Graduation book - BFRP

1
DEDICATION
We Dedicate This Book And Our Project For Those Who Helped Us And
Trusted Us We Would Like To Specially Thank:
Prof.Dr / Mohamed El-Shaer
Thank For Believing In Us, You Have Guided Us Throw Our Way And We Really
Count You As One Of Us, We Wouldn't Have Done It Without You.
Also Thanks To The Engineering Staff Of The Higher Technological Institute,
Thanks To :
Prof.Dr / Mohamed El-Shaer
We Couldn't Have Managed Without Your Help, We Appreciate You So Much.

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ABSTRACT OF THESIS
SHEAR FLEXURAL BEHAVIOUR OF RC BEAMS
STRENGTHENED BY NEAR SURFACE MOUNTED FRP BARS
Strengthening With Near-Surface-Mounted (NSM) Fiber-Reinforced-Polymer (FRP)
Reinforcement Has Become A Well-Known Technique, Which Provides A Good Bond
Between The FRP Element And Concrete. However, One Of The Most Common Failure
Modes Of NSM-FRP Strengthened Beams Is Concrete Cover Separation (CCS). In This
Research, The Shear Flexural Behavior Of RC Beams Strengthened With Fully And Partially
Bonded NSM BFRP Bars Was Studied. One Type Of Bars Configurations With Straight End
And U-Stirrups (Ø10) Were Used. The U-Stirrups Were Used To Act As A Bond Between
The Concrete And The BFRP, Which Might Delay The CCS Failure. The Results Indicated
That The U-Stirrups Was Effective In Preventing The CCS And Increasing The Ultimate
Carrying Capacity. The Ultimate Load Of The Beams Strengthened With Two NSM BFRP
Bar Having U-Stirrups Increased By 133.3% Compared To Beams Without U-Stirrups. On
The Other Hand, Un-Bonding The NSM Bars Along The Mid-Span Zone Slightly Decreased
The Ultimate Load Compared With The Fully Bonded Bars; However It Slightly Increased
The Beam Deformability. Increasing The Un-Bonded Length Shifted The Failure Mode From
CCS To NO CCS, Which Is Not Preferred From The Point Of View Of The Structural Safety.

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Chapter One: Introduction
General :1.1
Strengthening Of Reinforced Concrete (RC) Structures Has Attracted A Significant
Amount Of Attention. Damage Of RC Structures May Result From Many Factors Such As
Excessive Deflections, Inadequate Structural Design, Reinforcement Corrosion, And
Insufficient Bearing Capacity. Various Strengthening Methods Have Been Developed To
Upgrade Both Stiffness And Strength Of The Deficient Structural Members. Over The Past
Decade, Conventional Concrete And Steel Were Replaced By Fiber Reinforced Polymers
(FRPS) In The Strengthening Of RC Structures. High Strength-To-Weight Ratios, Versatility
Of Fabrication, And Resistance To Electromechanical Corrosion Have Made FRP
Composites Attractive To The Civil Engineering Community.
Composite FRP Materials Are Available In The Form Of Strips Made Of Unidirectional
Strips, Or In The Form Of Sheets Made Of Unidirectional, Bidirectional, Or Random
Discontinuous Fibers. The Available Fiber Types Include Carbon (C), Basalt (B), Aramid
(A), And High Strength Steel (S). FRP Composites Can Be Used To Strengthen RC
Structures In Two Techniques: Externally Bonded (EB) And Near Surface Mounted (NSM)
Techniques.
The EB Technique Can Be Applied In Two Forms: Wet Lay-Up Sheets Or Fabrics And
Procured Strips. However Strengthening By EB FRPS Performed Very Well In Practice,
Premature Debonding Of The FRP Material From The Adjacent Concrete Reduced The
Efficiency Of This Technique. Numerous Solutions Were Proposed To Avoid This Type Of
Failure, Which Is Unacceptable From The Point Of View Of Structural Safety. Besides That,
EB FRPS Could Be Highly Susceptible To Different Damage Resources Such As Collision,
Ultraviolet Rays, Fire, And Moisture Absorption.
The NSM FRP Involves The Embedment Of The FRP Reinforcement Into Slits Precut
Into The Tension Side Of The Strengthened Elements. Compared With The EB Technique,
The NSM Technique Is Less Exposed To External Damage Sources And Provides A Stronger
Bond To The Surrounding Substrate. However, One Of The Most Common Failure Modes
Of RC Beams Strengthened With The NSM Technique Is Debonding By Concrete Cover

