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SEISMIC RETROFITTING OF UNREINFORCED LOAD BEARING BRICK WALLS

IN HISTORIC BUILDINGS USING FIBER-REINFORCED POLYMER STRINGS

by

Onur Seren

B.S. , Civil Engineering, Boğaziçi University, 2009

Submitted to the Institute for Graduate Studies in

Science and Engineering in partial fulfillment of

the requirements for the degree of

Master of Science

Graduate Program in Civil Engineering

Boğaziçi University

2013

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SEISMIC RETROFITTING OF UNREINFORCED LOAD BEARING BRICK WALLS

IN HISTORIC BUILDINGS USING FIBER-REINFORCED POLYMER STRINGS

APPROVED BY:

Assoc. Prof. Cem Yalçın . . . . . . . . . . . . . . . . . . .

(Thesis Supervisor)

Assis t. Prof. Kutay Orakçal . . . . . . . . . . . . . . . . . . .

Assoc. Prof. Ercan Yüksel . . . . . . . . . . . . . . . . . . .

DATE OF APPROVAL: 15.01.2013

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ACKNOWLEDGEMENTS

I would like to express my grat itude to everyone who contributed the development of

this research. I would like to express my sincere gratitude to my advisor Assoc. Prof. Dr.

Cem Yalçın for his valuable help in instructing, guiding and supporting me throughout theduration of this thesis.

Also, I would like to thank the members of my Master’s thesis examinationcommittee; Assist. Prof. Ku tay Orakçal, and Assoc. Prof. Ercan Yüksel, for their in-depth

comments and advice.

I would like to thank Assist. Prof. Ahmet Anil Dindar for his important contribution

to the analysis stage of this study with the software he developed.

Civil Engineer Ali Bayraktar and Hafez Keypour from SGM Construction provided

required materials and contributed this research financially, which is highly appreciated.

Special thanks to my friends Tevfik Terzioğlu, Hasan Altun and Furkan Çelenli fortheir assistance and suggestions during the construction and testing of the specimens, and

to the technicians, Hasan Şenel, Hamdi Ayar, Ümit Melep and Mesut Kardaş for theirhelp

in the experimental phase of this research.

I would like to thank my supervisors Ramiz Soylu and Tayfun Bayramkaya from

SURYAPI End. Tic. A.Ş. for their patience and tolerance at work for the time required forthis thesis to be completed.

Finally, I would like to thank my family and my love Ece Uçar for their continuoussupport and encouragement.

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ABSTRACT

SEISMIC RETROFITTING OF UNREINFORCED LOAD BEARING

BRICK WALLS IN HISTORIC BUILDINGS USING FIBER-

REINFORCED POLYMER STRINGS

Most of the historical buildings and monuments in the world are unreinforced

masonry (URM) type and they are vulnerable to seismic actions. Considering the seismic

activities in the regions where historical masonry structures are located, their structural

assessment and rehabilitation or retrofitting if necessary against seismic forces are needed

in order to preserve them for future generations. International organizations such as

UNESCO (United Nations educational, Scientific and Cultural Organization) and

ICOMOS (International Council on Monuments and Sites) try to increase the awareness in

need for preserving these world-heritage structures. However, historical masonry structures

still need retrofitting techniques that are much different than that of buildings that were

built using conventional construction practice since the architectural features of the historic

buildings must remain unchanged after the retrofitting process. Therefore, conventional

methods have been used in retrofitting works are not suitable for such purposes. In this

study, the use of carbon fiber-reinforced polymer (CFRP) strings placed in mortar joints

for strengthening of URM structures was investigated. Nearly full-scaled four URM brick

wall specimens with aspect ratio of 1.00 were tested under varying axial load and cyclic

lateral loading. Two of the specimens were tested as control specimens while other two

specimens were retrofitted with horizontally-oriented CFRP strings. Also, one of the tested

control specimens were repaired and retrofitted and re-tested in order to see the effect of

this retrofitting technique after substantial damage occurred. Test results showed that

energy dissipation capacity of the wall specimens were enhanced with the proposed

technique. In addition, the crack openings due to shear effects were minimized while

keeping the historic and aesthetical view of the structures intact, since they were directly

placed inside the mortar joints and debonding of strings were prevented. However, nosignificant increase in the lateral load carrying capacity of the specimens was observed.

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ÖZET

TARİHİ BİNALARDAKİ DONATISIZ TUĞLA - YIĞMA YÜK

TAŞIYICI DUVARLARIN FİBER TAKVİYELİ POLİMER İPLER

İLE SİSMİK GÜÇLENDİRMESİ

Yeryüzündeki birçok tarihi bina ve anıtın kâgir oluşu bu yapıları sismik etkilere karşı

savunmasız kılmaktadır. Tarihi yapıların konumlandığı bölgelerdeki sismik aktiviteler gözönünde bulundurulduğunda; yapısal durum değerlendirme, iyileştirme ve gerekligörüldüğünde sismik etkilere karşı güçlendirme çalışmalarının yapılması, bu yapılarıngelecek nesillere aktarılabilmesi adına zorunluluk arz etmektedir. UNESCO ve ICOMOS

gibi uluslararası organizasyonlar , dünya mirası olarak nitelendirilen bu yapıların geleceknesillere aktarılabilmesi adına gerekli farkındalığın oluşturulması için çalışmalaryürütmektedirler.Ancak, tarihi kâgir yapılar için, güçlendirme sonrası tarihi doku ve

mimari özelliklerin korunması gerektiğinden, diğer yapılarda kullanılan tekniklerden farklıyöntemlere ihtiyaç duyulmaktadır. Bu nedenle, tarihi kâgir yapıların güçlendirmeçalışmalarında kullanılan konvansiyonel teknikler, bahsi geçen zorunlulukların sağlanması konusunda yetersiz kalmaktadır . Bu tez çalışmasında, fiber takviyelikarbon polimer iplerin

(CFRP) derz aralarında çekme elemanı olarak kullanılmasıyla donatısız tuğla-yığma yapıların depreme karşı güçlendirilmesi konusunda çalışılmıştır. Bu yöntemin etkinliği,gerçek ölçeğe yakın, 1.00 narinlik oranına sahip donatısız tuğla duvarnumuneleriyle,

değişen düşey ve periyodik yatay yük tesirleri altında test edilmiştir . Numunelerden ikisikontrol numunesi olar ak kullanılırken, diğer iki numune, derz aralarına yatay d oğrultuda yerleştirilen CFRP ipler ile güçlendirilmiştir. Ayrıca, kontrol numunelerinden biri,

güçlendirme yönteminin ağır hasarlı bir yapıda etkisini incelemek adına, test edildikten

sonra tamir ed ilip güçlendirilmiş ve yeniden test edilmiştir. Test sonuçları, numunelerinenerji sönümleme kabiliyetlerinin önerilen güçlendirme tekniği ile arttığını göstermiştir. Buna ek olarak, CFRP ipler in doğrudan derz aralarına uygulanması ve sıyrılmalarınınönlenmesi numunelerde kesme etkisiyle oluşan çatlakların azal masını sağlarken, yapınıntarihi ve estetik görünümünü korumuştur. Ancak, yapılan testlerde numunelerin yatay yüktaşıma kapasitelerinde belirgin bir artış tespit edilememiştir.

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TABLE OF CONTENTS

ACKNOWLEDGEMENTS .............................................................................................. iii

ABSTRACT ..................................................................................................................... iv

ÖZET……........................................................................................................................ v

LIST OF FIGURES .......................................................................................................... ix

LIST OF TABLES ......................................................................................................... xiv

LIST OF SYMBOLS ...................................................................................................... xvi

LIST OF ACRONYMS/ABBREVIATIONS ................................................................. xvii

1. INTRODUCTION ........................................................................................................ 1

1.1. General ................................................................................................................ 1

1.2. Problem Definition .............................................................................................. 2

1.3. Literature Review ................................................................................................ 6

1.3.1. Mechanical Properties of URM Structures and Their Components ......... ... 6

1.3.2. Seismic In Plane Behavior of URM Structures ......................................... 7

1.3.3. Testing of Masonry Structures for Seismic Assessment .......................... 10

1.3.4. Conventional Retrofitting Techniques for Historical URM Structures

Against Seismicity .................................................................................. 11

1.3.4.1. Filling of Cracks Using Grout and Epoxy Injections............. ...... 11

1.3.4.2. External Jacketing by Shotcreting .............................................. 12

1.3.4.3. Confining URM Using RC Tie Columns and Beams ......... ......... 13

1.3.4.4. Post-Tensioning With Steel Ties ................................................ 13

1.3.5. Evaluation of the Performance FRP Retrofitted Historical URM

Structures with FRP................................................................................ 14

1.4. Research Significance and Rationale .................................................................. 17

1.5. Objective and Scope .......................................................................................... 17

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1.6. Methodology ..................................................................................................... 18

1.7. Report Outline ................................................................................................... 19

2. EXPERIMENTAL SETUP ......................................................................................... 20

2.1. Description of Testing Program ......................................................................... 20

2.2. Description of Test Setup ................................................................................... 20

2.2.1. Typology of Specimens .......................................................................... 20

2.2.2. Placement of CFRP Strings on Specimens .............................................. 23

2.2.3. Test Setup and Instrumentation ............................................................... 24

3. EXPERIMENTAL STUDY ........................................................................................ 28

3.1. General .............................................................................................................. 28

3.2. Test Observations .............................................................................................. 28

3.2.1. Specimen BW0....................................................................................... 28

3.2.2. Specimen BW1-C ................................................................................... 30

3.2.3.

Specimen BW2-RR ................................................................................ 34

3.2.4. Specimen BW3-R1 ................................................................................. 37

3.2.5. Specimen BW4-R2 ................................................................................. 39

3.3. Analysis of Test Results ..................................................................................... 43

3.3.1. Normalized Lateral Load versus Drift Level Relationship ......... .......... .... 43

3.3.2. Vertical Load versus Lateral Load Relationship ......... ......... .......... ......... . 46

3.3.3. Moment-Base Rotation Relationship ...................................................... 47

3.3.4. Lateral Force-Shear Deformation Relationship ....................................... 54

3.3.5. Rigidity – Drift Level Relationship ......................................................... 59

3.3.6. Energy Dissipation – Drift Level Relationship ........................................ 62

4. CONCLUSIONS AND RECOMMENDATIONS ....................................................... 67

4.1. Summary ........................................................................................................... 67

4.2. Conclusions ....................................................................................................... 67

4.3. Recommendations.............................................................................................. 68

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APPENDIX A: CRACK PATTERNS ............................................................................. 70

A.1. Specimen BW1-C ......... ......... .......... ......... ......... ......... ......... .......... ......... ......... ... 70

A.2. Specimen BW2-RR ......... ......... .......... ......... ......... ......... ......... .......... ......... ......... 74

A.3. Specimen BW3-R1 ......... ......... ......... ......... .......... ......... ......... ......... .......... ......... . 78

A.4. Specimen BW4-R2 ......... ......... ......... ......... .......... ......... ......... ......... .......... ......... . 82

REFERENCES ................................................................................................................ 88

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LIST OF FIGURES

Figure 1.1. Wrong application of concrete lintel on masonry load carrying walls. ......... 3

Figure 1.2. Wrong application of reinforced concrete retaining wall with masonry

load carrying walls...................................................................................... 3

Figure 1.3. Wrong application of strengthening with steel clamping. ......... .......... ......... 4

Figure 1.4. Wrong application of strengthening with steel profiles at facade of

structure. ..................................................................................................... 4

Figure 1.5. A representative sketch for a sample application of CFRP strings. ......... ..... 5

Figure 1.6. In-plane failure modes of laterally loaded URM wall (a) shear failure;

(b) sliding failure; (c) rocking failure (d) toe crushing (ElGawady et al. ,

2007). ......................................................................................................... 7

Figure 1.7. Assumptions for rocking strength calculation of a wall (Magenes and

Calvi, 1997). ............................................................................................... 8

Figure 1.8. Shear tests for masonry structural elements (Bosiljkov et al. , 2010). ......... 10

Figure 1.9. FRP retrofit details for wallettes specimens (Mahmood and Ingham,2011).16

Figure 2.1. Test setup.................................................................................................. 20

Figure 2.2. FRP band layout. ......... .......... ......... ......... ......... .......... ........ .......... ......... ... 21

Figure 2.3. Brick wall & foundation joint detail. .......... ......... ......... ......... .......... ......... . 22

Figure 2.4. Repairing of BW2-RR specimen. .......... ......... .......... ......... ......... ......... ...... 22

