FLEXURAL STRENGTHENING OF REINFORCED CONCRETE …

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FACULTY OF ENGINEERING

STRUCTURAL ENGINEERING DEPARTMENT

FLEXURAL STRENGTHENING OF REINFORCED CONCRETE

GIRDERS USING POST-TENSIONED CONCRETE JACKETS

Thesis

Submitted in partial fulfillment of the

requirements for the degree of

MASTER OF SCIENCE

in

CIVIL ENGINEERING (STRUCTURES)

by

DINA YEHIA ZAKARIA

Supervised by

Prof. Dr. Amr Ali Abd El Rahman

Professor of Reinforced Concrete Structures

Ain Shams University

Dr. Hussein Okail

Associate Professor of Structural Engineering

Ain Shams University

Cairo – 2017

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AIN SHAMS UNIVERSITY

FACULTY OF ENGINEERING

STRUCTURAL ENGINEERING DEPARTMENT



by

Eng. DINA YEHIA ZAKARIA EWAIS B.Sc. in Civil Engineering (Structural Engineering)

Faculty of Engineering – Ain Shams University – Cairo, EGYPT, June 2011

Examiners Committee

Name and Affiliation Signature

Prof. Dr. Ashraf Hassan Mohamed El Zanaty Professor of Concrete Structures,

Cairo University, Cairo, Egypt

………………

Prof. Dr. Amr Hussein Zaher Professor of Concrete Structures,

Ain Shams University, Cairo, Egypt

………………

Prof. Dr. Amr Ali Abd El Rahman Professor of Concrete Structures


………………

Dr. Hussein Osama Okail Associate Professor

Structural Engineeering Department


………………

Date: 15 October 2017

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STATEMENT

This thesis is submitted to Ain Shams University in partial

fulfillment of the requirements for the degree of Master of Science

in Civil Engineering (Structural).

No part of this thesis has been submitted for a degree or a

qualification at any other university or institution.

Date : 15 / 10 / 2017

Name : Dina Yehia Zakaria

Signature :

iv

ACKNOWLEDGEMENT

First, thanks are all direct to Allah, for blessing this work until it

has reached its end, as a part of generous help throughout my life.

I would like to thank my supportive parents and specially my lovely

husband for encouraging me to complete this work and for always

being there for me.

I would like to express my deep appreciation to Prof. Amr

Abdelrahman, Professor of concrete structures, faculty of

engineering, Ain Shams University, for his guidance and valuable

suggestions. I'm also extremely grateful to Dr. Hussein Okail,

Associate Professor of concrete structures, faculty of engineering,

Ain Shams University, for his experienced advice, continuous

support and his efforts in completing this work.

Finally, I would like to thank my friends and colleagues who helped

me in the completion of this work.

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AUTHOR

Name : Dina Yehia Zakaria

Date of birth : 30 April 1989

Place of birth : Cairo, Egypt

Academic Degree : B.Sc. in Structural Engineering

University : Ain Shams University

Date : July 2011

Grade : Very Good

Current job : Teaching & Research Assistant

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SUMMARY

Flexural strengthening of reinforced concrete girders is an important side of the

construction industry and its importance is on the rise. There are different techniques used

to study the response of repaired and strengthened girders, each with different advantages

and drawbacks. External pre-stressing was initially developed for retrofitting of bridges,

but now it is used for both retrofitting and in building new structures. Due to its simplicity

and cost effectiveness, pre-stressed concrete bridges with external pre-stressing are

becoming popular.

This study discusses the flexural behavior of reinforced concrete girders strengthened

using post-tensioning embedded in concrete jackets. The concept benefits from the

external jacket to help increase the cross-section inertia as well as to host the post-

tensioning tendons without the need of external deviators. This study incorporated two

phases namely, experimental and analytical phases.

The experimental phase of this study was conducted on two stages. The first stage deals

with girders loaded on their original section firstly and then strengthened with the post-

tensioned jacket and loaded to failure, while the second had the girders that were

strengthened before being subjected to loads. In addition to the stage of jacket

introduction, the difference between the original girder and the jacket’s concrete

compressive strength was also studied. The experimental results showed that both the

strength and the stiffness of the girders were enhanced significantly, this means that this

technique can be used for mitigating the effect of increased deflections as well as loss of

strength, the stage at which the jacket is introduced slightly affects the strength and

stiffness of the girders.

In the analytical phase of the study, a numerical model was built using the finite element

method to simulate the response of the tested girders in the experimental phase. The

analytical results show a very good match and correlation with the experimental results.