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Separation, Which Initiates And Completes At Relatively Low Strain Levels In The FRP
Element.
Objectives :1.2
Based On The Above Introduction, The Current Thesis Is Presented With The Following
Objectives:
1. To Study The Flexural Behavior Of RC Beams Strengthened In Flexure By BFRP Bars
And U-Stirrups, Which Are Used With The Aim Of Delaying Or Preventing The
Concrete Cover Separation.
2. To Investigate The Effects Of FRP Cross Sectional Area-Stirrups, And Strong Bonding
Of The NSM Bars.
Thesis Layout :1.3
In This Section, A Brief Description Of The Contents Of Each Chapter Is Presented:
Chapter (2) : Describes The Experimental Program Carried Out In This Study. The
Mechanical Properties Of Concrete, Steel And BFRP Bars Are Presented.
Chapter (3) : Presents The Experimental Test Results. The Overall Behaviour Of RC
Beams Strengthened With NSM BFRP Bars Is Discussed.
Chapter (4) : Concludes The Major Findings Of This Research And Summarizes
Recommendations For Future Work.

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Chapter Two: Experimental Program
2.1 Introduction :
The Main Objective Of This Experimental Study Is To Investigate The Shear-
Flexural Behavior Of RC Beams Strengthened With BFRP Bars. Most Of Beams
Strengthened By This System Face The Early Delamination Of BFRP Bars Before
Reaching Its Maximum Strain. So, This Study Will Work To Delay The Delamination Of
BFRP Bars That Placed In The Lower Concrete Cover Of The Beams And Carried By
U-Stirrup. It Is Also To Investigate The Most Probable Bonded Length Between The
BFRP Bars And The Concrete And Give Approach Results.
2.2 Test Specimens :
Five Simply-Supported Beams With Rectangular Cross Section (150 X 250) Mm
Were Constructed And Tested. As A Reference to Comparison, One Beam without Any
Strengthening Served As A Control Specimen (Control) With Longitudinal Steel Only.
The Remaining Four Were Strengthened With Different System Of BFRP Bars. One
Types of FRP Rod Was Used: Basalt Fiber Reinforced Polymer BFRP With A Diameter
Of 10 mm And A 2200 mm Length. Table (2.1) List the Experimental Test Matrix.

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Table (2-1) Beams Test Matrix.
2.3 RC Beams And Internal Reinforcement :
All Beams Had a Total Length 2200 mm and a Cross Section 150 mm Width,
250 mm Height. All The Beams Have A Flexural Reinforcement Made Of Two Steel
Bars (10 mm Diameter) On Tension Side And (8 mm Diameter) On Compression Side.
The Details And Cross-Section Of The Specimens Are Illustrated In Figure (2.1) .
The Shear Reinforcement Was Designed In Order To Ensure That Flexural Failure
Would Control The Test. It Consisted Of Smooth Steel Stirrups (8 mm Diameter) Spaced
In All Five Beams Every 200 mm.
Beam ID. Definition
Control
Beam
Typically reinforced
with steel bars only
1B 1-BFRP (without u-str)
1B+ 1-BFRP (with u-str)
2B 2-BFRP (without u-str)
2B+ 2-BFRP (with u-str)

7
(a) Details Of ( Control Beam )
Figure 2.3.1 Details and Side Views of Specimen "All Dimensions on Millimeter"

8
(b) Details Of Beam ( 1B )
Figure 2.3.2 (Continue) Details and Side Views of Specimen "All Dimension on Millimeter"

9
(c) Details Of Beam ( 1B+ )
Figure 2.3.3 (Continue) Details and Side Views of Specimen "All Dimensions on Millimeter"

10
(d) Details Of Beam ( 2B )

11
(e) Details Of Beam (2B+)

