielding strain

for the tension steel used is 2750 microstrain, while the debonding microstrain of this

group of one layer and two layers strengthened are 12600 and 9018 respectively;



microstrain.


The slab ultimate load (Pu) was 10.17 kN with a corresponding

deflection (δu) of 11.5 mm. The deflection at which the steel yielded (δy) was 2.06

mm and the failure deflection (δf) was 13. 1 mm. The failure mode of the slab

matches the typical failure mode of an under-reinforced slab which started with the

yielding of the steel, followed by membrane action failure without concrete crushing

at the top. The strain in the concrete didn’t reach the crushing strain of 2530, while the

strain in the steel reached the yielding strain of 2750. Figure 31 shows the load strain

response, andFigure32 shows the failed specimen, both of which support the

argument about the mode of failure.


0

2

4

6

8

10

12

-2000 -1000 0 1000 2000 3000 4000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

60

Figure 32: Slab Steel Rupture and beam failure

4.1.4.2 Slab (C 70 LR 1L)

This slab was strengthened with one 100 mm width sheet of CFRP

attached to the center of the soffit. The load versus micro-strain graph is

shown in Figure 33. This slab was cast to see the effect of strengthening on the

increase of load carrying capacity and other properties. The slab ultimate load

(Pu) is 26.6kN with a corresponding deflection (δu) of 13.46 mm. The

deflection at which the steel yielded (δy) was 1.56 mm and the failure

deflection (δf) was 37.48 mm. The failure mode of this slab started with the

steel yielding followed by the CFRP debonding. Figure 32 shows the mode of

failure. The maximum microstrain in the concrete was less than 2530 which

indicates that no crushing happened, on the other hand, the microstrain in the

steel reached 2750, which is the yield strain. Moreover, the microstrain in the

CFRP was below 12600, which is the debonding strain; hence the brittle

failure of the specimen happened. Figure 34 shows the failed specimen.

61

Figure 33: Load versus microstrain for slab specimen (C 70 LR 1L)


4.1.4.3 Slab (C 70 LR 2L)


the center of the soffit. The load versus micro-strain graph is shown in Figure 35. This

slab was cast to see the effect of strengthening on the increase of load carrying

capacity and other properties. The slab ultimate load (Pu) is 42.1 kN with a

0

5

10

15

20

25

30

-2000 0 2000 4000 6000 8000

Lo

ad

(k

N)

Microstrain

Concrete

Microstr

ainSteel

Microstr

ain

62



this slab started with the steel yielding followed by CFRP debonding. The strain in the

concrete didn’t reach the crushing strain of 2530 while the steel reached the yielding

strain of 2750 and the CFRP almost reached the debonding strain of 9018 which is the

debonding strain where the specimen experienced a brittle failure. Figure 36 shows


.



0

10

20

30

40

50

60

-2000 0 2000 4000 6000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

CFRP

Microstrain

63

4.1.5 Group C 70 MR

The fifth group of this study is the C 70 MR. This group was cast with






strain for the tension steel used is 2750 microstrain, while the debonding microstrain

of this group one layer and two layers strengthened are 12600 and 9018 respectively,

hence if the strain reaches this level a brittle failure is bound to happen. In addition,


microstrain.

4.1.5.1 Control Slab (C 70 MR C)

The slab ultimate load (Pu) is 26kN with a corresponding deflection (δu) of

71.75 mm. The deflection at which the steel yielded (δy) was 3.7 mm and the failure

deflection (δf) was 80 mm. The failure mode of the slab started with the yielding of

the steel, followed by membrane action failure followed by concrete crushing at the

top with the neutral axis shifting up. The strain in the concrete almost reached the

crushing strain of 2530, while the strain in the steel reached the yielding strain of

2750. Figure37 shows the load strain response, andFigure38 shows the failed

specimen, both of which support the argument about the mode of failure.


0

5

10

15

20

25

30

-4000 -2000 0 2000 4000 6000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrai

nSteel

Microstrai

n

64


4.1.5.2 Slab (C 70 MR 1L)


the center of the soffit. This slab was cast to see the effect of one sheet strengthening

on the increase of load carrying capacity and other properties. The load versus micro-

strain graphs is shown in Figure 39. The slab ultimate load (Pu) is 45.2kN with a

corresponding deflection (δu) of 33.57mm. The deflection at which the steel yielded


this slab started with the steel yielding followed by the CFRP debonding. The

maximum microstrain in the concrete was less than 2530 which indicates that no

crushing happened, on the other hand, the microstrain in the steel reached 2750 which

is the yield strain. Moreover, the microstrain in the CFRP was below 12600 which is

the debonding strain; hence the brittle failure of the specimen happened. Figure 40

shows the failed specimen.

65



0

10

20

30

40

50

60

-4000 -2000 0 2000 4000 6000 8000 10000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

CFRP

Microstrain

66

4.1.5.3 Slab (C 70 MR 2L)




versus micro-strain graphs is shown in Figure 41. The slab ultimate load (Pu) was

47.44 kN with a corresponding deflection (δu) of 25.67 mm. The deflection at which

the steel yielded (δy) was 2.3 mm and the failure deflection (δf) was 33.33 mm. The

failure mode of this slab started with the steel yielding followed by CFRP debonding.

The strain in the concrete didn’t reach the crushing strain of 2530 while the steel

reached the yielding strain of 2750 and the CFRP almost reached the debonding strain

of 9018 where the specimen experienced a brittle failure. Figure42 shows the failed

specimen.


0

10

20

30

40

50

60

-2000 0 2000 4000 6000 8000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

CFRP

Microstrain

67


4.1.6 Group C 70 HR:

The sixth group of this study is the C 70 HR. This group was cast with







microstrain of this group one layer and two layers strengthened are 12600 and 9018

respectively, hence if the strain reaches this level a brittle failure is bound to happen.




The slab ultimate load (Pu) is 33.04kN with a corresponding deflection (δu) of




The strain in the concrete almost reached the crushing strain of 2530, while the strain

in the steel reached the yielding strain of 2750. Figure 43 shows the load strain

68

response, and Figure 44 shows the failed specimen, both of which support the


Figure 43: Load versus microstrain for slab specimen (C 70 HR C)

Figure 44: Failed slab specimen (C 70 HR C)

69

4.1.6.2 Slab (C 70 HR 1L)


the center of the soffit. The load versus micro-strain graphs is shown in Figure 45.

This slab was cast to see the effect of single sheet strengthening on the increase of

load carrying capacity and other properties. The slab ultimate load (Pu) is 56.08kN

with a corresponding deflection (δu) of 34.91 mm. The deflection at which the steel

yielded (δy) was 3.6 mm and the failure deflection (δf) was 36.01 mm. The failure

mode of this slab started with the steel yielding followed by concrete crushing at the

top shifting the neutral axis up, at the end CFRP debonding. The maximum


the top. On the other hand, the microstrain in the steel reached 2750 which is the yield

strain. Moreover, the microstrain in the CFRP was below 12600 which is the

debonding strain; hence the brittle failure of the specimen happened. Figure 46 shows



0

10

20

30

40

50

60

-4000 -2000 0 2000 4000 6000 8000 10000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

CFRP

Microstrain

70


4.1.6.3Slab (C 70 HR 2L)




versus micro-strain graphs are shown in Figure 47. The slab ultimate load (Pu) is

59.3kN with a corresponding deflection (δu) of 30.95 mm. The deflection at which the

steel yielded (δy) was 2.15 mm and the failure deflection (δf) was 31.67 mm. The


at the top shifting the neutral axis up, at the end CFRP debonding. The strain in the

concrete was near the crushing strain of 2530 while the steel reached the yielding

strain of 2750 and the CFRP almost reached the debonding strain of 9018 where the

specimen experienced a brittle failure. Figure 48supports the claim of the mode of

failure.

71

Figure 47: Load versus microstrain slab specimen (C 70 HR 2L)


4.1.7 Group C 100 LR

The seventh group of this study is the C 100 LR. This group was cast with

concrete of compressive strength of 100 MPa and equal to minimum reinforcement

0

10

20

30

40

50

60

70

-4000 -2000 0 2000 4000 6000 8000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

CFRP

Microstrain

72

ratio with two tension rebars of 8 mm diameter. The reinforcement ratio in this group

is 0.45 % which is equal to minimum 0.45%. The reason behind the choice of this

reinforcement ratio is to explore the applicability of FRP strengthening over vast

range of reinforcement ratios and concrete compressive strengths. The yielding strain

for the tension steel used is 2750 microstrain, while the debonding microstrain of this

group one layer and two layers strengthened are 12600 and 10718 respectively, hence

if the strain reaches this level, a brittle failure is bound to happen. In addition, the

strain (ϵο) at which the concrete reaches its compressive strength ( 𝑓𝑐′ ) is 2930

microstrain.




deflection (δf) was 41.34 mm. The failure mode of the slab matches the typical failure

mode of an under-reinforced slab which started with the yielding of the steel,

followed by the membrane action failures without concrete crushing at the top. The

strain in the concrete didn't reach the crushing strain of 2930, while the strain in the

steel reached the yielding strain of 2750. Figure 49 shows the load strain response,

and Figure 50 shows the failed specimen, both of which support the argument on the

mode of failure.


0

2

4

6

8

10

12

14

-2000 -1000 0 1000 2000 3000 4000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

73

Figure 50: Failed slab specimen (C 100 LR C)

4.1.7.2 Slab (C 100 LR 1L)




ultimate load (Pu) is 30.56 kN with a corresponding deflection (δu) of 29.8 mm. The

deflection at which the steel yielded (δy) was 1.8 mm and the failure deflection (δf)

was 34.8 mm. The failure mode of this slab started with the steel yielding followed by

the CFRP debonding. Figure 51shows the load strain response and Figure 52 shows

the failed specimen, both of which support the claim about the failure mode. The

maximum microstrain in the concrete was less than 2930 which indicates that no



the debonding strain; hence the brittle failure of the specimen happened.

74



4.1.7.3 Slab (C 100 LR 2L)




versus microstrain graph is shown in Figure 53. The slab ultimate load (Pu) is 40.2 kN

0

5

10

15

20

25

30

35

-2000 0 2000 4000 6000 8000

Lo

ad

(k

N)

Microstrain

Concrete Microstrain

Steel Microstrain

CFRP Microstrain

75

with a corresponding deflection (δu) of 11.95 mm. The deflection at which the steel

yielded (δy) was 0.23 mm and the failure deflection (δf) was 12.25 mm. The failure

mode of this slab started with the steel yielding followed by CFRP debonding. Figure

54 shows the mode of failure. The strain in the concrete didn’t reach the crushing

strain of 2930 while the steel reached the yielding strain of 2750 and the CFRP almost

reached the debonding strain of 10718 which is the debonding strain where the

specimen experienced a brittle failure.



0

5

10

15

20

25

30

35

40

45

-2000 0 2000 4000 6000 8000

Lo

ad

(k

N)

Microstrain

Concrete

MicrostrainSteel

MicrostrainCFRP

Microstrain

76

4.1.8 Group C 100 MR

The eighth group of this study is the C 100 MR. This group was cast with






strain for the tension steel used is 2750 microstrain, while the debonding microstrain

of this group one layer and two layers strengthened are 12600 and 10718 respectively,



microstrain.

4.1.8.1 Control slab (C 100 MR C)

The slab ultimate load (Pu) is 38.75 kN with a corresponding deflection (δu) of






response, and Figure 56 shows the failed specimen, both of which support the



0

5

10

15

20

25

30

35

40

45

50

-4000 -2000 0 2000 4000 6000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

77


4.1.8.2 Slab (C 100 MR 1L)




ultimate load (Pu) is 43.5kN with a corresponding deflection (δu) of 27.15 mm. The


was 38.88 mm. The load versus micro-strain graph is shown in Figure 57. The failure

mode of this slab started with the steel yielding followed by the CFRP debonding.

