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COMMONLY ENCOUNTERED SEISMIC DESIGN FAULTS IN REINFORCED CONCRETE RESIDENTIAL ARCHITECTURE IN TURKEY

A THESIS SUBMITTED TO THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES

OF THE MIDDLE EAST TECHNICAL UNIVERSITY

BY

CENGİZ ÖZMEN

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

IN

THE DEPARTMENT OF ARCHITECTURE

MAY 2002

Approval of the Graduate School of Natural and Applied Sciences.

______________________________

Prof. Dr. Tayfur Öztürk

Director

I certify that this thesis satisfies all the requirements as a thesis for the degree of Master of Science

______________________________

Assoc. Prof. Dr. Selahattin Önür

Head of Department

This is to certify that we have read this thesis and that in our opinion it is fully adequate, in scope and quality, as a thesis for the degree of Master of Science.

______________________________

Assoc. Prof. Dr. Ali İhsan Ünay

Supervisor

Examining Committee Members

Part-time Inst. Dr. Erhan Karaesmen _____________________________

Kayhan Yüceyalçın _____________________________

Inst. Türel Saranlı _____________________________

Part-time Inst. Dr. Coşkun Erkay _____________________________

Assoc. Prof. Dr. Ali İhsan Ünay _____________________________

ABSTRACT

COMMONLY ENCOUNTERED SEISMIC DESIGN FAULTS IN

REINFORCED CONCRETE RESIDENTIAL ARCHITECTURE IN

TURKEY

Özmen, Cengiz

M.S., Department of Architecture

Supervisor: Assoc. Prof. Dr. Ali İhsan Ünay

May 2002, 108 Pages

This thesis is about the architectural design faults, which negatively affect

the structural behavior of reinforced concrete residential buildings during an

earthquake. In Turkey, earthquake resistant design is considered to be under

the responsibility of structural engineers. As a result, architects and

especially students of architecture are not well informed about the effect of

their design decisions on the seismic performance of the buildings. This

thesis will demonstrate that most of the design faults that lead to the

destruction of a building are due to architectural decisions.

iii

This thesis also intends to present the concept of earthquake resistant design

in a comprehensible format for the architects and students of architecture

and therefore aims to contribute to the efforts of creating a better awareness

of earthquake resistant building design.

This thesis begins by explaining the nature of earthquakes and the material

properties of reinforced concrete to create a base of knowledge for the

earthquake resistant design topic. In the fourth chapter, commonly

encountered seismic design faults are explained in a way, which gives

emphasis to the role of the architect. In the fifth chapter, the effects of the

design faults on the seismic performance of the buildings is demonstrated

with the help of computer generated models based on actual collapsed

buildings in İzmit, Bekirpaşa District in 1999 earthquakes.

Keywords: Earthquake Resistant Design, Seismic Design, Seismic Design

Faults, Earthquake Architecture.

iv

ÖZ

TÜRKİYE’DE BETONARME KONUT YAPILARINDA SIKÇA

KARŞILAŞILAN DEPREM TASARIMI HATALARI

Özmen, Cengiz

Yüksek Lisans, Mimarlık Bölümü

Tez Yöneticisi: Assoc. Prof. Dr. Ali İhsan Ünay

Mayıs 2002, 108 sayfa

Bu çalışma, betonarme konut türü yapıların bir deprem sırasındaki strüktürel

davranışlarını olumsuz yönde etkileyen mimari tasarım hatalarını

araştırmaktadır. Türkiye’de depreme dayanıklı yapı tasarımı, inşaat

mühendislerinin sorumluluğu altında görülmektedir, bunun sonucu olarak,

mimarlar ve özellikle mimarlık öğrencileri verdikleri tasarım kararlarının,

tasarladıkları yapıların deprem davranışları üzerindeki etkisi hakkında

yeterli düzeyde bilgi sahibi değillerdir. Bu çalışma, bir binanın yıkılmasına

neden olan hataların çoğunun mimari tasarımdan kaynaklandığını

göstermektedir.

v

Bu çalışma ayrıca depreme dayanıklı yapı tasarımı konusunu mimarların ve

özellikle mimarlık öğrencilerinin anlayabileceği şekilde anlatmaktadır. Bu

sayede halen sürmekte olan, insanları depreme dayanıklı yapı konusunda

bilinçlendrme çalışmalarına bir katkıda bulunmayı hedeflemektedir.

Bu tezde öncelikle depremin genel özellikleri ve betonarmenin malzeme

özellikleri konusunda bilgi verilerek okuyucuda temel bir bilgi birikimi

oluşturmak amaçlanmıştır. Daha sonra sıkça karşılaşılan deprem tasarımı

hataları mimarların sorumlulukları açısından anlatılmıştır. Son olarak İzmit,

Bekirpaşa bölgesinde 1999 depremleri sırasında yıkılan gerçek binalara

dayalı bilgisayar modelleri kullanılarak bu anlatılanların geçerliliği

gösterilmiştir.

Anahtar Kelimeler: Depreme Dayanıklı Tasarım, Sismik Dizayn, Deprem

Tasarımı Hataları, Deprem Mimarlığı.

vi

To My Parents

And

My Grandfather

Kayhan Yüceyalçın

Y. Mühendis Mimar

(Engineer & Architect)

vii

ACKNOWLEDGMENTS

I express heartfelt gratitude to Dr. Erhan Karaesmen for his guidance and

his priceless contribution, which made the field study possible.

I also express sincere appreciation to Dr. Ali İhsan Ünay for his excellent

supervision and insight through the research.

Thanks go to my parents, for their unshakable faith in me, and their

willingness to endure with me the difficulties of my endeavors.

I offer sincere thanks to my grandfather, Kayhan Yüceyalçın, who inspired

me to become an architect.

viii

TABLE OF CONTENTS

ABSTRACT ..................................................................................... iii

ÖZ .................................................................................................... v

ACKNOWLEDGMENTS ................................................................ viii

TABLE OF CONTENTS .................................................................. ix

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

LIST OF FIGURES .......................................................................... xv

LIST OF SYMBOLS ....................................................................... xix

CHAPTER

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

1.1 Subject ........................................................................... 1

1.2 Methodology ................................................................... 5

2. EARTHQUAKE .................................................................. 7

2.1 Definition of the Earthquake Phenomenon .................... 7

2.2 Types of Seismic Faults ................................................. 12

2.3 Types of Earthquakes ..................................................... 13

2.3.1 According to the Depth ...................................... 13

2.3.2 According to the Distance .................................. 13

2.3.3 According to the Magnitude ............................... 14

ix

2.3.4 According to the Origin ..................................... 14

2.4 Earthquake Parameters ................................................... 15

2.4.1 Hypocenter .......................................................... 15

2.4.2 Epicenter ............................................................. 15

2.4.3 Focal Depth ........................................................ 16

2.4.4 Isoseismic Map ................................................... 17

2.5 Types of Seismic Waves ................................................ 18

2.6 Intensity of an Earthquake ............................................... 20

2.7 Magnitude of an Earthquake .......................................... 22

2.8 Earthquake Recording Devices ..................................... 23

2.9 Seismic Characteristics of Turkey ................................... 24

3. EARTHQUAKE BEHAVIOR OF REINFORCED

CONCRETE STRUCTURES .............................................. 26

3.1 Properties of Reinforced Concrete .................................. 26

3.2 Essential Definitions in Earthquake-Building

Interaction ....................................................................... 29

3.2.1 Definition of Earthquake Load ........................... 29

3.2.2 Natural Period of a Building ............................... 31

3.2.3 Absorption of Energy ......................................... 33

3.2.4 Effective Ground Acceleration ........................... 34

3.2.5 Ground Structure Interaction .............................. 36

3.3 Fundamental Concepts in Seismic Design ...................... 38

3.3.1 Strength ............................................................... 39

3.3.2 Ductility ............................................................... 39

x

3.3.3 Rigidity ............................................................... 42

3.4 Seismic Design Criteria in Turkey ................................. 43

4. SEISMIC DESIGN FAULTS IN REINFORCED

CONCRETE BUILDINGS .................................................. 44

4.1 Importance of Seismic Resistance in Architectural

Design ............................................................................. 44