Figure 2.5. Placement of FRP strings, Horasan mortar removal process. ......... ......... ... 23

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Figure 2.6. Epoxy application on CFRP strings and BW3-R1 from the construction

site. ........................................................................................................... 23

Figure 2.7. Preparation of BW4-R2........... ......... .......... ......... ......... .......... ........ .......... . 24

Figure 2.8. Vertical actuator, RC beam and test specimen joint detail. ......... ......... ...... 25

Figure 2.9. Brick wall and RC beam joint detail. .......... ......... ......... ......... .......... ......... . 25

Figure 2.10. The displacement based loading protocol used in the tests. ......... ......... ...... 26

Figure 2.11. Sensor layout. .......... ......... ......... ......... .......... ......... ......... ......... .......... ....... 27

Figure 3.1. Setup and deformations of BW0 at first test. ........ .......... ......... ......... ......... 29

Figure 3.2. Deformations on BW0 at the second test. ......... ......... ......... ......... .......... .... 29

Figures 3.3. Setup and deformations on BW0 at the third test. ......... ......... .......... ......... . 30

Figure 3.4. Shear cracks and crushing at the toes of BW1-C. ......... ......... .......... ......... . 31

Figure 3.5. Lateral load versus top displacement for specimen BW1-C. .......... ......... ... 32

Figure 3.6. Lateral force-shear displacement relationship for BW1-C (DG1-2). ......... . 33

Figure 3.7. Lateral force-shear displacement relationship for BW1-C (DG3-4). ......... . 33

Figure 3.8. Shear cracks and crushing at the toes of BW2-RR. ........ .......... ......... ......... 35

Figures 3.9. Lateral load versus top displacement for specimen BW2-RR. ......... .......... . 35

Figure 3.10. Lateral force-shear displacement relationship for BW2-RR (DG1-2). ........ 36

Figure 3.11. Lateral force-shear displacement relationship for BW2-RR (DG3-4). ........ 36

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Figure 3.12. Shear cracks, crushing at the toes of BW3-R1, and de-bonding of strings. . 38

Figure 3.13. Lateral load versus top displacement for Specimen BW3-R1. ................ ... 38

Figure 3.14. Lateral force-shear displacement relationship for BW3-R1 (DG1-2). ........ 39


Figure 3.16. Shear cracks, crushing at the toes of BW4-R2, and rupture of strings. ....... 41

Figure 3.17. Rupture of strings and location of strings. ......... .......... ......... ......... ......... ... 41

Figure 3.18. Lateral load versus top displacement for specimen BW4-R2. ......... .......... . 41



Figure 3.21. Normalized lateral load vs. drift level for BW1-C. ........ .......... ......... ......... 44

Figure 3.22. Normalized lateral load vs. drift level for BW2-RR. .......... ......... ......... ...... 44

Figure 3.23. Normalized lateral load vs. drift level for BW3-R1. .......... ......... ......... ...... 45

Figure 3.24. Normalized lateral load vs. drift level for BW4-R2. .......... ......... ......... ...... 45

Figure 3.25. Backbone curves of all specimens for normalized lateral load-drift

relationship. .............................................................................................. 46

Figure 3.26. Comparison of vertical load vs. lateral load relationship for all

specimens. ................................................................................................ 47

Figure 3.27. Vertical displacement readings and base rotation measurement. ........ ........ 48

Figure 3.28. Moment-base rotation relationship for BW1-C at first level. ......... ......... ... 48

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Figure 3.29. Moment-base rotation relationship for BW1-C at second level. ......... ........ 49

Figure 3.30. Moment-base rotation relationship for BW1-C at third level. ......... .......... . 49

Figure 3.31. Moment-base rotation relationship for BW2-RR at first level. ........ .......... . 50

Figure 3.32. Moment-base rotation relationship for BW2-RR at second level. .......... .... 50

Figure 3.33. Moment-base rotation relationship for BW2-RR at third level. ......... ......... 50

Figure 3.34. Moment-base rotation relationship for BW3-R1 at first level. ........ .......... . 51

Figure 3.35. Moment-base rotation relationship for BW3-R1 at second level. ......... ...... 51

Figure 3.36. Moment-base rotation relationship for BW3-R1 at third level. ......... ......... 52

Figure 3.37. Moment-base rotation relationship for BW4-R2 at first level. ........ .......... . 52

Figure 3.38. Moment-base rotation relationship for BW4-R2 at second level. ......... ...... 53

Figure 3.39. Moment-base rotation relationship for BW4-R2 at third level. ......... ......... 53

Figure 3.40. Shear deformation measurement. .......... ......... .......... ......... ......... ......... ...... 54

Figure 3.41. Lateral force-shear deformation curves for BW1-C (DG1-2). ......... .......... . 55

Figure 3.42. Lateral force-shear deformation for BW1-C (DG3-4). .......... ......... ......... ... 55

Figure 3.43. Lateral force-shear deformation relationship for BW2-RR (DG1-2). ......... 56

Figure 3.44. Lateral force-shear deformation relationship for BW2-RR (DG3-4). ......... 56

Figure 3.45. Lateral force-shear deformation relationship for BW3-R1 (DG1-2). ......... . 57


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Figure 3.47. Lateral force-shear deformation relationship for SP4- R2 (DG1-2). .......... . 58


Figure 3.49. Comparison of normalized lateral force-shear deformation backbone

curves. ...................................................................................................... 58

Figure 3.50. Stiffness and energy calculations.............. ......... .......... ......... ......... ......... ... 59

Figure 3.51. Rigidity-drift level relationship for BW1-C. ......... .......... ......... ......... ......... 60

Figure 3.52. Rigidity-drift level relationship for BW2-RR. ......... .......... ......... ......... ...... 60

Figure 3.53. Rigidity-drift level relationship for BW3-R1. ......... ......... .......... ........ ........ 60

Figure 3.54. Rigidity-drift level relationship for BW4-R2. ......... ......... .......... ........ ........ 61

Figure 3.55. Superposed rigidity-drift level relationship for all specimens. ........ .......... . 61

Figure 3.56. Cumulative energy dissipation-drift level relationship for BW1-C. ........... 62

Figure 3.57. Cumulative energy dissipation-drift level relationship for BW2-RR. ......... 63

Figure 3.58. Cumulative energy dissipation-drift level relationship for BW3-R1........... 63

Figure 3.59. Cumulative energy dissipation-drift level relationship for BW4-R2........... 64

Figure 3.60. Comparison of all specimens for cumulative energy dissipation. ......... ...... 64

Figure 3.61. Loop-wise normalized energy dissipation ratio vs. drift level

relationship. .............................................................................................. 65

Figure 3.62. Cumulative normalized energy dissipation ratio vs. drift level

relationship. .............................................................................................. 65

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LIST OF TABLES

Table 3.1. Max. lateral load and drift levels of under incremental vertical load sets

for BW1-C ................................................................................................ 31


for BW2-RR. ............................................................................................ 34


for BW3-R1. ............................................................................................. 37


for BW4-R2. ............................................................................................. 40

Table A.1. Observations of specimen BW1-C. ......... .......... ......... ......... ......... .......... .... 70

Table A.2. Observations of specimen BW1-C (cont.). ......... .......... ......... ......... ......... ... 71



Table A.5. Observations of specimen BW2-RR. .......... ......... ......... ......... .......... ......... . 74

Table A.6. Observations of specimen BW2-RR (cont.). ......... .......... ......... ......... ......... 75



Table A.9. Observations of specimen BW3-R1. ......... ......... .......... ......... ......... ......... ... 78

Table A.10. Observations of specimen BW3-R1 (cont.). ......... ......... .......... ........ .......... . 79

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Table A.13. Observations of specimen BW4-R2. ......... ......... .......... ......... ......... ......... ... 82






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LIST OF SYMBOLS

b Pier aspect ratio

c Global strength parameter

D Pier length

D Effective uncracked section of masonry wall panel

D1-2 Diagonal distances of deformed shape of the wall panel

DG 1-4 Readings of sensors for shear displacement

f tu Diagonal tensile strength of masonryf u Compressive strength of masonry

hR,L Initial length of rocking LVDTs

H0 Effective pier length

K Vertical stress distribution coefficient

Lwidth Width of the specimens

p Mean vertical stress

P Axial loadR 1-2 Retrofitting number

R 1-6 Readings of sensors for rocking measurement

t Pier thickness

Vd Ultimate shear load

V r Maximum shear strength under rocking

Y Height and width of wall panel

αv Shear ratio

ΔR,L Displacement reading of LVDT

εR,L Strain due to rocking

γ Base rotation angle

μ Sliding coefficient

ψ Boundary condition parameter for masonry wall panels

σv Mean vertical stress

τu Average ultimate shear stress

θ Rotation angle

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LIST OF ACRONYMS/ABBREVIATIONS

BW Brick wall

CFRP Carbon fiber reinforced polymer

CR# Crack number

EB Externally bonded

FRP Fiber reinforced polymer

GFRP Glass fiber reinforced polymer

ICOMOS International Council on Monuments and SitesLVDT Linear variable differential transformer

NSM Near surface mounting

RC Reinforced concrete

RR Repaired and retrofitted

SR Surface repointing

UNESCO United Nations Educational, Scientific and Cultural

OrganizationURM Unreinforced masonry

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1. INTRODUCTION

1.1. General

It is of great importance, due to the probability of strong seismic event occurrence

being high in the near future, to determine the seismic safety of historical masonry

structures and to improve and spread the technical knowledge for strengthening, especially

considering our country which experienced the devastating earthquakes in the year 1999.

Masonry structures are usually rigid, highly resistant against compressive stresses, but in

horizontal direction effect, especially in plane and out of plane forces induced by

earthquakes, are very weak and could get severe damages. Therefore, they are be classified

as brittle in nature and one of the most vulnerable among the different types of structural

buildings under seismic loads. Besides, masonry structures are one of the oldest types

among the historical buildings and it is necessary to preserve them for contributing

common heritage of mankind. For that reason, restoration of historical buildings in the

earthquake zones, and continuously strengthening them is a major necessity.

According to Calvi et al . (1996), lateral load resistance of masonry structures is

highly dependent on shear resistance of in-plane walls. In addition, shear resistance of in-

plane walls are directly related to its constituents; masonry brick, binding unit=mortar

ability and workmanship. Therefore, improvement techniques should target these

constituents’ bonding and adhesion capacities (Somerset al ., 1996). For the historical

building cases, the chosen method of seismic retrofitting must preserve the architecturaland historical features of the structure. A variety of techniques have been applied for

strengthening historical masonry structures. However, most of the methods do not take into

account the historical features of the building, which leads incompatible views of the

interior and exterior facades and thus, losing the entire historical features of the structure.

Use of lightweight materials, especially fiber-reinforced polymer (FRP) composites

in the form of strips or sheets, have a significant role in the development of repairing andstrengthening of civil engineering structures due to their superior properties such as cost

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effectiveness, high tensile strength and ease of application. In this study, by taking the

advantages of using FRP and the necessity of preserving architectural and historical

features of the structures into account, placing carbon fiber reinforced polymer (CFRP)into the brick masonry load carrying structural wa lls’ joints may offer the optimum

strengthening technique for historic unreinforced masonry structures.

1.2. Problem Definition

Historic and older buildings are vulnerable against forces induced by earthquakes

due to their well-known brittle and inflexible behavior. Furthermore, solid mass and heavy

weight of the materials used in these buildings could increase the probability of

counteracting with high seismic forces. Therefore, severe damage followed by collapse

mechanism could be observed in structural supports, walls, floors, stairs and other

structural members.

Under earthquake effect, tension zones become critical for the load carrying walls in

historical buildings. Considering low tensile resistance capacity of bricks and mortar,

diagonal cracking could start developing and rapidly propagate within the member or wall

element. Therefore, reinforcement against tension is needed to be implemented within the

members during repairing and renovation of the structure. However, since the architectural

and historic condition of the existing structure is needed to be preserved, the retrofitting

method should not give any damage or alter its architectural and historic condition (Arun

G.,2005; Altın et al. , 2005).

There are conventional methods used for retrofitting and restoration of historical

buildings. The tension capacity of the critical or damaged sections on the structural

members are generally increased by means of additional reinforced concrete or steel

supporting members, steel clamping, jacketing with plaster (Bayraktar, 2006). Although

these methods are commonly used in Turkey, they have serious disadvantages such as

difficulty in application and causing damage on historical and architectural view of the

structures. Also, the integrity of the structures no longer exists after these applications.