The maximum microstrain in the concrete was less than 2930 which indicates that no



the debonding strain; hence the brittle failure of the specimen happened. Figure 58

shows the failed specimen.

78



0

10

20

30

40

50

60

70

-4000 -2000 0 2000 4000 6000 8000 10000 12000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

CFRP

Microstrain

79

4.1.8.3 Slab (C 100 MR 2L)




ultimate load (Pu) is 49.58kN with a corresponding deflection (δu) of 24.3 mm. The


was 24.86 mm. The load versus micro-strain graphs is shown in Figure 59. The failure

mode of this slab started with the steel yielding followed by CFRP debonding. The

strain in the concrete didn’t reach the crushing strain of 2930 while the steel reached

the yielding strain of 2750 and the CFRP almost reached the debonding strain of

10718 where the specimen experienced a brittle failure. Figure 60 shows the failed

specimen.


0

10

20

30

40

50

60

-4000 -2000 0 2000 4000 6000 8000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

CFRP

Microstrain

80


4.1.9 Group C 100 HR

The ninth group of this study is the C 100 HR. This group was cast with







microstrain of this group one layer and two layers strengthened are 12600 and 10718

respectively, hence if the strain reaches this level, a brittle failure is bound to happen.









81


response, andFigure62 shows the failed specimen, both of which support the


Figure 61: Load versus microstrain for slab specimen (C 100 HR C)

Figure 62: Failed slab specimen (C 100 HR C)

0

5

10

15

20

25

30

35

40

-4000 -2000 0 2000 4000 6000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

82

4.1.9.2 Slab (C 100 HR 1L)




versus micro-strain graph is shown in Figure 63.The slab ultimate load (Pu) is


steel yielded (δy) was 1.96 mm and the failure deflection (δf) was 37.15 mm. The


at the top shifting the neutral axis up, at the end CFRP debonding. The maximum


the top, on the other hand, the microstrain in the steel reached 2750 which is the yield

strain. Moreover, the microstrain in the CFRP was below 12600 which is the

debonding strain; hence the brittle failure of the specimen happened. Figure 64 shows


Figure 63: Load versus microstrain slab specimen (C 100 HR 1L)

0

10

20

30

40

50

60

-4000 -2000 0 2000 4000 6000 8000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

CFRP

Microstrain

83


4.1.9.3 Slab (C 100 HR 2L)


the center of the soffit. This slab was cast to see the effect of strengthening on the

increase of load carrying capacity and other properties. The slab ultimate load (Pu) is


steel yielded (δy) was 2.11 mm and the failure deflection (δf) was 30.63 mm. The load

versus micro-strain graph is shown in Figure 65. The failure mode of this slab started

with the steel yielding followed by concrete crushing at the top shifting the neutral

axis up, at the end CFRP debonding. The maximum microstrain in the concrete was

near 2930 which indicates that crushing happened at the top, while the steel reached

the yielding strain of 2750 and the CFRP almost reached the debonding strain of

10718 which is the debonding strain where the specimen experienced a brittle failure.

Figure 66 shows the failed specimen.

84



0

10

20

30

40

50

60

70

-4000 -2000 0 2000 4000 6000 8000

Lo

ad

(k

N)

Microstrain

Concrete

Microstrain

Steel

Microstrain

CFRP

Microstrain

85

4.2. Summary of the Results Obtained:

In this section, a summary of the tested data is presented. Table 15 provides

the loads including the ultimate load (Pu) and the yielding load (Py), calculation of the

slab's stiffness (K= Py/δy), percentage increase of (Pu) and (K) for each specimen over

the control slab of the group.

Table 15: Summary of the average load data

Group Specimen Py

(kN)

δy

(mm)

K=Py/δy

(kN/mm)

%

Increase

in K

Pu (kN)

%

Increase

in Pu

C 40 LR

C 40 LR

C

12.5 21.01 0.59 - 12.5 -

C 40 LR

1L

21 18.9 1.11 86.76 21.37 70.96

C 40 LR

2L

25.1 15.02 1.67 180.88 37.43 199.44

C 40 MR

C 40 MR

C

15.2 18.2 0.84 - 23.15 -

C 40 MR

1L

21.3 30.03 0.71 -15.07 45.16 95.08

C 40 MR

2L

40.6 21.78 1.86 123.20 49.57 114.13

C 40 HR

C 40 HR

C

19.1 7.5 2.55 - 45.88 -

C 40 HR

1L

36.07 20.74 1.74 -31.71 52.03 13.40

C 40 HR

2L

39.1 19.62 1.99 -21.75 53.73 17.11

C 70 LR

C 70 LR

C

8.1 10.2 0.79 - 9.49 -

C 70 LR

1L

15.84 13.01 1.22 53.32 26.25 176.61

C 70 LR

2L

40.16 22.28 1.80 126.98 45.31 377.45

C 70 MR

C 70 MR

C

15.54 10.29 1.51 - 27.45 -

C 70 MR

1L

32.44 26.22 1.24 -18.08 47.36 72.53

86

C 70 MR

2L

34.63 17.69 1.96 29.63 45.92 67.29

C 70 HR

C 70 HR

C

18.1 13.9 1.30 - 35.55 -

C 70 HR

1L

38.57 22.28 1.73 32.94 53.08 49.31

C 70 HR

2L

51.31 26.11 1.97 50.91 58.28 63.94

C 100 LR

C 100

LR C

11.26 23.7 0.48 - 11.1 -

C 100

LR 1L

26.7 21.7 1.23 158.98 29.61 166.76

C 100

LR 2L

34.11 10.21 3.34 603.18 38.35 245.50

C 100 MR

C 100

MR C

32.84 18.4 1.78 - 40.58 -

C 100

MR 1L

34.9 20.15 1.73 -2.96 43 5.96

C 100

MR 2L

36.29 17.27 2.10 17.74 48.89 20.48

C 100 HR

C 100

HR C

22.56 18.65 1.21 - 36.37 -

C 100

HR 1L

39.82 24.2 1.65 36.03 51.97 42.89

C 100

HR 2L

56.9 27.09 2.10 73.64 62.55 71.98

In principle, ductility is an advantageous property in that it allows for stress

distribution in structures in a post cracked section. Another advantage of ductility is

the warning and resiliency that it provides in times of sudden threats on the structure

such as earthquakes or impacts. Reinforced concrete beams are under reinforced by

the guidelines of ACI 318, since they recommend a reinforcement ratio of 25% less

than the balanced reinforcement ratio where the steel and concrete fail at the same

time. Due to this constraint in the design, the failure of these flexural elements starts

with the yielding of steel followed by huge deformation without compromising the

load carrying ability. At the end, the concrete crushes at the top in the compression

area causing the element to fail [29].

87

In the case of FRP strengthened sections, the process is different. The design

of FRP strengthened sections is based on compatibility of strains and the assumptions

that plane sections remain plane. This assumption is valid only if the perfect bond

between FRP and concrete remains, and the concrete is able to transfer loads to the

FRP sheets by shear loads. In FRP strengthened sections, the ductility is widely

available up to the point of steel yielding. After the yielding of steel, the section can

carry more loads but the rate of deflection with the increase of load gets lower until it

gets to the point of failure. During this process, the FRP remains in the elastic region

until failure happens suddenly. The possible modes of failure in FRP strengthened

sections are FRP debonding or rupture, or concrete crushing at the top, all of which

are considered sudden brittle failures [29].

Table 16 provides the deflection results including the deflection at the onset of

steel yielding (δy), the deflection at the ultimate (δu), and the deflection at failure (δf).

The ductility of the specimens is also reported and computed as follows:

(Eq5)

(Eq6)

Table 16: Summary of deflection data

Group Specimen δy (mm) δu (mm) δf

(mm) μ1 = δu/δy μ1/μ1CB μ2= δf/δy μ2/μ2CB

C 40 LR

C 40 LR C 21.01 21.01 31.07 1.00 1.00 1.48 1.00

C 40 LR 1L 18.9 19.86 23.3 1.05 1.05 1.23 0.83

C 40 LR 2L 15.02 24.5 25.88 1.63 1.63 1.72 1.17

C 40 MR

C 40 MR C 18.2 28.4 29.2 1.56 1.00 1.60 1.00

C 40 MR 1L 30.03 35.13 41.7 1.17 0.75 1.39 0.87

C 40 MR 2L 21.78 24.48 26 1.12 0.72 1.19 0.74

C 40 HR C 40 HR C 7.5 21.5 22.3 2.87 1.00 2.97 1.00

μ1 =δ𝑢

δ𝑦

μ2 =δ𝑓

δ𝑦

88

Toughness of a concrete flexural element by definition is the ability of the

element to absorb energy without failing in a brittle matter. The measure of toughness

in the flexural elements is equal to the area under the load versus mid-span deflection

until the point of failure is reached. In general, the higher the toughness of values in

flexural element, the larger the energy that the specimen can absorb energy before

failing in a brittle manner is. This property is as important as the ultimate capacity

since it can be very helpful in times of earth quakes, impacts, and attacks since it can

absorb more energy.

C 40 HR 1L 20.74 30.22 45 1.46 0.51 2.17 0.73

C 40 HR 2L 19.62 20.38 21.7 1.04 0.36 1.11 0.37

C 70 LR

C 70 LR C 10.2 11.15 13.1 1.09 1.00 1.28 1.00

C 70 LR 1L 13.01 27.78 37.48 2.14 1.95 2.88 2.24

C 70 LR 2L 22.28 13.78 28.06 0.62 0.57 1.26 0.98

C 70 MR

C 70 MR C 10.29 71.75 80 6.97 1.00 7.77 1.00

C 70 MR 1L 26.22 33.57 37.35 1.28 0.18 1.42 0.18

C 70 MR 2L 17.69 25.76 33.33 1.46 0.21 1.88 0.24

C 70 HR

C 70 HR C 13.9 35.77 40.45 2.57 1.00 2.91 1.00

C 70 HR 1L 22.28 34.91 36.01 1.57 0.61 1.62 0.56

C 70 HR 2L 26.11 30.95 31.67 1.19 0.46 1.21 0.42

C 100 LR

C 100 LR C 23.7 40.86 41.34 1.72 1.00 1.74 1.00

C 100 LR 1L 21.7 29.8 34.8 1.37 0.80 1.60 0.92

C 100 LR 2L 10.21 11.95 12.25 1.17 0.68 1.20 0.69

C 100 MR

C 100 MR C 18.4 32.45 35.68 1.76 1.00 1.94 1.00

C 100 MR 1L 20.15 27.15 38.88 1.35 0.76 1.93 1.00

C 100 MR 2L 17.27 24.3 24.86 1.41 0.80 1.44 0.74

C 100 HR

C 100 HR C 18.65 36.9 42 1.98 1.00 2.25 1.00

C 100 HR 1L 24.2 35.3 37.15 1.46 0.74 1.54 0.68

C 100 HR 2L 27.09 29.75 30.63 1.10 0.56 1.13 0.50

89

Table 17 below provides the toughness measure as it also provides the modes

of failures for each slab specimen that is denoted by the following abbreviations:

CC: concrete crushing.

SY: steel yielding.

FD: CFRP debonding.