4.2 Seismic Design Faults in Plan ........................................ 47

4.2.1 Torsion Eccentricity ............................................ 47

4.2.2 Floor Discontinuities ........................................... 50

4.2.3 Projections in Plan ............................................. 52

4.2.4 Non-Parallel Axis of Structural Elements ........... 54

4.2.5 Fundamental Concepts About Reinforced

Concrete Beams .................................................. 55

4.2.5.1 Non-Continuous Beams ................................ 55

4.2.5.2 Irregular Spans and Beam Cross-Sections .... 56

4.2.5.3 Beam-to-Beam Connections ......................... 57

4.2.5.4 Beam and Frames with Broken Axis ............. 58

4.2.6 Fundamental Concepts About Reinforced

Concrete Slabs .................................................. 59

4.2.6.1 Over-Stretched One-Way Slab ...................... 59

4.2.6.2 Rules About Joist-Slabs ................................. 60

4.2.6.3 Cantilever Slabs ............................................ 62

4.2.7 Fundamental Concepts About R/C Columns ..... 63

4.2.7.1 Columns with Broken Axis ........................... 63

xi

4.2.7.2 Column-to-Beam Connections ...................... 64

4.2.7.3 Column Configuration .................................. 65

4.2.8 Fundamental Concepts About Reinforced Concrete

Shear-Walls ......................................................... 66

4.2.8.1 Location of Shear-Walls ............................... 66

4.2.8.2 Configuration of Shear-Walls ....................... 67

4.3 Seismic Design Faults in Elevation ................................ 68

4.3.1 Weak Storey (Inter-storey Strength) Irregularity . 68

4.3.2 Soft Storey Irregularity ........................................ 70

4.3.3 Discontinuity of Vertical Structural Members .... 72

4.3.4 Irregular Motion of Buildings ............................. 73

4.3.5 The Pounding Effect ............................................ 75

4.3.6 Irregular Distribution of Masses ......................... 77

4.3.7 Short Columns .................................................... 78

4.3.8 Strong Beam-Weak Column Formation .............. 80

4.3.9 Irregularities in Foundation ................................ 82

5. THE EFFECT OF COMMONLY ENCOUNTERED SEISMIC

DESIGN FAULTS ON THE BUILDING STRUCTURE: A

SAMPLE STUDY CONDUCTED WITH COMPUTER

GENERATED STRUCTURAL MODELS .......................... 83

5.1 The Objective of The Study ............................................ 83

5.2 The Scope and The Procedure ......................................... 84

5.3 Computer Models of Defective Buildings ...................... 86

5.3.1 A Residential Building with Irregular Plan ........ 86

xii

5.3.2 A Building with Deficient Column

Configuration ...................................................... 89

5.3.3 Building Model with Soft Storey Formation ....... 92

5.3.4 Building Model with Short-Column Formation .. 95

5.3.5 Building Model with Weak-Storey Formation .... 97

5.3.6 Building Model with Shear-Wall Eccentricity .... 99

5.4 The Results of the Study ................................................. 101

6. CONCLUSION ..................................................................... 102

BIBLIOGRAPHY ....................................................................... 105

xiii

LIST OF TABLES

TABLE

2.1 Major Earthquakes of the 20th Century ..................................... 8

2.2 Modified Mercalli Scale ............................................................ 20

2.3 Intensity-Magnitude Relationships ............................................ 22

3.1 Effective Ground Acceleration Coefficients for Turkey ............ 35

xiv

LIST OF FIGURES

FIGURE

2.1 The Inner Structure of the Earth ............................................. 9

2.2 Tectonic Plates ........................................................................ 10

2.3 Development of an Earthquake ............................................... 11

2.4 Types of Seismic Faults .......................................................... 12

2.5 Earthquake Parameters ............................................................ 16

2.6 An Example of Isoseismic Map .............................................. 17

2.7 Seismic Waves ........................................................................ 19

2.8 A Simple Seismograph ............................................................ 23

2.9 Seismic Plates Around Turkey ................................................ 24

2.10 Seismic Faults in Turkey ......................................................... 25

3.1 Concrete & Reinforced Concrete ............................................ 27

3.2 Stress-Strain Diagrams of Steel and Plain Concrete ............... 28

3.3 A Typical Earthquake Loading Pattern ................................... 29

3.4 Natural Period .......................................................................... 31

3.5 Modes for a 3-Storey Building ................................................ 32

xv

3.6 Absorption of Energy by Plastic Deformation ......................... 33

3.7 Ground Accelerations for Erzincan 1992 Earthquake .............. 34

3.8 Damages due to the Liquefaction of the Soil in Adapazarı ..... 36

3.9 Stress-Strain Relationship of a RFC Element with Various

Levels of Reinforcement ........................................................... 39

3.10 The Energy Consumption Capacity of Structural Elements ..... 40

3.11 A Comparison Between Elastic and Elasto-Plastic Structures ... 41

3.12 Modes of a High-Rise Building ................................................ 42

3.13 Partial and Total Collapse Examples ........................................ 43

4.1 A Building Collapsed in Marmara 1999 Earthquake ................ 45

4.2 Papa Tongarewa Museum, New Zealand, An Earthquake

Country ...................................................................................... 46

4.3 Torsion Eccentricity .................................................................. 47

4.4 Modifying The Center of Rigidity ............................................ 48

4.5 A Building Damaged due to Torsion Eccentricity .................... 48

4.6 Torsion Eccentricity in Turkish Earthquake Code .................... 49

4.7 Discontinuities in Floor Slab ..................................................... 50

4.8 A2 Type Irregularities According to Turkish Earthquake Code .. 51

4.9 Disadvantages of Projections in Plan ........................................ 52

4.10 A3 Type Irregularity in Turkish Earthquake Code ................... 53

4.11 Improved Building Plans .......................................................... 53

4.12 A4 Type Irregularity in Turkish Earthquake Code ................... 54

4.13 Non-Continuous Beam ............................................................... 55

4.14 Joints between Beams with Different Cross-Sections .............. 56

xvi

4.15 Beams Intersecting without Vertical Support ........................... 57

4.16 Beams and Frames with Broken Axis ....................................... 58

4.17 Over-Stretched One-Way Slab .................................................. 59

4.18 Deflection Damage near Shallow Beams in a Block-Joist Slab ... 60

4.19 Irregular Joist-Slab Directions in a Floor .................................. 61

4.20 Cantilever Slabs ........................................................................ 62

4.21 Columns with Broken-Axis ...................................................... 63

4.22 Column-to-Beam Connections and An Example of Damage due

To Weak Column-to-Beam Connection in Marmara 1999

Earthquake ................................................................................ 64

4.23 Irregular vs. Regular Configuration of Columns ...................... 65

4.24 Location of Shear-Walls ........................................................... 66

4.25 Irregular vs. Regular Configuration of Shear-Walls ................ 67

4.26 Weak Storey ............................................................................. 68

4.27 Earthquake Joints in Partition Walls ........................................ 69

4.28 Soft Storey by Deflection Criterion ......................................... 70

4.29 Collapse Mechanism due to Soft Storey .................................. 71

4.30 Discontinuity of Vertical Members in Earthquake Code ......... 72

4.31 The Effect of Building Shape to Seismic Performance ............. 73

4.32 Seismic Design Improvement for Buildings with Several

Blocks ........................................................................................ 74

4.33 Pounding Effect on Adjacent Buildings .................................... 75

4.34 Pounding in Buildings with Different Floor Levels .................. 76

4.35 Irregular Distribution of Masses and Setbacks .......................... 77

xvii

4.36 Short Column Example, Nicaragua 1972 Earthquake ............... 78

4.37 Types of Short Column Formations ........................................... 79

4.38 Collapse Mechanisms in Various Systems ................................. 81

4.39 Irregular vs. Regular Foundation ................................................ 82

5.1 A Soft Storey Formation in İstanbul .......................................... 85

5.2 Site Plan and Typical Structural Floor Plan ................................ 86

5.3 Perspective Views ....................................................................... 87

5.4 Torsion Diagram ......................................................................... 88

5.5 Site Plan and Typical Structural Floor Plan ............................... 89

5.6 Perspective Views ...................................................................... 90

5.7 Large and Irregular Floor Displacements ................................... 91

5.8 The Structural Floor Plan for Sections 5.3.3/4/5/6 ..................... 92

5.9 Model Building with Soft-Storey ............................................... 93

5.10 Shear Force Diagram .................................................................. 94

5.11 Torsion Diagram ......................................................................... 94

5.12 Model Building with Short-Column ........................................... 95

5.13 Shear-Force Diagram .................................................................. 96

5.14 Torsion Diagram ......................................................................... 96

5.15 Model Building with Weak-Storey ............................................ 97

5.16 Shear-Force Diagram ................................................................. 98

5.17 Torsion Diagram ........................................................................ 98

5.18 Model Building with Shear-Wall Eccentricity .......................... 99

5.19 Shear-Force Diagram ................................................................. 100

5.20 Torsion Diagram ........................................................................ 100

xviii

LIST OF SYMBOLS

A Effective ground acceleration

a Acceleration of the building

Ao Effective ground acceleration coefficient

b Column dimension perpendicular to earthquake direction

F Equivalent earthquake force

fck Characteristic strength of concrete

Fe Chemical symbol for Iron

fyk Characteristic yielding strength of steel

g Acceleration due to Earth’s gravity

h Column dimension parallel to earthquake direction

I Moment of inertia of the column

M Magnitude according to Richter Scale

m Mass of the building

Mg Chemical symbol for Magnesium

O Chemical symbol for Oxygen

Si Chemical symbol for Silica

T Natural period of the building

(∆i)max Maximum storey drift

xix

(∆i)average Average storey drift

ηc Shear irregularity coefficient

η∆i Torsion irregularity factor

ηki Displacement coefficient

ΣAe Effective shear area of a floor

ΣAg Total area of columns in a floor

ΣAk Total area of partition walls without door and window openings in

ΣAw Total area of shear-walls in a floor a floor

xx

CHAPTER I

INTRODUCTION

1.1 Subject

Turkey is located on the Alp-Himalayan Seismic Belt. This is one of the most

active earthquake areas on earth. Nearly 96 % of Turkey is on very risky

seismic zones. Therefore high-magnitude earthquakes commonly occur in this

country. The structures suffer a very high amount of damage during these

seismic activities. Many people are killed in the collapsed buildings. In fact, the

spiritual and material damage is so high that the earthquake phenomenon is

considered as a disaster.

During an earthquake, in a neighborhood, which consists of similar buildings,

some buildings collapse and some buildings remain standing. This indicates

that the undamaged buildings behaved in a special way, which helped them

survive earthquake conditions. In other words, these buildings had a better

1

seismic performance. This performance is affected by several factors. Some of

these factors are:

• The architectural design of the building.

• The quality of structural materials.

• The quality of construction applications.

• The choice of geographical location (Closeness to seismic faults).

• The soil conditions.

• The surrounding building pattern, etc.

Every item above requires the skill of people from different professional

disciplines such as architects, civil engineers, contractors, geological engineers,

city planners, etc. The cooperation of these people is essential to build an

earthquake resistant building. This study concentrates on the responsibilities of

the architects. More specifically, this thesis is about the effect of the

architectural design on the seismic performance of a building.

To determine the role of the architect in the seismic design of a building, one

must understand the difference between an architect and a civil engineer. There

was a time when these two disciplines were one and the same. Roman or

Ottoman architects were responsible for every aspect of the spatial and

structural design of their buildings. In those times architecture was truly a

marriage of science and art. With the modern times, the rapidly increasing

amount of scientific knowledge required specialization, therefore engineering

2

was separated from architecture. Engineers concentrated on the structural issues

while the architects focused on the aesthetical, functional and the philosophical

aspects of building design. Doing so the engineers became the scientists and

architects became more and more the artists. The question about the role and

position of architecture is still an issue today. It is no surprise to see that the

schools of architecture function within the schools of fine arts, the departments

of engineering as well as in the form of independent faculties. This confusion

affects the nature and the content of the architectural education.

The definitions of the architect and the civil engineer by Semih S. Tezcan seem

to be close to today’s common understanding. He suggests that the architect is

the master of art who designs a building, which contains certain functions of

life, by the help of technology and artistic creativity. The aim is to provide a

healthy, comfortable and happy environment for the occupants. On the other

hand, the engineer is the specialist who ensures that the structural system

designed by the architect has the necessary strength, durability, and economy

under the external and internal forces.1 Notice the phrase “structural system

designed by the architect”. This is the key idea for this thesis.

The architect decides on all the major design factors affecting the seismic

performance of a structure, such as the shape of the building, the location of

1 Tezcan, Semih. S. Depreme Dayanıklı Yapı İçin Bir Mimarın Seyir Defteri İstanbul: Turkish Earthquake Foundation Pub., 1998, 1-2.

3

every architectural element, the type of the structural system, the configuration

of the structural elements even the preliminary dimensioning of columns and

beams; therefore, no matter what the civil engineer does, the earthquake

behavior of a building is very much a result of the architect’s decisions.

Due to the complexity of the earthquake phenomenon, the reasons of a collapse

are almost unique for every building. However many buildings have collapsed

in a similar way during the earthquakes. Observation showed that these

buildings shared some design characteristics, which negatively affected their

seismic performance. These characteristics are called seismic design faults.

Some of these faults are very common. This indicates that Turkish architects

have a lack of knowledge about the concept of seismic behavior. The aim of

this thesis is to make a classification of these common design faults and present

them in a comprehensible format for the architects.

The target readers of this thesis are the architects and especially the students of

architecture. The results of the research are presented in a format and language

that will help them develop an intuition about the earthquake behavior of their

designs and avoid making simple faults, which will cause a lot of spiritual and

material damage. This thesis hopes to make a contribution to the development

of a higher level of professional quality in architecture.