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Examples of wrong applications of retrofitting and restoration works are presented in the

Figures 1.1 to 1.4.

Figure 1.1. Wrong application of concrete lintel on masonry load carrying walls.

Figure 1.2. Wrong application of reinforced concrete retaining wall with masonry

load carrying walls.

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Figure 1.3. Wrong application of strengthening with steel clamping.

Figure 1.4. Wrong application of strengthening with steel profiles at facade ofstructure.

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As it is seen from the above figures, wrong applications have damaged or altered the

structures permanently in terms of historical and architectural point of view. Also, the

structural continuity and integrity of the structures are disturbed by these applications.Therefore, more practical and efficient techniques are needed in retrofitting of historical

structure.

In order to overtake the excessive tensile forces developed in load carrying walls,

CFRP strings could be used as tension elements. The application differs from other

conventional techniques since the CFRP strings are embedded into mortar joints

horizontally and vertically which is also called as structural repointing (SR). Infunctionality point of view, it does not affect the structure visually and at the same time it

provides high durability against tension due to the high strength capacity of CFRP

(Tumialan and Nanni, 2002).

Representative application of CFRP strings shown in Figure 1.5.

CFRP strings in horizontal direction

Reinforcing Plaster

Existing wall

CFRP strings in vertical direction

Figure 1.5. A representative sketch for a sample application of CFRP strings.

This research investigates and evaluates the performance of CFRP strings as a means

for seismic strengthening technique that are horizontally placed between the joints of

unreinforced masonry brick walls. The wall specimens represent the load carrying walls of

a historical building and they are constructed with blend brick and Horasan mortar which

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are the common construction materials exist in historical buildings in Anatolia region of

Turkey (Arioglu and Acun, 2006).

1.3. Literature Review

1.3.1. Mechanical Properties of URM Structures and Their Components

Behavior of masonry assemblage is highly dependent on the characteristics and

interface of their constituents. Usually, masonry walls have high compressive strength

whereas their tensile strength capacity is low. Besides, non-homogeneity of masonry units

and complexity of the interaction between masonry unit and mortar make it hard to predict

the lateral load capacity of these structures. Therefore, understanding these properties is

important for going further in seismic in-plane behavior of URM structures.

There are various researches on identifying the mechanical properties of masonry

structures both in individual material case and their interaction as masonry member: brick

unit and mortar, and shear/tensile bond strength and interface friction (McNary and

Abrams, 1985; Binda et al. , 1994; Atkinson et al ., 1994).

McNary and Abrams (1985) studied on different types of mortars and brick units that

vary in strength. Compression tests were performed for indicating the effect of

confinement in increasing compressive strength and ductility of mortar. In addition, the

tensile strength of mortar found to be negligible compared to its compressive strength. Rad(1978) examined the variation of compressive strength of different types of brick units. In

these studies, it was found to be that compressive strength of brick units on average was 2

to 3 times larger than the tensile strength. It is found that typical compressive strengths of

clay bricks range between 8.60 MPa and 17.20 MPa (Rad, 1978).

The interface between mortar and brick unit is ruled by two mechanisms; bonding

due to chemical interaction and friction. Thus, depending on the mechanism, two main

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types of failures are associated with brick-unit mortar interface which are tension (mainly

governed by chemical bond) and shear (mainly ruled by friction).

1.3.2. Seismic In Plane Behavior of URM Structures

According to Vas concelos and Lourenço (2009), with the condition of prevented outof plane failure, resistance of URM structures against seismic action was sustained by in

plane behavior of masonry walls. In an earthquake, in-plane walls could deform or fail due

to diagonal shear failure, rocking at toe sections of the walls, sliding shear deformation

along bed joint and compression failure (toe crushing) (Magenes and Calvi, 1997).

Analytical studies were performed in the scope of experimental researches for

identifying the failure mechanisms due to in-plane forces that are subjected to URM walls

in terms of material properties, geometry and boundary conditions of the structures as seen

in Figure 1.6.

In general, rocking failure tends to prevail among other mechanism for masonry

walls that have slender geometry whereas sliding failure tends to occur in squat walls

(Magenes and Calvi, 1992; Abrams, 1992). Shear failure (i.e. diagonal cracking) prevails

over sliding and rocking failure mechanisms in masonry walls that have moderately

slender geometry with increase in vertical load (Mahmoud et al. , 1995; Bosilijkov et al .,

2003).

Figure 1.6. In-plane failure modes of laterally loaded URM wall (a) shear failure; (b)

sliding failure; (c) rocking failure (d) toe crushing (ElGawady et al. , 2007).

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Assumptions and maximum rocking strength evaluation of a URM wall under static

in-plane loading ( V r ) could be determined by Equation 1.1 with reference to Figure 1.7.

2

0

1 1

2 2r u v u

D t p p Dt p pV

H Kf Kf

(1.1)

In the above equation, D is the pier length, H 0 is the effective pier height, t is the pier

thickness, p=P/(D t ) is the mean vertical stress on the pier due to the axial load P , K is a

coefficient which takes the vertical stress distribution at the compressed toe (a common

assumption is an equivalent rectangular stress block with K =0.85) into account, f u is the

compressive strength of masonry. The effective height H 0 is determined by the boundary

conditions of the wall and is related to the shear ratio of αv which was expressed in

Equation 1.2.

0'

=v

H M H

VD D D

(1.2)

Figure 1.7. Assumptions for rocking strength calculation of a wall (Magenes and Calvi,

1997).

The parameter ψ has a value of 1.00 if the piers is fixed on one end and free to rotate

at the other end. If the pier is fixed at both ends, ψ has a value of 0.50 (Magenes and Calvi,

1997).

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Shear strength associated to diagonal cracking is expressed by Turnsek and

Cacovic’s model which simply considers the masonry wall as elastic, homogenous and

isotropic structural material as a function of diagonal tensile strength ( f tu) in Equation 1.3.

tu 1 , ,1.0 1.5d

tu

f Dt p hV b b

b f l (1.3)

Here, b is the empirically based parameter that represents the pier aspect ratio

(Turnsek and Cacovic, 1971).

In addition, diagonal cracking due to mortar bed and head joint failure could be

formulated in the form of ultimate shear strength which is based on Mohr-Coulomb

approach, as indicated in Equation 1.4.

u vc (1.4)

Evaluation of ultimate load, V d , of a wall could be calculated with Equation 1.5.

1.5

1 3d

v

P p c pV Dt c Dt c Dt

c Dt p

(1.5)

Where D is the effective un-cracked section mentioned in Equation 1.6 with respect

to Figure 1.7 (Magenes and Calvi, 1997).

01 1

' 3 32 2

v

H V V D D D D

P P D

(1.6)

However, it was noted that these formulations describe local phenomenon and failure

envelopes and they cannot be directly used as a shear failure criteria for masonry (Calvi et

al. , 1996). But, the researchers briefly explained the strength characterization of URM

walls subjected to seismic forces. Therefore, direct experimental studies on structural

member, which is the wall panels in this case, is necessary for identifying the conventional

tensile strength f tu.

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1.3.3. Testing of Masonry Structures for Seismic Assessment

Monitoring the performance and shear resistance of masonry members due to in-

plane forces induced by seismic loading could be done by simulating the static or

kinematic boundary conditions. Application of a monotonic or cyclic shear force (or

displacement) under a certain axial load have been generally used in the literature (Abrams

P, 2001; D’Ayalaet al ., 1997; Tomazevic and Lutman, 1993; Magenes G, 1992; Manfredi

et al ., 1992; Calvi et al ., 1996). Testing arrangements commonly used for cyclic and

monotonic loading are presented in Figure 1.8. Although these test setups do not simulate

the real conditions, the required behavioral parameters for seismic evaluation and

performance analysis of masonry structures are sustained by these setups.

Figure 1.8. Shear tests for masonry structural elements (Bosiljkov et al. , 2010).

In addition to quasi-static loading tests, dynamic test procedures are applied on brick

masonry as well (Magenes and Calvi, 1994). According to the experiments by Calvi et al .,

(1996), although the seismic excitation is resembled better in dynamic tests, quasi-static

loading tests prevail since inducing of large loads to specimen, observing crack patterns

and measuring displacements and forces are easier compared to dynamic tests. On the

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contrary, masonry specimens under quasi-static loading exhibit more damage and lower

strengths compared to dynamic tests which could be defined as conservative. Therefore,

both testing techniques could result in differences in the evaluation of stiffness andstrength parameters of URM brick walls (Calvi et al. , 1996).

1.3.4. Conventional Retrofitting Techniques for Historical URM Structures Against

Seismicity

The need for preserving, restoring and strengthening of historical structures againstseismicity has been noticed for years. Development in interventions for strengthening

techniques has been followed by international collaborations since the Athens Charter for

the Historic Monuments 1931 (ICOMOS 1931). The general requirement for the

strengthening techniques are; being reversible in means of application and preserving the

character and features of the structures. In this section, by taking the expectations into

account, frequently used conventional strengthening and retrofitting techniques will be

reviewed.

1.3.4.1. Filling of Cracks Using Grout and Epoxy Injections. This technique has been

commonly used for filling the cracks and voids within the multi-wythe masonry structures

for maintaining the integrity. As a grout material, both epoxy resin and cement based

grouts could be used for injection. The methodology for this technique could be defined as

the following steps (Hamid et al .,1999; Calvi and Magenes,1994; Schuller et al .,1994):

As a first step, injection docks should be anchored in the determined sections. Then,

the openings around the docks and other cracks should be sealed.

Cracks and other openings should be cleaned with water by injecting water from the

docks.

Finally, grout should be injected with low injection pressure.

A case study was carried by Perret et al ., (2002) which evaluates the performance ofhigh strength cement grout in a 130-year old masonry bridge pier. According to in-situ

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pullout bond and sonic tomographic tests, grouting technique managed to increase the

performance of the tested pier. Furthermore, studies of Schuller (1984) showed that this

technique could increase the compressive strength of URM walls up to 0.8 of the un-retrofitted masonry compressive strength. A real application of this technique was studied

by Valluzzi et al ., (2002) in Modena, Italy for the Bell Tower of Cathedral of Monza.

Although different studies on this technique proved that a significant increase in

ultimate load capacity is acquired, correct application requires a comprehensive pre-study

on composition of the type of grout and its penetration into the structure. In addition, sonic

tests should be conducted in order to evaluate the effectiveness of the technique during theapplication (Valluzzi, 2007).

1.3.4.2. External Jacketing by Shotcreting. The principle of jacketing technique for

strengthening reinforced concrete (RC) structures is also valid for masonry structures as

well. Masonry members under excessive compression are confined by either reinforced

concrete units or steel plates. Since the treatment is practiced on the surface, the historical

and architectural features of the structure are highly affected by this technique.

Other than RC and steel members, ferrocement, reinforced plasters, and shotcrete

could be used.

Ferrocement could be defined as mesh of fine rods placed in a high-strength mortar

matrix. Abrams and Lynch (2001) found that lateral resistance of masonry walls that had

been retrofitted by ferrocement technique increased by a factor of 1.5 (Abrams and Lynch,2001).

In contrast to ferrocement intervention, high strength reinforcing steel is covered by a

thin plaster layer in reinforced plaster surface treatment technique. Shepperd and Tercelj

(1980) studied on this technique and in the reference of diagonal compression and static

cyclic loading experiment results, it was found that in-plane resistance of masonry walls is

linearly proportional with the thickness of the application, mortar strength and

reinforcement quality whereas, it is inversely proportional with the damage condition of

the structure (Sheppard and Tercelj, 1980).

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Similar to reinforced plaster technique, this technique was applied by spraying the

cement based shotcrete on masonry wall surface that covered with steel reinforcing bar

mesh. Studies showed that this technique increased the ultimate load capacity of theretrofitted walls (Kahn, 1984; Abrams and Lynch, 2001).

1.3.4.3. Confining URM Using RC Tie Columns and Beams. Use of vertical RC tie

columns that are constructed at intersections of masonry walls and connected to tie beams

is one of the frequently used conventional techniques. Simply, confinement is maintained

by these RC members where it leads to improvement in ductility and structural integrity of

masonry. However, effect of this technique in the increase of ultimate lateral load capacity

of masonry walls is found to be insignificant except very squat walls (Chuxian et al . 1997,

Zhang et al . 1997, Zezhen et al . 1984).