MA: Membrane Action

Table 17: Summary of deflection data

Group Specimen UT UT/UTCB

Mode of failure

C 40 LR

C 40 LR C 105.30 1.00 SY_MA

C 40 LR 1L 87.64 0.83 SY_FD

C 40 LR 2L 349.28 3.32 SY_MA_FD

C 40 MR

C 40 MR C 209.05 1.00 SY_CC

C 40 MR 1L 450.38 2.15 SY_CC_FD

C 40 MR 2L 192.15 0.92 SY_CC_FD

C 40 HR

C 40 HR C 480.17 1.00 SY_CC

C 40 HR 1L 1113.67 2.32 SY_FD

C 40 HR 2L 99.29 0.21 SY_FD

C 70 LR

C 70 LR C 23.47 1.00 SY_MA

C 70 LR 1L 545.64 23.25 SY_FD

C 70 LR 2L 191.46 8.16 SY_FD

C 70 MR

C 70 MR C 1469.57 1.00 SY_MA_CC

C 70 MR 1L 439.10 0.30 SY_FD

C 70 MR 2L 654.36 0.45 SY_FD

C 70 HR C 70 HR C 698.38 1.00 SY_CC

90

4.3. Repeatability of Results:

For the purpose of this study, two samples from each type were cast to ensure

the repeatability of the result and to verify the conclusions of the study. In this

section, Figures 67 through 73 show some of the loads versus mid-span deflection

curves of this study, but the reminder of the figures are shown in Appendix A of this

thesis. It is clearly indicated from Figures 67 through 73 that the results are almost

identical for each pair of specimens. The slight differences between the same

specimens could be due to human errors which are present in casting and curing of the

concrete, positioning of the steel cages, attachment of the CFRP sheets, distribution of

the epoxy adhesive over the sheets, and other variation errors in the materials due to

manufacturing. In addition, at the end of this section, Table 18 summarizes the

ultimate load (Pu), ultimate deflections (δu), percentage difference in the ultimate

loads and deflections, and failure modes for each pair of tested specimens. The full

comparison is presented in the Appendix.

C 70 HR 1L 653.23 0.94 SY_CC_FD

C 70 HR 2L 306.10 0.44 SY_CC_FD

C 100 LR

C 100 LR C 193.31 1.00 SY_MA

C 100 LR 1L 369.42 1.91 SY_FD

C 100 LR 2L 75.50 0.39 SY_FD

C 100 MR

C 100 MR C 615.57 1.00 SY_CC

C 100 MR 1L 733.63 1.19 SY_FD

C 100 MR 2L 326.82 0.53 SY_FD

C 100 HR

C 100 HR C 685.89 1.00 SY_CC

C 100 HR 1L 618.84 0.90 SY_CC_FD

C 100 HR 2L 214.03 0.31 SY_CC_FD

91

4.3.1 Load versus mid-span deflection

In this section Figures 67 through Figure 73 present the load versus deflection

data for some of the tested specimens

Figure 67: Load versus Mid-span Deflection for (C 40 LR 1L) slabs

Figure 68: Load versus Mid-span Deflection for (C 40 LR 2L) slabs

0

5

10

15

20

25

0 5 10 15 20 25

Lo

ad

(K

N)

Deflection (mm)

C 40 LR1L 1

C 40 LR 1L 2

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25 30

Lo

ad

(K

N)

Deflection (mm)

C 40 LR2L 1

C 40 LR 2L 2

92

Figure 69: Load versus Mid-span Deflection (C 70 HR C) slabs

Figure 70: Load versus Mid-span Deflection for (C 70 HR 1L) slabs

0

5

10

15

20

25

30

35

40

45

0 10 20 30 40 50

Lo

ad

(K

N)

Deflection (mm)

C 70 HR C 1

C 70 HR C 2

0

10

20

30

40

50

60

0 10 20 30 40

Lo

ad

(K

N)

Deflection (mm)

C 70 HR 1L 1

C 70 HR 1L 2

93

Figure 71: Load versus Mid-span Deflection for (C 70 HR 2L) slabs

Figure 72: Load versus Mid-span Deflection for (C 100 MR 1L) slabs

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35

Lo

ad

(K

N)

Deflection (mm)

C 70 HR 2L 1

C 70 HR 1L 2

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50

Lo

ad

(K

N)

Deflection (mm)

C 100 MR 1L 1

C 100 MR 1L 2

94

Figure 73: Load versus Mid-span Deflection for (C 100 HR 1L)

0

10

20

30

40

50

60

0 10 20 30 40

Lo

ad

(K

N)

Deflection (mm)

C 100 HR 1L 1

C 100 HR 1L 2

95

Table 18: Summary of all tested specimens

Group Specimen δu (mm) % Difference

of δu Average δu Pu (kN)

% Difference

of Pu Average Pu Failure Mode

C 40 LR

C 40 LR C 1 21.01 28.03 23.96

11.63 8.94 12.15

SY_MA

C 40 LR C 2 26.9 12.67 SY_MA

C 40 LR 1L 1 19.36 2.58 19.61

21.04 3.09 21.37

SY_FD

C 40 LR 1L 2 19.86 21.69 SY_FD

C 40 LR 2L 1 24.5 -5.06 23.88

38.5 -5.56 37.43

SY_MA_FD

C 40 LR 2L 2 23.26 36.36 SY_MA_FD

C 40

MR

C 40 MR C 1 28.4 5.81 29.23

22.6 4.87 23.15

SY_CC

C 40 MR C 2 30.05 23.7 SY_CC

C 40 MR 1L 1 32.7 7.43 33.92

43.52 7.54 45.16

SY_CC_FD

C 40 MR 1L 2 35.13 46.8 SY_CC_FD

C 40 MR 2L 1 28.02 -12.63 26.25

48.6 3.97 49.57

SY_CC_FD

C 40 MR 2L 2 24.48 50.53 SY_CC_FD

C 40 HR

C 40 HR C 1 22.5 -4.44 22.00

46.88 -4.27 45.88

SY_CC

C 40 HR C 2 21.5 44.88 SY_CC

C 40 HR 1L 1 29.34 3.00 29.78

51.8 0.87 52.03

SY_FD

C 40 HR 1L 2 30.22 52.25 SY_FD

C 40 HR 2L 1 20.38 1.08 20.49

53.85 -0.46 53.73

SY_FD

C 40 HR 2L 2 20.6 53.6 SY_FD

C 70 LR

C 70 LR C 1 13.46 -5.65 13.08

10.17 -13.47 9.49

SY_MA

C 70 LR C 2 12.7 8.8 SY_MA

C 70 LR 1L 1 27.78 -10.26 26.36 26.6 -2.63 26.25 SY_FD

96

C 70 LR 1L 2 24.93 25.9 SY_FD

C 70 LR 2L 1 24.52 11.01 25.87

44.18 5.12 45.31

SY_FD

C 70 LR 2L 2 27.22 46.44 SY_FD

C 70

MR

C 70 MR C 1 35.2 103.84 53.48

28.9 -10.03 27.45

SY_MA_CC

C 70 MR C 2 71.75 26 SY_MA_CC

C 70 MR 1L 1 33.57 -7.80 32.26

45.2 9.56 47.36

SY_FD

C 70 MR 1L 2 30.95 49.52 SY_FD

C 70 MR 2L 1 25.76 -0.97 25.64

47.44 -6.41 45.92

SY_FD

C 70 MR 2L 2 25.51 44.4 SY_FD

C 70 HR

C 70 HR C 1 38.75 -7.69 37.26

38.05 -13.17 35.55

SY_CC

C 70 HR C 2 35.77 33.04 SY_CC

C 70 HR 1L 1 34.91 -11.40 32.92

56.08 -10.70 53.08

SY_CC_FD

C 70 HR 1L 2 30.93 50.08 SY_CC_FD

C 70 HR 2L 1 30.95 -5.56 30.09

59.3 -3.44 58.28

SY_CC_FD

C 70 HR 2L 2 29.23 57.26 SY_CC_FD

C 100

LR

C 100 LR C 1 40.86 -17.67 37.25

10.73 6.90 11.10

SY_MA

C 100 LR C 2 33.64 11.47 SY_MA

C 100 LR 1L 1 27.68 7.66 28.74

28.65 6.67 29.61

SY_FD

C 100 LR 1L 2 29.8 30.56 SY_FD

C 100 LR 2L 1 11.95 28.87 13.68

40.2 -9.20 38.35

SY_FD

C 100 LR 2L 2 15.4 36.5 SY_FD

C 100

MR

C 100 MR C 1 34.12 -4.89 33.29

42.41 -8.63 40.58

SY_CC

C 100 MR C 2 32.45 38.75 SY_CC

C 100 MR 1L 1 27.15 10.76 28.61

43.5 -2.30 43.00

SY_FD

C 100 MR 1L 2 30.07 42.5 SY_FD

97

C 100 MR 2L 1 24.3 -0.82 24.20

49.58 -2.78 48.89

SY_FD

C 100 MR 2L 2 24.1 48.2 SY_FD

C 100

HR

C 100 HR C 1 39.9 -7.52 38.40

37.74 -7.26 36.37

SY_CC

C 100 HR C 2 36.9 35 SY_CC

C 100 HR 1L 1 35.3 -4.67 34.48

55.14 -11.50 51.97

SY_CC_FD

C 100 HR 1L 2 33.65 48.8 SY_CC_FD

C 100 HR 2L 1 27.1 9.78 28.43

59.9 8.85 62.55

SY_CC_FD

C 100 HR 2L 2 29.75 65.2 SY_CC_FD

98

Chapter 5: Discussion of Results

This chapter discusses the testing results of each group separately. In each

group, a combined load versus mid span deflection is drawn to illustrate the behavior

of each beam compared to the control specimen. Each beam will be compared on the

bases of the ultimate strength (Pu), failure deflection (δf), ductility (K), toughness (UT).

Moreover, there are two load strain curves; one for the strain in steel, and the other is

for strain in CFRP.

5.1 Group (C 40)

5.1.1 Load-deflection and ultimate performance

The C 40 group has the lowest concrete compressive strength of all other

group, hence it has a lower ultimate capacity of all groups. The reinforcement ratio of

this group varies between specimens as the LR specimen has 2T8 with a

reinforcement ratio of 0.45%. The reinforcement ratio of the MR group is 1.0% which

is coming from 2T12, and the third reinforcement ratio of the HR group is 1.79%

which is cast with 2T16. Figure 74 shows the load versus mid-span deflection for all

specimens.

Figure 74: Group C 40 - load (kN) versus deflection (mm)

0

10

20

30

40

50

60

0 10 20 30 40

Lo

ad

(k

N)

Deflection (mm)

C 40 LR C

C 40 LR 1L

C 40 LR 2L

C 40 MR C

C 40 MR 1L

C 40 MR 2L

C 40 HR C

C 40 HR 1L

C 40 HR 2L

99

All specimens in this group followed a similar behavior in the pre-cracked

(elastic) region. However, when the cracks started to initiate, each specimen followed

a different path. There was no clear sign on a similar system performance although

some specimens have similar effective reinforcement ratio.

Typically, in all subgroups, the control specimen has the highest deflection,

hence the highest ductility. This is due to the fact that the more capacity the section

has, the less ductility it has since they are inversely proportional. This phenomenon

happens because of the increase in the cracked stiffness which will increase the

tension force in the tension steel. It is noted that among all control specimens across

all subgroups, the MR control has the highest load carrying capacity. This indicates

that the combination between the concrete compressive strength and the

reinforcement ratio.

Slabs in all strengthening scenarios have shown a better percentage of increase

when a 2 sheets are attached to the soffits of the slab. This is due to the fact that the

width of the specimen is relatively larger than the depth and the 2 bars are not enough

to resist all applied loads. The only outlier of this conclusion is the MR 1L since it

achieved more than the MR 2L, which is due to the fact that the effective

reinforcement of this group is considered sufficient to use the full capacity of the

concrete block until crushing. Moreover, a notable outcome is that with an increase of

reinforcement ratio, the contribution of the CFRP in load carrying capacity decreases.

Another conclusion is the fact that this study proves the effectiveness of using CFRP

in external strengthening for increasing the load carrying capacity of flexural

members.