A parametric study was developed on the flexural behavior of strengthen girders to

investigate the effect of the damage level of girder before strengthening as well as

increasing the pre-stressing ratio, also to study the effect of increasing the compressive

strength of the original girder. The analytical results showed that, the stiffness and the

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strength of the strengthened girders increase with the decrease of the damage level for the

original girder, and the load carrying capacity increases by increasing the percentage of

pre-stressing area to the total cross-sectional area. Also, it was observed that the stiffness

of the girders was enhanced significantly by increasing the concrete compressive strength

of the original girder.

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Table of Contents

AUTHOR ...................................................................................................................... v

SUMMARY ................................................................................................................. vi

ABSTRACT ................................................................................................................ 15

Introduction ................................................................................................................. 16

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

1.2Objectives ............................................................................................................... 17

1.3Thesis Outlines ....................................................................................................... 17

Chapter 2 ..................................................................................................................... 19

Literature Review ........................................................................................................ 19

2.1 Introduction ........................................................................................................... 19

2.2 Pre-stressed Structures ........................................................................................... 20

2.2.1 General: .............................................................................................................. 20

2.2.2 Pre-Tensioning .................................................................................................... 20

2.2.3 Post-tensioning .................................................................................................... 21

2.3 External Pre-stressing ............................................................................................. 22

2.3.2 Advantages of External Pre-Stressing Technique:................................................ 23

2.3.3 Disadvantages and Limitations of External Pre-stressing ..................................... 24

2.3.4 Profiles of External Post-Tensioning Tendons ..................................................... 26

2.3.5 Previous Studies for Strengthening using External Pre-stressing .......................... 27

2.4 Strengthening of Girders using RC Jackets ............................................................. 29

2.4.1 Using of Concrete as Strengthening Material ....................................................... 30

2.4.2 Previous studies for strengthening using concrete jacket ...................................... 31

Chapter 3 ..................................................................................................................... 33

Experimental Program ................................................................................................. 33

3.1 Introduction ........................................................................................................... 33

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3.2 Description of Test Girders .................................................................................... 33

3.2.1 Stage 1 ................................................................................................................ 34

3.2.2 Stage 2 ................................................................................................................ 34

3.3 Material Properties ................................................................................................. 36

3.3.1 Concrete .............................................................................................................. 36

3.3.2 Steel Reinforcement ............................................................................................ 36

3.3.3 Components of External Post-Tensioning System................................................ 37

3.3.4 Grout ................................................................................................................... 37

3.3.5 Shear Dowels ...................................................................................................... 37

3.4 Fabrication and Casting of the Girders ................................................................... 38

3.4.1 Stage 1 ................................................................................................................ 38

3.4.2 Stage 2 ................................................................................................................ 38

3.5 Jacking the Tendons ............................................................................................... 39

3.6 Instrumentation ...................................................................................................... 40

3.6.1 Steel Strain Measurements .................................................................................. 40

3.6.2 Deflection Measurements .................................................................................... 40

3.6.3 Data Output ......................................................................................................... 41

3.7 Test Setup .............................................................................................................. 41

3.8 Loading Protocol .................................................................................................... 41

Chapter 4 ..................................................................................................................... 43

Experimental Results ................................................................................................... 43

4.1 Introduction ........................................................................................................... 43

4.2 Experimental Results of Stage One ........................................................................ 44

4.2.1 Behavior of Girder B1 ......................................................................................... 44

4.2.1.1Crack pattern ..................................................................................................... 45

4.2.1.2 Deflection ........................................................................................................ 46

4.2.2 Behavior of Girder B2: ........................................................................................ 48

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4.2.2.1 Crack pattern 48

4.2.2.2 Deflection 49

4.3 Experimental Results of Stage 2 ............................................................................. 50

4.3.1 Compressive Concrete Strength ........................................................................... 51

4.3.2 Behavior of Girder BL 30-30............................................................................... 51

4.3.2.1 Crack pattern .................................................................................................... 52

4.3.2.2 Deflection ........................................................................................................ 53

4.3.2.3 Ultimate Loading capacity ................................................................................ 55

4.3.2.4 Mode of failure................................................................................................. 55

4.3.3 Behavior of girder BL 30-60 ............................................................................... 55

4.3.3.1 Crack Pattern .................................................................................................... 56

4.3.2.2 Deflection ........................................................................................................ 57


4.3.2.4 Mode of failure................................................................................................. 59

4.3.4 Behavior of girder BN 30-30 ............................................................................... 59

4.3.4.1 Crack Pattern .................................................................................................... 60

4.3.4.2 Deflection ........................................................................................................ 61


4.3.4.4 Mode of failure ................................................................................................ 63