1.3.4.4. Post-Tensioning With Steel Ties. Retrofitting of historical masonry structures by

post tensioning with steel ties could be either applied externally or internally. Basics of this

technique depend on compensating the tensile stresses on masonry due to lateral loads by

the compressive forces used for post tensioning. Among the other conventional techniques,

externally post-tensioning with steel ties prevails since being relatively reversible, ease in

application and efficient. On the contrary, aesthetical view of the structures is highly

disturbed by this method. Besides, steel bars used in the tendons for post tensioning

without grout cover could be susceptible to corrosion.

Application of this technique requires a socketing section on the structure that could

be either filled with grout (Rosenboom and Kowalsky 2003, Al-Manaseer and Neis 1987)

or left empty (Mojsilovic and Marti, 2000). Orientation of the tendons could be both in

vertical and horizontal direction. Studies on vertical post-tensioning proved that, this

method was effective in increasing the ultimate load capacity of the walls against both in-

plane and out-of-plane forces. The contribution of horizontal post-tensioning in ultimate

load capacity of masonry walls was experimentally studied by Page and Huizer (1994) and

analytically by Karantoni and Fardis (1992). The results from both researches found to be

there were no significant improvement.

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1.3.5. Evaluation of the Performance FRP Retrofitted Historical URM Structures

with FRP

The use of FRP has been increasing in various industries with discovering the

effectiveness of these materials in strength, durability, and workability. FRP materials have

been already introduced to structural engineering by means of strengthening reinforced

concrete structures which extensive research could be found about in literature. For

retrofitting and strengthening of URM historical structures with FRP, studies mainly

focused on the structural walls and in-plane panels.

Use of FRP in reinforced concrete is followed by strengthening of masonry

structures both in out-of-plane and in-plane under cyclic loading, in the form of carbon

laminates (Schwegler, 1994; Abrams and Lynch, 2001). Schwegler studied on retrofitting

configuration with FRP laminates and compared single-side retrofitting with double side

retrofitting of squad specimens. The studies of Schwegler concluded by the finding that

full surface coverage and inclined plates were the best configuration (Schwegler, 1994).

Another retrofitting technique with FRP laminates were studied on cracked specimen

with diagonal configuration for seismic retrofitting of URM historical structures. The

studies showed that proposed technique with the diagonal configuration was unsuccessful

(ElGawady et al , 2005a). Similar study on both damaged and non-damaged specimens

showed that retrofitting with diagonal configuration was effective only in non-damaged

specimen case (Zhao et al , 2003).

In-plane static cyclic loading performance of URM walls that had been retrofitted

with FRP were evaluated before and after retrofitting procedure (ElGawady et al , 2007).

As URM wall specimen, one-half scale single-wythe walls that had been constructed using

half-scale hollow clay brick and weak mortar. Three specimens were tested as reference

specimens. Later on, the damaged specimens were retrofitted by FRP on the surface and

tested again. One specimen was retrofitted directly after the construction stage and tested.

In total, seven specimens were tested. Experiment results proved that for particularspecimens, lateral load capacity were increased after retrofitting by a factor of 1.4 to 5.9.

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Besides, it was found that the severity of the existing damage in the specimen before

retrofitting had an influence in the ultimate lateral strength of the specimen after

retrofitting. Furthermore, it was observed that cracking load and pattern were effectivelycontrolled after FRP retrofitting.

Performance of in-plane shear behavior of URM that strengthened by near surface

mounted (NSM) CFRP strings was experimentally investigated (Petersen et al ., 2010). In

this study, different orientation of CFRP strings was tested including effect of

nonsymmetrical reinforcement. Dimension of all solid clay brick panel specimens was

1.2m x 1.2m (aspect ratio of 1.00) whereas unidirectional pultruded CFRP strings were15mm wide and 2.8mm thick. CFRP strings were glued using epoxy, into rectangular

grooves which were 20mm deep and 6mm wide and had been cut into surface of the

masonry panels by a circular saw. Seven URM panels with and four URM panels without

FRP strengthening were tested under diagonal shear compression test. The test results

proved that vertical orientation of CFRP strings prevented sliding failure effectively. In

addition, it was found to be nonsymmetrical reinforcement didn’t cause any change in in-

plane behavior of URM panels. Furthermore, it was observed that diagonal cracking was

prevented by horizontal oriented CFRP strings.

More recent study that examine the effectiveness of FRP systems as a seismic retrofit

intervention for in-plane loaded URM walls under seismic effects was done by Mahmood

and Ingham (2011). Seventeen URM wallettes were retrofitted with externally bonded

(EB) glass FRP fabrics (GFRP), EB pultruded carbon FRP (CFRP) plates, or near-surface

mounted pultruded CFRP rectangular bars. Dimension of specimens were classified in

three stages (1170mm x 1170mm x 225mm for Stage 1 and Stage 2, 1170mm x 1075mm x

225mm for Stage 3) with aspect ratios of 1.00 and 1.08. By taking architectural features of

façade into account, FRP retrofitting was only practiced on single surface of the wallettes.

The orientation of FRP that had been used in the experimental study was presented in

Figure 1.9. Specimens were tested under diagonal compression.

According to the test results, up to 325% increase in shear strength was observed for

FRP retrofitting. However, it was noted that out-of-plane displacements were observed in

one façade retrofitted specimens. In addition, positive effect of vertical and diagonal FRP

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orientation in preventing sliding failure was examined, whereas horizontal orientation of

FRP used with weak mortar found to be ineffective. Furthermore, insignificant change in

stiffness with FRP retrofitting was noted (Mahmood and Ingham, 2011).

Figure 1.9. FRP retrofit details for wallettes specimens (Mahmood and Ingham,2011).

Mossallam and Banerjee (2011) tested unreinforced concrete masonry unit walls that

had 1:1 aspect ratio and externally retrofitted with FRP bands. Six specimens were tested

under the action of cyclic lateral load and vertical gravity load. Increase in lateral load

capacity was obtained for all retrofitted specimens according to the test results. In addition,

especially in retrofitted specimens, governing failure mechanism was observed to be

compression at toe sections (Mossallam and Banerjee, 2011).

In addition to all, dynamic tests for evaluating the in-plane behavior of URM walls

that retrofitted with FRP were performed (ElGawady et al ., 2005a,b). Glass fiber

reinforced polymer (GFRP) and CFRP were applied either oriented diagonally or covering

the all surface of the specimen. Both studies confirmed that lateral load capacities of the

specimens were increased. In addition, rocking mechanism prevailed in geometrically

slender specimens whereas shear cracking with some degrees of rocking was dominantly

observed in squat specimens. Besides, it was found to be the retrofitting materials did not

change the fundamental frequencies and initial st iffness of the specimens (ElGawady et al .,

2005a,b).

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The intervention in FRP retrofitting of URM structures has great potential and a wide

research area. Common understanding of the mentioned researches is FRP retrofitting of

URM walls have influence in lateral load capacity of these structures. Besides, diagonalcracking and other in-plane failure mechanisms due to forces generated by seismic actions

could be prevented or controlled. However, nearly all applications require great surface

area on the structure which could result loss in aesthetical view and features in the

historical structures case. Therefore, studies on this issue should continue.

1.4. Research Significance and Rationale

The aim of this current research is to strengthen unreinforced masonry brick, load

carrying structural walls of older and historical structures against seismicity without

changing or affecting their architectural and historical features. The proposed technique in

this research is the retrofitting of load carrying masonry brick structural walls’ joints withfiber reinforced polymer, FRP strings. Strengthening methods that could positively affect

the tensile capacity of masonry members such as proposing use of high bonding and tensile

strength capacity mortar, use of GFRP, having different orientation of FRP strings other

than horizontal position or change in typology of wall formation are out of the scope of this

study. In addition, out-of-plane strengthening of the URM walls was not investigated.

An experimental research was carried on near full-scaled unreinforced load carrying

masonry brick walls in same typology. It aimed to evaluate and validate the performance

of proposed strengthening technique under in-plane cyclic lateral force action whether such

a technique is suitable for seismic strengthening of older and historical masonry structures

located in seismic regions.

1.5. Objective and Scope

This experimental study was mainly focused on the development and evaluation of

an applicable FRP retrofitting technique that increase the lateral load (shear) capacity of

structural walls of historical masonry buildings.

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The objectives of this study could be summarized as follows:

To evaluate the performance of FRP strings in increasing the lateral load capacity ofURM structural walls under the effect of seismic loading by comparing the test

results of retrofitted and post-strengthened specimen with control specimen,

To evaluate the performance of FRP strings in in-plane shear behavior of URM brick

walls,

To increase the resistance of URM brick walls against diagonal cracking,

To identify the effects of varying vertical load on unreinforced masonry structural

walls in lateral load capacity, To identify different failure mechanisms on masonry structural walls under cyclic

loading case,

To show FRP bands maintain the integrity in between masonry load carrying walls in

the structure properly.

In this study, unreinforced masonry structural wall specimens were tested under

varying vertical load and reversed cyclic loading. At the first phase of the study, a controlspecimen was tested in order to determine the behavior and natural lateral load capacity of

the member. As a second step, the first specimen had been repaired and strengthened, and

then was tested in order to compare the performance of the technique in post-strengthening

with control specimen. As a third step, second specimen that had been retrofitted by

mentioned technique was tested in order to evaluate and compare its performance with

control specimen. Fourth and final step was to test final specimen that had been retrofitted

by the same technique in addition to enhanced bonding of CFRP strings.

1.6. Methodology

This study investigates the actual behavior of unreinforced masonry brick structural

walls and evaluates the performance of CFRP string retrofitting that is developed for

improving the seismic behavior of historical masonry structures without damaging their

architectural and historical features.

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First of all, literature related with strengthening of historical masonry structures was

reviewed. Then, four specimens with the same typology, in other terms same formation of

bricks and use of same material, were produced. In scope of literature review, availablefacilities at the Structural Laboratory of Bogazici University were determined and a

preliminary test was conducted. According to the results of this test, the most suitable

testing conditions were determined. First three specimens were tested with the established

testing conditions and the results were compared. Fourth and the final specimen was

improved in order to prevent debonding of CFRP strings, and with this specimen the final

test was conducted.

1.7. Report Outline

This thesis presents the experimental research on the seismic behavior of

unreinforced load carrying URM structural walls and evaluation of retrofitting of these

members by using CFRP strings.

Brief information about the mechanical behavior of unreinforced load carrying

masonry structural walls under seismic action, literature review and previous studies

aiming strengthening historical masonry structures, and the objectives of the study with the

methodology are given in Chapter 1. In Chapter 2, experimental setup with the details of

construction, instrumentation and testing procedure is provided. Analysis on experimental

results, discussions and comparisons according to these results are presented in Chapter 3.

Finally, Chapter 4 gives a summary of the study, indicates the final outcomes, and

recommendations for further studies.

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2. EXPERIMENTAL SETUP

2.1. Description of Testing Program

The experimental investigation is aimed to test the behavior of unreinforced brick

walls under seismic loading. And hence, the evaluation of the performance of CFRP

strings in increasing the shear capacity of the specimens is aimed. Therefore, four single-

storey unreinforced brick wall specimens of 1:1 aspect ratio were tested subjected to cyclic

quasi-static loadings with the variation of axial load. This setup has been adopted from

several research programs (Magenes and Calvi 1997; Bosiljkov et al ., 2003) and altered to

suit this experimental research. The test setup is shown schematically in Figure 2.1.

Figure 2.1. Test setup.

2.2. Description of Test Setup

2.2.1. Typology of Specimens

Four brick wall specimens with 2.00 meters high and 2.00 meters wide and 0.19

meter thick were prepared in two batches. The dimensions of the specimens were chosen

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such that they could be successfully tested with the available facilities in the Structural

Laboratory of Bogazici University. A special type of mortar, Horasan that was used in the

Anatolian region for centuries, is used to build the walls.

Specimens were named in terms of their masonry unit constituent name (brick), test

number and initial letter of their condition. Accordingly, BW1-C refers to first tested brick

wall which was used as control specimen whereas BW2-RR stands for second tested brick

wall which is repaired and retrofitted. Similarly, BW3-R1 is the third tested brick wall with

retrofitting. And, BW4-R2 is the fourth tested brick wall with retrofitting.

One specimen (BW0) was tested for optimization of test setup. Second specimen

(BW1-C) was tested as it is, and later it was repaired, retrofitted (BW2-RR), and tested

again, while the other two (BW3-R1, BW4-R2) were only retrofitted and then tested.

CFRP strings were used as main retrofitting technique. They were horizontally inserted

between the brick elements and inside the mortar. A total of three lines at the top and three

lines at the bottom of the specimen with 20 cm offset of the strings were placed. The

middle portion of the walls is left non-retrofitted since the formation of shear cracks are

first expected to propagate at the corners of the top and the bottom sections (Figure 2.2).