It is clearly shown in Figure 74 that the load carrying capacities of

strengthened specimens have increased by 19.99% to 231.04% over the control

specimens; this shows the validity of strengthening of thin slabs with CFRP laminated

attached to their soffits. With this percentage of increase, it is safe to say that the

CFRP can be used to increase the load carrying capacity of the specimens that are cast

with C40 concrete.

5.1.2 Strain response

In this section, detailed discussion of the load strain response is done for both

the strain response of the steel and the CFRP. The concrete crushing microstrain of

100

concrete as defined in ACI 318-14 is equal to 2090. The yielding strain for the tension

steel used is 2750 microstrain, while the debonding microstrains of this group one

layer and two layers strengthened are 9687 and 6849 respectively; hence if the strain

reaches this level, a brittle failure is bound to happen. Figure 75 below shows the

strain response of tension steel in this group.

Figure 75: Steel strain response for Group C 40

The strain steel response shows similar response in the elastic region while

going into the inelastic region. The response starts to deviate and that is due to the

different arrangement and configurations of the CFRP strengthening. It is clear from

Figure 75 that almost all specimens reached the yielding strain. However, control

specimens and specimens with one CFRP layer reached the yielding strength and

continued yielding until failure, while the specimens with two CFRP layers didn’t

show any plastic behavior after the yielding point, which supports the claim of the

brittle failure. This is due to the fact that CFRP is considered reinforcement and with

the double layers strengthening, the section becomes over reinforced, hence the

section doesn’t have enough tension capacity to yield the steel until failure and

debond or rupture the CFRP happens.

0

10

20

30

40

50

60

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Lo

ad

(k

N)

Microstrain

C 40 LR C

C 40 LR 1L

C 40 LR 2L

C 40 MR C

C 40 MR 1L

C 40 MR 2L

C 40 HR C

C 40 HR 1L

C 40 HR 2L

101

The CFRP strain response is shown in Figure 76.

Figure 76: FRP strain response for Group C 40

It is noted that the single sheet has the maximum utilization of the CFRP since

the area of the CFRP present in this configuration is less than the area present in the

double sheet configuration. This phenomenon is explained with the fact that with

double sheet strengthening, not all the area is used since it is considered as over

reinforcement of the section. Another conclusion reached form Figure 76 can be that

in the specimens with low reinforcement ratio, the CFRP sheets sustained the largest

strain in all specimens with the two arrangements; the single and the double layers. It

is clearly noted that all specimens experienced brittle failure mode, although not all of

them reached the debonding strain in Figure 76. The reason behind this is that the

strain gauge, that was installed on the specimens, might not have been in the location

of maximum strain, or that the application and distribution of the epoxy were not

equal, hence not all the sheet experienced equal stain distribution.

0

10

20

30

40

50

60

0 1000 2000 3000 4000 5000 6000 7000 8000

Lo

ad

(k

N)

Microstrain

C 40 LR 1L

C 40 LR 2L

C 40 MR 1L

C 40 MR 2L

C 40 HR 1L

C 40 HR 2L

102

As for the strain response of concrete, some samples experienced crushing of

concrete at the top while others didn’t. Figure 77 shows the strain versus load

response of the specimens in this group.

Figure 77: Concrete strain response for Group C 40

It is clear that all of the specimens didn’t reach the crushing strain of

2090.This doesn’t mean that the specimens didn’t experience crushing of concrete at

the top; it only means that the strain gauge wasn’t placed in the location of maximum

strain. It's clearly noted that some specimens had low ultimate strain. This particularly

happened in the specimens that experienced the membrane action tensile failure and

the FRP debonding failure. Another notable conclusion is with the increase of the

reinforcement ratio, the ultimate strain in the specimens increased. This easily

explained with the fact that when the reinforcement ratio increases, the tension force

in the specimen increases, hence increasing the balancing compression forces.

5.1.3 Ductility measures

Figure 78 shows the elastic and final ductility with respect to the control

specimen from each group.

0

10

20

30

40

50

60

0 500 1000 1500 2000 2500 3000

Lo

ad

(k

N)

Microstrain

C 40 LR C

C 40 LR 1L

C 40 LR 2L

C 40 MR C

C 40 MR 1L

C 40 MR 2L

C 40 HR C

C 40 HR 1L

C 40 HR 2L

103

Figure 78: Ductility comparison

Figure 78 shows that the highest ductility was recorded for both ultimate and

final in the high reinforced group. This means that high reinforced slabs with one and

two layers of CFRP have almost four times of ductility as the control slab. This

ductility could be due to the perfect utilization of CFRP and steel with the concrete

crushing. All other specimens have shown same ductility as the control specimen.

5.1.4 Toughness measures

Figure 79 shows the comparison between the specimen and the control of each

group.

Figure 79: Toughness comparison (UT/UTCB)

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

C 40 LR C C 40 LR 1L C 40 LR 2L C 40 MR C C 40 MR 1LC 40 MR 2L C 40 HR C C 40 HR 1L C 40 HR 2L

µ1/µ1CB

µ2/µ2CB

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

C 40 LR C C 40 LR 1L C 40 LR 2L C 40 MR C C 40 MR 1L C 40 MR 2L C 40 HR C C 40 HR 1L C 40 HR 2L

104

It is noted from the Figure 79 that in the group of low reinforcement ratio, the

two layers showed a substantial increase in the toughness over the control specimen

as it showed 113% increase while the single layer showed an increase of only 13%.

This can be simply explained in the fact that double layered has better utilization of

materials. The same explanation is applicable for the difference in the increase of the

high reinforced group since the one layer showed an increase of 209%, while the

double layer showed only 33%. The case is different for the medium reinforcement

ratio group. For this group, there is full utilization of the concrete crushing capacity,

since all specimens experienced concrete crushing before the final failure. This

explains the increase of toughness with the increase of effective reinforcement.

5.2 Group (C 70)


This group has a compressive strength on 70 MPa with different reinforcement

ratios. The reinforcement ratios used in this group are the same as the C 40 group.

This was done to examine the effect of the reinforcement ratio in strengthening of the

sections. Figure 80 shows the load versus mid-span deflection response for this group.

Figure 80: Group C 70 - load (kN) versus deflection (mm)

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90

Lo

ad

(k

N)

Deflection (mm)

C 70 LR C

C 70 LR 1L

C 70 LR 2L

C 70 MR C

C 70 MR 1L

C 7O MR 2L

C 70 HR C

C 70 HR 1L

C 70 HR 2L

105

It is shown from Figure 80 that the strengthening of the specimens adds to the

ultimate strength of the section while compromising its ductility. Moreover, it is

shown that it is valid to assume that over strengthening of section does increase the

capacity. Another conclusion is that the low reinforcement subgroup of this group is

the greatest since there are deficiencies due to the low reinforcement.

It is clearly indicated in Figure 80 that the load carrying capacities of





with C70 concrete. It also shows that the increase in the load carrying capacity in this

group is greater than the increase in the load carrying capacity of the C40 group. This

is due to the extra force that the concrete can endure due to the increase of the

compressive strength until the CFRP debonds.


Figure 81 shows the steel strain response for this group.

Figure 81: Group C 70 – Steel strain response

The steel strain response showed in Figure 81 shows that not all the specimens

have reached the yielding stage and only three of the specimens have reached the

rupture strain. This happens usually in the control specimens that are under

0

10

20

30

40

50

60

70

0 1000 2000 3000 4000 5000 6000

Lo

ad

(k

N)

Microstrain

C 70 LR C

C 70 LR 1L

C 70 LR 2L

C 70 MR C

C 70 MR 1L

C 70 MR 2L

C 70 HR C

C 70 HR 1L

C 70 HR 2L

106

reinforced. The steel response in the single sheet reached the yielding strain, while on

the other hand, the steel in the double sheets did not; which is due to the fact of over

reinforcing the section with the CFRP sheets. It is also noted that the low

reinforcement specimen with one layer of CFRP showed similar behavior of the

medium reinforced control specimen. This is due to the fact that both of them have

similar effective reinforcement ratio.

For the CFRP strain response, Figure 82 shows that almost all specimens

reached the debonding microstrain of this group; one layer and two layers

strengthened are 12600 and 9018 respectively, hence all specimens experienced brittle

failure. Not all specimens reached the exact debonding strain. This doesn’t mean that

the conclusion of brittle failure is incorrect but it only means that the strain gauge is

not in the location of maximum strain. Another notable conclusion is for this

compressive strength of concrete. All specimens show similar response in terms of

FRP strain in the elastic region but the deviations start to occur in the beginning of the

inelastic region, which is due to the sensitivity of the cracking moment in concrete.

Another conclusion that could be drawn is the maximum utilization of FRP that

happens when one sheet is used because of the strain uniformity in the sheet, unlike

the irregularity of distribution in the double sheet due to the over strengthening.

Figure 82: Group C 70 –FRP strain response

0

10

20

30

40

50

60

70

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Lo

ad

(k

N)

Microstrain

C 70 LR 1L

C 70 LR 2L

C 70 MR 1L

C 70 MR 2L

C 70 HR 1L

C 70 HR 2L

107

The strain response in the concrete was similar in almost all specimens, as

shown by Figure 83.

Figure 83: Group C 70 –Concrete strain response

Figure 83 shows that the specimens that had crushing of concrete at the top

have reached values near to the crushing strain of 2530. In contrast, specimens who

incurred membrane action tensile failure, and specimens who experienced brittle

failure of FRP debonding didn’t come close to the crushing strain because the

specimens failed before the compressive force in the concrete reaches a value that will

be able to strain the concrete and cause it to crush.


Figure 84 shows the ductility comparison between the specimen and the

control specimen of the group. It is noted that the highest ductility was recorded for

the ultimate ductility in the low reinforcement ratio group with the single and double

layer strengthening. Although the single layer showed a huge difference over the

double layer, low reinforced slabs with one and two layers of CFRP have huge

increase in the ductility over the control slab. This ductility could be due to the perfect

utilization of CFRP and steel with the concrete crushing. All other specimens have

shown same ductility as the control specimen. The reason behind this behavior can be

0

10

20

30

40

50

60

70

0 500 1000 1500 2000 2500 3000

Lo

ad

(k

N)

Microstrain

C 70 LR C

C 70 LR 1L

C 70 LR 2L

C 70 MR C

C 70 MR 1L

C 70 MR 2L

C 70 HR C

C 70 HR 1L

C 70 HR 2L

108

accredited to the increase in the compressive strength of the concrete, so the crushing

happens instantly before the final failure.



Figure 85 shows the toughness ratio between the specimen and the control of

the group. It is noted that the behavior of toughness in the low reinforcement group is

the highest due to the fact that this group has the maximum utilization of the materials

in all groups. Another reason behind the high increase in toughness is also the fact

that this group has the biggest increase in the ultimate load over the control slab, and

since the toughness is equivalent to the area under the curve, the more increase in the

ultimate load, the more toughness or energy the specimen absorbs. All other

specimens had almost equivalent toughness as the control specimen. This is logical

since none of the specimens showed substantial increase in the ultimate load over the

control specimen.

0.00

0.50

1.00

1.50

2.00

2.50

C 70 LR C C 70 LR 1L C 70 LR 2L C 70 MR C C 70 MR 1L C 70 MR 2L C 70 HR C C 70 HR 1L C 70 HR 2L

µ1/µ

1CB

µ2/µ

2CB

109


5.3 Group (C 100)


This group of specimens was cast with a 100 MPa compressive strength with

the same reinforcement ratios as the other two groups to examine the response of high

strength concrete in strengthening. Figure 86 shows load versus mid-span deflection

of all specimens in this group compared to the control specimens to see the effect of

strengthening and reinforcement ratio on the ultimate capacity.