4

1.2 Methodology

Earthquake resistant building design is a popular research subject in countries

located on active seismic zones. Turkey, being one of them, has a considerable

collection of up-to-date scientific works and publications on this matter;

furthermore, the architectural design aspect of the issue is also investigated

many times. However, because the earthquake resistance topic is believed to be

in the field of engineering in this country, nearly all of the studies are made by

the civil engineers. Naturally, the related theses, papers and publications are

most of the time too technical for the architects. The architectural design issues

are scattered through engineering books. These factors make it difficult for the

architects, who already feel themselves distant to the subject, to reach the

information they need.

The reasons behind the poor seismic performance of the buildings in Turkey are

several. E. Karaesmen makes a general classification of these factors as

follows:

• The universal lack of knowledge in the sciences related with earthquake

engineering.

• The indifference of the public and some members of the engineering

and architecture community towards the earthquake threat.

5

• The ignorance of geological and geo-technical conditions in the choice

of location for urban settlements in countries with fast and undisciplined

city growth.

• The structural defects in masonry buildings due to the general lack of

understanding of this structural system and poor construction quality.

• The structural defects in R/C buildings, which are built on every scale

and everywhere from the remote villages to large urban settlements.

This thesis concentrates on Reinforced Concrete (R/C)2 buildings because R/C

is the dominant structural system in Turkey. Most of the buildings that have

collapsed during the earthquakes were made of R/C. Furthermore 90 % of the

buildings constructed in Turkey are residential buildings. This is why this study

is about the earthquake behavior of this type of building.

The architects are responsible for every aspect of their design. The architect

acts as the coordinator between the different parties involved in the building

project such as, the engineers, the contractors and the client. This role requires

an optimum awareness of all the factors affecting the seismic performance of a

building; however, this study focuses on the responsibilities of the architect as

the designer. What this thesis searches for, are the design faults that are made

on the drawing table of the architect.

2 From this point on the abbreviation R/C will be used for Reinforced Concrete

6

CHAPTER II

EARTHQUAKE

2.1 Definition of the Earthquake Phenomenon

The earthquake phenomenon influenced human life since the beginning of

history. M. E. Tuna states that the records about earthquakes date back to 2000

B.C. Aristotle (born 384 B.C.) made researches and classifications about

earthquakes. The first earthquake recording device was made in China in 132

A.D. John Hoff published an earthquake catalogue, which includes the entire

world in 1840. Robert Mallet made the first field survey after the 1857 Naples

Earthquake. Palmieri produced a primitive seismograph to record the

earthquakes in Italy. Oldham solved the equation of P and S waves (Section

2.5.) based on the recordings of seismographs.3

3 Tuna, Mehmet Emin, Depreme Dayanıklı Yapı Tasarımı. Ankara: Tuna Eğitim ve Kültür Vakfı Pub. November 2000, 1.

7

Table 2.1 Major Earthquakes of the 20th century4

DATE LOCATION CASUALTIES MAGNITUDE*

04.04.1905 India 19.000 8.6

31.01.1906 Colombia 1000 9

17.08.1906 Chile 20.000 8.6

16.12.1920 China 200.000 8.6

01.02.1923 Japan 143.000 8.3

02.03.1933 Japan 2.990 8.3

30.05.1935 Pakistan 60.000 7.5

26.12.1939 Turkey(Erzincan) 39.000 7.4

31.05.1970 Peru 66.000 7.8

27.07.1976 China 255.000 8.0

19.09.1985 Mexico 9.500 8.1

17.08.1999 Turkey(Marmara) 45.000 7.4

* The magnitudes are in Richter Scale (Section 2.7)

The mechanics of an earthquake are closely related with the inner structure of

the earth. R. Yılmaz and R. Demirtaş describe this structure in the form of three

layers. These are: the crust (Continental Crust: 25-70 km, Oceanic Crust: 5-10

km) at the outer surface, the core at the center and the mantle in-between. The

crust is made of granite and basaltic rocks. The major elements of the mantle

are Fe, Mg, Si and O. The crust rests on the solid layer of the upper mantle,

which is called the Lithosphere. Under the lithosphere there is the relatively

4 Tuna, Mehmet Emin, Depreme Dayanıklı Yapı Tasarımı. Ankara: Tuna Eğitim ve Kültür Vakfı Pub. November 2000, 1.

8

soft layer of the upper mantle. This is the Astenosphere. The composition of

the core is 85 % Fe. The outer core is of liquid nature but the inner core is solid

(Figure 2.1).5

Figure 2.1 The Inner Structure of the Earth6

Yılmaz and Demirtaş further state that the heat currents generated from the

astenosphere cause cracks on the solid layer above. As a result, the lithosphere

is divided to several pieces, which are called tectonic plates (10 major and

several minor plates). The plates aren’t fixed. They travel on the liquid mantle

5 Yılmaz, Rüçhan. and Demirtaş, Ramazan. “Depremler ve Türkiye’nin Depremselliği”, Deprem ve Sonrası. ed. Dr. Erhan Karaesmen, Ankara: Türkiye Müteahhitler Birliği Pub. 1996, 13. 6 Yılmaz and Demirtaş, Deprem ve Sonrası, 13.

9

with a speed of 1-10 cm per year (Fig 2.2). The nature of this movement is very

complex. The plates may travel away from each other; one plate may go under

another one or move side-by-side along their common border. These borders

are called seismic faults. The movements cause stresses and deformations

along the edges of the plates, which affect the geographical formations. The

Himalayas and the Andes came into being as the result of such movements.7

Figure 2.2 Tectonic Plates8

7 Yılmaz, Rüçhan. and Demirtaş, Ramazan. “Depremler ve Türkiye’nin Depremselliği”, Deprem ve Sonrası. ed. Prof. Dr. Erhan Karaesmen, Ankara: Türkiye Müteahhitler Birliği Pub. 1996, 14-15. 8 Bayülke, Nejat. ed. Depremler ve Depreme Dayanıklı Yapılar, Ankara: T.C. İmar ve İskan Bakanlığı Deprem Araştırma Enstitüsü Başkanlığı Pub. 1978, 4.

10

Earthquakes happen due to the movement of the tectonic plates. Tuna states that

the majority of the earthquakes occur in the elastic layer (the first 12 km) of the

crust. Below that, because the temperature is above 400 °C, the energy of the

movements is absorbed by plastic deformations. The displacements add up to

each other through the years. However, due to the friction between the layers of

rock, the plates can’t move. As a result, a huge amount of energy is stored on

the fault lines. When this energy becomes higher than the friction capacity of

the rocks, it is suddenly released with the movement of the plates in a very

short period of time. This release of energy is called the earthquake.9

Figure 2.3 Development of an Earthquake10

9 Tuna, Mehmet Emin, Depreme Dayanıklı Yapı Tasarımı. Ankara: Tuna Eğitim ve Kültür Vakfı Pub. November 2000, 2-6. 10 Saları, Nasrın. Figure 1, “Mimari Form ve Elemanlatın Depreme Dayanıklı Yapı Tasarımına Etkileri” Graduate Thesis, Trabzon: Karadeniz Teknik Üniversitesi Pub, 1999, 7.

11

2.2 Types of Seismic Faults

There are various types of seismic faults regarding the characteristics of the

seismic movement. Yılmaz describe the main types of seismic faults:

• Lateral (Strike-Slip) Faults: In this category, the plates make a

sideways movement with respect to the fault plane.

• Normal (Thrust) Faults: The plate, which is at the top of the fault

plane moves downwards with respect to the other plate.

• Reversed Faults: The plate, which is at the top of the fault plane moves

upwards with respect to the other plate.

It is difficult to see seismic faults, which strictly fall in one of these categories,

in the nature. The movement of most seismic faults is a combination of these

three types.11

Figure 2.4 Types of Seismic Faults12

11 Yılmaz, Rüçhan. and Demirtaş, Ramazan. “Depremler ve Türkiye’nin Depremselliği”, Deprem ve Sonrası. ed. Prof. Dr. Erhan Karaesmen, Ankara: Türkiye Müteahhitler Birliği Pub. 1996, 18-19. 12 Erkoç, Turan. Baran, Belgin. Hamzaçebi, Gülşah. Deprem Nedir?, Ankara: 2000, 3.

12

2.3 Types of Earthquakes

2.3.1 According to the depth

The classification made by Erkoç, Baran and Hamzaçebi separates the

earthquakes into the following groups regarding their various properties. First,

according to the depth of the hypocenter (Section 2.4.1): 13

• Shallow Earthquakes: The focal depth is between 0-70 km.

• Medium-Depth Earthquakes: The focal depth is between 71-300 km.

• Deep Earthquakes: The focal depth is between 301-700 km.

The earthquakes that occur in Turkey are mostly shallow. The focal depth

varies between 0 and 30 km.

2.3.2 According to the Distance

The earthquakes can be classified into four groups according to their distance

from the recording devices:

• Local Earthquake: The distance is less than 100 km.

• Proximity Earthquake: The distance is between 100-1000 km.

• Regional Earthquake: The distance is between 1000-5000 km.

• Distant Earthquake: The distance is more than 5000 km. 13 Erkoç, Turan. Baran, Belgin. Hamzaçebi, Gülşah. Deprem Nedir?, Ankara: 2000, 4-5.

13

2.3.3 According to the Magnitude

The earthquakes can be classified into six groups according to their magnitude

(M) in Richter Scale (Section 2.7):

• Very Strong Earthquake: M > 8.0

• Strong Earthquake : 7.0 < M < 8.0

• Medium Earthquake : 5.0 < M < 7.0

• Small Earthquake : 3.0 < M < 5.0

• Micro Earthquake : 1.0 < M < 3.0

• Ultra-Micro Earthquake: M < 1.0

2.3.4 According to the Origin

The Earthquakes can be classified into the following categories by their origin:

• Tectonic Earthquakes: Due to seismic movements.

• Volcanic Earthquakes: Due to volcanic eruptions.

• Subsidence Earthquakes: Due to the collapse of caves and mines

• Non-natural Earthquakes: e.g. nuclear explosions.

14

2.4 Earthquake Parameters

2.4.1 Hypocenter

People generally observe the surface effects of an earthquake, however as

Bayülke states, earthquakes actually happen in the depths of the earth’s crust.

The hypocenter or the focus of the earthquake is the theoretical point where the

seismic energy is released (Figure 2.5). In fact, the energy is released in an area

rather than a point but such a definition provides some practical advantages in

making calculations and measurements.14

2.4.2 Epicenter

Bayülke further states that the epicenter is the closest point, on the surface of

the earth, to the hypocenter (Figure 2.5). This point is also where the

earthquake is felt the most intense. The amount of damage is very high near the

epicenter. Actually, the epicenter is also an area rather than a point. The size of

this area is related with the magnitude of the earthquake. Sometimes, even

though the magnitude is small, the damage can be great in the epicenter area.15

14 Bayülke, Nejat. ed. Depremler ve Depreme Dayanıklı Yapılar, Ankara: T.C. İmar ve İskan Bakanlığı Deprem Araştırma Enstitüsü Başkanlığı Pub. 1978, 6. 15 Bayülke, Depremler ve Depreme Dayanıklı Yapılar, 7.