Figure 2.2. FRP band layout.

Specimens were constructed on previously-built reinforced concrete foundations that

were designed for the experimental evaluation of the lateral load behavior of squat

structural walls by Terzioğlu T. (2011). The reinforced concrete structural wall had beenremoved from its foundation while the vertical reinforcement steel bars at 20-30 cm height

was kept in order to maintain a fixed support mechanism and prevent any premature

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sliding of the brick wall. Two holes were drilled on bricks that were laid on the first two

rows, as seen on Figure 2.3. Thus, sliding of the brick walls from the foundation was

prevented.

Figure 2.3. Brick wall & foundation joint detail.

First four specimens (BW0, BW1-C, BW2-RR, BW3-R1) were built in 2010 within

the same batch whereas fourth specimen, BW4-R2 was prepared more recently, in 2012,with different FRP string arrangement.

BW1-C was repaired after testing (BW2-RR). Damaged sections were rebuilt and

specimen was retrofitted with CFRP strings as shown in Figure 2.4.

Figure 2.4. Repairing of BW2-RR specimen.

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2.2.2. Placement of CFRP Strings on Specimens

After the unreinforced brick wall was built, Horasan mortar on the surface of the

selected three layers at the top and bottom portions of the wall was slightly removed as

seen in Figure 2.5. These sections were cleaned with wire brush in order to make the

surface suitable for interaction with CFRP strings.

Figure 2.5. Placement of FRP strings, Horasan mortar removal process.

Figure 2.6. Epoxy application on CFRP strings and BW3-R1 from the construction

site.

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On the other side, CFRP strings with 5 meters of length each, were fully covered

with epoxy binder, BASF MBT-MBRACE, and left to dry for approximately 5 minutes.

Drying process is necessary for hardening of the CFRP strings which enables them to getthe desired shape. After the drying process was done, the CFRP strings were placed

horizontally in the specified sections where the Horasan mortar had been removed as

shown in Figure 2.6. The CFRP strings should be as tight as possible and should fully

cover the section. As a final step, Horasan mortar was applied on the sections that had been

reinforced with CFRP strings.

BW4-R2 was retrofitted during the construction stage since it was experienced fromtests of BW3-R1 and BW2-RR that the lateral load capacity of the specimen did not

decrease due to removal process of mortar for CFRP retrofitting. Two steel re-bars were

placed at two ends of the wall without anchoring to the foundation and CFRP strings were

tied around these re-bars in order to provide proper confinement and also minimize

possible slip of the CFRP strings from the mortar joint during testing as seen in Figure 2.7.

Therefore, the continuity of FRP strings was maintained.

Figure 2.7. Preparation of BW4-R2.

2.2.3. Test Setup and Instrumentation

Varying pre-compression loads were applied using a servo-controlled verticalactuator with a maximum capacity of 1000 kN, with reaction on the strong floor by means

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of vertical pre-stressing cables, which kept the vertical load approximately constant. The

lateral load was applied based on the displacement-control criteria via the horizontal

actuator which had a capacity of 250 kN and connected to the reaction wall. Both thevertical and horizontal loads were transmitted by means of a reinforced concrete beam that

had been designed in a way that it could be easily placed on and removed from the top of

the wall (Figure 2.9). A set of steel rollers were used between the vertical actuator and the

reinforced concrete beam in order to allow relative displacement between the vertical

actuator and the beam (Figure 2.8).

Figure 2.8. Vertical actuator, RC beam and test specimen joint detail.

Figure 2.9. Brick wall and RC beam joint detail.

In any quasi-static cyclic loading, the specimens were subjected to predetermined

numbers of displacement-controlled loading cycles. Under a certain vertical load set, three

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cycles of the same amplitude in story drift were repeated and then displacement amplitude

was increased (Figure 2.10). Loading cycles were applied until the specimens reached their

yield strength under a certain vertical load case. Depending on the vertical load,approximately 15-21 reversed cycles were applied throughout the test for a specific vertical

load set. All data were recorded by using data acquisition system. Crack propagation,

rocking mechanism, de-bonding and other failures were also recorded.

Figure 2.10. The displacement based loading protocol used in the tests.

Critical sections where displacement was expected to be observed had been

instrumented by Linear Variable Differential Transformers (LVDTs) as it is seen in Figure

2.11.

Six LVDTs’ were placed at two sides of the specimens in order to measure

deformations due to rocking, One LVDTs was placed to control and measure any relative displacement between

top beam and the specimens,

Two LVDTs were mounted for measuring the top displacement of beam,

Two LVDTs were placed on the beam diagonally for measuring the diagonal

displacements between the beam and the foundation,

Two LVDTs were placed on the specimens diagonally for measuring the diagonal

displacements between the top and bottom parts of the specimens,

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One LVDT was placed on the strong floor for measuring any relative displacement

of foundation and the strong floor.

All of the LVDTs were connected to the data acquisition system.

Figure 2.11. Sensor layout.

In order to investigate the contribution of applied vertical load in the lateral load

capacity of the specimens, five different vertical load sets were determined (from 50 kN to250 kN). At each vertical load set, lateral load cycles were applied until yielding was

observed in the lateral load capacity in order to prevent any damage that could occur on the

specimens. Here, yielding is referred as lateral load capacity to stay constant for increasing

target displacement where rocking mechanism is observed.

After the tests were completed for each vertical load set, the test procedure was

followed until the specimens failed due to shear cracking under 300 kN vertical load.

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3. EXPERIMENTAL STUDY

3.1. General

In this section, test results and observations related to behavior of URM wall

specimens during experiments will be given. In addition, performance evaluation of each

specimen in terms of deformations, crack formations, energy dissipation, lateral load-

displacement hysteresis response, and failure modes are presented. At last, effectiveness of

proposed technique will be discussed by means of ultimate drift level and lateral load,

energy dissipation and stiffness degradation.

3.2. Test Observations

In this section, observations related with the tests and the results obtained from the

instrumentation are presented for each specimen. Basically, lateral force versus topdisplacement and diagonal displacement relationships are provided.

3.2.1. Specimen BW0

There were three distinct tests were applied on this specimen for understanding the

behavior of the specimen and optimizing the test setup.

The first test was conducted under the weight of two heavy concrete blocks,

positioned on top of the beam as dead load. The dead load due to the weight of these

blocks was measured approximately 30 kN. In this test (Figure 3.1), no shear and crushing

were observed. Rocking mechanism was prevailed and horizontal cracks were observed at

the toe section of the specimen. Maximum lateral load of 33.96 kN was reached at 0.75 %

drift level. The test was ended at 1.75 % drift level since only rocking mechanism was

developed rather than diagonal shear cracking which was desired failure mode.

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Figure 3.1. Setup and deformations of BW0 at first test.

At the second test, a hydraulic jack was used for inducing vertical load which was

increased from 100 kN to 250 kN in four sets. However, during the cyclic loading tests, it

was observed that the hydraulic jack’s position waschanging at push and pull cycles which

led varying vertical load instead of desired constant load. Under 250 kN vertical load,110.79 kN lateral load capacity was recorded at 1.75 % drift level. Rocking was observed

at all drift levels during the test (Figure 3.2). Furthermore, V-shaped crack which followed

the mortar and brick joints, and crushing of the toe sections of BW0 at the same drift and

lateral load level were observed. The second test was ended at 1.75 % drift level.

Figure 3.2. Deformations on BW0 at the second test.

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The third test was aimed to stabilize the vertical load on BW0 by means of spherical

steel rollers which would allow the hydraulic jack to move freely at the displacement

cycles.

The objective of this test was to determine whether the spherical steel rollers would

properly function. Hence, only one vertical load set was applied which was 200 kN. In this

set, 89.90 kN in the push direction was recorded as the highest lateral load capacity at 1.00

% drift level. Rocking mechanism at 0.60% drift level was observed at the sections of

BW0 where the V-shaped cracks had been formed in the second test (Figure 3.3). Besides,

V-shaped cracks became longer whereas shear cracks were started to propagate at the bottom corners of BW0 at 0.75 %. The test was ended at 1.25 % drift level since the lateral

load capacity of BW0 was decreased by 50%. Throughout the test, variation of vertical

load was prevented which figured out that use of steel rollers provided the desired loading

conditions.

Figures 3.3. Setup and deformations on BW0 at the third test.

3.2.2. Specimen BW1-C

As it was mentioned previously, this specimen belonged to control specimen.

Incremental vertical load started with 50 kN and ended with 300 kN. The pre-determined

target displacement cycles were followed until yielding is observed in lateral load vs.

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displacement relationship for each incremental vertical load sets (50 kN to 250 kN). The

variation of maximum lateral load and the target displacement cycle is given in Table 3.1.

Table 3.1. Max. lateral load and drift levels of under incremental vertical load sets for

BW1-C

VerticalLoad [kN]

Max. LateralLoad [kN]

Max. TopDisplacement

[mm] Drift Level [%]

50 33.05 2.6370 0.15

100

46.50

3.1155

0.15

150 62.00 4.1276 0.20

200 75.25 5.1546 0.25

250 87.46 5.9219 0.30

At 300 kN vertical load set, when the drift level reached to 0.30%, rocking

mechanism was observed at the toe sections of the wall. At 0.50% drift level, crushing was

started at the toe sections due to increasing rocking mechanism. At 0.60% drift level,

where maximum lateral load capacity was reached to 116.48 kN, shear cracks started to

propagate whereas crushing at the toe sections started to increase. After this drift level,

lateral load capacity started to decrease. At 1.25 % drift level, depth of shear cracks

reached to their maximum and total crushing of the toe sections was observed (Figure 3.4).

The cyclic loading set was ended at this drift level.

Figure 3.4. Shear cracks and crushing at the toes of BW1-C.

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The lateral load versus displacement relationship of specimen BW1-C under 300 kN

vertical load is provided in Figure 3.5. Pinching effect could be clearly observed in the

hysteresis curves. In addition, stiffness degradation was occurred during the repeatedcycles of drift levels. Decrease in strength started after 20 mm lateral displacement.

Figure 3.5. Lateral load versus top displacement for specimen BW1-C.

According to Equation 1.1, maximum rocking load, V r , is found to be 139 kN.

Average compressive strength was taken as 12.9 MPa according to studies of Rad (1978).

In addition, K was taken as 0.85 whereas boundary condition ψ was taken as 1.00 since the

specimen was fixed only at one end. In the tests, it was observed that rocking mechanism

was started at 0.075% drift level under 43.42 kN lateral force action.

Crack patterns and load history are provided in Table A.1. at Section A.1.

As it was indicated in S ection 2.2.3, four diagonal LVDT’s were located forrecording the diagonal di splacements. Readings from these LVDT’s on BW1-C are

provided in Figures 3.6 and 3.7. Measurements obtained from diagonal LVDTs on wall

panel are classified as DG1-2 whereas other two measurements are presented in the name

of DG3-4.

From Figure 3.7, in every push and pull cycles, almost symmetric diagonaldisplacements were recorded. In contrast to Figure 3.7, shear displacement hysteresis

PUSH

PULL

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cycles were predominantly remained in the tension zone as indicated in Figure 3.6. This

could be related with lack of reinforcement which would have provided resistance against

the movement. In addition, in the elastic region, displacement values corresponded tomaximum lateral load values tend to be close to y-axis of the graph. This could show that

the specimen exhibited a rigid body motion in this region which resulted in rocking

mechanism. As the lateral force-shear displacement curves shifted away from y-axis,

excessive damage on the specimen was expected.

-30 -20 -10 0 10 20 30-150

-100

-50

0

50

100

150

Shear Displacement [mm]

Lateral Force [kN]

Shear 2

Shear 1

Figure 3.6. Lateral force-shear displacement relationship for BW1-C (DG1-2).

-30 -20 -10 0 10 20 30-150

-100

-50

0

50

100

150


Lateral Force [kN]

Shear 4

Shear 3

Figure 3.7. Lateral force-shear displacement relationship for BW1-C (DG3-4).

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3.2.3. Specimen BW2-RR

As it was defined in previous chapter, specimen BW1-C was repaired after the

experiment and reinforced with FRP strings. In Table 3.2 variation of maximum lateral

load and the target displacement for each incremental vertical load set are given:


BW2-RR.

VerticalLoad [kN] Max. Lateral

Load [kN]



50 30.28 9.9153 0.50

100 41.28 12.3051 0.60

150 53.02 15.1375 0.75

200 71.36 18.2106 1.00

250

78.71

15.2749

0.75

In this specimen, the quality of workmanship in repairing was not good enough for

recovering the cracks fully. There were sections where the cracks had been formed at

previous test were still visible and couldn’t be repaired.