Figure 86: Group C100 - load (kN) versus deflection (mm)

0.00

5.00

10.00

15.00

20.00

25.00

C 70 LR C C 70 LR 1L C 70 LR 2L C 70 MR C C 70 MR

1L

C 70 MR

2L

C 70 HR C C 70 HR 1LC 70 HR 2L

0

10

20

30

40

50

60

70

0 10 20 30 40 50

Lo

ad

(k

N)

Mid-span Deflection (mm)

C 100 LR C

C 100 LR 1L

C 100 LR 2L

C 100 MR C

C 100 MR 1L

C 100 MR 2L

C 100 HR C

C 100 HR 1L

C 100 HR 2L

110

From Figure 86, it is clear that almost all specimens showed the same behavior

of ductility and showed the same deflections. This could be explained with the fact

that with the increase of the compressive strength of concrete, the cracking moment

increases and it becomes less sensitive. This graph also confirms the validity of

strengthening the section to increase the ultimate load carrying capacity.

It is clearly indicated in Figure 86 that the load carrying capacities of





with C70 concrete. It also shows that the increase in the load carrying capacity in this

group is less than the increase in the load carrying capacity of the C70 group, which is

due to the fact that the CFRP cannot handle the applied force before the crushing of

the concrete, and hence the CFRP debonds before the concrete reaches its

compressive strength.


Figure 87 shows the load versus steel strain response for all specimens in this

group. It is clear that all specimens reached the yield strength of the tensile strain of

the steel. It is also noted that almost all specimens had similar response in the elastic

and plastic region. It is also noted that the medium reinforcement ratio configuration

utilizes the steel capacity better than the other two configurations. The reason behind

this utilization is the high strength of concrete for the delay of concrete crushing until

the steel reaches the yielding point.

111

Figure 87: Steel strain response for Group C100

For the CFRP strain response that is shown in Figure 88, it's clear that all of

the specimens experienced brittle mode of failure with the debonding of CFRP. It

means that all specimens reached the debonding microstrain of this group; one layer

and two layers strengthened are 12600 and 10718 respectively. Although Figure X

shows that not all of the specimens reached the pre-specified microstrain, this doesn’t

debunk the conclusion of the brittle failure, but it only means that the strain gauge

wasn’t in the location of maximum microstrain. Another conclusion is that almost all

specimens follow a similar trend for the elastic region, and part of the plastic region.

Figure 88: FRP strain response for Group C 100

0

10

20

30

40

50

60

70

0 2000 4000 6000 8000 10000

Lo

ad

(k

N)

Microstrain

C 100 LR C 1

C 100 LR 1L 1

C 100 LR 2L 1

C 100 MR C 1

C 100 MR 1L 1

C 100 MR 2L 1

C 100 HR C 1

C 100 HR 1L 1

C 100 HR 2L 1

0

10

20

30

40

50

60

70

0 5000 10000 15000

Lo

ad

(k

N)

Microstrain

C 100 LR 1L

C 100 LR 2L

C 100 MR 1L

C 100 MR 2L

C 100 HR 1L

C 100 HR 2L

112

The strain response for the concrete is shown in Figure 89.

Figure 89: Concrete strain response for Group C 100

As shown in Figure 89, all specimens have shown similar response in the pre-

cracking region. Moreover, this similarity in behavior also continued in the after-

cracking region. It is also noted that specimens who experienced concrete crushing of

the microstrain values were close to 2930 which is the crushing strain, unlike the

specimens that incurred either tensile membrane action failure or the brittle failure of

FRP debonding where the microstrain values were far from the crushing strain.


Figure 90 shows the ductility comparison between the specimen and the

control specimen of the group. It is noted that the highest ductility was recorded for

the ultimate ductility in the low reinforcement ratio group with the double layer

strengthening. This means that low reinforced slabs with double layers of CFRP have

huge increase in the ductility over the control slab. This ductility could be due to the

perfect utilization of CFRP and steel with the concrete crushing. All other specimens

have shown same ductility as the control specimen or even lower. The reason behind

this behavior can be the increase in the compressive strength of the concrete, so the

0

10

20

30

40

50

60

70

0 500 1000 1500 2000 2500 3000

Lo

ad

(k

N)

Microstrain

C 100 LR C

C 100 LR 1L

C 100 LR 2L

C 100 MR C

C 100 MR 1L

C 100 MR 2L

C 100 HR C

C 100 HR 1L

C 100 HR 2L

113

crushing happens instantly before the final failure or the crushing might not even

happen before the final failure.



Figure 91 shows the toughness ratio between the specimen and the control of

the group. It is noted that the behavior of toughness in the low reinforcement double

layer CFRP strengthened specimen is the highest due to the fact that this specimen has

the maximum utilization of the materials in all groups. Another reason behind the

high increase in toughness is also the fact that that this group has the largest increase

in the ultimate load over the control slab and since the toughness is equivalent to the

area under the curve, the more increase in the ultimate load, the more toughness or

energy the specimen absorbs. Some other specimens showed some notable increase in

toughness although it is low in the range of 40%. All other specimens had almost

equivalent toughness as the control specimen. This is logical since none of the

specimens showed substantial increase in the ultimate load over the control specimen.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

C 100 LR C C 100 LR

1L

C 100 LR

2L

C 100 MR C C 100 MR

1L

C 100 MR

2L

C 100 HR C C 100 HR

1L

C 100 HR

2L

µ1/µ

1CB

µ2/µ

2CB

114


5.4 Conclusions

5.4.1 Effect of reinforcement ratio

5.4.1.1 Group C 40

Figure 92 shows the effect of reinforcement ratio on the increase of flexural

capacity in the C40 group.

Figure 92: Reinforcement ratio effect on C40

0.00

0.50

1.00

1.50

2.00

2.50

C 100 LR C C 100 LR

1L

C 100 LR

2L

C 100 MR C C 100 MR

1L

C 100 MR

2L

C 100 HR C C 100 HR

1L

C 100 HR

2L

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0.00 0.50 1.00 1.50 2.00

Mn

/Mn

con

t

Reinforcment Ratio

C 40 C

C 40 1L

C 40 2L

115

It is clear from the above graph that with the increase of the reinforcement

ratio, the contribution of the CFRP reduces. This trend is very clear in the two layers

strengthened specimens. For the case of one layer strengthened specimens, the

contribution is at its highest with the medium reinforcement because it is the point of

over reinforcement where the steel doesn’t yield before the crushing of the concrete.

5.4.1.1 Group C 70





ratio, the contribution of the CFRP reduces and it becomes constant with the high

reinforcement ratio as well. The reason behind this is that with the increase in CFRP

layers, most of the area of the CFRP becomes unstressed, and the section becomes

over reinforced.

5.4.1.3 Group C 100



0.00

1.00

2.00

3.00

4.00

5.00

6.00

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00

Mn

/Mn

con

t

Reinforcment Ratio

C 70 C

C 70 1L

C 70 2L

116



ratio, the contribution of the CFRP reduces until the point of over reinforcement

where the steel doesn’t yield before the crushing of the concrete. In the region of high

reinforcement ratio, the contribution increases although this increase is not high but it

is notable.

5.4.2 Effect of concrete compressive strength

5.4.2.1 Low reinforcement

Figure 95 shows the effect of compressive strength of concrete on the increase

of flexural capacity in the low steel reinforcement group.

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00

Mn

/Mn

con

t

Reinforcment Ratio

C 100 C

C 100 1L

C 100 2L

117

Figure 95: Concrete compressive strength effect on LR

It is noted from the above graph that for the low reinforcement ratio group that

the contribution of CFRP in increasing the flexural capacity was at its maximum

when the compressive strength of concrete was equal to 70 MPa. After that the

contribution is more seen in the high compressive strength of concrete over the low

compressive strength. It is safe to say that the best arrangement that should be used in

low reinforcement group is a medium strength concrete.

5.4.2.2 Medium reinforcement


of flexural capacity in the medium steel reinforcement group.

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0.00 20.00 40.00 60.00 80.00 100.00 120.00

Mn

/Mn

con

t

f'c (Mpa)

LR C (0.45)

LR 1L (0.45)

LR 2L (0.45)

118

Figure 96: Concrete compressive strength effect on MR

It is noted from Figure 96 that for the medium reinforcement ratio group that

when the contribution of CFRP increases, the flexural capacity reduces with the

increase of the compressive strength of the concrete. This response is explained

because with the increase in the compressive strength of concrete, the CFRP debonds

without the concrete crushing at the top. Hence, no full utilization of the materials is

achieved.

5.4.2.3 High reinforcement


of flexural capacity in the high steel reinforcement group.

0.00

0.50

1.00

1.50

2.00

2.50

0.00 20.00 40.00 60.00 80.00 100.00 120.00

Mn

/Mn

con

t

f'c (Mpa)

MR C (1.0)

MR 1L (1.0)

MR 2L (1.0)

119

Figure 97: Concrete compressive strength effect on HR

From Figure 97 above, it is noted that the contribution CFRP strengthening

increases when the compressive strength of concrete increases in the high

reinforcement ratio group. This is due to the fact that with the increase in the

reinforcement ratio, increasing the number CFRP sheets will allow the concrete at the

top to reach the crushing strain hence all of the materials are utilized.

5.4.3 Effect of CFRP reinforcement ratio

5.4.3.1 CFRP reinforcement ratio on low steel reinforcement ratio

Figure 98 shows the effect of CFRP reinforcement ratio on the increase of

flexural capacity in the low steel reinforcement group.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

0.00 20.00 40.00 60.00 80.00 100.00 120.00

Mn

/Mn

con

t

f'c (Mpa)

HR C (1.79)

HR 1L (1.79)

HR 2L (1.79)

120

Figure 98: CFRP ratio effect on LR

There is a clear trend in Figure 98; it is clear that with the increase of the

CFRP reinforcement ratio, the load carrying capacity increases. This is due to the fact

that the CFRP will aid in the deficiency in the flexural steel reinforcement, hence

increasing the load carrying capacity.

5.4.3.2 CFRP reinforcement ratio on medium steel reinforcement ratio


flexural capacity in the medium steel reinforcement group.

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0.0000 0.0020 0.0040 0.0060 0.0080 0.0100

Mn

/Mn

con

t

FRP Ratio

C 40 LR

C 70 LR

C 100 LR

121

Figure 99: CFRP ratio effect on MR

There is a clear trend in Figure 99; it is clear that with the increase of the

CFRP reinforcement ratio, the load carrying capacity increases. This is due to the fact

that the CFRP will aid in the deficiency in the flexural steel reinforcement until the

point of medium reinforcement is reached. Afterwards, the increase is there but the

rate of increase gets lower because the section is going into the perfect utilization of

the tension and compression forces.

5.4.3.3CFRP reinforcement ratio on high steel reinforcement ratio


flexural capacity in the high steel reinforcement group.

0.00

0.50

1.00

1.50

2.00

2.50

0.0000 0.0020 0.0040 0.0060 0.0080 0.0100

Mn

/Mn

con

t

FRP Ratio

C 40 MR

C 70 MR

C 100 MR

122

Figure 100: CFRP ratio effect on HR

It is clear that for this group that the contribution of the CFRP reinforcement

ratio is maximum with the 100 MPa compressive strength of concrete. This can be

attributed to the fact that the concrete crushes in the lower compressive strengths

faster than the higher one before it allows for steel yielding.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

0.0000 0.0020 0.0040 0.0060 0.0080 0.0100

Mn

/Mn

con

t

FRP Ratio

C 40 HR

C 70 HR

C 100 HR

123

Chapter 6: Theoretical Models

In this chapter, the theoretical behavior will be validated through two

theoretical models. The first model is the flexibility model which relies on concept of

effective flexibility of cracked reinforced concrete. This model will be able to predict

the theoretical deflection versus the loads applied on the slabs. The second model is

used to predict the load carrying capacity of the slab specimens and the mode of

failure; this model relies on the concept of strain compatibility. Both models are found

in ACI- 440.02R-08. On the other hand, the moment capacity of the control sections

where calculated using ACI318-11. All capacities calculations are the nominal

capacities; hence no reduction factor is included.