15

Figure 2.5 Earthquake Parameters16

2.4.3 Focal Depth

The focal depth is defined by Bayülke as the shortest distance from the point

where the energy is released to the surface of the earth. In other words, it is the

distance between the hypocenter and the epicenter (Figure 2.5). When the focal

depth is short, the energy of the earthquake is concentrated on a very narrow

area on the surface; therefore the damage is very high. When the focal point is

deep, the damage is relatively less. However, since the seismic waves are

dispersed, the earthquake is felt in a very wide area.17

16 Bayülke, Figure 3, Depremler ve Depreme Dayanıklı Yapılar, 7. 17 Bayülke, Depremler ve Depreme Dayanıklı Yapılar, 6.

16

2.4.4 Isoseismic Map

Erkoç, Baran and Hamzaçebi state that isoseismic maps are made by connecting

the points, where the earthquake is felt with the same intensity, to each other by

isoseismic lines (Figure 2.6). For damage assessment and ease of calculation, it

is assumed that all the locations in the area between two isoseismic lines feel

the tremor with the same intensity. That’s why the level of intensity is written

in the area between the lines.18

Figure 2.6 An Example of Isoseismic Map19

18 Erkoç, Turan. Baran, Belgin. Hamzaçebi, Gülşah. Deprem Nedir?, Ankara: 2000, 6. 19 Celep, Zekai. Kumbasar, Nahit. Figure 1.11, Deprem Mühendisliğine Giriş ve Depreme Dayanıklı Yapı Tasarımı, İstanbul: Beta Dağıtım Pub. 2000, 9.

17

2.5 Types of Seismic Waves

After an earthquake various types of waves are propagated. The characteristics

of this propagation are related with the physical and chemical composition of

the rocks. The frequency of some of these waves can be within the hearing

threshold of men. These waves are called the seismic waves (Figure 2.7). These

waves can be classified to three categories according to Saları.20

• Longitudinal Waves: These waves propagate similar to sound waves.

Their speed is around 7-8 km per second. The particles in the earth

vibrate in the same direction with the propagation of the waves. They

are known as the undae primae or the (P) waves because they are the

first waves to reach the measurement stations. These waves can

propagate through solids, liquids and gases.

• Transversal Waves: The particles in the earth vibrate perpendicular to

the propagation direction of the waves. These are the second waves to

arrive the measurement stations; therefore, they are called the undae

secundae or the (S) waves. They can only propagate through solid

objects. Researches have shown that these waves can’t travel through

the earth’s core. That’s why the outer core is assumed to be of liquid

nature.

20 Saları, Nasrın. Figure 1, “Mimari Form ve Elemanların Depreme Dayanıklı Yapı Tasarımına Etkileri” Graduate Thesis, Trabzon: Karadeniz Teknik Üniversitesi Pub, 1999, 10.

18

• Surface Waves: These waves are produced very close to the surface.

Their magnitude is very high. They travel perpendicular to the particle

vibration. They have two categories with respect to the scientists who

discovered them: Rayleigh Waves and Love Waves. These are the

most destructive seismic waves.

Figure 2.7 Seismic Waves21

21 Saları, Nasrın. Figure 1, “Mimari Form ve Elemanların Depreme Dayanıklı Yapı Tasarımına Etkileri” Graduate Thesis, Trabzon: Karadeniz Teknik Üniversitesi Pub, 1999, 7.

19

2.6 Intensity of an Earthquake

The intensity of an earthquake is measured by the help of subjective criteria.

Some of these criteria are: The effect on people, the amount of damage on

various types of buildings, the effect on the landscape, etc. When an earthquake

occurs, previously determined intensity parameters are compared to the actual

amount of damage. The locations, which are affected with the same intensity,

are marked in the form of isoseismic lines on maps. The development of

intensity scales dates back to 19th century. The scale that is actually used in

Turkey is the Modified Mercalli Scale (Table 2.2).22

Table 2.2 Modified Mercalli Scale

Intensity Effect

I Felt by very few people. Has no effect on the environment.

II Felt by people at rest (sitting, lying down) and on the top floors of

high buildings.

III Felt clearly by people indoors. Vehicles at rest are slightly shaken.

IV Felt by everyone indoors. People at sleep may wake up. Doors,

windows and small furniture are slightly shaken. Cracking noises

come from the walls. Vehicles at rest are shaken.

22 Bayülke, Nejat. Depremler ve Depreme Dayanıklı Yapılar, Ankara: Teknik Yayınevi Pub. 1998, 14.

20

Table 2.2 (continued)

V Everybody feels it. Windows may be broken. Wall plasters may

crack. Small objects may fall over. Trees and poles are shaken

VI Heavy furniture may fall over. Defective masonry walls may crack.

Chimneys may collapse.

VII People have difficulties standing up. Defective masonry walls may

partially collapse. Chimneys collapse. Well-made masonry walls

may crack. The structural system-partition wall joints may crack in

R/C buildings.

VIII Defective Masonry walls totally collapse. Well-made masonry

walls partially collapse. Heavy damage in timber frame systems.

Damage in defective R/C buildings. Landslides may occur. Seismic

faults may become visible on the surface.

IX Masonry buildings collapse. R/C skeletons may crack. The cover

around the reinforcement bars cracks. Buckling begins. Deflections

are seen in R/C buildings. Sub-surface pipes crack.

X Heavy damage or collapse in timber and R/C skeleton systems.

Railways buckle. Landslides occur.

XI Very few buildings remain intact. Bridges are destroyed. Major

landslides happen.

XII The seismic waves become visible on the earth’s surface. Nothing

stays upright.

21

2.7 Magnitude of an Earthquake

The magnitude (M) is a measurement of the released energy during an

earthquake. Since there is no way of directly measuring the amount of energy, a

method based on the measurements made by the seismographs (Section 2.8), is

developed by Richter in 1930’s. In this method, the maximum amplitude of the

ground motion is measured by a seismograph, which is located 100 km away

from the epicenter of the earthquake. Then, a chart is produced by taking the

10-based logarithmic rates of the maximum amplitude values. This chart is

called the Richter Scale. The maximum value measured up to this day is the

1906 Colombia earthquake, which had an 8.9-9 magnitude according to Richter

Scale.

The magnitude measured by the observatories doesn’t necessarily indicate the

amount of damage caused by the earthquake. A shallow earthquake will cause

considerably more damage than a deep earthquake with the same magnitude.23

Table 2.3 Intensity-Magnitude Relationships24

Intensity IV V VI VII VIII IX X XI XII

Magnitude 4 4.5 5.1 5.6 6.2 6.6 7.3 7.8 8.4

23 Erkoç, Turan. Baran, Belgin. Hamzaçebi, Gülşah. Deprem Nedir?, Ankara: 2000, 7. 24 Erkoç, Turan. Baran, Belgin. Hamzaçebi, Gülşah. Deprem Nedir?, Ankara: 2000, 8.

22

2.8 Earthquake Recording Devices

Seismographs (Figure 2.8) are very sensitive devices, which were developed to

measure and record the magnitudes of the earthquakes. A seismograph consists

of two parts. The seismometer is affected from the earthquake and makes

movements, which are proportional with the amplitude of the waves. The

recording device inscribes the properties of various seismic waves.25

Figure 2.8 A Simple Seismograph26

25 Erkoç, Turan. Baran, Belgin. Hamzaçebi, Gülşah. Deprem Nedir?, Ankara: 2000, 9. 26 Bayülke, Nejat. ed. Depremler ve Depreme Dayanıklı Yapılar, Ankara: T.C. İmar ve İskan Bakanlığı Deprem Araştırma Enstitüsü Başkanlığı Pub. 1978, 12.

23

2.9 Seismic Characteristics of Turkey

Turkey is located on the Alp-Himalayan Seismic Belt, which starts from the

Azores in the Atlantic Ocean and stretches away into the Southeast Asia. The

seismic activity is very complex around the East-Mediterranean region. Most of

the country is on the Anatolian plate, which is located in the middle of the

Eurasian, African and Arabic Plates. The African and Arabic plates travel north

and forces the Anatolian plate to move west. The majority of the destructive

earthquakes take place on the borders of the Anatolian Plate. 27

Figure 2.9 Seismic Plates Around Turkey28

27 Yılmaz, Rüçhan. and Demirtaş, Ramazan. “Depremler ve Türkiye’nin Depremselliği”, Deprem ve Sonrası. ed. Prof. Dr. Erhan Karaesmen, Ankara: Türkiye Müteahhitler Birliği Pub. 1996, 20-21. 28 Celep, Zekai. Kumbasar, Nahit. Figure 1.20, Deprem Mühendisliğine Giriş ve Depreme Dayanıklı Yapı Tasarımı, İstanbul: Beta Dağıtım Pub. 2000, 26.

24

The North Anatolian Fault consists of several shorter fault lines and stretches

over 1000 km. The width of the seismic zones varies between 100m and 25 km.

The annual average slide is about 0.5-0.8 cm. The East Anatolian Fault runs

400 km from Karlıova to İskenderun Bay. The width is between 2-3 km and the

annual slide is around 0.6 cm. The most destructive earthquakes take place on

these two fault lines. Bitlis Compression Zone is in a relatively silent state since

the beginning of the last century. The Aegean Graben Zone is the reason for the

earthquakes in West-Anatolia. The Anatolian Plate expands in the North-South

direction and causes the formation of fault lines in East-West direction.29

Figure 2.10 Seismic Faults in Turkey30

29Yılmaz, Rüçhan. and Demirtaş, Ramazan. “Depremler ve Türkiye’nin Depremselliği”, Deprem ve Sonrası. ed. Prof. Dr. Erhan Karaesmen, Ankara: Türkiye Müteahhitler Birliği Pub. 1996, 21-24. 30 Celep, Zekai. Kumbasar, Nahit. Figure 1.20, Deprem Mühendisliğine Giriş ve Depreme Dayanıklı Yapı Tasarımı, İstanbul: Beta Dağıtım Pub. 2000, 26.

25

CHAPTER III

EARTHQUAKE BEHAVIOR OF REINFORCED CONCRETE

STRUCTURES

3.1 Properties of Reinforced Concrete

Reinforced concrete is the dominant building material in Turkey. It is necessary

to have some basic knowledge about the material properties of R/C to

understand its seismic behavior. Atımtay states that R/C is a composite

material. It is made of concrete, which is very strong in compression forces but

weak in tension forces, and steel, which is strong, both in compression and

tension forces. The steel is used in the form of bars with circular cross-sections.

These bars are called reinforcing bars. The reinforcing bars are used where

tension forces occur, to compensate the tensile weakness of concrete.31

31 Atımtay, Ergin. Reinforced Concrete Fundamentals, Ankara: Bizim Büro Basımevi Pub., February 1998, 3.

26

Figure 3.1 Concrete & Reinforced Concrete32

Atımtay further explains the causes of R/C being the dominant building

material by economic reasons. The raw materials of concrete (calcium

carbonate, aggregates, water) are very plentiful in nature and relatively cheap to

obtain. Steel, on the other hand, is an expensive material and the raw materials

are scarce; however, the percentage of steel in R/C is only about 1%, which is

an economically acceptable ratio.