12
2.4 Material Properties :
The Material Used In The Experiments Are Concrete, Steel Reinforcement, BFRP
Bars And Super Plasticizer Admixture, Their Engineering Properties Are Reported In This
Section.
2.4.1. Concrete :
The Properties Of The Hardened Concrete (Compressive Strength) Were Measured At 7
Days And 28 Days By Testing Six Concrete Cubes (width= 150 mm, height= 150 mm) The
Specimens Were Removed From Their Modules 24 Hours After Casting And Stored For 7
Days and 28 Days In Water. The Cubes Were Tested At The Same Time Of Testing The
Specimen In Direct Compression. The Obtained Concrete Compressive Strength Scoring
( 34.2 , 37.5 ,And 31.8 ) Mpa After 7 Days And Scoring( 47.7 , 44.9 ,And 43.9 ) Mpa After
28 Days.
The Average Compressive Strength Was 45 Mpa.
Table (2-2) Concrete Mix design.
W/C
Ratio
Quantity ( /m3
)
Cement Gravel Fine
Aggregate
Water
0.3 500 Kg 1100 Kg 733 Kg 150 liter
With Using Super Plasticizer Admixture With 2% of Cement Weight = 10 Kg

13
Figure 2.2 Material used in concrete mix.
Gravel after Washing .Sand after Filterization .
Cement with CEM (52.5 N).
(b)(a)
(c)

14
Figure 2.3 Weight of materials according to table(2-2).
(c)
Gravel Weight =20.4kg
Sand Weight =13.8 kg
(b)
(a)
Superplasticizer Admixture = 460 ml

15
Figure 2.3 (Continue) Weight of materials according to table (2-2).
Water Weight =4 kg
Cement Weight =10.2 kg
(e)
(d)

16
2.4.2. Superplasticizer Admixture :
The Role Of Superplasticizer Is To Strengthen the Concrete with High Workability
But Lower Water Content . Types (Sikament-NN) Produced By Sika Was Used In This
Study. The (Sikament-NN) Is Shown In Figure (2.4).
Figure 2.4 Superplasticizer Manufacturing Sheet & Component.
(b) Sikament-NN(a) Manufacturing Sheet.

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2.5 RC Beams Manufacturing :
Five Timber Formed Were Built For Casting RC Beams To Ensure That All Beams
Were Cast Using A Single Concrete Mix. The Figure (2.5) Shows All The Stages Of The RC
Beams Fabrication Starting From Preparation Of The Steel Reinforcement Cages And The
Deformed Ribs On The Steel Reinforcement Were Removed Where Strain Gauges Were
Applied To Ensure A Smooth Surface For Attaching The Gauge.
The Reinforcing Cages Were Placed In The Formwork And Finally, All Beams Were
Cast In The Two Batches By Using Mixed Concrete With Several Cubes To Determine The
Concrete Mechanical Properties. The Concrete Was Vibrated Manually By Using Special
Concrete Rod And The Top Surface Was Leveled By Using A Trowelling.
All Beams Were Left Under Curing For Seven Days Before Beginning Any
Strengthening. As The Cubes Were Immersed In Water And The Beams Were Spraying With
Water Every Six Hours.

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Figure 2.5 Stages of ihe RC Beams Fabrication.
Preparation of the mould for casting
process.
(b)
(a)
Preparing Of Stirrups

19
Figure 2.5 (Continue) Stages Of The RC Beams Fabrication
(c)
U-Stirrup Shape.
BFRP Bars.
(d)

20
Figure 2.5 (Continue) Stages Of The RC Beams Fabrication.
Appearance of the steel cage.
(f)
Attaching A Strain Gauge With The BFRP
Bar.
(e)

21
Figure 2.5 (Continue) Stages of The RC Beams Fabrication
Preparation of the mould for casting
process.
(d)
(g)
(d)
Strain Gauges