6.1. Flexibility Model for Cracked Sections

In general, flexibility is the inverse of stiffness. In a structural element, both

flexibility and stiffness are properties of the cross sections that are used to predict

maximum deflections of loaded members. For the field of reinforced concrete

elements, the definition of flexibility and stiffness is well defined using theoretical

and empirical approaches. However, for the field of strengthening, there are many

difficulties due to differences of properties of FRP and steel reinforcements, and the

fact that both of them behave and fail differently under loading. However, ACI-

440.02R-08 provided the concept of flexibility in a semi-empirical equation that is

able to predict the max deflection under different loading scenarios.

Equations 7 through 9[17] outline the procedure of finding the deflection

response of the tested specimens under the two points loading scenario that is adopted

in the study.

1

𝐸𝑐𝐼𝑒𝑓𝑓=

1

𝐸𝑐𝐼𝑐𝑟[1 +

𝜔

1 + 𝜔] ≤

1

𝐸𝑐𝐼𝑔, 𝑓𝑜𝑟 𝑀 ≥ 𝑀𝑐𝑟 (Eq7)

where:

𝜔 = (𝑀𝑐𝑟

𝑀)

3

(𝛽𝑑𝐼𝑔

𝐼𝑐𝑟− 1) (Eq8)

and,

𝛽𝑑 = 𝛼𝑏 (𝐸𝑓

𝐸𝑠+ 1) , 𝛼𝑏 = 0.5 (Eq9)

124

Where:

Ec: Modulus of elasticity of concrete

Ef: Modulus of elasticity of FRP

Es: Modulus of elasticity of steel

M: The applied bending moment on the element

Mcr: The cracking moment of reinforced concrete

Ig: Gross moment of inertia

Icr: Cracked moment of inertia

The main assumption of this flexibility model is that the moment of inertia is

the gross one until the section reaches the cracking load. Afterwards, the moment of

inertia changes to be a combination of the gross moment of inertia and the cracked

moment of inertia. These moments of inertia are used to estimate the instantaneous

flexibility to the applied load. Another main result of this model is with the increase

of load, where the stiffness reduces due to the fact that the neutral axis of the section

shifts up with the increase of load. Equation 10 [17] is the final product of this model

which has the calculation of the maximum deflection of the tested specimens, hence

mid-span deflection.

∆𝑚𝑎𝑥 =𝑃𝑎

24(

1

𝐸𝑐𝐼𝑒𝑓𝑓) (3𝑙2 − 4𝑎2) (Eq10)

where:

P: The applied load

a: The shear span of the point load from the support in the third-point loading

configuration

Ec: Modulus of elasticity of concrete

Ieff: Effective moment of inertia

l: The total beam’s span

125

6.2. Beams graphs and predicted curves

Figures 101 through 127 below compare the predicted deflection model with

the actual load mid-span deflection that is obtained from testing.

Figure 101: Load versus Mid-span Deflection of C 40 LR C

Figure 102: Load versus Mid-span Deflection of C 40 LR 1L

0

2

4

6

8

10

12

14

0 5 10 15 20 25 30 35

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

0

5

10

15

20

25

0 5 10 15 20 25

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

126


Figure 104: Load versus Mid-span Deflection of C 40 MR C

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25 30

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

0

10

20

30

40

50

60

0 5 10 15 20 25 30

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

127

Figure 105: Load versus Mid-span Deflection of C 40 MR 1L


0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20 25 30 35

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

0

10

20

30

40

50

60

0 5 10 15 20 25

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

128

Figure 107: Load versus Mid-span Deflection of C 40 HR C

Figure 108: Load versus Mid-span Deflection of C 40 HR 1L

0

5

10

15

20

25

0 5 10 15 20 25 30 35

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

0

10

20

30

40

50

60

0 10 20 30 40 50

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

129



0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

0

2

4

6

8

10

12

0 5 10 15

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

130



0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20 25 30

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

131

Figure 113: Load versus Mid-span Deflection of C 70 MR C


0

5

10

15

20

25

30

0 20 40 60 80 100

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

132



0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

0

5

10

15

20

25

30

35

40

45

0 10 20 30 40 50

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

133



0

10

20

30

40

50

60

0 5 10 15 20 25 30 35 40

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

134



0

5

10

15

20

25

30

0 20 40 60 80 100

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35 40

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

135



0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25 30

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

136



0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

0

10

20

30

40

50

60

0 5 10 15 20 25 30

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

137



0

5

10

15

20

25

30

35

40

45

0 10 20 30 40 50

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35 40

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

138


There are many conclusions that can be drawn from the above models. One

conclusion is that most of the specimens showed a typical trend in the elastic range of

loading. After the specimens reach the plastic range, the behavior of the model

deviates from the tested data as they are increasing with steeper slopes than the tested

specimens. Some specimens, however, followed the exact, actual tested specimens,

which could be due to the fact that the theoretical cracking moment is the actual

cracking moment; hence the flexibility model used the true moment of inertia.

Another conclusion from the models is that after ultimate the models don’t predict the

mode of failure, hence they backtrack as the load decreases. To cope with this effect,

the models were terminated after the ultimate load capacity of the specimens. In

conclusion, flexibility models validate the testing results since both models and the

tested data follow similar trends.

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35

Lo

ad

(k

N)

Deflection (mm)

Actual Data

Predicted Data

139

6.3. Ultimate Moment Capacity Prediction:

In this section calculation for the ultimate load capacities of the specimens is

predicted using ACI-440.02R-08 as presented. Afterwards, a comparison with the

actual strength is founded by testing. Calculations of ultimate section capacity in ACI-

440.02R-08 depend on the principle of force equilibrium and strain compatibility.

There are many modes of failure for the FRP outlined in the code; the most

according one is steel yielding, followed by concrete crushing at the top without

brittle failure of the FRP. Figure 128 below illustrates the analysis of FRP section

under loading.

Figure 128: Section behavior under loading

Equations11 through 18 [17] outline the process of finding the ultimate

capacity of a strengthened flexural member.

𝐶 = 𝛼1𝛽1𝑓′𝑐 𝑏 𝑐 (Eq11)

𝑇𝑠 = 𝐴𝑠𝜀𝑠𝐸𝑠 (Eq12)

𝜀𝑠 = 𝜀𝑐

𝑑 − 𝑐

𝑐 (Eq13)

𝑇𝑓 = 𝐴𝑓𝐸𝑓𝜀𝑓 (Eq14)

𝜀𝑓 = 𝜀𝑐

𝑑𝑓 − 𝑐

𝑐 (Eq15)

All the above equations must satisfy the balance force equation (10) and (11) below:

(𝛼1𝛽1 𝑏 𝑓′𝑐 𝑐) − (𝐴𝑠𝜀𝑠𝐸𝑠) − 𝐴𝑓𝐸𝑓𝜀𝑓 = 0

(0.5𝛼1𝛽1 𝑏 𝑓′𝑐)𝑐2 + (𝐴𝑠𝜀𝑠𝐸𝑠)(𝑑 − 𝑐) + 𝐴𝑓𝐸𝑓𝜀𝑓(𝑑𝑓 − 𝑐) = 0

(Eq 16)

(Eq 17)

After satisfying equations 16 and 17 [17], the moment capacity can be calculated with

equation 18[17] below:

𝑀𝑛 = 𝑇𝑠 (𝑑 −𝛽1𝑐

2) + 𝑇𝑓 (𝑑𝑓 −

𝛽1𝑐

2) (Eq 18)

140

where:

C: Compressive force in the concrete.

TS: Tension force from the steel.

𝜀𝑠: Strain of the steel in the section.

𝑇𝑓: Tension force from the FRP.

𝜀𝑓: Strain of the FRP in the section.

𝛼1, 𝛽1 : Concrete compression blocks parameters.

The process of calculations FRP strengthened section above involves an

iterative process for finding the neutral axis since the other option is to solve a

quadratic equation. In this iterative process, a neutral axis depth and mode of failure

are assumed. This process was followed by iterations until force equilibrium

equations are satisfied, hence strain compatibility is met. For the purpose of this

study, all reduction factors are dropped since the aim is to analyze the section not to

design it.

Table 19 illustrates the ultimate capacity of sections with the error estimations.

The results presented in Table 19 are plotted in figure 129. A 100% line was also

plotted to demonstrate the % error. The results show the over and under estimation of

the results, hence any value that falls under the line is over estimated and any value

that stands over the line is over estimated. Furthermore, it is clear that almost all of

the results are over estimated. This is anticipated since the ACI-440.02R-08 usually

over estimates the load carrying capacities of flexural sections. Moreover, a

regression line was plotted and the coefficient of regression was determined to be

0.754 which is a measure of data precision. This means for this study that the ACI-

440.02R-08 predicted the ultimate load with a75.4 % of accuracy. This load accuracy

could be due to the fact that the section of this study is thin and the code is not

capable of predicting these sections with 100% accuracy. Another reason for this

inaccuracy might be due to human errors associated with the human errors that are

induced with every step of fabrication. From the data points, we can see that for this

141

type of specimens some calculations are over estimated while the others are under

estimated.

Table 19: Load predictions and error estimations.

Group Specimen Pu, exp

(kN)

Pu, pred

(kN) % Error Pu/Pn

C 40 LR

C 40 LR C 11.63 13.12 -11.36 0.89

C 40 LR 1L 21.69 16.71 29.80 1.30

C 40 LR 2L 38.5 19.01 102.52 2.03

C 40

MR

C 40 MR C 22.6 28.19 -19.83 0.80

C 40 MR 1L 46.8 33.50 39.70 1.40

C 40 MR 2L 50.53 35.70 41.54 1.42

C 40 HR

C 40 HR C 44.88 46.92 -4.35 0.96

C 40 HR 1L 52.25 54.33 -3.83 0.96

C 40 HR 2L 53.85 55.70 -3.32 0.97

C 70 LR

C 70 LR C 10.17 13.31 -23.59 0.76

C 70 LR 1L 26.6 16.86 57.77 1.58

C 70 LR 2L 42.1 19.81 112.52 2.13

C 70

MR

C 70 MR C 26 29.14 -10.78 0.89

C 70 MR 1L 45.2 34.21 32.13 1.32

C 70 MR 2L 47.44 36.49 30.01 1.30

C 70 HR

C 70 HR C 33.04 49.46 -33.20 0.67

C 70 HR 1L 56.08 57.53 -2.52 0.97

C 70 HR 2L 59.3 59.71 -0.69 0.99

C 100

LR

C 100 LR C 10.73 13.38 -19.81 0.80

C 100 LR 1L 30.56 16.92 80.61 1.81

C 100 LR 2L 40.2 19.26 108.72 2.09

C 100

MR

C 100 MR C 38.75 29.53 31.22 1.31

C 100 MR 1L 43.5 34.54 25.94 1.26

C 100 MR 2L 49.58 36.74 34.95 1.35

C 100

HR

C 100 HR C 35 51.19 -31.63 0.68

C 100 HR 1L 55.14 58.27 -5.37 0.95

C 100 HR 2L 65.2 60.50 7.77 1.08

142

Figure 129: Experimental versus predicted ultimate load capacities

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80 90

Pu

, p

red

(K

N)

Pn, exp (KN)

143

Chapter 7: Summary and Conclusion

The field of reinforced concrete strengthening is ever-growing. There are

many advantages of strengthening of the concrete structure elements, such as helping

in the case of damage, design errors, or deficiencies of flexural steel. The use of fiber

polymers is gaining great popularity because of the attractive properties that fiber

polymers have. The main property that makes them very attractive is the high strength

to weight ratio.