Concrete is made of cement, aggregate and water. When cement is mixed with

water, a chemical reaction called hydration occurs, as a result of which concrete

hardens. The hardening of the concrete is called the curing process. During this

chemical reaction an important amount of heat is generated. To minimize the

volume changes due to this heat generation aggregates, which are inert to the

reaction are added to the mixture. Sometimes additional ingredients called

admixtures can be added to modify the speed of curing, the amount of heat

generated during hydration, resistance to corrosion, etc. 32 Atımtay, Ergin. Reinforced Concrete Fundamentals, Ankara: Bizim Büro Basımevi Pub., February 1998, 5-19.

27

There are various classes of concrete and reinforcing steel. Concrete classes are

determined by the characteristic strength (fck) of concrete while the steel classes

are determined by the characteristic yielding stress (fyk) of steel. For example,

C16 means that the characteristic strength of that concrete is 160 kgf/cm² and

S420 means that the characteristic yielding stress of that steel is 4200 kgf/cm².

According to the Turkish Earthquake Code C16 or higher classes of concrete

will be used in R/C buildings constructed in earthquake zones. C20 or higher

classes must be used in first and second-degree earthquake zones.33

Figure 3.2 Stress-Strain Diagrams of Steel and Plain Concrete34

33 Hasol, Doğan. Ansiklopedik Mimarlık Sözlüğü, 6th ed. İstanbul: Yapı-Endüstri Merkezi Pub. 1995, 77. 34 Atımtay, Ergin. Reinforced Concrete Fundamentals, Ankara: Bizim Büro Basımevi Pub. February 1998, 19.

28

3.2 Essential Definitions in Earthquake-Building Interaction

3.2.1 Definition of Earthquake Load

In the minds of many architects, the concept of earthquake loading is not very

different then any other type of conventional loads. It can be represented in the

form of force vectors affecting the vertical section of a building (Figure3.3)

and engineers make the necessary calculations by the help of some rather dull

formulas. These may be true to a certain extent. However, to understand the

earthquake behavior of a building, one must try to see what really happens to a

building during an earthquake.

29

Figure 3.3 A Typical Earthquake Loading Pattern35

It has been previously mentioned in Chapter II that an earthquake is a release of

energy. According to Atımtay, when this energy travels through the layers of

the crust and reaches the foundation of a building, it causes movements in every

direction. If we assume that the structure is in a Cartesian Coordinate System,

the building will make displacements in (x), (y) and (z) directions. The load

carrying capacity and the safety factors in the vertical direction are very high in

R/C systems; therefore, the forces in the (z) direction are negligible. On the

other hand, the movements in (x) and (y) directions cause important

accelerations in the system based on the Newton rule F = m · a where (m) is the

mass of the building; (a) is the ground acceleration and (F) is the equivalent

earthquake force.36

Structures are often represented as two-dimensional diagrams for the easy

analysis, however, one shouldn’t forget that buildings are three-dimensional

objects and every molecule has its own mass; therefore, there is an infinite

number of forces that occur when a building is subjected to earthquake

conditions. It is of course impossible to make an analysis with an infinite

number of forces; that’s why, a simplification is made in the calculations. It is

35 Atımtay, Ergin. Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 617. 36 Atımtay, Ergin. Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 1, 207.

30

assumed that every floor has its own mass and that the weights of columns,

partition walls, etc. are effective on a floor-by-floor basis.

3.2.2 Natural Period of a Building

This is an essential concept to understand for an architect because the natural

period is independent from the loading conditions. As Atımtay states, it is

related with the mass, lateral rigidity (Section 3.3.3) and the energy absorption

(Section 3.2.3) of a structure. It should be noticed that these properties are

determined by the geometric configuration –the design- of the building and are

very much the result of architectural decisions. Let’s make a basic definition:

Suppose that the mass (m) made a displacement to the point (1) and is released

from there. The period is the time for (m) to complete the trajectory (1-0-2-0-1).

The natural period is shown as (T) and measured by seconds (s).37

37 Atımtay, Ergin. Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 1, 209.

31

Figure 3.4 Natural Period38

The period of a building decreases if the lateral rigidity is increased. On the

other hand, the period increases if the mass of a building is increased; therefore,

a tall building has a greater period then a shorter building with the same lateral

rigidity. The ground also has a characteristic period. The most critical situation

for a building is to have a natural period, which is very close to the

characteristic period of the ground. In this case, the building goes into a

dangerous kind of vibration, which may cause a total collapse. It is wrong to

assume that, tall buildings are less resistant to earthquakes. A short building,

which has the same period with the ground, may collapse while a tall building

will remain undamaged because it has a greater period. The seismic resistance

is increased by the correct choice of location and proper design.39

38 Atımtay, Ergin. Figure 5.4, Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 1, 209. 39 Gönençen, Kaya. Mimari Proje Tasarımında Depreme Karşı Yapı Davranışının Düzenlenmesi, Ankara: Teknik Yayınevi Pub. 2000, 7.

32

Figure 3.5 Modes for a 3-storey building40

3.2.3 Absorption of Energy

The energy released by the earthquake travels through the earth and reaches the

foundation of the building. It is then transferred into the building structure,

therefore, as Atımtay states, the earthquake can be considered as an energy

loading. Energy means the ability to do work. The building must perform some

work to spend this energy. Structures consume energy in various ways: the

displacement of the building, formation of cracks and plastic deformations, heat

generated by the friction between the molecules, etc. In a successful seismic

design the energy is consumed by displacements and deformations in

previously determined locations, therefore, the collapse is prevented.41

40 Karaesmen, Erhan., ed., Figure 4.1, Figure4.2 “Depremler ve Türkiye’nin Depremselliği”, Deprem ve Sonrası, Ankara: Türkiye Müteahhitler Birliği Pub. 1996, 46. 41 Atımtay, Ergin. Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 1, 207.

33

Figure 3.6 Absorption of energy by plastic deformation42

3.2.4 Effective Ground Acceleration

In modern seismology and earthquake engineering, the magnitude of an

earthquake is calculated with the help of the ground acceleration measured at

that point. The motion of a point consists of three components perpendicular to

each other. These measurements are made with Strong Motion

Accelerographs.43

42 Bayülke, Nejat. Figure 2.22 Depremlerde Hasar Gören Yapıların Onarım ve Güçlendirilmesi, 3rd ed. İzmir: İnşaat Mühendisleri Odası İzmir Şubesi Pub. 1995, 32 43 Sucuoğlu, Haluk. “Yapılarda Deprem Kuvvetlerinin Oluşması”, Deprem ve Sonrası, Erhan Karaesmen ed. Ankara: Türkiye Müteahhitler Birliği Pub. 1996, 29.

34

Figure 3.7 Ground Accelerations for Erzincan 1992 Earthquake44

There is a relation between the ground acceleration created by the earthquakes

and the seismic behavior of the buildings. That relation is called the Effective

Ground Acceleration. Atımtay states that the effective ground acceleration is

expressed as a ratio of the acceleration due to earth’s gravity g = 9.81 m/s². In

Turkish Earthquake Code there are four accepted levels of effective ground

acceleration and it is expressed as the Effective Ground Acceleration

Coefficient, Ao. The effective ground acceleration (A) is calculated with the

formula A = Ao (g).

Table 3.1 Effective Ground Acceleration Coefficients for Turkey45

44 Karaesmen, Erhan., ed., Figure 3.2, Figure4.2 “Depremler ve Türkiye’nin Depremselliği”, Deprem ve Sonrası, Ankara: Türkiye Müteahhitler Birliği Pub. 1996, 30. 45 Atımtay, Ergin. Table 5.3, Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 1, 212.

35

Earthquake Zone Ao 1 0.40 2 0.30 3 0.20 4 0.10

Although this is an engineering issue, an architect can use the following rule of

thumb:

• When A = (0.1) g, Buildings, which aren’t earthquake resistant may

suffer minor damages.

• When A = (0.2) g, people feel the movement very intensely and motion

related sicknesses like dizziness can be seen.

• When A = (0.3) – (0.4) g, medium and high earthquake damages may

occur.

3.2.5 Ground-Structure Interaction

The properties of the soil on which the structure stands play a very important

role in the seismic performance of a building. In fact, no matter how carefully

the superstructure is designed, the building will be damaged or will totally

collapse if the seismic behavior of the foundation soil is ignored. Soil

mechanics is in the field of the related branch of engineering and not directly in

the scope of this thesis, however, some basic information about the commonly

encountered types of damaging soil behavior will be mentioned here.

36

Figure 3.8 Damages Due to the Liquefaction of the Soil in Adapazarı 199946

The effects of the earthquake waves and the ground acceleration were

previously mentioned (Section 3.2.2 &Section 3.2.4) so we will concentrate on

the effects of the soil, on which the building stands, in this section. According

to Saları the direct effects of the foundation soil are as follows:47

• If the foundation area is large, there can be different types of soil with

different seismic capacities under the building. In case of an earthquake

these soil types will behave differently and the foundation elements on

the weaker soil can be damaged affecting the entire structural system.

46 Demirtaş, Ramazan. ed., 17 Ağustos 1999 İzmit Körfezi Depremi Raporu, Ankara: January 2000, 194. 47 Saları, Nasrın., “Mimari Form ve Elemanlatın Depreme Dayanıklı Yapı Tasarımına Etkileri” Graduate Thesis, Trabzon: Karadeniz Teknik Üniversitesi Pub, 1999, 21.

37

• Cracks may occur in the foundation soil due to the earthquake

displacements. These cracks may cause important and sometimes fatal

deformations in the structural system of the building.

• A very important and destructive soil phenomenon is the liquefaction

(Figure 3.8). Especially in sandy soils and filled grounds, which haven’t

completed their settlements, the load carrying capacity is based only on

the friction between the particles. During an earthquake, the water

pressure increases and separates the grains from each other, therefore,

the load carrying capacity is compromised and the ground acts like a

liquid.

• Landslides may occur due to the unforeseen movements of the water in

the layers of earth. Soil may turn into mud and act like a liquid. There is

especially great risk on inclined sites.

3.3 Fundamental Concepts in Seismic Design

The concepts that were mentioned so far were either related with the nature of

the earthquake phenomenon or with the effects of the environmental factors on

a building. In this section however, the fundamental properties, which the R/C

structure itself has to possess to be resistant to earthquake loading will be seen.

These properties are:

• Strength

• Ductility

38

• Rigidity

3.3.1 Strength

The first condition for a R/C structure to perform well in any kind of situation is

that the materials in the structural system should have both individually and

collectively the necessary cross-sections to resist the calculated loads. The

architectural and engineering projects must be prepared according to the proper

technical criteria –in this case the Turkish Earthquake Code- and the

applications in the construction site must be in conformity with the projects.48

3.3.2 Ductility

Ductility is the most critical characteristic of a R/C structure against the lateral

loads such as the earthquake loading. Ductility is the ability of the structure to

consume energy with elastic displacements and plastic deformations. While

doing this, the structure shouldn’t have an important loss in its load-carrying

capacity. Ductility of a R/C structure is closely related with the percentage of

reinforcement. The area under the stress-strain diagram of a R/C element gives

the amount of energy consumed before failure.