22
Figure 2.5 (Continue) Stages of The RC Beams Fabrication.
Casting the RC beams.
(e)
(f)
Seven days moist curing

23
2.6 Test Setup :
The Flexural Test Setup And Loading The Beams Specimens Are Shown In Figure
(2.6). All The Tested Beams Were Tested Under A Static Four-Point Load With Clear Span
2200 Mm To Study Their Shear-Flexural Behavior And Ultimate Load Capacity. A Loading
Frame And Hydraulic Jack With A Capacity 1000 KN Was Used To Apply The Load At The
Mid-Span Of The Beams Through A Very Strong Steel Plate.
The Tested Beams Had A Roller Support At Both Ends To Ensure The Free Rotation
Of The Tested Beams. Each Support Was Placed At A Distance 100 Mm From The Beam
Ends.
The Load Was Applied In Load Control Mode At A Rate Of 5 KN / Min. And All
Data Were Collected By A Data Acquisition System. The Data From All Strain Gauge,
LVDT And The Load Cell Were Stored Within A PC Computer And Subsequently Exported
To Excel Spreadsheet For Analysis.
2.7 Instrumentation :
The Instrumentation Used During The Test Of The Beams Specimens Is Shown In
Figure (2.7). In Measuring The Deflection Of Beams Three Vertical Linear Variable
Differential Transducers (LVDTS) Were Used. One Was Placed At The Mid-Span Of The
Beams.
One Electrical Strain Gauge Was Installed At The BFRP Bars Mid-Span Where The
Strain Gauges Were Applied To Measure The Strain According To The Loading Process. The
Strain Gauges Were Type FLA-6-11 From TML, With A Resistance Of 120 ± 0.5 Ω, A
Gauge Factor Of 2.12 ± 1%, A Gauge Length Of 6 mm, And A Gauge Width Of 2.2 mm.
Data Logger To Measure The Strain From Strain Gauge, Deflection And Load.

24
Figure 2.6 Test Setup and Instrumentation of Beams Specimens.
Load Cell and LVDT.
Strain Gauges.
(c)
(b)
(a)
Data Logger.

25
Figure 2.7 Test Setup And Instrumentation Of Beams Specimens.
(a)
Load Cell on beam.
Position of beam on Two Steel
Supports.
(b)

26
Figure 2.7 (Continue) Test Setup And Instrumentation Of Beams Specimens.
LDVT.
(c)
(d)
Strain Gauge cable connected to Data Logger.

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Chapter Three: Experimental Test Results and Discussion
Introduction :3.1
This Chapter Is Devoted To Present The Data Obtained From The Experimental Work
State In Chapter 2. These Data Include The Crack Pattern, Mode Of Failure, Load Deflection
Behavior, And Load Strain Of Strengthened Beams Compared With The Result Obtained
From The Control Beams, To Investigate The Effects Of BFRP Cross Section, And U-
Stirrups Of The BFRP Bars.
Results and Discussion:3.2
The Test Result Of Tested All Beams In Terms Of Applied Load And Deflection
And The Modes Of Failure Are Shown In Table (3-1)
Beam ID. Pu (KN) ∆u (mm) εf (BFRP)
Control Beam 95.645 31.2 εf (Steel Bars)
4940.791
1B 80.615 20.85 1336.378
1B+ 55.07 5.05 2054.2
2B 65.345 5.9 2369.559
2B+ 130.132 28.45 4940.791
Pu And Δu = Load And Midspan Deflection At Ultimate
Ζu = % Increase In The Ultimate Load,
ζu = ; εf = Maximum Strain Obtained In The BFRP Bar
ζs = Strengthening Efficiency,
ζs =

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3.2.1 Failure Mode :
The Modes Of Failure Of All Tested Beams Are Shown In Figures (3.1) To (3.5)
For The Control Beam Which Haven’t Any Strengthening Failed By Concrete Crashing
After Steel Yielding. Flexural Cracks Were Formed On The Tension Bottom Side Of The
Beam While The Load Was Applied Starting With A First Crack At The Mid-Span Of The
Beam .When The Load Was Increased These Flexural Cracks Propagated Vertically Upward,
And A New Flexural Cracks Were Formed Between The Earlier Cracks At The Mid-Span
And Were Spread To The Support Direction.
Beams (1B) , (1B+) , (2B) And (2B+) Failed Due To Concrete Crushing With Concrete
Cover Separation Occurred , When The Test Started Flexure Cracks Started To Come Up At
The Tension Bottom Side Of Each Beam At Mid-Span , Steel Yielded And No Fracture
Occurred In BFRP Bars .