Horizontal cracks due to rocking mechanism were first observed at 0.50 % drift level

under 50 kN vertical load set. At 0.75% drift level under 250 kN vertical load, additional

shear cracks started to form at the same time with rocking mechanism.

In 300 kN vertical load set, at 0.75 % drift level, 90.02 kN was measured as

maximum lateral load capacity in the push direction. Shear cracks that had been formed in

250 kN vertical load set grew longer and additional shear cracks were also observed.

Crushing at the toe sections of the specimen was started at this drift level (Figure 3.8). In

addition, rocking started at 0.075% drift level that corresponded to 32.44 kN of lateral

force.

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The test was ended at 1.00 % drift level due to the 40% decrease in lateral load

capacity which was 53.12 kN.

Figure 3.8. Shear cracks and crushing at the toes of BW2-RR.

The lateral load versus displacement relationship of specimen BW2-RR under 300

kN vertical load is provided in Figure 3.9. Compared to previous specimen, load

deformation hysteresis cycles in specimen BW2-RR became fuller and no pinching effect

was observed. However, lateral load capacity stayed under the previous specimen BW1-

C’s lateral load capacity due to low quality of repairing workmanship.

Figures 3.9. Lateral load versus top displacement for specimen BW2-RR.

Lateral force versus shear displacement relationship for BW2-RR is presented in

Figures 3.10 and 3.11.

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From Figure 3.10, symmetric lateral force-shear displacement curves were obtained

which was a result of free movement of the specimen in push and pull cycles. For the pull

cycle case, it was observed that maximum diagonal displacement values tended to be closeto vertical axis whereas they were away from vertical axis in the push cycles. That could

be related with the existing un-repaired deformations on the wall which could alter the

behavior of the specimen in push and pull cycles. Furthermore, distance of the maximum

values from vertical axis is relatively larger than the ones in BW1-C. That could be related

with the excessive deformation occurred on this specimen.

-30 -20 -10 0 10 20 30-150

-100

-50

0

50

100

150


Lateral Force [kN]

Shear 2Shear 1

Figure 3.10. Lateral force-shear displacement relationship for BW2-RR (DG1-2).

-30 -20 -10 0 10 20 30-150

-100

-50

0

50

100

150


Lateral Force [kN]

Shear 4

Shear 3

Figure 3.11. Lateral force-shear displacement relationship for BW2-RR (DG3-4).

Crack patterns and load history are provided in Table A.5 at Section A.2.

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3.2.4. Specimen BW3-R1

BW3-R1 is the first retrofitted specimen. The same test procedure was applied as

before. The variation of maximum lateral load and the target displacement cycle for each

incremental vertical load case are given in Table 3.3.


BW3-R1.

VerticalLoad [kN] Max. Lateral

Load [kN]



50 40.26 4.0943 0.20

100 47.49 3.1165 0.15

150 63.90 3.9578 0.20

200 78.18 5.0151 0.25

250

93.67

6.1320

0.30

In 300 kN vertical load set, at 0.30% drift level, rocking mechanism was observed at

the toe sections of the specimen. At 0.50% drift level maximum lateral load capacity was

reached to 119.32 kN. At this level, shear cracks started to propagate whereas crushing at

the toe sections tended to increase. At proceeding drift levels, lateral load capacity started

to decrease. At 1.50 % drift level the cyclic loading set was ended at which crushing and

shear cracks reached up their maximum. In addition, rocking started under 67.62 kN of

lateral force at 0.10% drift level.

However, in this test, it was realized that the CFRP strings was de-bonded just before

lateral load capacity was reached at its maximum drift level of 0.50% in push direction

(Figure 3.12). Since there were no signs of de-bonding on the lateral load vs. displacement

diagram before that level, this failure couldn’t be predicted. De-bonding of CFRP strings

was highly due to low bonding of the strings with mortar and bricks. A stronger epoxy

resin that would maintain the desired bonding should have been used. Alternatively, strings

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should have been located without any overlapping from the corners of the specimen as it

would be at a continuous wall.

Figure 3.12. Shear cracks, crushing at the toes of BW3-R1, and de-bonding of strings.

Figure 3.13. Lateral load versus top displacement for Specimen BW3-R1.

The lateral load versus displacement relationship of specimen BW3-R1 under 300

kN vertical load is provided in Figure 3.13. Compared to BW1-C control specimen, up to

10 mm displacement, the load deformation hysteresis cycles exhibited a rigid behavior.

However, after the de-bonding of CFRP strings at 0.50 % drift level, with increase in shear

cracks and crushing at toe sections, pinching effect was observed at load deformation

hysteresis cycles.

According to Figures 3.14 and 3.15, similar lateral force versus shear displacement

relationship was obtained from both DG1-2 and DG3-4. In Figure 3.14, it could be seen

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The variation of maximum lateral load and the target displacement cycle for each

incremental vertical load case are given in Table 3.4.


for BW4-R2.

VerticalLoad [kN]

Max. LateralLoad [kN]



50 25.90 4.5122 0.25

100 42.62 5.0979 0.25

150 48.68 4.1052 0.20

200 68.78 5.2647 0.25

250 72.64 5.5787 0.30

The first horizontal cracks due to rocking mechanism were observed at 0.30% drift

level under 50 kN vertical load set. Similarly, first crushing cracks at toe sections wereexamined again in this vertical set at 0.075% drift level. However, this crack was

developed due to stress concentration around the screw that was attached to the specimen

for holding at that section. Therefore, the type of this crack was differed from other crush

cracks that had been observed in previous specimens.

In 300 kN vertical load set, maximum lateral load capacity was reached at 0.60%

drift level which was 90.16 kN at push. First local diagonal hair line cracks were

developed at 0.15% drift level. Moreover, diagonal shear cracks at upper-sides of BW4-R2

were examined at 0.60% drift level. Furthermore, rupture of CFRP strings at the bottom

line was observed at that drift level which was followed by a sudden decrease in lateral

load capacity. Crushing at toe sections on the right from front of BW4-R2 was observed

after the rupture of CFRP strings. In addition, out-of-plane deformation was recorded

towards to the surface where the ruptured CFRP strings were located.

The test was ended at 0.75% drift level due to the decrease in the lateral load

capacity (Figures 3.16 and 3.17).

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During the experiment, it was observed th at rocking mechanism didn’t prevailamong other failure modes for low levels of lateral displacement.

Figure 3.16. Shear cracks, crushing at the toes of BW4-R2, and rupture of strings.

Figure 3.17. Rupture of strings and location of strings.

Figure 3.18. Lateral load versus top displacement for specimen BW4-R2.

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The lateral load versus displacement relationship of specimen BW4-R2 under 300

kN vertical load is provided in Figure 3.18. Compared to BW1-C and BW3-R1 specimens,

the load deformation hysteresis cycles became fat and specimen exhibited a rigid behavior.Stiffness and strength degradation could be clearly observed at 13.93 mm that corresponds

to rupture of CFRP strings.

In contrast to previous specimens, BW4-R2 remained its integrity in terms of

deformation. But, the maximum lateral load capacity in this specimen couldn’t overwhelmthe others. That could be explained by the difference in batches which specimens had been

prepared (BW0, BW1-C, BW3-R1 were constructed in the first batch and BW4-R2 prepared in the second batch).

-30 -20 -10 0 10 20 30-150

-100

-50

0

50

100

150


Lateral Force [kN]

Shear 2

Shear 1

Figure 3.19. Lateral force-shear displacement relationship for BW4-R2 (DG1-2).

-30 -20 -10 0 10 20 30-150

-100

-50

0

50

100

150


Lateral Force [kN]

Shear 4

Shear 3

Figure 3.20. Lateral force-shear displacement relationship for BW4-R2 (DG3-4).

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In Figures 3.19 and 3.20, it was observed that shear deformations were recorded

mostly in compression zone for push and pull cycles in contrast to control specimen. This

could be explained by the contribution of CFRP strings in restricting the movementtowards tension zone. In addition, it could be stated that restricted movement at tension

zone resulted in diagonal compression.

Crack patterns and load history are provided in Table A.13 at Section A.4.

3.3. Analysis of Test Results

In this section, analysis of test results will be provided. Normalized lateral load

versus drift level envelopes, lateral force-shear deformation, and moment-base rotation

relationships of the wall specimens will be presented. In addition, lateral load versus drift

level backbone curve, energy dissipation and change in rigidity graphs for all specimens

will be compared.

3.3.1. Normalized Lateral Load versus Drift Level Relationship

Normalized lateral load versus drift level graphs are provided for each specimen in

Figures 3.21 to 3.24. Hysteresis loops that stayed under 80% of the maximum lateral load

value at both push and pull cycle regions were neglected.

From Figure 3.21, it could be observed that yielding of specimen BW1-C started

after 0.25% drift level which corresponded to 85% of the maximum lateral load capacity.

Yielding plateau continued up to 1.00% drift level where lateral load capacity started to

decrease. At 1.25% drift level, lateral load capacity decreased up to 80% of the maximum

value. Furthermore, slope of the curves drastically decreases after 0.50% drift level which

resulted decrease in rigidity.

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Figure 3.21. Normalized lateral load vs. drift level for BW1-C.

Figure 3.22. Normalized lateral load vs. drift level for BW2-RR.

In BW2-RR, increase in lateral load capacity continued linearly up to 0.60% drift

level where yielding started to be observed after this point (Figure 3.22). Maximum lateral

load capacity was reached at 0.75% drift level. After this drift level, load capacity startedto decrease. The behavior of BW2-RR could be defined as rigid by taking small change in

the slope of the load – drift level curves into account. In other terms, loss in rigidity was

controlled in BW2-RR.

From Figure 3.23, yielding of BW3-R1 could be seen at 0.30% drift level where the

slope of load-drift level curves started to decrease slightly. In addition, 90% of maximum

load capacity was reached at that drift level. At 0.50% drift level, maximum load capacity

was reached. Prior to that level; de-bonding of CFRP strings had been recorded. After that

level, decrease in slope of the load-drift level curves was increased. At 1.00% drift level,

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85% of the maximum load capacity was recorded. 80% of the maximum load capacity was

observed at 1.25% drift level where the test was stopped.

Figure 3.23. Normalized lateral load vs. drift level for BW3-R1.

Figure 3.24. Normalized lateral load vs. drift level for BW4-R2.

In Figure 3.24, linear increase in lateral load capacity was observed up to 0.25% drift

level. After this level of drift, slope of load-drift level curves started to change slightly.

Increase in lateral load capacity continued up to 0.60% drift level where maximum load

capacity was reached. A sudden decrease in lateral load capacity was recorded which was

initiated with the rupture of the CFRP strings at that drift level. According to Figure 3.37.,

it could be stated that BW4-R2 exhibited a rigid behavior in general.

Backbone curves for lateral load versus displacement curves for all specimens are

given in Figure 3.25.

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Figure 3.25. Backbone curves of all specimens for normalized lateral load-drift

relationship.

As it is seen from Figure 3.25, a smooth S-shape could be observed from backbone

curves for BW1-C, BW3-R1, and BW4-R2 whereas curve for BW2-RR is almost linear

with smaller slope. In addition, BW1-C, BW3-R1, and BW4-R2 showed similar behavior

in terms of normalized lateral force versus top displacement relationship.

3.3.2. Vertical Load versus Lateral Load Relationship

Results from incremental vertical load sets were analyzed to show effect of increased

vertical load in lateral load capacity.

As it had been expected, the lateral load capacities of all specimens were increased

with increasing vertical load. Comparison of all four specimens was provided in Figure

3.26.

In Figure 3.26, it is clearly seen that, there is a linear relationship between lateral load

capacity and the vertical load for all specimens. Here, lateral load capacity refers to the

recorded lateral load at yield point in each vertical load set explained in Chapter 2. In

addition, it could be stated that, BW1-C and BW3-R1, which were constructed in the same

batch, exhibited nearly same behavior in terms of lateral load capacity under incremental

vertical loading sets. Moreover, the fourth specimen, BW4-R2, showed relatively lower

capacity compared to BW1-C and BW3-R1.

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Figure 3.26. Comparison of vertical load vs. lateral load relationship for all

specimens.

According to compression tests on clay bricks, an average compressive strength of

12.9 MPa was taken as reference for this study (Rad, 1978). By assuming a square cross

section for a unit brick wall (190mm x 190mm), an ultimate vertical load capacity of 465

kN was found for the specimens. Thus, it could be stated that, up to 65% of ultimate

vertical load capacity increase, lateral load capacity increases linearly.