48 Gönençen, Kaya. Mimari Proje Tasarımında Depreme Karşı Yapı Davranışının Düzenlenmesi, Ankara: Teknik Yayınevi Pub. 2000, 30.

39

Figure 3.9 Stress-Strain Relationship of a R/C Element at Various Levels of Reinforcement.49

A high percentage of steel doesn’t necessarily make a building more resistant to

earthquakes. In fact, over-reinforced structures often have a lower energy

absorption capacity. R/C elements are designed as under-reinforced for a better

ductile behavior under earthquake loads. Theoretically, the most desirable

situation for a structure is to absorb the earthquake energy within elastic limits,

which means without permanent deformations. However, in practice, it is

impossible and uneconomical for a building to survive an earthquake without

any damage. The correct approach is to design the structural system such that,

in smaller earthquakes, the energy will be consumed with elastic deformations

and displacements. In strong earthquakes however, there will be cracks and

49 Bayülke, Nejat. Figure 1.4 Depreme Dayanıklı Betonarme ve Yığma Yapı Tasarımı, 2nd ed. İzmir: İnşaat Mühendisleri Odası İzmir Şubesi Pub. 1998, 18

40

plastic deformations in structural joints without compromising the load-

carrying capacity. The building may be severely damaged but it will not

collapse and the loss of lives will be prevented.

Figure 3.10 The Energy Consumption Capacity of Structural Elements50


41

Figure 3.11 A Comparison Between Elastic and Elasto-Plastic Structures51

3.3.3 Rigidity

Rigidity means making small displacements under lateral loads. Making the

columns and shear-walls more rigid, means increasing their moments of inertia

(I = bh³/12). Notice that the moment of inertia will increase in proportion with

the 3rd exponential of the dimension parallel to the direction of the earthquake.

There must be a balance between the ductility and the rigidity of a building.

Especially in high-rise buildings (Figure 3.12), if the building is over-ductile,

additional secondary moments and stresses will occur during an earthquake,


42

furthermore the comfort conditions will not be satisfied due to excessive

displacements caused by wind loads, etc. If the building is over-rigid the

building will be unable to absorb energy with plastic deformations.

Figure 3.12 Modes of a High-Rise Building52

3.4 Seismic Design Criteria in Turkey

There are various factors that should be taken into consideration when the

criteria of the seismic design in Turkey are determined. Building construction

brings very heavy financial burdens; on the other hand, the safety of human life

cannot be compromised. So the following principles are adopted in the Turkish

Earthquake Code. The structural and non-structural elements of a building

shouldn’t be damaged during a small earthquake. The damages that occur

during a medium-intensity earthquake should be within repairable limits. In


43

case of a strong earthquake the total and partial collapse of a building should be

prevented. The capital priority is the protection of human life.

Figure 3.13 Partial and Total Collapse Examples53

53 Arısoy, E. Sami. Çünkü, Bu Yaşananlar Nasıl Olsa Bir Rüyaydı, İstanbul: Nobel Tıp Kitabevleri Pub. 2001, 47

44

CHAPTER IV

SEISMIC DESIGN FAULTS IN REINFORCED CONCRETE

BUILDINGS

4.1 Importance of Seismic Resistance in Architectural Design

For a society, which is committed to create a better environment for the present

and future generations, there are significant lessons to be learned from the

devastations of past earthquakes. It is very unfortunate for Turkey to be on an

active seismic as it suffers from the spiritual and economic losses. However, it

is also lucky in a sense because the scenes of damaged and collapsed buildings

offer a unique natural laboratory, which no money can buy; furthermore, it

allows the scientists to make first-hand observations and test the validity of the

existing theories. It is the professional and ethical responsibility of the

architects to participate in these efforts of research and observation to be able to

better understand the seismic behavior of the buildings they design.

44

The various types of architectural design faults will be mentioned in this

chapter, however, based on the observations made after the past earthquakes it

is possible to make a general classification about the causes of structural

damage in R/C buildings. Ali İhsan Ünay describes these categories as

follows:54

• Undesirable Geometric Configuration

• Inadequate Lateral Stiffness

• Flaws in Detailing

The building below (Figure 4.1) is a good example to a collapse triggered by

the combination of these factors. Excessive lateral displacement caused the

columns to fail and compromised the vertical stability of the structure.

Figure 4.1 A Building Collapsed in Marmara 1999 Earthquake55

54 Ünay, İ. Ali. “Mimari Tasarımda Deprem Bilincinin Geliştirilmesi” Mimarlık No:290 1999, 46-48 55 Arısoy, E. Sami. Çünkü, Bu Yaşananlar Nasıl Olsa Bir Rüyaydı, İstanbul: Nobel Tıp Kitabevleri Pub. 2001, 47

45

There is a general misunderstanding between architects and students of

architecture that the seismic design rules and specifications set a limit to the

creative freedom of a designer. This idea is further enhanced by the indifference

of the system of architectural education to the issue and the current Turkish

Earthquake Code, which is apparently written for the understanding of civil

engineers.

The seismic design fault definitions in this chapter are made for the architects

and especially for the students of architecture. It is the author’s belief that an

adequate verbal definition supported by the apt graphic material will be more

meaningful for an architect than a set of formulas. The rules of seismic design

are not constraints on the imagination of an architect (Figure 4.2). They are the

precautions we have to take to protect human life.

Figure 4.2 Papa Tongarewa Museum, New Zealand, An Earthquake Country56

56 Orman, Kemal. trans. Earthquake Architecture. By Belén Garcia. ed. İstanbul: Tasarım Yayın Grubu Pub. 2001, 71

46

4.2 Seismic Design Faults In Plan

4.2.1 Torsion Eccentricity

In the floor plan, the distance between the center of gravity and the center of

rigidity should be minimum. If eccentricity is large, there will be a torsion

moment around the center of rigidity due to lateral earthquake forces. This

moment will create additional shear forces in the columns, which are already

under great shear stress. It is very difficult to change the location of the center

of gravity; on the other hand, the center of rigidity can be modified by playing

with the cross-sections and the locations of columns and shear-walls.57

Figure 4.3 Torsion Eccentricity58

57 Atımtay, Ergin. Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 499. 58 Atımtay, Ergin. Figure 8.23 Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 499.

47

The example below shows how the center of gravity and the center of rigidity

can be modified by the addition of shear-walls to decrease the torsion

eccentricity and the consequent shear forces.

Figure 4.4 Modifying the Center of Rigidity59

The building below was damaged due to torsion eccentricity. Notice that the

shear-walls are located on one corner of the building creating an over-rigid core

around which the building has rotated. As a result, the columns have failed.

Figure 4.5 A Building Damaged due to Torsion Eccentricity60

59 Atımtay, Ergin. Figure 8.22/8.24 Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 499.

48

The Turkish Earthquake Code mentions the torsion eccentricity as follows:

A1. Torsion Irregularity The case in which the Torsion Irregularity Factor, which is defined as the ratio of the maximum storey drift to the average storey drift at any storey exceeds 1.2 in any one of the two perpendicular earthquake directions. [ η ∆i = (∆i)max / (∆i)average > 1.2]

For any earthquake direction, if the rigidity of a building isn’t symmetrically

distributed, the less rigid portion of the structure will make a greater

displacement than the more rigid portion. If the ratio of the maximum

displacement to the average displacement at any floor is more than 1.2 than

there is a torsion irregularity in the building.

Assuming that the slab acts as a rigid diaphragm in the floor plane

(∆i)average = ½ [(∆i)max + (∆i)min]

Figure 4.6 Torsion Eccentricity in Turkish Earthquake Code61

60 Tuna, Mehmet Emin, Figure 8.8 Depreme Dayanıklı Yapı Tasarımı. Ankara: Tuna Eğitim ve Kültür Vakfı Pub. November 2000, 234. 61 Turkish Earthquake Code: Figure 6.1 Afet Bölgelerinde Yapılacak Yapılar Hakkında Yönetmelik. Ankara: 1998, 9.

49

4.2.2 Floor Discontinuities

The lateral forces on the structure are transferred to columns and shear-walls

through the floor slabs. Generally, in static calculations, it’s assumed that the

floor slabs have infinite in-plane rigidity. However, if there are large openings

in slabs or drastic changes in slab rigidity, this assumption will not be valid.

Without a rigid floor slab, there will be critical and unpredictable changes in the

distribution of lateral loads to columns and shear-walls. Furthermore, the

dynamic behavior of the building will be negatively affected. There will be

irregular lateral displacements causing additional shear stresses on the columns.

Figure 4.7 Discontinuities in the Floor Slab62

62 Atımtay, Ergin. Figure 8.44 Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 521.

50

The Turkish Earthquake Code describes floor discontinuity as follows:

A2 Floor Discontinuities The cases in which;

1. The total area of the openings including those of stairs and elevator shafts exceeds 1/3 of the gross floor area of any storey.

2. Local floor openings making the transfer of seismic loads to the vertical structural members difficult or even impossible.

3. Abrupt reductions made in the in-plane stiffness and strength of the floors.

Figure 4.8 A2 Type Irregularities According to Turkish Earthquake Code63

If it is absolutely necessary to make discontinuities on the plan, the rigidity of

the columns and beams around the opening should be increased or shear-walls

should be positioned around the openings.64

63 Turkish Earthquake Code: Figure 6.2 Afet Bölgelerinde Yapılacak Yapılar Hakkında Yönetmelik. Ankara: 1998, 10. 64 Atımtay, Ergin. Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 521.

51

4.2.3 Projections in Plan

Almost all R/C structures and especially residential buildings contain

projections in plan due to architectural considerations or functional necessities.

The ratio of these projections to the entire plan is very important in terms of

seismic behavior of the building. When the projections are too large, they will

cause additional stresses on the structure. The most critical shear forces and

moments occur in the intersection line (Figure 4.9) of the projection and the

main body. Furthermore, there will be torsion eccentricities (Section 4.2.1) on

the building. If the projections are absolutely necessary, the structural engineers

should be consulted for additional reinforcements. If possible, the structure

should be divided into several sections with structural joints (Figure 4.11).

Figure 4.9 Disadvantages of Projections in Plan65

65 Atımtay, Ergin. Açıklamalarl ve Örneklerle Afet Bölgelerinde Yapılacak Yapılar Hakkında Yönetmelik Ankara: Bizim Büro Basımevi Pub. 2000, 147.

52

The Turkish Earthquake Code Describes the Projections in Plan Irregularity as

follows:

A3 Projections In Plan: The cases where projections beyond the re-entrant corners in both of the two principal directions in plan exceed the total plan dimensions of the building by more than 20% in the respective dimensions.

Figure 4.10 A3 Type Irregularity in Turkish Earthquake Code66

The irregular structures above can be improved with structural joints as follows:

Figure 4.11 Improved Building Plans67

66 Turkish Earthquake Code: Figure 6.3 Afet Bölgelerinde Yapılacak Yapılar Hakkında Yönetmelik. Ankara: 1998, 10. 67 Tezcan, Semih. S. Depreme Dayanıklı Yapı İçin Bir Mimarın Seyir Defteri İstanbul: Turkish Earthquake Foundation Pub., 1998, 12.