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 Control Beam :
)ontrol BeamC(OfFigure 3.1 The Mode Of Failure

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Control Beam )(span Deflection Curve OfMid-Figure 3.1.1 Load
Control Beam )(Steel Strain Curve Of-Figure 3.1.2 Load
0
20
40
60
80
100
120
0 5 10 15 20 25 30 35 40
Load(kn)
Mid Def (mm)
Load-Mid span Deflection curve
0
20
40
60
80
100
120
0 1000 2000 3000 4000 5000 6000
Load(kn)
Steel-strain (µ)
Load-Steel Strain Curve

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Control Beam )(Strain Curve OfConcrete Compression-Figure 3.1.3 Load
( Control Beam )Curve OfSpan DeflectionthirdFigure 3.1.4 Load
0
20
40
60
80
100
120
-3000-2500-2000-1500-1000-5000
Load(kn)
Comp. in mid span strain (µ)
Load-Concrete Compression strain upper surface
0
20
40
60
80
100
120
0 5 10 15 20 25 30 35
Load(kn)
Third Span Def (mm)
Load third Span Deflection curve

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 Beam ( 1B ) :
)1B(amBeStrengthenedOfFigure 3.2 The Mode Of Failure

33
Figure 3.2.1 Load-Mid span Deflection Curve Of Beam ( 1B )
Figure 3.2.2 Load-BFRP Strain Curve Of Beam ( 1B )
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 35
Load(kn)
Mid Def (mm)
Load-Midspan Deflection Curve
0
20
40
60
80
100
0 500 1000 1500
Load(kn)
BFRP strain (µ)
Load-BFRP Strain

34
( 1B )BeamConcrete Compression Strain Curve Of-Figure 3.2.3 Load
Beam ( 1B )Span Deflection Curve Ofthird-Figure 3.2.4 Load
0
10
20
30
40
50
60
70
80
90
100
-3000-2500-2000-1500-1000-5000
Load(kn)
Comp in mid span conc strain (µ)
Load-Concrete Compression strain
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25
Load(kn)
Third Span Def (mm)
Load-third Span Deflection Curve

35
 Beam ( 1B+ ) :
1B+ )(Of Strengthened BeamFigure 3.3 The Mode Of Failure

36
Figure 3.3.1 Load-Mid span Deflection Curve Of Beam ( 1B+ )
Figure 3.3.2 Load-BFRP Strain Curve Of Beam ( 1B+ )
0
10
20
30
40
50
60
70
80
0 5 10 15 20 25 30 35 40
Load(kn)
MID Def (mm)
Load-mid span Deflection Curve
0
20
40
60
80
0 500 1000 1500 2000 2500
Load(kn)
BFRP Strain (µ)
Load-BFRP Strain

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( 1B+ )BeamConcrete Compression Strain Curve Of-Figure 3.3.3 Load
Figure 3.3.4 Load third Span Deflection Curve Of Beam ( 1B+ )
0
10
20
30
40
50
60
70
80
-2000-1500-1000-5000
Load(kn)
Load-Concrete Compression strain Curve
0
10
20
30
40
50
60
70
80
0 5 10 15 20 25
Load(kn)
Third Span Def (mm)
Load third Span Deflection Curve

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 Beam ( 2B ) :
Figure 3.4 The Mode Of Failure Of Strengthened Beam ( 2B )

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Figure 3.4.1 Load-Mid span Deflection Curve Of Beam ( 2B )
Figure 3.4.2 Load-BFRP Strain Curve Of Beam ( 2B )
0
10
20
30
40
50
60
70
0 1 2 3 4 5 6 7
Load(kn)
Mid Def (mm)
Load-Mid span Deflection
0
20
40
60
80
0 1000 2000 3000
Load(kn)
BFRP (µ)
Load-BFRP Strain