3.3.3. Moment-Base Rotation Relationship

Six LVDT’s were instrumented on both sides of the specimens for measuringdisplacements due to rocking mechanism. These LVDT’s could be grouped into threelevels which each level could refer to three distinct plane of base rotation due to rocking

mechanism. Rotation calculation for each rotation level can be done using Equation 3.1

according to Figure 3.27.

Li Ri

Li Ri

Li Ri

width width

= tan' tan'

i

h h

L L

(3.1)

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h L1

h L2

h L3

h R1

h R2

h R3

ε Li

ε Ri

L width

γ

Figure 3.27. Vertical displacement readings and base rotation measurement.

Sub-indices i in Equation 3.1 refers to the number of the level of base rotation

described previously. Δ is the displacement measured from corresponding LVDT wheresub-indices R and L are representing the position of LV DT’s (right or left). Similarly,h is

the initial length of corresponding LVDT located on the right or left side of the specimens.

ε is the calculated strain value for each base rotation level. Moment was calculated with

respect to the toe section of the specimens. The moment-base rotation relationships for all

specimens are presented in Figures 3.28 to 3.39.

Figure 3.28. Moment-base rotation relationship for BW1-C at first level.

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Figure 3.29. Moment-base rotation relationship for BW1-C at second level.

Figure 3.30. Moment-base rotation relationship for BW1-C at third level.

From Figures 3.28 to 3.30, base rotations were observed for both push and pull

cycles at all levels in BW1-C. However, rotations were remained in -0.9 x 10 -4 and 0.3 x

10 -4 radians which could be classified as small rotations. Shifts in moment-base rotation

curves indicate a permanent deformation due to rotations which are induced by rocking

mechanism. At maximum moment level (239.0 kN.m both in push and pull cycles), base

rotations of -0.12 x10 -4, -0,23 x10 -4, and 0.04 x10 -4 radians were obtained in first, second

and third levels respectively in pull cycles. For the push cycles, at maximum moment level,

base rotations were calculated as -0.07 x10 -4, 0.03 x10 -4, and 0.26 x10 -4 radians in first,

second and third levels respectively.

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Figure 3.31. Moment-base rotation relationship for BW2-RR at first level.

Figure 3.32. Moment-base rotation relationship for BW2-RR at second level.

Figure 3.33. Moment-base rotation relationship for BW2-RR at third level.

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From Figures 3.31 to 3.33, rotations in the limits of -0.3 x 10 -4 and 0.0 radians were

obtained in BW2-RR. In addition, compared to other two levels, rotations, and hence

deformations, in the third level were relatively higher, which pointed out rockingmechanism at that level. In push cycles, base rotations of -0.05 x 10 -4, -0.06 x 10 -4, and -

0.13 x 10 -4 radians were obtained in first, second, and third levels respectively at maximum

moment. For the pull cycle case, rotations were calculated as -0.06 x 10 -4, -0.07 x 10 -4, and

-0.13 x 10 -4 radians in first, second, and third level respectively.

Figure 3.34. Moment-base rotation relationship for BW3-R1 at first level.

Figure 3.35. Moment-base rotation relationship for BW3-R1 at second level.

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Figure 3.36. Moment-base rotation relationship for BW3-R1 at third level.

In BW3-R1, from Figures 3.34 to 3.36, rotations were remained in the limits of -0.2

x 10 -4 and 0.2 x 10 -4 radians. Compared to control specimen, no significant difference in

rotations was observed in all levels for BW3-R1. In push cycles, -0.05 x 10 -4, 0.13 x 10 -4,

and -0.02 x 10 -4 radians of rotations were obtained in first, second, and third levels.

Similarly, in pull cycles, -0.05 x 10 -4, 0.06 x 10 -4, and 0.02 x 10 -4 radians of rotations were

calculated under maximum moment in first, second, and third levels respectively.

Figure 3.37. Moment-base rotation relationship for BW4-R2 at first level.

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Figure 3.38. Moment-base rotation relationship for BW4-R2 at second level.

Figure 3.39. Moment-base rotation relationship for BW4-R2 at third level.

In BW4-R2, from Figures 3.37 to 3.39, rotations were predominantly remained in the

limits of -0.2 x 10 -4 and 0.2 x 10 -4 radians. In the second level, base rotations were

relatively smaller than the ones in first and third levels. Under maximum moment, -0.13 x

10 -4, 0.08 x 10 -4, and -0.17 x 10 -4 radians of rotations were calculated in first, second, and

third levels respectively at push cycles. Similarly, in pull cycles, -0.11 x 10 -4, -0.08 x 10 -4,

and 0.01 x 10 -4 radians of rotations were obtained in first, second, and third levels

respectively under the maximum moment. Compared to control specimen, shifts in base

rotations were controlled and minimized in all levels for BW4-R2.

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3.3.4. Lateral Force-Shear Deformation Relationship

As it was indicated in section 2.2.3., four diagonal LVDT’s were located forrecording diagonal displacements. The readings from these LVDT’s could be used incalculations for shear deformations by using Equation 3.2 with reference to Figure 3.40.

D2

D1

Y

Y

θ

Defromed Shape

Undefromed Shape

Figure 3.40. Shear deformation measurement.

2 2 2 21 2 = tan'

2

D Y D Y

Y

(3.2)

D1 and D2 refers to the deformed length of diagonal LVDT’s.

According to Equation 3.2, two types of deformation angles for each specimen were

calculated: Shear deformation angle of wall panel that obtained from readings of diagonal

LVDTs on the specimen (DG1-2), and deformation which was calculated by using

readings from diagonal LVDTs on reinforced concrete beam and foundation (DG3-4).

Lateral force versus shear deformation relationships are presented in Figures 3.41 to 3.48.

From Figure 3.41, it could be seen that, -2.00 x 10 -3 and 2.25 x 10 -3 radians of shear

deformations in push and pull cycles respectively was observed at 110 kN lateral force

level. This level of lateral force was obtained around 0.25% drift level (Figure 3.5). After

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Figure 3.43. Lateral force-shear deformation relationship for BW2-RR (DG1-2).

Figure 3.44. Lateral force-shear deformation relationship for BW2-RR (DG3-4).

In Figure 3.45, shear deformation values stayed between -1.00 x 10 -3 and 1.80 x10 -3

radians until 116 kN lateral force level. After that level, which corresponded to 0.30% drift

level according to Figure 3.20, shear deformation angle started to increase and shifts in

lateral force-shear deformation curves were observed. Similar to previous tests, shear

deformations calculated for the reinforced concrete members found to be close to the ones

for wall panel (Figure 3.46). A maximum shear deformation of 0.01 radians was recorded

at the final pull cycle (Figure 3.45).

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Figure 3.45. Lateral force-shear deformation relationship for BW3-R1 (DG1-2).


In Figures 3.47 and 3.48, it was seen that up to a lateral force of 90 kN, shear

deformation angles remained between -1.00 x 10 -3 and 2.85 x 10 -3 radians in push and pull

cycles respectively. After that level, shear deformations started to increase. At 85 kN

lateral force level, shear deformations were observed around -4.00 x 10 -3 radians which

were followed by sudden increase in shear deformation angles. This increase could be

explained by the rupture of FRP strings which occurred at 0.60% drift level under 90.16

kN lateral force (Figure 3.18). After the rupture of FRP strings, maximum shear

deformation of -6.95 x 10 -3 radians was reached.

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Figure 3.47. Lateral force-shear deformation relationship for SP4- R2 (DG1-2).


Figure 3.49. Comparison of normalized lateral force-shear deformation backbone

curves.

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In general, it could be summarized that maximum shear deformation of wall panels

stayed within the range of -0.01 and 0.01 radians which could be classified as small shear

deformations. Comparison of normalized lateral force-shear deformation relationship backbone curves is provided in Figure 3.49. From Figure 3.49, in push cycles, at 80% of

the maximum lateral force level, BW1-C and BW4-R2 have almost zero shear deformation

whereas -1.5 x 10 -3 radians of shear deformation was reached for BW3-R1 at the same

level. Especially at the push direction and at the pull direction in general, compared to

control specimen, lower shear deformations were observed in retrofitted specimens for the

same lateral force level.

3.3.5. Rigidity – Drift Level Relationship

Rigidity of the specimens could be calculated from the slope of lateral force versus

displacement and drift level curves in the elastic region which are presented in Section 3.2.

A representative sketch for definition of rigidity is given in Figure 3.50. Rigidity

calculations were performed until the lateral load capacity of the specimens decreased

down to 80% of the maximum value.

Figure 3.50. Stiffness and energy calculations.

Change in rigidity with increasing drift level for all specimens is presented from

Figures 3.51 to 3.54.

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Figure 3.54. Rigidity-drift level relationship for BW4-R2.

Comparison of rigidity versus drift level and displacement relationship is provided in

Figure 3.55.

Figure 3.55. Superposed rigidity-drift level relationship for all specimens.

It is observed that BW2-RR has the lowest rigidity among other specimens. This

could be explained by poor repairing workmanship and existence of unrepaired cracks on

the specimen. On the other hand, there is no significant difference between BW3-R1,

BW4-R2 and control specimen BW1-C in terms of rigidity versus drift level and

displacement relationship.

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3.3.6. Energy Dissipation – Drift Level Relationship

Cumulative dissipated energy could be defined as the total area under the hysteresis

loops in lateral force and displacement response as it is illustrated in Figure 3.50.

Accordingly, the hysteresis loops in lateral force and displacement response are discretized

and the area under each loop is calculated. From Figure 3.56 to Figure 3.59, cumulative

energy dissipation versus displacement and drift level response is provided. In the analysis,

calculations were performed until the lateral load capacity decreases down to 80% of the

maximum recorded value. Therefore, ultimate cumulative energy dissipation levels vary

for all specimens due to varying number of cycles that remained within specified the

limits.

It is observed from Figure 3. 56 that, up to 0.50% drift level, 3,291 kN·mm energywas dissipated. Cumulative energy dissipation reached to 16,000 kN·mm at the final driftlevel.

Figure 3.56. Cumulative energy dissipation-drift level relationship for BW1-C.

From Figure 3.57, a cumulative energy of 2,339 kN·mm up to 0.50% drift level was

recorded. Compared to control specimen, cumulative energy dissipation was decreased by

a factor of 0.72 at this drift level. At the final drift level, 8,41 9 kN·mm cumulative energylevel was reached.

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Figure 3.57. Cumulative energy dissipation-drift level relationship for BW2-RR.

From Figure 3.58, up to 0.50% drift level, 4,455 kN·mm cumulative energydissipation was reached. Compared to control specimen, cumulative energy dissipation was

increased by a factor of 1.36 at this drift level. At the final drift level, 12,462 kN·mmenergy was recorded.

Figure 3.58. Cumulative energy dissipation-drift level relationship for BW3-R1.

For specimen BW4-R2, it c ould be stated that, 5,498 kN·mm cumulative energy wasdissipated up to 0.50% drift level (Figure 3.59). Compared to control specimen, cumulative

energy dissipation was increased by a factor of 1.68 at this drift level. However, ultimate

cumulative dissipa ted energy was recorded as 7,206 kN·mm at the final drift.

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Figure 3.59. Cumulative energy dissipation-drift level relationship for BW4-R2.

In Figure 3.60, comparison of energy dissipation response of all specimens is

provided.

Figure 3.60. Comparison of all specimens for cumulative energy dissipation.

Up to 0.60% drift level, the maximum cumulative energy was dissipated by BW4-

R2. Similarly, BW3-R1 also exhibited better performance compared to BW1-C and BW2-

RR in the same region. After 0.60% drift level, due to the rupture of FRP strings and

decrease in lateral load capacity of BW4-R2 down to 80% of the maximum recorded value,

comparison of cumulative energy dissipation is not available for this specimen. Although

FRP strings on BW3-R1 were de-bonded at 0.50% drift level, cumulative energy

dissipation was larger than BW1-C. BW2-RR showed the poorest performance in energydissipation.

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Normalized energy was simply evaluated by taking the ratio between the area of each

force-displacement curve and the area of the rectangle that enclosed the maximum

boundaries of the corresponding cycle (Figure 3.50). In addition, same ratio for cumulativeenergy dissipation was also evaluated. Accordingly, loop-wise and cumulative normalized

energy dissipation ratio versus displacement and drift level relationship of all specimens is

compared.