53

4.2.4 Non-Parallel Axis of Structural Elements

If a R/C structure contains columns, shear-walls or frames, which have inclined

axes with respect to the perpendicular earthquake directions, additional

moments and shear stresses may occur in the structural elements during an

earthquake. In fact, if the structural system is too complicated, the calculations

can only be made with detailed computer analysis. Turkish Earthquake Code

requires an increase of the design loads in the calculations, therefore; if such

irregularities exist in the plan, the structural engineer must be consulted. The

Turkish Earthquake Code describes the Non-parallel Axis of Structural

Elements Irregularity as follows:

A4 Non-Parallel Axis of Structural Elements: The cases where, the principal axes of the structural elements do not coincide with the earthquake directions, taken perpendicular to each other.

Figure 4.12 A4 Type Irregularity in Turkish Earthquake Code68

68 Turkish Earthquake Code: Figure 6.4 Afet Bölgelerinde Yapılacak Yapılar Hakkında Yönetmelik. Ankara: 1998, 10.

54

4.2.5 Fundamental Concepts About Reinforced Concrete Beams

4.2.5.1 Non-Continuous Beams

The architect should avoid designing non-continuous beams in the floor plan E.

Atımtay states that when the beam doesn’t continue, the lateral forces will be

distributed to the vertical elements through the relatively thin floor slab. It is

very difficult for the structural engineer to calculate the pattern and the effects

of this distribution. If such a configuration is absolutely necessary the slab

thickness can be increased or a joist slab can be used. The designer should

always keep in mind the lateral displacement properties of the entire design.69

Figure 4.13 Non-Continuous Beam70


55

4.2.5.2 Irregular Spans and Beam Cross-Sections

In a design jury, the most fervent debates between the architects and the

engineers are made because the engineers recommend structures having regular

spans, “called 6m by 6m frame rule” by M.E.T.U students. Architects however,

find such a limitation to their creative freedom revolting. Both sides have

reason in their own terms. Nevertheless, there is a simple explanation for this

advice of the engineers. Firstly, with irregular spans the lateral rigidity of the

entire system will be very unpredictable in an earthquake situation. Besides

this, if there are altering beam cross-sections it’s very difficult to estimate the

critical stresses in the structural elements under lateral loads. Furthermore, the

formwork cost will be very expensive. The reinforcement details will be very

complicated and difficult to produce especially in Turkey. That’s why standard

spans and uniform cross-sections are recommended for R/C structures.

Figure 4.14 Joint Between Beams with Different Cross-Sections71

71 Atımtay, Ergin. Figure 8.20/8.21 Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 495.

56

4.2.5.3 Beam-to-Beam Connections

Sometimes vertical load-bearing members are omitted in beam-to-beam

connections due to spatial considerations. Such a configuration may be

dangerous under lateral loading (Figure 4.15 A). There will be a large point

load on the connection point creating critical moments. Large deflections and

cracks may occur on the beams. Additional reinforcements plus very large and

uneconomical beam cross-sections will be needed. If such a connection is

absolutely necessary the connection point shouldn’t be near the support (Figure

4.15 B). Otherwise very critical torsion moments will occur on the beams. 72

A B

Figure 4.15 Beams Intersecting Without Vertical Support73

72 Atımtay, Ergin. Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 504-505. 73 Atımtay, Ergin. Figure 8.28/8.29 Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 504-505.

57

4.2.5.4 Beams and Frames with Broken-Axis

A structural calculation can be successful only if the engineers are able to make

a realistic prediction of the forces applied on the system. Most of the time the

three-dimensional structure is separated into two-dimensional frames to make

an efficient analysis. As Atımtay suggests, if the frames have broken-axis, it is

impossible to handle the system with two-dimensional analysis; therefore, the

loads cannot be realistically determined. Furthermore, beams with broken axis

are less resistant to lateral forces (Figure 4.16 A). Configurations in (Figure

4.16 B) should be avoided due to the excessive torsions that may occur.74

A B

Figure 4.16 Beams and Frames with Broken Axis75

74 Atımtay, Ergin. Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 508-509. 75 Atımtay, Ergin. Figure 8.32/8.33 Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 508-509.

58

4.2.6 Fundamental Concepts About Reinforced Concrete Slabs

4.2.6.1 Over-Stretched One-Way Slabs

As mentioned before (Section 4.2.2), lateral forces are distributed to vertical

elements through floor slabs. It is very difficult to calculate the shear stresses

acting on the columns if the slab doesn’t have complete in-plane rigidity. Over-

stretched one-way slabs can easily make large deflections under lateral loads.

Furthermore, there will be frequent contraction cracks due to the difficulty of

placing reinforcements in the long direction. Another disadvantage is breaking

the continuity of beams (Section 4.2.5.1). 76

Figure 4.17 Over-Stretched One-way Slab77


59

4.2.6.2 Rules About Joist-Slabs

Joist-slabs and especially block-joist slabs are very commonly used in

residential buildings in Turkey due to aesthetic reasons and the ease of

formwork. In block-joist slabs the side-beams are made shallow to match with

the dimensions of the joists for easy formwork. According to Karaesmen, this

makes the beams vulnerable to deflections due to lateral forces. The large

lateral displacements in the slab may damage the beams. More critically, the

bond between the floor blocks and the joists may be destroyed. The floor blocks

will fall down causing great material damage and possibly human casualties. 78

Figure 4.18 Deflection Damage near Shallow Beams in a Block-Joist Slab79

78 Karaesmen, Erhan. & Buğdaycıoğlu, B. Elif. Yapısal Hasar Türleri ve Ek Hasarı Arttırıcı Unsurlar N.p 79 Demirtaş, Ramazan. ed., 17 Ağustos 1999 İzmit Körfezi Depremi Raporu, Ankara: January 2000, 245.

60

Atımtay states that there are two critical concerns in the designing of joist slabs.

The first is to choose the direction of the joists parallel to the critical lateral

force direction. This is generally parallel to the shorter side of the building on

the plan, thus, the lateral forces will only create axial stresses on the joists

instead of shear forces and torsions. The slab rigidity will be increased and

consequently, the lateral displacement of the structure will be limited. The

second important issue is to choose the joist direction parallel to the longer side

of the slab. Choosing the longer span may seem contradictory to the structural

logic at first. However, keep in mind that, in such a configuration, the beams on

the shorter span will easily carry the load of the joists.80

Figure 4.19 Irregular Joist-Slab Directions in a Floor81

80 Atımtay, Ergin. Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 506-507. 81 Atımtay, Ergin. Figure 8.30 Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 506-507.

61

4.2.6.3 Cantilever Slabs

Open and closed cantilever projections are commonly used to enlarge the rooms

and create space for balconies in residential buildings in Turkey. It should be

remembered that a long cantilever slab will make a large deflection even when

it isn’t under lateral loads. Under earthquake motion, especially closed

projections will make critical displacements, which may lead to a partial

collapse. If cantilever projections are to be made, the beams should be

continuous under the cantilever slab. A side beam should be designed around

the periphery of the projection. This way the overall rigidity will be increased

and all the separate frames will act uniformly under earthquake loads.82

Figure 4.20 Cantilever Slabs83

82 Atımtay, Ergin. Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 517-518. 83 Atımtay, Ergin. Figure 8.41 Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 517.

62

4.2.7 Fundamental Concepts About R/C Columns

4.2.7.1 Columns with Broken Axis

Columns with broken axis should be avoided, otherwise additional moments

will occur in the columns. It is relatively easy to design interior columns with

matching axis (Figure 4.21 a), however, the task is more difficult with the

exterior columns since the façade of the building is generally desired smooth. A

stucco or brick wall can be made to level the surface (Figure 4.21 b) but such a

wall can also be very dangerous during earthquake motion if not constructed

properly. If the column axes don’t match the moments that occur at the

extremities of the columns may cause cracks on the beams (Figure 4.21 c).

Figure 4.21 Columns with Broken-Axis84

84 Atımtay, Ergin. Figure 8.35/8.36 Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 511-512.

63

4.2.7.2 Column-to-Beam Connections

The eccentricities should be minimum in column-to-beam connections,

especially in situations where beams with different cross-sections come

together (Figure 4.22 A.). Otherwise, additional torsion moments will occur at

the joint, which is already under great shear stress. If the connection isn’t

properly reinforced, the concrete will be easily crushed. Below, (Figure 4.22

B.) is a building damaged in a similar condition. Notice that the axis of the

undamaged beam and the collapsed one –one can see the location of the

damaged joint- doesn’t match. The resulting torsion destroyed the connection.

A. B.

Figure 4.22 Column-to Beam Connections85 and An Example of Damage due

to Weak Column-to-Beam Connection in Marmara 1999 Earthquake. 86

85 Atımtay, Ergin. Figure 8.34 Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 510.

64

4.2.7.3 Column Configuration

Two extreme cases are represented below (Figure 4.23) to explain the

advantages of a regular column configuration. It will be very difficult to

establish continuous frames in the irregular plan (Figure 4.23 A.). The beams

will have broken-axis, therefore, the lateral forces will create critical torsion

moments on the system. The lateral rigidity of the building will differ

throughout the plan thus, uneven displacements will occur. To make such a

system resistant to earthquakes, very large and uneconomical element cross-

sections will be needed. On the regular plan (Figure 4.23 B.), the columns are

organized according to an axial system and distributed evenly for every

earthquake direction. The building has high lateral rigidity; therefore, the

displacements are limited. Stresses on the elements will be reduced.

A. B.

Figure 4.23 Irregular vs. Regular Configuration of Columns87

86 Demirtaş, Ramazan. ed., 17 Ağustos 1999 İzmit Körfezi Depremi Raporu, Ankara: January 2000, 247. 87 Tuna, Mehmet Emin, Figure 5.22/5.26 Depreme Dayanıklı Yapı Tasarımı. Ankara: Tuna Eğitim ve Kültür Vakfı Pub. November 2000, 133-135.

65

4.2.8 Fundamental Concepts About R/C Shear-Walls

4.2.8.1 Location of Shear-Walls

Shear-walls are the most effective method of making earthquake resistant

buildings. They increase the lateral rigidity of the structure and reduce

excessive displacements. The location of the shear-walls should be chosen

carefully keeping in mind that the centers of gravity and rigidity are supposed

to be as near as possible. If the shear-walls are concentrated on one side of the

building (Figure 4.24 A.), there will be excessive torsion eccentricities

(Section 4.2.1) and uneven displacements on the structure. Shear-walls should

be located symmetrically and near the center of the building (Figure 4.24 B.).

A. B.

Figure 4.24 Location of Shear-walls.88

88 Gönençen, Kaya. Figure 2/Figure 3A Mimari Proje Tasarımında Depreme Karşı Yapı Davranışının Düzenlenmesi, Ankara: Teknik Yayınevi Pub. 2000, 10-12.