4.3.5 Behavior of girder BN 30-60 ............................................................................... 63

4.3.5.1 Crack Pattern .................................................................................................... 64

4.3.5.2 Deflection ........................................................................................................ 65


4.3.5.4 Mode of failure................................................................................................. 67

4.3.6 Comparison between the Girders in the Two Stages ............................................ 67

Chapter 5 ..................................................................................................................... 73

Finite Element Analysis ............................................................................................... 73

5.1 Introduction ........................................................................................................... 73

5.2 Material Model ...................................................................................................... 74

5.3 Meshing Technique ................................................................................................ 76

5.4 Bonding between Core and Post-Tensioned Concrete jacket ................................... 76

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5.5 Loading Method ..................................................................................................... 77

5.6 Boundary Conditions and Initial Conditions ........................................................... 77

5.7 Predefined Fields ................................................................................................... 78

5.8 Model Verification ................................................................................................. 79

5.8.1 Load versus Deflection Response ........................................................................ 80

5.8.2 Mode of Failure ................................................................................................... 86

Chapter 6 ..................................................................................................................... 88

Parametric Study .......................................................................................................... 88

6.1 Introduction ........................................................................................................... 88

6.2 Parametric Study Using FE Models ........................................................................ 89

6.2.1 The Effect of Damage Level of Concrete Core before Strengthening and percentage

of Prestressing reinforcement ....................................................................................... 89

6.2.1.1 Load versus Deflection Response ..................................................................... 90

6.2.1.2 Load versus Concrete Strain Response ............................................................. 94

6.2.1.3 Maximum Principle Stresses Before and After Strengthening ........................... 97

6.2.2 The Effect of Compressive Strength of Concrete Core ....................................... 100

6.2.3 The Effect of the Interface between the Concrete Core and the Post-Tensioned

Concrete Jacket .......................................................................................................... 101

Chapter 7 ................................................................................................................... 104

Conclusions and Recommendations ........................................................................... 104

7.1 Conclusions ......................................................................................................... 104

7.3 Recommendations for Future Work ...................................................................... 106

References ................................................................................................................. 106

Appendix A ............................................................................................................... 109

Appendix B................................................................................................................ 112

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List of Figures

Figure 2- 1 :Steps of Pre-tensioning method ............................................................... 21

Figure 2- 2: Steps of Post-tensioning method .............................................................. 22

Figure 2- 3: External Pre-stressing Tendons Layout .................................................... 23

Figure 2- 3: External posttensioning using straight profile cables ................................ 26

Figure 2- 4: Schematic of external post-tensioning using straight profile Cables ......... 26

Figure 2- 5: External post-tensioning using draped profile cables ............................... 27

Figure 2- 6: Schematic of external posttensioning using draped profile Cables ........... 27

Figure 2- 7: Construction Technique for Girder Jacketing ........................................... 30

Figure 3- 1: Cross section of the main reinforced concrete girders before repair and

strengthening. ............................................................................................................... 34

Figure 3- 2 : Cross Section of Strengthened Girders. ......................................................... 35

Figure 3- 3: Jacking and Grouting the Girders .................................................................. 39

Figure 3- 4: Deflection and steel strain measurement for all girders in the two stages ............ 40

Figure 3- 5: Test Setup for all girders in the two stages ...................................................... 41

Figure 4- 1: Crack Pattern for B1 at load level 15 kN.................................................. 45

Figure 4- 2: Crack Pattern for girder B1...................................................................... 46

Figure 4- 3: Load versus mid-span deflection for B1 .................................................. 47

Figure 4- 4: Deterioration of the stiffness for beam B1 ............................................... 47

Figure 4- 5: Crack Pattern for B1 at load level 15 kN.................................................. 49

Figure 4- 6: Crack Pattern for girder B2...................................................................... 49

Figure 4- 7 :Load versus mid-span deflection for B2.................................................. 50

Figure 4- 8 : Deterioration of the stiffness for beam B2 ............................................. 50

Figure 4- 9: Crack pattern at failure for girder BL 30-30 ............................................. 53

Figure 4- 10: Load versus mid-span deflection for BL 30-30 ...................................... 54

Figure 4- 11: Deterioration of the stiffness for BL 30-30 ............................................ 54

Figure 4- 12: Crushing of concrete for girder BL 30-30 at a load level of 125 kN ....... 55

Figure 4- 13: Crack Pattern at failure for girder BL 30-60........................................... 57

Figure 4- 14: Load versus mid-span deflection for girder BL 30-60 ............................ 58

Figure 4- 15: Deterioration of the stiffness for girder BL 30-60 .................................. 58