40
( 2B )BeamStrain Curve OfConcrete Compression-.3 Load4Figure 3.
Figure 3.4.4 Load third Span Deflection Curve Of Beam ( 2B )
0
10
20
30
40
50
60
70
-800-700-600-500-400-300-200-1000
Load(kn)
0
10
20
30
40
50
60
70
0 1 2 3 4 5 6
Load(kn)
Third Span Def (mm)
Load-third Span Deflection

41
 Beam ( 2B+ ) :
Figure 3.5 The Mode Of Failure Of Strengthened Beam ( 2B+ )

42
Figure 3.5.1 Load-Mid span Deflection Curve Of Beam ( 2B+ )
Figure 3.5.2 Load-BFRP Strain Curve Of Beam ( 2B+ )
0
20
40
60
80
100
120
140
160
0 5 10 15 20 25 30 35 40 45
Load(kn)
Mid Def (mm)
Load-Mid span Deflectin
0
20
40
60
80
100
120
140
160
0 1000 2000 3000 4000 5000 6000
Load(kn)
BFRP strain (µ)
Load-BFRP Strain

43
Figure 3.5.3 Load-Concrete Compression Strain Curve Of Beam ( 2B+ )
Figure 3.5.4 Load third Span Deflection Curve Of Beam ( 2B+ )
0
20
40
60
80
100
120
140
160
-2500-2000-1500-1000-5000
Load(kn)
comp in mid span conc strain (µ)
0
20
40
60
80
100
120
140
160
0 5 10 15 20 25 30 35 40
Load(kn)
Third Span Def (mm)
Load-third Span Deflection

44
3.2.2 Load-Deflection Response And Capacity Increase :
The Load-Midspan Deflection (P-Δ) Response Of The Tested Beams Is Shown In
Figure (3.6) Generally, The Beams Exhibited A Semi-Tri-Linear Response Defined By Three
Stages. The First Stage Corresponds To The Beam Behavior Before Cracking. The Behavior
In This Stage Was Linear Elastic And The NSM Reinforcement Did Not Contribute To
Increase The Stiffness. In The Second Stage, The Beam Started To Crack At The Midspan
Section Where The Maximum Moment Was Located. Further Increase Of Load, The Cracks
Became Wider And New Flexural Cracks Initiated. Many Uniformly Distributed Narrow
Cracks, With Different Depths, Were Observed Along The Whole Length Of The Tested
Beam. The Developed Cracks Did Not Cross The Adhesive Because Of Its Low Elastic
Modulus. Furthermore, A Nonlinear Behavior Was Observed Up To Failure. In This Stage,
The NSM Reinforcement Significantly Increased The Stiffness, And Decreased The Crack
Widths Comparing With The Control Beam. The Second Stage Ends With Yielding Of The
Steel Reinforcement. Comparing To The Control Beams (CB)
The Third Stage Starts By Yielding Of The Steel Reinforcement And Ends With The
Failure Of The Tested Beams. After The Steel Yielding, The Crack Width Was Controlled
By The NSM Bar. The Global Stiffness Of The Tested Beams Decreased In This Stage Due
To Yielding Of The Steel Reinforcement And The Weak Modulus Of The NSM
Reinforcement. Using The NSM BFRP Bars Significantly Increased The Ultimate Carrying
Capacity Of The Strengthened Beams Compared With The Un-Strengthened Beam. Beam
(1B+), Strengthened With One Straight BFRP Bar, Failed At A Load Of 75 Kn; Because Of
The Compression Failure. , Doubling The FRP Area Increased The Ultimate Load Up To
138.8 KN For Beam (2B+) Recording 37.9% Over That Of Control Beam.