Figure 3.61. Loop-wise normalized energy dissipation ratio vs. drift level

relationship.

Figure 3.62. Cumulative normalized energy dissipation ratio vs. drift level

relationship.

From Figures 3.61 and 3.62, it was observed that retrofitted specimens BW3-R1 andBW4-R2 performed better in terms of energy dissipation at each loading cycle.

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4. CONCLUSIONS AND RECOMMENDATIONS

4.1. Summary

This study investigated use of CFRP strings in the joints of unreinforced masonry

brick walls in historic structures as a near surface retrofitting technique which would

preserve the historic and architectural features of the structures. An experimental study was

carried out on four nearly real-scaled unreinforced masonry brick walls subjected to cyclic

lateral loads at Structural Engineering Laboratory of Boğazici University. The effect of proposed strengthening technique on seismic behavior and lateral load capacity of the

specimens was evaluated. In addition, effect of vertical load on lateral load capacity was

examined.

4.2. Conclusions

The main objectives of the research were to improve seismic behavior of

unreinforced masonry brick walls while preservation of historic and aesthetic features of

the structures are maintained. The following conclusions could be derived from the results

and analysis of the experimental study.

Pinching effect in the lateral force versus top displacement relationship was

eliminated in the last retrofitted specimen BW4-R2, which provided larger

dissipation of energy under cyclic loading.

Cumulative energy dissipation was increased in the retrofitted specimens compared

to control specimen by a factor of 1.68, and 1.36 for BW4-R2 and BW3-R1,

respectively, at 0.50 drift level. This factor was found to be 0.72 for the repaired

specimen BW2-RR. However, loop-wise and cumulative normalized energy

dissipation curves showed that, BW2-RR performed better in dissipating the

encountered energy compared to BW1-C.

Compared to control specimen, crack propagation and deformation resistance were

enhanced in the last retrofitted specimen. Diagonal displacements were restrained

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which compelled compressive reaction at the retrofitted specimen. In other terms,

confinement effect was provided by CFRP strings. Rupture of CFRP strings proved

that excessive tension was encountered by the proposed technique. In addition,crushing at toe sections were controlled due to the confinement effect of CFRP

strings.

Rotations were minimized by the proposed technique which also means rocking

mechanism was also controlled.

No significant difference in rigidity of retrofitted specimens was observed compared

to control specimen. Due to poor repairing workmanship, BW2-RR had the lowest

rigidity value at each drift level compared to other specimens. Due to the aspect ratio, failure modes of rocking, diagonal cracking (shear failure)

and toe crushing were simultaneously observed in all specimens except the last

retrofitted specimen, BW4-R2. In addition, rocking mechanism prevailed among the

other failure mechanisms in control and first retrofitted specimens.

Effect of vertical load on the lateral load capacity was verified by tests carried out

under incremental vertical load sets. It was proved that, increase in vertical load up to

65% of its ultimate, increased the lateral load capacity of all specimens. According to Eq (1.1), maximum rocking strength of the specimens was estimated as

139.20 kN. In all specimens, maximum lateral load capacity stayed below this value.

Therefore, by taking the deformation patterns and estimated rocking force into

account, it could be stated that failure mode of the specimens were not pure rocking.

No significant increase in lateral load capacity due to proposed technique was

obtained.

Due to de-bonding of CFRP strings in BW3-R1, a solid comparison with controlspecimen couldn’t be done in terms of lateral load capacity and rotation.

As it was aimed, application of the proposed technique didn’t damage the existingwall specimens in aesthetical and functionality point of view.

4.3. Recommendations

In this study, single orientation of CFRP strings was examined in one typology and

one aspect ratio of brick walls. Further experimental research with different

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orientations of CFRP strings in varying formations and aspect ratios of specimens is

needed. In addition, for solid verification of improvements due to proposed

technique, number of the tested specimen should increase. Use of CFRP strings in the middle section of the wall could provide better

confinement at that part of the specimens. Besides, use of vertical CFRP strings in

both sides of the wall could prevent rocking mechanism in retrofitted specimens

significantly.

Density of CFRP strings used in the brick wall specimens is another parameter that

would affect seismic behavior of the specimens. Therefore, this parameter should

also be investigated in further studies. All specimens should be built in the same batch if it is possible. If several batches

required for the construction phase, at least one control specimen should be prepared

for each batch.

In order to avoid de-bonding and thus increase the confinement effect, moderate

strength of mortar instead of Horasan mortar or high strength epoxy on CFRP strings

could be used in specimens for further studies.

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APPENDIX A: CRACK PATTERNS

A.1. Specimen BW1-C

Table A.1. Observations of specimen BW1-C.

DriftLevel

[%]

Observations (Vertical Load: 300 kN) Crack Pattern

0.035

Max. lateral load: (+) 23.57 kN (Push)

(-) 26.89 kN (Pull)

No additional cracks were observed.

0.050


(-) 31.70 kN (Pull)


0.075


(-) 40.44 kN (Pull)

Hairline cracks on mortar due to shear was

observed locally.

0.100


(-) 52.56 kN (Pull)

Local small hairline cracks were observed

both on brick and mortar.

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Table A.2. Observations of specimen BW1-C (cont.).

DriftLevel[%]


0.150


(-) 68.66 kN (Pull)

Additional local hairline cracks were

observed both on brick and mortar.

0.200


(-) 80.39 kN (Pull)

Horizontal cracks started to get longer at toe

sections.

0.250


(-) 89.31 kN (Pull)

New diagonal cracks started to propagate

parallel to old ones at corner sections.

Besides, rocking mechanism started at toe

sections.

0.300


(-) 96.53 kN (Pull)

Rocking mechanism continued. Diagonal

cracks got wider and longer.

0.400


(-) 103.49 kN (Pull)

Vertical cracks and crushing of toe sections

were observed. In addition, diagonal cracks

at lower part of the wall started to get longer

to the upper direction by following themortar-brick joints.

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Table A.3. Observations of specimen BW1-C (cont.).

DriftLevel[%]


0.500


(-) 109.42 kN (Pull)

Diagonal cracks at upper right part of the

wall at front got longer and wider. Rocking

mechanism continued.

0.600


(-) 113.77 kN (Pull)

Diagonal cracks got longer. Upper-right part

of the wall from front started to separate

0.750


(-) 116.73 kN (Pull)

Crushing at toe sections started to get

severe.

Diagonal cracks got longer and wider.

1.000


(-) 115.04 kN (Pull)

Diagonal cracks tended to unit at the middle

of the wall. Crushing at the toe sections

increased significantly.

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A.2. Specimen BW2-RR

Table A.5. Observations of specimen BW2-RR.

DriftLevel[%]


0.035


(-) 29.04 kN (Pull)

After repairing, there were cracks thatcouldn’t be repaired from the previous test.


0.050


(-) 30.20 kN (Pull)


0.075


(-) 32.44 kN (Pull)

Horizontal cracks were observed at middle

– left and right side of the wall from front

due to rocking.

0.100


(-) 35.60 kN (Pull)

Diagonal shear cracks (CR1) started to form

at upper left side of the wall from front.

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Table A.6. Observations of specimen BW2-RR (cont.).

DriftLevel[%]


0.150


(-) 42.25 kN (Pull)

Vertical crack started to propagate from the

previously damaged section at upper-right

of the wall from front.

0.200


(-) 47.65 kN (Pull)

Vertical cracks at middle section started to

form. Diagonal cracks at upper-left got

longer.

0.250


(-) 57.03 kN (Pull)

Horizontal cracks at rocking sections got

longer. Additional diagonal cracks started to

form at middle section of the wall.

0.300


(-) 65.48 kN (Pull)

Diagonal cracks started to propagate at

lower-right part of the wall from front.

0.400


(-) 72.61 kN (Pull)

Additional vertical and horizontal cracks

were observed at the middle section of the

wall. Diagonal cracks continued to elongate.

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DriftLevel[%]


0.500


(-) 80.55 kN (Pull)

Additional diagonal cracks formed at upper

and lower right side of the wall from front.

Second line of horizontal cracks started to

propagate at lower left side under the first

horizontal crack.

0.600


(-) 83.38 kN (Pull)

Diagonal cracks united the diagonal cracks

at middle - left section. Diagonal cracks at

lower sides started to form. Horizontalcrack on the mortar surface was observed at

middle section.

0.750


(-) 86.45 kN (Pull)

Crushing at lower left side from front got

severe. In addition, crushing with diagonal

cracks at middle section was also observed.

Diagonal cracks at upper part of the wall

from front got wider and longer.

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DriftLevel[%]


1.000


(-) 83.05 kN (Pull)

Toe section at left side from front totally

crushed. Diagonal cracks propagated from

upper corners were united at the middle

section of the wall. Horizontal cracks at

mortar joints got deeper which resulted in

FRP strings to be seen on the surface.

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Table A.10. Observations of specimen BW3-R1 (cont.).

DriftLevel[%]


0.200


(-) 93.98 kN (Pull)

CR2: Vertical crack at middle section of the

wall was observed.

0.250


(-) 100.97 kN (Pull)

CR3 & CR4: Vertical cracks parallel to

CR2 were propagated at middle section of

the wall.

0.300


(-) 104.42 kN (Pull) CR5: Diagonal shear crack was formed at

upper-left of the wall from front.

0.400


(-) 111.47 kN (Pull)

CR6: Horizontal cracks at mortar joints at

corners of the lower section of the wall were

formed due to rocking. CR5 started to

propagate towards to upper corner of the

wall at left side from front.

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DriftLevel[%]


0.500


(-) 113.96 kN (Pull)

CR6: Horizontal cracks got longer. CR5

started to propagate towards to middle

section of the wall from front. CR7 & CR8:

Diagonal shear crack was formed at upper-

right section of the wall. De-bonding of

FRP strings observed in this drift level

0.600


(-) 112.17 kN (Pull)

CR7 & CR8 & CR4 started to get wider and

longer. CR9 was formed diagonally parallelto CR8. CR10 propagated from lower-right

side of the wall from front.

0.750


(-) 108.28 kN (Pull)

Crushing started to be observed at toe

sections of the wall. CR8 was continued to

get larger towards to middle section of the

wall. Additional vertical cracks occurred at

middle section.

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DriftLevel[%]


1.000


(-) 99.31 kN (Pull)

Crushing at toes section increased. Diagonal

cracks were united with vertical cracks at

middle sections. Diagonal cracks at lower

corners of the wall got longer and wider.

1.250


(-) 81.29 kN (Pull)

Lower – right section of the wall was totally

crushed. Diagonal cracks at lower sections

united with the vertical cracks at middle

section. Remarkable X shaped crack wasobserved.

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A.4. Specimen BW4-R2

Table A.13. Observations of specimen BW4-R2.

DriftLevel[%]


0.035


(-) 35.85 kN (Pull)


0.050


(-) 43.65 kN (Pull)


0.075


(-) 50.89 kN (Pull)


0.100


(-) 60.00 kN (Pull)

CR78: Flexural crack at brick

CR79: Flexural crack at brick (Back)

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DriftLevel[%]


0.250


(-) 76.88 kN (Pull)

CR98,101,102,103,109,110,112: Hairline

shear crack at brick.

CR 104,108,113: Flexural crack at brick.

CR 105: Crushing

(Front)

(Back)

0.300


(-) 79.82 kN (Pull)

LVDT’s for top displacement started to bend.

CR14 started to increase in length and in

width.

(Front)

(Back)

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DriftLevel[%]


0.300


(-) 79.82 kN (Pull)

LVDT’s for top displacement started to

bend.

CR14 started to increase in length and in

width.

(Front)

(Back)

0.400


(-) 83.53 kN (Pull)

Out-of-plane deformation started to be

observed. Shear cracks at top-corner

sections (CR14 and CR54 at back face of

the wall) continued to propagate. (Front)

(Back)

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DriftLevel[%]


0.500


(-) 84.33 kN (Pull)

Out-of-plane deformation continued.

Diagonal shear cracks at top sections (CR14

& CR52 at back, CR13,60,82 at front)

spreaded. (Front)

(Back)

0.600


(-) 82.23 kN (Pull)

Diagonal shear cracks and out-of-plane

deformation increased.

Rupture of FRP strings at right – bottom

part from back view of specimen was

observed.

(Front)

(Back)

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DriftLevel[%]


0.750


(-) 77.48 kN (Pull)

Crushing at toe sections got severe.

Out-of-plane deformation reached its

maximum level.

Right toe of the wall at front was relatively

less damaged and remained intact compared

to left toe at front.

Due to safety concerns, test was stopped.

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