Figure 4- 16: Crushing of concrete for girder BL 30-60 at a load level of 140 kN ....... 59

Figure 4- 17: Crack pattern at failure for girder BN 30-30 .......................................... 61

Figure 4- 18: Load versus mid-span deflection for girder BN 30-30 ............................ 62

Figure 4- 19: Deterioration of the stiffness for girder BN 30-30 .................................. 62

Figure 4- 20: Crushing of concrete for girder BN 30-30 at a load level of 145 kN ....... 63

Figure 4- 21: Crack pattern at failure for girder BN 30-60 .......................................... 65

Figure 4- 22: Load versus mid-span deflection for girder BN 30-60 ............................ 66

Figure 4- 23: Deterioration of the stiffness for girder BN 30-60 .................................. 66

Figure 4- 24: Crushing of concrete for girder BN 30-60 at a load level of 150 kN ....... 67

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Figure 4- 25: Load versus mid-span deflection ........................................................... 69



Figure 5- 1: Interaction between Core and Post-tensioned Concrete Jacket ................. 76

Figure 5- 2: Loading Scheme of Girders in the first stage ........................................... 77

Figure 5- 3: Loading Scheme of Girders in the second stage ....................................... 77

Figure 5- 4: Maximum Principle Stress Contours before Strengthening for Girders BL

30-30, BL 30-60, BN 30-30 and BN 30-60 respectively.............................................. 79

Figure 5- 5: Stage 1- (B1 and B2) Load-Mid span deflection before Strengthening ..... 81

Figure 5- 6: Stage 2 Load versus Mid-span Deflection for Analytical and Experimental

Results of Girders PC (2-1), PC (2-2), PC (2-3) and PC (2-4) respectively.................. 85

Figure 5- 7: Minimum Principle Stress Contours at Failure for Girders BL 30-30, BL

30-60, BN 30-30 and BN 30-60 respectively .............................................................. 88

Figure 6- 1: Load-mid span Deflection for girders with % of Aps/At 0.28 ............................. 91



Figure 6- 4: Ultimate Load at each % of Aps/At for different damage level of concrete core .... 93

Figure 6- 5: Load versus Strain at the top of concrete surface ............................................. 97

Figure 6- 6: Principle stresses contour at each damage level of concrete core before post-

tensioning ...................................................................................................................100

Figure 6- 7: Comparison between Specimens with different Core Compressive strength .......101

Figure 6- 8: Cross section of Girder PC ..........................................................................102

Figure 6- 9: Comparison between the girder PC and the strengthened girder PC 60-60 .........103

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List of Tables

Table (2.1) limitations for using concrete jacketing……………………………………12

Table (3-1): Properties of the tested girders in stage 2…………………………………17

Table (4-1): The main variables of girders in each

stage…………………………………………………………………………………….23

Table (4-2): Uniaxial compressive strength of different concrete core units…………..29

Table (4-3): Mid-Span Deflection at Load=45kN……………………………………...43

Table (4-4): Summary of the Experimental test results………………………………...45

Table (5-1): Comparison between Experimental and FE Model

results……………………………………………………………………......................55

Table (6-1): Parametric study for girders ……………………………….......................58

Table (6-2): Ultimate Capacity and mid-span deflection for each

girder…………………………………………………………………………………...61

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ABSTRACT

This thesis discusses the flexural behavior of reinforced concrete

girders strengthened using post-tensioning strands embedded in

concrete jackets. The concept benefits from the external jacket to

help increasing the cross-section inertia as well as to host the post-

tensioning tendons without the need of external deviators. This

results a significant enhancement to the strength and stiffness of

the original girder. This technique may be used to strengthen

severly deflected girders or cracked beams in buildings and

bridges. This study incorporated two phases namely, experimental

and analytical phases.

The experimental phase of the study was conducted on two stages

the first deals with two girders loaded on their original section

firstly and then strengthened with the jacket and loaded to failure,

while the second had the two girders that were strengthened before

being subjected to loads. In addition to the stage of jacket

introduction, the difference between the original girder and the

jacket’s concrete compressive strength was also studied. Key test

results first proved that both the strength and the stiffness of the

girders were enhanced significantly. Secondly, it was found that

the stage at which the jacket is introduced slightly affects the

strength and stiffness of the girders. Finally, increasing the jacket

concrete compressive strength may result in a slight increase in the

strength by about 10% of the original girder capacity.

In the analytical phase of the study, a numerical model was built

using the finite element method to simulate the response of the

tested girders in the two experimental stages. This thesis presents

findings of the experimental program as well as the comparison

with the analytical results of the model which shows a very good

match and correlation. A parametric study was developed on the

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