45
Figure 3.6 Load-Mid span Deflection Curves Of The Tested Beams
Figure 3.7 Load third Span Deflection Curves Of The Tested Beam
0
20
40
60
80
100
120
140
160
0 5 10 15 20 25 30 35 40 45
Load(kn)
Mid Def (mm)
Load-Mid-Deflection Curve
1 BFRP +
2 BFRP +
1 BFRP
CONTROL
2 BFRP
0
20
40
60
80
100
120
140
160
0 5 10 15 20 25 30 35 40
Load(kn)
Third span Def (mm)
Load-Third Span Deflection curve
CONTROL
1 BFRP +
1 BFRP
2 BAFRP
+
2 BFRP

46
3.2.3 Load-Strain Response At The Midspan Section Of The Strengthened Beams :
In This Section, The Load-Strain (P-Ε) Response Is Discussed And Compared For The
Strengthened Beams. The (P-Ε) Responses In The BFRP Bar, Tension Steel And Extreme
compression Fiber Of Concrete At The Midspan Location Are Presented In Figure (3.8) .
Figure 3.8 Load-BFRP Strain Curves For All Strengthened Beams
Generally, Up To Concrete Cracking In Tension, The Strain Increased In A Linear
Manner With The Increase Of The Applied Load. After Cracking, All The Tensile Forces
Carried By Concrete Were Transferred To The Tension Steel And NSM Reinforcement. As
A Result, The Flexural Stiffness Of The Beam Decreased Causing A Reduction In The (P-Ε)
Slope; However The Relation Remained Linear Up To Yielding Of The Tension Steel. After
Yielding, The Flexural Stiffness Of The Beam Was Significantly Reduced And Another
Decrease Occurred In The Slope Of The (P-Ε) Curves.
For Each Strengthened Beam And Presented In Table (3.1).
The Efficiency Factor (Ζs) Is Defined As The Ratio Of The Developed Strain In The BFRP
Bar To Its Specified Ultimate Strain. The Ultimate BFRP Strain As Obtained From The
Laboratory Tests Is 0.0125 ε. Estimating The Factor (Ζs) Gives A Good Indication Of The
Material Utilization
The Measured Steel Strain At Yielding Ranged Between 0.0029 ε and 0.00373 ε ,
Which Is Slightly Higher Than The Average Yield Strain Of 0.0031 ε For The Tested Steel
0
20
40
60
80
100
120
140
160
0 1000 2000 3000 4000 5000 6000
Load(kn)
BFRP strain (µ)
Load-BFRP Strain Curve
1 BFRP
2 BFRB +
1 BFRB +
2 BFRP

47
Bars. This Is Possibly Due To The Tension Stiffening Effect Generated At The Bottom Of
The Tested Beams. It Can Be Seen In Figure (3.5) and Figure (3.3) That Doubling The BFRP
Cross Sectional Area In Beam (2B+) Significantly Decreased The Measured Steel Strains At
The Same Load Levels Compared To Beam (1B+)
And It Took A Longer Time Than It To Reach Its Maximum Strain, Also The Beam Carried
A Greater Value Of Deflection.
Summary :3.3
In This Chapter, The Experimental Test Results Of Five RC Beams Involved In This
Program Were Presented And Analyzed. The Test Variables Comprised The FRP Cross
Sectional Area, U-Stirrups Anchoring Of The BFRP Bar, Strengthening By Partially Bonded
Systems With Different Unbonded Lengths. The Anchoring Of The BFRP Bars Was
Provided By Using U-Shaped Stirrups With 90˚ Hooked Ends With The Aim Of Delaying Or
Preventing The Concrete Cover Separation Failure. A General Comparison Was Performed
Between The Control And Strengthened Beams To Study The Effects Of The Mentioned
Variables On The Flexural Behavior Of The Tested Beams. The Results Were Presented And
Analyzed In Terms Of Failure Mode, Cracking Behavior, Load-Deflection Behavior, Load-
Strain Responses, Stiffness And Deformability.
In The Next Chapter, A Comprehensive Study Was Conducted On The Finite Element
Simulation Of RC Beams Strengthened By NSM BFRP Bar.