The use of FRP for strengthening of structural elements is best option over its

ancestries such as steel plating and jacketing. The problem with the older methods is

the durability of steel used in strengthening, as steel is a very corrosive material, and

that it tends to degrade with the environment. Another advantage of the FRP is the

practicality and the ease of installation and protection.

This research aimed to study the behavior of high-strength reinforced concrete

slabs bonded externally with CFRP composite sheets to improve their flexural

capacity. A total of fifty-four slabs has been cast and tested to prove the theory and

the objective of the proposed study. The slabs were tested in a two-point loading

arrangement until failure. The variables of the experimental program were the

concrete compressive strength, longitudinal steel reinforcement ratio, and number of

layers of CFRP composite sheets. The results of these tests were compared together to

conclude the range of the enhancement of the CFRP and effect of the mentioned

variables on the performance of high-strength RC slabs. Another aim of this study

was to validate and check the ACI440.2R-08 capacity prediction equations, and to

develop analytical models with flexibility formula to ensure the limits of code

provisions applicability.

As many variables were examined in this study, many observations have been

noticed in this study, many of which are listed below:

1. Typically, in all groups the control specimen has the highest deflection,

hence the highest ductility.

2. The strain steel response of all specimens within the same group showed

similar response in the elastic region. However, the response starts to

144

deviate in the plastic region, which is due to the different CFRP

strengthening reinforcement ratio.

3. It was noted that single sheet configurations have the maximum utilization

of the CFRP since the area of the CFRP present in this configuration is

less than the area present in the double sheet configuration.

4. It is clearly noted that all strengthened specimens experienced brittle

failure mode by debonding of CFRP Laminates.

5. With the increase of the reinforcement ratio, the ultimate strain in the

concrete at the top fibers increases.

6. Slabs in all subgroups under the C70 groups have reached the yielding

strain in steel, unlike the C40 group where in some specimens, the

concrete crushed before the steel gets to the yielding stage.

7. Specimens who incurred tensile membrane action (tension-controlled)

failure and specimens who experienced brittle failure of FRP debonding,

their ultimate compressive strain of concrete didn’t come close to the

crushing strain that is because the specimens failed before the

compressive force in the concrete reaches the crushing strain.

8. It is noted that in the C70 group, the highest ductility was recorded for the

specimens in the low reinforcement ratio group, with single and double

CFRP layers strengthening.

9. It was noted in the C70 group that the behavior of toughness in the low

reinforcement group was the highest, due to the fact that this group had

the maximum utilization of the materials among all other groups.

10. In the C100 group, it was also noted that the medium reinforcement ratio

configuration utilizes the steel capacity better than the other two

configurations.

11. In the C100 group it was noted that the highest ductility was recorded for

the low reinforcement ratio group with double layer strengthening.

12. It was noted in the C100 group that the behavior of toughness in the low

reinforcement ratio group with two layers of CFRP sheet was the highest

due to the fact that this specimen has the maximum utilization of the

materials in all groups.

145

13. It was also noted in all groups of specimens that as the steel reinforcement

ratio increases, the percent increase in the load-carrying capacity

decreases.

14. For the low reinforcement ratio group, it was noted that when the

contribution of CFRP was increasing, the flexural capacity was at its

maximum when the compressive strength of concrete was equal to 70

MPa.

15. For the medium reinforcement ratio group, it was noted that the

contribution of CFRP increases, the gain in flexural capacity is reduced

with the increase in the compressive strength of concrete.

16. For the concrete compressive strength effect on HR group, it is noted that

the contribution CFRP strengthening increases when the compressive

strength of concrete increases in the high reinforcement ratio group.

From the above, the following conclusions could be drawn;

1. Strengthening of high strength thin concrete slab in flexural is a valid

option to increase in their load carrying capacity. In some specimens, an

increase of over 350% was recorded, while in others, the increase was just

a little over 15%.

2. The system of thin slabs cast with high strength concrete with CFRP

strengthening can be equivalent to conventional RC slabs system if

designed properly.

3. Slabs with low reinforcement ratios had shown the highest increase in the

load-carrying capacity, since CFRP strengthening increased the flexural

reinforcement ratio.

4. ACI 440 provisions gave accurate results for the load carrying capacities

and the deflection response which indicated the applicability of the code

for such elements.

5. For strengthened specimens, the single layer configuration showed better

utilization of the material over that with double layer configurations.

6. For the contribution of CFRP strengthening with different concrete

compressive strengths, the C70 group showed the best response since

specimens cast with 70 MPa concrete compressive strength were able to

reach the CFRP debonding strain and concrete crushing strain at failure.

146

It should be noted that specimens in high reinforcement ratio group (HR) has a

reinforcement ratio close to the balanced reinforcement ratio and with CFRP

strengthening the section goes from tension-controlled to compression-controlled

which proves the conclusion of the stability of the increase in the load-carrying

capacity with the increase in the CFRP strengthening ratio.

For future research studies, it is recommended to develop Finite Element (FE)

models to study the performance of thin high strength slabs strengthened with

different composite materials and configurations. This will ensure a better

understanding of the subject in hand and assess the contribution of each variable in

increasing the flexural strength in high strength thin slabs. Furthermore, a crack based

monitoring system would be installed on the specimens in future research studies to

assess the cracking moment variability with different combinations of variables.

147

References

[1] A. El-Sayed, R. Al-Zaid, A. Al-Negheimish, A. Shuraim, and A. Alhozaimy,

“Long-term behavior of wide shallow RC beams strengthened with externally

bonded CFRP plates,” Construction and Building Materials, vol. 51, pp. 473-

483, Sep 2014.

[2] H. Niu, A. Vasquez, and V. Karbhari, “Effect of material configuration on

strengthening of concrete slabs by CFRP composites,” Composites Part B:

Engineering, vol. 37, pp. 213-226, 2006.

[3] H. Lee, S. Cheong, S. Haw, and C. Lee, “Concrete girders with composites:

Installation, design and inspection,” Construction and Building Materials, vol.

23, pp. 1495-1507, 2010.

[4] A. Al-Saidy, F. Klaiber, T. Wipf, K. Al-Jabri, and A. Al-Nuaimi, “Parametric

study on the behavior of short span composite bridge girders strengthened

with carbon fiber reinforced polymer plates,” Construction and Building

Materials, vol. 22, pp. 729-737, 2008.

[5] M. Islam, M. Mansur, and M. Maalej, “Shear strengthening of RC deep beams

using externally bonded FRP systems,” Cement and Concrete Composites,

vol. 27, pp. 413-420, 2005.

[6] H. Lee, S. Cheong, S. Haw, and C. Lee, “Behavior and performance of RC T-

section deep beams externally strengthened in shear with CFRP sheets,”

Composite Structures, vol. 93, pp. 911-922, 2011.

[7] C. Wu, D. Oehlers, M. Rebentrost, J. Leach, and A. Whittaker, “Blast testing

of ultra-high performance fiber and FRP-retrofitted concrete slabs,”

Engineering Structures, vol. 31, pp. 2060-2069, 2009.

[8] J. Dong, Q. Wang, and Z. Guan, “Structural behaviour of RC beams with

external flexural and flexural–shear strengthening by FRP sheets,) Composites

Part B: Engineering, vol. 44, pp. 604-612, 2013.

[9] Ö. Anil, N. Kaya, and O. Arslan, “Strengthening of one way RC slab with

opening using CFRP strips,” Construction and Building Materials, vol. 48, pp.

883-893, 2013.

[10] E. Rochdi, D. Bigaud, E. Ferrier, and P. Hamelin, “Ultimate behavior of

CFRP strengthened RC flat slabs under a centrally applied load,” Composite

Structures, vol. 72, pp. 69-78, 2006.

[11] D. Faria, J. Einpaul, A. Ramos, M. Ruiz, and A. Muttoni, “On the efficiency

of flat slabs strengthening against punching using externally bonded fiber

reinforced polymers,” Construction and Building Materials, vol. 73, 366-377,

2014.

148

[12] B. Mohammed, L. Ean, and M. Malek, “One way RC wall panels with

openings strengthened with CFRP,” Construction and Building Materials, vol.

40, pp. 575-583, 2013.

[13] L. Michel, E. Ferrier, D. Bigaud, and A. Agbossou, “Criteria for punching

failure mode in RC slabs reinforced by externally bonded CFRP,” Composite

Structures, vol. 81, pp. 438-449, 2007.

[14] F. Fathelbab, M. Ramadan, and A. Al-Tantawy, “Strengthening of RC bridge

slabs using CFRP sheets,” Alexandria Engineering Journal, vol. 53, pp. 843-

854, 2014.

[15] J. L. Borgerson and W. L. Vogt, “Evaluation of Externally Bonded Fiber-

Reinforced Polymer Systems to Concrete Structures,” Concrete Repair

Bulletin, pp. 18-21, Sep. 2011.

[16] M. Rezazadeh, I. Costa, and J. Barros, “Influence of prestress level on NSM

CFRP laminates for the flexural strengthening of RC beams,” Composite

Structures, vol. 117, pp. 489-500, Nov. 2014.

[17] American Concrete Institute, "ACI 440.2-08: Guide for the Design and

Construction of Externally Bonded FRP Systems for Strengthening Concrete

Structures," USA, 2008.

[18] A. R. Bunsell “Fiber Reinforcement,” in Int. Encyclopedia of Composites,

vol. 2, New York: VCH publishers, 1990, pp. 149.

[19] F. Al-Mahmoud, A. Castel, R. François, and C. Tourneur, “Strengthening of

RC members with near-surface mounted CFRP rods,” Composite Structures,

vol. 42, pp. 138-147, 2009.

[20] M. Rezazadeh, J. Barros, and I. Costa, “Analytical approach for the flexural

analysis of RC beams strengthened with prestressed CFRP,” Composites Part

B: Engineering, vol. 28, pp. 16-34, 2015.

[21] S. Bagherpour, “Fiber Reinforced Polyester Composites,” Polyester, vol. 41,

pp. 211, 2012.

[22] G. Campione, A. Monaco, and G. Minafò, “Shear strength of high-strength

concrete beams: Modeling and design recommendations,” Engineering

Structures, vol. 85, pp.116-122, 2014.

[23] A. Cladera, and A. Marí, “Experimental study on high-strength concrete

beams failing in shear,” Engineering Structures, vol. 29, pp.1519-1527, 2005.

[24] R. Al-Rousan, M. Issa, and H. Shabila, “Performance of reinforced concrete

slabs strengthened with different types and configurations of CFRP,”

Composites Part B: Engineering, vol. 77, pp. 510-521, 2012.

[25] H. Toutanji, L. Zhao, and Y. Zhang, “Flexural behavior of reinforced

concrete beams externally strengthened with CFRP sheets bonded with an

inorganic matrix,” Engineering Structures, vol. 89, pp. 557-566, 2006.

149

[26] R. Al-Zaid, A. Al-Negheimish, M. Al-Saawani, and A. El-Sayed, “Analytical

study on RC beams strengthened for flexure with externally bonded FRP

reinforcement,” Composites Part B: Engineering, vol. 55, pp. 129-14, 2012.

[27] S. Floruţ, G. Sas, C. Popescu, and V. Stoian, “Tests on reinforced concrete

slabs with cut-out openings strengthened with fibre-reinforced polymers,”

Composites Part B: Engineering, vol. pp. 71, 484-493, 2014.

[28] British Standards Institution, "BS EN 10080; B500A Steel for the

reinforcement of concrete, weldable, ribbed reinforcing steel," London, 2005.

[29] T. Dat, and A. Starnes, “Strength and ductility of concrete beams reinforced

with carbon FRP and steel,” Gaithersburg, MD: U.S. Dept. of Commerce,

Technology Administration, National Institute of Standards and Technology,

vol. 9, pp. 15-17, 2013.