48
Table (3-2) Test Result
Data
Beam
ID
Ultimate load
( KN )
Max. Def. 1/3
span
( mm )
Max. Def. Mid.
span
( mm )
Comp. Strain
( µ )
BFRP strain
( µ )
Type of failure Shape of failure
Control
Beam
95.645 26.45 31.2 -2162.227
(Steel strain)
4940.791 Moment Failure
1B 80.615 13.475 20.85 -2005.836 1336.378 Shear Failure
1B+ 55.07 4.65 5.05 -603.557 2054.2 Compression Failure
2B 65.345 5.275 5.9 -689.854 2369.559 Concrete Cover
Separation
2B+ 130.132 21.85 28.45 -2236.897 4940.791 Compression Failure

49
Chapter Four: Conclusions and Future Work
Introduction :3.4
In This Chapter, The Conclusions Of This Research And The Recommendations For
Future Work Are Illustrated. In The Experimental Part Of The Research, A Limited Test
Matrix Of 5 RC Beams Was Designed To Investigate The Effects Of The FRP Cross
Sectional Area, And U-Stirrups. Results Obtained In This Research Might Not Be Significant
Because Of The Limited Test Matrix, However, A Better Understanding On The Flexural
Strengthening With U-Stirrups Would Be Provided By These Results.
Conclusions :3.5
Five RC Beams Were Cast And Tested In Four-Point Bending Up To Failure. One Beam
Was Unstrengthened To Serve As A Benchmark Control Beams And The Other Four Beams
Were Strengthened In Flexure By NSM BFRP Deformed Bars. To Study The Effect Of FRP
Cross Sectional Area, Two Beams Were Strengthened With Different Number Of Fully
Bonded Straight Bars With 200 mm Spacing Between Stirrups And U-Stirrups With The
Same Spacing. Meanwhile, The Other Two Beams Were Strengthened With Fully Bonded
Straight Bars With The Same Number With The Same Spacing Between Stirrups Were 200
mm But Without The U-Stirrups, To Evaluate The Influences Of U-Stirrups And Fully
Bonding Of The NSM Systems.
Based On The Results Of The Five Beams, The Following Conclusions Are Drawn:
1. Strengthening With The NSM BFRP Bars Is Very Effective In Increasing Both
Flexural Strength And Stiffness. The NSM Strengthening System Improved The Load-
Deflection Response Of The Tested Beams, And Limited The Deflections And Crack
Widths At Different Loading Stages. The Concrete Cover Separation Was The
Predominant Failure Mode Of All The Strengthened Beams.

50
2. Strengthening By Two Fully Bonded Straight Bar Increased And Ultimate Loads By
133.3% Over The Control Beam.
3. Strengthening With The U-Stirrups Was Effective In Delaying The CCS Failure And
Further Increasing The Ultimate Load Compared With The Straight Bars Only. This Is
Because The U-Stirrups Provided A Bond Action Besides Acting As Shear Dowels At
The Concrete Interface. Using The Fully Bonded U-Stirrups Increased The Ultimate
Load And Effective Pre-Yield Stiffness Over The Control Beam. And Increase The
Ultimate Load By 33.3 % Over The Unstrengthened Control Beams.
4. Unbonding The BFRP Bar Along The Mid-Spans lightly Affect The Ultimate Carrying
Capacity Compared To The Fully Bonded Bar; However It Decreased The Effective
Pre-Yield Stiffness, Further Increase In The Unbounded Length Shifted The Failure
Mode From CCS To No CCS.
Recommendations For Future Work :3.6
Based On The Results Obtained In The Current Research, The Following Topics Are
Suggested For Future Work:
1. Studying The Performance Of RC Beams Strengthened With NSM FRPS Subjected To
Different Types Of Exposure Such As Ultra Violet Radiation, Oxidation, Chemical
Solutions, Etc.
2. Investigating Seismic And Dynamic Behavior Of The NSM FRP Strengthened Beams.
3. Conducting An Experimental Work To Study The Behavior Of The RC Beams
Strengthening Using NSM FRP Subjected To Fatigue Loading.
4. Use BFRP Bars And CFRP Bars Which Has Hight Modulus Of Elasticity With U-
Stirrups Compared To BFRP Bars With U-Stirrups To Increase Stiffness And Strength.
5. Study The Behavior Of Concrete Structures In ﬂexure Internally Reinforced With FRP
Bars And Strengthened With NSM FRP Reinforcement.

51
6. Use The Available Experimental Data Concerning To The NSM FRP Strengthening
Technique To Arrive At Design Equations Able To Predict The Failure Load Of The
Strengthened Beams.
7. Conducting an Experimental Work to Evaluate the Effect of the Clear Spacing between
Multiple.

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