[30] P. Collins, and D. Mitchell, “Materials,” in Prestressed Concrete Structures,

5th

ed., Englewood Cliffs: Prentice Hall, 1991, pp. 766.

150

Appendix

Appendix A: Load deflection graphs

Figure 130: Load versus Mid-span Deflection for C40 LR C specimens

Figure 131: Load versus Mid-span Deflection for C40 LR 1L specimens

0

2

4

6

8

10

12

14

0 10 20 30 40

Lo

ad

(K

N)

Deflection (mm)

C 40 LR C 1

C 40 LR C 2

0

5

10

15

20

25

0 5 10 15 20 25

Lo

ad

(K

N)

Deflection (mm)

C 40 LR1L 1

C 40 LR 1L 2

151


Figure 133: Load versus Mid-span Deflection for C40 MR C specimens

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25 30

Lo

ad

(K

N)

Deflection (mm)

C 40 LR2L 1

C 40 LR 2L 2

0

5

10

15

20

25

30

0 10 20 30 40

Lo

ad

(K

N)

Deflection (mm)

C 40 MR C 1

C 40 MR C 2

152

Figure 134: Load versus Mid-span Deflection for C40 MR 1L specimens


0

10

20

30

40

50

60

0 10 20 30 40

Lo

ad

(K

N)

Deflection (mm)

C 40 MR1L 1

C 40 MR 1L 2

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35

Lo

ad

(K

N)

Deflection (mm)

C 40 MR 2L 1

C 40 MR 2L 2

153

Figure 136: Load versus Mid-span Deflection for C40 HR C specimens

Figure 137: Load versus Mid-span Deflection for C40 HR 1L specimens

0

10

20

30

40

50

60

0 5 10 15 20 25

Lo

ad

(K

N)

Deflection (mm)

C 40 HR C 1

C 40 HR C 2

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35

Lo

ad

(K

N)

Deflection (mm)

C 40 HR 1L 1

C 40 HR 1L 2

154



0

10

20

30

40

50

60

0 5 10 15 20 25

Lo

ad

(K

N)

Deflection (mm)

C 40 HR 2L 1

C 40 HR 2L 2

0

2

4

6

8

10

12

0 5 10 15

Lo

ad

(K

N)

Deflection (mm)

C 70 LR C 1

C 70 LR C 2

155



0

5

10

15

20

25

30

0 10 20 30 40

Lo

ad

(K

N)

Deflection (mm)

C 70 LR 1L 1

C 70 LR 1L 2

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35

Lo

ad

(K

N)

Deflection (mm)

C 70 LR 2L 1

C 70 LR 2L 2

156



0

5

10

15

20

25

30

0 20 40 60 80 100

Lo

ad

(K

N)

Deflection (mm)

C 70 MR C 1

C 70 MR C 2

0

10

20

30

40

50

60

0 10 20 30 40

Lo

ad

(K

N)

Deflection (mm)

C 70 MR 1L 1

C 70 MR 1L 2

157



0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20 25 30 35 40

Lo

ad

(K

N)

Deflection (mm)

C 70 MR 2L 1

C 70 MR 2L 2

0

5

10

15

20

25

30

35

40

45

0 10 20 30 40 50

Lo

ad

(K

N)

Deflection (mm)

C 70 HR C 1

C 70 HR C 2

158



0

10

20

30

40

50

60

0 10 20 30 40

Lo

ad

(K

N)

Deflection (mm)

C 70 HR 1L 1

C 70 HR 1L 2

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35

Lo

ad

(K

N)

Deflection (mm)

C 70 HR 2L 1

C 70 HR 1L 2

159



0

2

4

6

8

10

12

14

0 10 20 30 40 50 60

Lo

ad

(K

N)

Deflection (mm)

C 100 LR C 1

C 100 LR C 2

0

5

10

15

20

25

30

35

0 10 20 30 40

Lo

ad

(K

N)

Deflection (mm)

C 100 LR 1L 1

C 100 LR 1L 2

160



0

5

10

15

20

25

30

35

40

45

0 5 10 15 20

Lo

ad

(K

N)

Deflection (mm)

C 100 LR 2L 1

C 100 LR 2L 2

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40

Lo

ad

(K

N)

Deflection (mm)

C 100 MR C 1

C 100 MR C 2

161



0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50

Lo

ad

(K

N)

Deflection (mm)

C 100 MR 1L 1

C 100 MR 1L 2

0

10

20

30

40

50

60

0 5 10 15 20 25 30

Lo

ad

(K

N)

Deflection (mm)

C 100 MR 2L 1

C 100 MR 2L 2

162



0

5

10

15

20

25

30

35

40

45

0 10 20 30 40 50

Lo

ad

(K

N)

Deflection (mm)

C 100 HR C 1

C 100 HR C 2

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35 40

Lo

ad

(K

N)

Deflection (mm)

C 100 HR 1L 1

C 100 HR 1L 2

163


0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35

Lo

ad

(K

N)

Deflection (mm)

C 100 HR 2L 1

C 100 HR 2L 2

164

Table 20: Repeatability comparison

Group Specimen Py (kN) δy(mm) Pf (kN) δf (mm) δu (mm) Pu (kN) Failure Mode

C 40 LR

C 40 LR C 1 11.63 21.01 9.304 31.07 21.01 11.63 SY_MA

C 40 LR C 2 12.67 22.3 9.5 32.1 26.9 12.67 SY_MA

C 40 LR 1L 1 21 18.9 17.352 23.3 19.36 21.04 SY_FD

C 40 LR 1L 2 20.5 19.2 17.22 24.11 19.86 21.69 SY_FD

C 40 LR 2L 1 25.1 15.02 30.8 25.88 24.5 38.5 SY_MA_FD

C 40 LR 2L 2 25.22 16.1 29.42 22.31 23.26 36.36 SY_MA_FD

C 40 MR

C 40 MR C 1 15.2 18.2 18.08 29.2 28.4 22.6 SY_CC

C 40 MR C 2 14.45 20.2 19.01 32.14 30.05 23.7 SY_CC

C 40 MR 1L 1 21.3 30.03 37.44 41.7 32.7 43.52 SY_CC_FD

C 40 MR 1L 2 20.98 29.3 39.8 42.1 35.13 46.8 SY_CC_FD

C 40 MR 2L 1 40.6 21.78 40.424 26 28.02 48.6 SY_CC_FD

C 40 MR 2L 2 39.6 22.45 39.88 27.1 24.48 50.53 SY_CC_FD

C 40 HR

C 40 HR C 1 19.1 7.5 35.904 22.3 22.5 46.88 SY_CC

C 40 HR C 2 20.12 7.04 34.91 23.01 21.5 44.88 SY_CC

C 40 HR 1L 1 36.07 20.74 41.8 45 29.34 51.8 SY_FD

C 40 HR 1L 2 35.34 20.55 42.5 44.13 30.22 52.25 SY_FD

C 40 HR 2L 1 39.1 19.62 43.08 21.7 20.38 53.85 SY_FD

C 40 HR 2L 2 40.15 20.9 41.66 23.3 20.6 53.6 SY_FD

C 70 LR

C 70 LR C 1 8.1 10.2 7.04 13.1 13.46 10.17 SY_MA

C 70 LR C 2 9.3 11.34 7.56 14.6 12.7 8.8 SY_MA

C 70 LR 1L 1 15.84 13.01 21.28 37.48 27.78 26.6 SY_FD

C 70 LR 1L 2 16.32 14 22.1 36.34 24.93 25.9 SY_FD

165

C 70 LR 2L 1 40.16 22.28 33.68 28.06 24.52 44.18 SY_FD

C 70 LR 2L 2 40.44 24.11 34.63 29.15 27.22 46.44 SY_FD

C 70 MR

C 70 MR C 1 15.54 10.29 20.8 80 35.2 28.9 SY_MA_CC

C 70 MR C 2 16.24 10.87 25.1 82.2 71.75 26 SY_MA_CC

C 70 MR 1L 1 32.44 26.22 36.16 37.35 33.57 45.2 SY_FD

C 70 MR 1L 2 33.4 25.98 36.65 35.94 30.95 49.52 SY_FD

C 70 MR 2L 1 34.63 17.69 37.952 33.33 25.76 47.44 SY_FD

C 70 MR 2L 2 33.96 16.99 36.13 33.94 25.51 44.4 SY_FD

C 70 HR

C 70 HR C 1 18.1 13.9 26.432 40.45 38.75 38.05 SY_CC

C 70 HR C 2 19.44 14.65 27.01 41.53 35.77 33.04 SY_CC

C 70 HR 1L 1 38.57 22.28 44.864 36.01 34.91 56.08 SY_CC_FD

C 70 HR 1L 2 39.23 23.86 45.12 32.11 30.93 50.08 SY_CC_FD

C 70 HR 2L 1 51.31 26.11 47.44 31.67 30.95 59.3 SY_CC_FD

C 70 HR 2L 2 50.24 25.54 48.45 30.3 29.23 57.26 SY_CC_FD

C 100 LR

C 100 LR C 1 11.26 23.7 8.584 41.34 40.86 10.73 SY_MA

C 100 LR C 2 12.54 24.1 9.05 42.43 33.64 11.47 SY_MA

C 100 LR 1L 1 26.7 21.7 24.448 34.8 27.68 28.65 SY_FD

C 100 LR 1L 2 25.6 23.1 24.45 34.5 29.8 30.56 SY_FD

C 100 LR 2L 1 34.11 10.21 32.16 12.25 11.95 40.2 SY_FD

C 100 LR 2L 2 34.53 10.6 32.95 11.94 15.4 36.5 SY_FD

C 100 MR

C 100 MR C 1 32.84 18.4 31 35.68 34.12 42.41 SY_CC

C 100 MR C 2 33.1 19.3 30.94 36.1 32.45 38.75 SY_CC

C 100 MR 1L 1 34.9 20.15 34.8 38.88 27.15 43.5 SY_FD

C 100 MR 1L 2 33.66 21.3 35.4 40.1 30.07 42.5 SY_FD

C 100 MR 2L 1 36.29 17.27 39.664 24.86 24.3 49.58 SY_FD

C 100 MR 2L 2 35.22 18.3 41.3 25.5 24.1 48.2 SY_FD

166

C 100 HR

C 100 HR C 1 22.56 18.65 28 42 39.9 37.74 SY_CC

C 100 HR C 2 23.14 19.23 29.26 41.54 36.9 35 SY_CC

C 100 HR 1L 1 39.82 24.2 44.112 37.15 35.3 55.14 SY_CC_FD

C 100 HR 1L 2 38.95 23.93 44.13 36.64 33.65 48.8 SY_CC_FD

C 100 HR 2L 1 56.9 27.09 52.16 30.63 27.1 59.9 SY_CC_FD

C 100 HR 2L 2 56.1 27.5 52.53 30.01 29.75 65.2 SY_CC_FD

167

Vita

Hasan Saleh Mahmoud was born on February 26th

, 1992, in Kuwait City,

Kuwait. He is originally from Palestine, but his parents moved to Kuwait in the

1970s. Hasan graduated from NWPS with honors in 2009. He continued his higher

education in the American University of Sharjah, which he joined as a student to

pursue a Bachelor of Science degree in Civil Engineering in 2010. He was awarded

the Bachelor degree in 2014. He then decided to continue his graduate studies in the

Master's program in the American University of Sharjah. During his master program,

he won the Huston Technology Center Award in Mai Bangkok Business Challenge

2016, making AUS the first Arab university to win such a prestigious award. Hasan

worked as a research assistant on many project, where he showed excellent problem

solving and leadership skills.

Documents

STRENGTHENING OF HIGH STRENGTH REINFORCED CONCRETE …