66

4.2.8.2 Configuration of Shear-Walls

A shear-wall is a vertical load-bearing element whose longer side to shorter

side ratio is greater than seven. According to the Turkish Earthquake Code the

width of a shear-wall can be 20 cm minimum. Similar to the configuration of

columns (Section 4.2.7.3), it is better if the shear-walls are organized according

to an axial system. A symmetrical configuration is the most preferable one.

Shear-walls should be distributed evenly for every earthquake direction.

Remember that the critical lateral force direction is parallel to the shorter side

of the building. Shear-walls should be perpendicular to the building façades in

this direction. For architectural purposes, shear-walls can be hidden around

staircase and elevator shafts or placed on the façades of the building.

A. B.

Figure 4.25 Irregular vs. Regular Configuration of Shear-Walls89

89 Tuna, Mehmet Emin, Figure 5.33/5.34 Depreme Dayanıklı Yapı Tasarımı. Ankara: Tuna Eğitim ve Kültür Vakfı Pub. November 2000, 139-140.

67

4.3 Seismic Design Faults in Elevation

4.3.1 Weak Storey (Inter-storey Strength) Irregularity

The columns, shear-walls and partition walls may not be continuous through

the entire building height. Especially in the ground floor, partition walls may be

omitted for architectural and functional reasons. The ratio of effective shear

area ( [total column and shear-wall areas on that floor] + 0.015 [total partition

wall area without the door and window openings] ) in a floor to the effective

shear area of the upper floor is called the shear irregularity coefficient (ηc). If

this coefficient is between 0.8 and 0.6 there is a weak storey irregularity in the

structure. If the coefficient is smaller than 0.6, the building must be redesigned.

Figure 4.26 Weak Storey90

90 Bayülke, Nejat. Figure 2.15 Depreme Dayanıklı Betonarme ve Yığma Yapı Tasarımı, 2nd ed. İzmir: İnşaat Mühendisleri Odası İzmir Şubesi Pub. 1998, 55.

68

The Turkish Earthquake Code describes the Weak Storey Irregularity as

follows:

B1 Weak Storey (Inter-storey Strength) Irregularity: The case in which the ratio of the storey shear strength of any storey, in the specified earthquake direction, to that of the storey above, ηc, is less than 0.80. Σ Ae = Σ Aw + Σ Ag + 0.015 Σ Ak [ηc = (Σ Ae)I / (Σ Ae)I + 1 < 0.80]

During an earthquake partition walls may create additional stresses on the

columns, they may cause short-column irregularities, therefore, they should be

isolated from the structure with earthquake joints.

Figure 4.27 Earthquake Joints in Partition Walls91


69

4.3.2 Soft Storey Irregularity

Soft storey irregularity is similar to the weak storey irregularity. Instead of the

shear strength, the relative displacements of the floors are critical. Soft storey is

commonly seen in the ground floors of residential buildings in Turkey, which

are used as stores. The following factors cause the creation of soft storey:

• If the ground floor columns have the same cross-section but longer

height with respect to other floors, the lateral rigidity will be less and

the displacements will be increased.

• If the shear-walls aren’t continuous in the ground floor, very critical

shear stresses will occur in the ground floor columns.

• Partition walls increase the lateral rigidity of upper floors during

earthquakes. (Figure 4.28) If they are omitted on the ground floor the

moments and the shear forces in the columns will significantly increase.

Figure 4.28 Soft Storey by Deflection Criterion92

92 Gönençen, Kaya. Figure 9 Mimari Proje Tasarımında Depreme Karşı Yapı Davranışının Düzenlenmesi, Ankara: Teknik Yayınevi Pub. 2000, 22.

70

The Turkish Earthquake Code describes the Soft Storey Irregularity as follows:

B2 Soft Storey Irregularity For any given earthquake direction, if the ratio of average displacement of any floor to the average displacement of the upper floor is more than 1.5, there is a soft storey irregularity. [ηki = (∆ I)avr / (∆ I + 1)avr > 1.5]

Figure 4.29 Collapse Mechanism due to Soft Storey93


71

4.3.3 Discontinuity of Vertical Structural Elements

Architects may choose to omit the vertical structural elements in some cases

due to spatial, functional or aesthetical concerns. It is possible for a beam to

carry the load of a column, however this will require uneconomical cross-

sections. There will be excessive moments and shear stresses on the beams

during an earthquake. The Turkish Earthquake Code describes this irregularity

as follows:

B3 Discontinuity of Vertical Structural Elements: There is B3 type irregularity in the cases, where the vertical structural elements (columns or shear-walls) are removed in some stories and supported by beams underneath, or the shear-walls in the upper stories are supported by columns underneath.

Figure 4.30 Discontinuity of Vertical Members in Earthquake Code94

94 Turkish Earthquake Code: Figure 6.5 Afet Bölgelerinde Yapılacak Yapılar Hakkında Yönetmelik. Ankara: 1998, 11.

72

4.3.4 Irregular Motion of Building Blocks

It has been previously mentioned (Section 3.2.1) that seismic behavior is

related with the mass of the building and every molecule creates loads of inertia

proportional with the earthquake energy. In this case the shape of the structure

becomes very critical. If a structure consists of too many building blocks with

different natural periods and lateral rigidities, these blocks will move

individually during an earthquake. There will be critical torsions and shear

stresses at the intersection areas (Section 4.2.3)

Figure 4.31 The Effect of Building Shape to Seismic Performance95


73

It isn’t always possible or architecturally desirable to design a building having a

symmetrical plan. In fact, most of the time, due to the requirements of the

building program, functional and aesthetical concerns the architects decide to

create more complex building forms. Even so, successful seismic performance

can be achieved by dividing the building into structurally independent sections

(Figure 4.32). The separate sections would behave individually without causing

additional torsion moments and shear forces on the entire building. The blocks

would be separated from each other by earthquake joints, which can be

designed in several ways (Section 4.3.5). This way, more creative and

functional buildings can be realized without compensating from the earthquake

safety of the structure.

Figure 4.32 Seismic Design Improvement for Buildings with Several Blocks96

96 Atımtay, Ergin. Figure 8.1/Figure 8.3 Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 466-475.

74

4.3.5 The Pounding Effect

The urban building pattern in Turkey sometimes allows R/C residential

buildings to be built wall-to-wall adjacent to each other. This is a very

dangerous configuration and should be avoided if possible. If the buildings

have to be adjacent, they should be separated with earthquake joints. During an

earthquake every building makes displacements according to its own natural

period. If the buildings make displacements towards each other and there is not

enough space between them, they will hit each other. As a result the adjacent

columns and shear-walls can be destroyed leading to a collapse.97

Figure 4.33 Pounding Effect on Adjacent Buildings98

97 Gönençen, Kaya. Mimari Proje Tasarımında Depreme Karşı Yapı Davranışının Düzenlenmesi, Ankara: Teknik Yayınevi Pub. 2000, 28. 98 Atımtay, Ergin. Figure 8.2c Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 474.

75

The most dangerous type of pounding is between buildings with different floor

levels. In this case, the floor slabs, which have infinite in-plane rigidity, will hit

the columns or shear-walls of the other building. Since the columns have much

less rigidity, critical damage is inevitable.

The Turkish Earthquake Code requires that minimum 30mm space should be

left between buildings up to 6m. After that, the distance will be increased

10mm for every raise of 3m in the height. It shouldn’t be forgotten that these

are only suggested dimensions. They should be confirmed for each particular

building by the calculations of the civil engineer.99

Figure 4.34 Pounding in Buildings with Different Floor Levels100

99 Atımtay, Ergin. Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 471. 100 Bayülke, Nejat. Figure 2.12 Depreme Dayanıklı Betonarme ve Yığma Yapı Tasarımı, 2nd ed. İzmir: İnşaat Mühendisleri Odası İzmir Şubesi Pub. 1998, 52.

76

4.3.6 Irregular Distribution of Masses

Atımtay suggests that irregular distribution of masses can occur in different

ways. A building can look regular from the outside. It may even have a regular

R/C structure but additional masses like heavy machinery and water tanks may

create torsion eccentricities and additional shear stresses (Figure 4.35 A.).

Setbacks and cantilever projections are another form of irregular mass

distribution commonly encountered in the Turkish urban pattern (Figure 4.35

B. & C.). Especially, if they are not on the central axis of the building, they will

create torsion irregularities plus their lateral rigidity will be different from the

floors below and above.101

A. B. C.

Figure 4.35 Irregular Distribution of Masses, Setbacks and Cantilevers102

101 Atımtay, Ergin. Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 476-486. 102 Atımtay, Ergin. Figure 8.4/ figure 8.12 Çerçeveli ve Perdeli Betonarme Sistemlerin Tasarımı, 2 vols. Ankara: METU Press, July 2001, Vol. 2, 476-486.

77

4.3.7 Short Columns

The structural calculations are usually made without taking the partition walls

into consideration. However, it has been previously mentioned (Section 4.3.1)

that partition walls have a critical effect on the seismic behavior of the

structure. This effect may be positive by acting as shear-walls and preventing a

collapse or negative by decreasing the ductility of the structure and causing

additional torsion and shear stresses on structural elements. Short columns are

most frequently caused by low partition walls, which weren’t isolated from the

R/C structure with earthquake joints (Figure 4.36).

78

Figure 4.36 Short Column Example, Nicaragua 1972 Earthquake103

The principal behind the short column formation is simple. According to

Gönençen, when the height of a column decreases, the lateral rigidity of the

element increases and the more rigid a column is, the more lateral force it

attracts on itself. For example, if the height of a column is reduced to half, there

will be two times more bending moment on that element. Short column can

occur at every location where the height of a column is decreased with respect

to other storeys. Low mechanical floors, irregular beam depths in a frame, strip

windows or foundations on inclined topography may cause short columns.104

Figure 4.37 Types of Short Column Formations105

103 Tezcan, Semih. S. Figure 8.3 Depreme Dayanıklı Yapı İçin Bir Mimarın Seyir Defteri İstanbul: Turkish Earthquake Foundation Pub., 1998, 38. 104 Gönençen, Kaya. Mimari Proje Tasarımında Depreme Karşı Yapı Davranışının Düzenlenmesi, Ankara: Teknik Yayınevi Pub. 2000, 35. 105 Gönençen, Kaya. Figure 15 Mimari Proje Tasarımında Depreme Karşı Yapı Davranışının Düzenlenmesi, Ankara: Teknik Yayınevi Pub. 2000, 36.

79

4.3.8 Strong Beam-Weak Column Formation

In case of a strong earthquake, the design priority for a R/C structure is to

prevent a total or partial collapse in order to save human life. To achieve this,

the structure must be able to absorb the maximum energy by ductile

deformations in column-beam connections, while the lateral stability of the

building is preserved.

If the beams of a building are more rigid than the columns (Figure 4.38 A.),

ductile deformations will occur at the top and bottom ends of the columns.

Excessive displacements will cause additional moments and the columns will

easily loose their lateral stability. Since the greatest earthquake forces occur at

the ground floor, these columns will collapse first, probably causing the

destruction of the entire building.

If the columns are more rigid than the beams (Figure 4.38 B.), ductile

deformations will occur at the ends of the beams. R/C beams can absorb a lot of

energy by ductile deformations without an important loss in the load carrying

capacity. In this system, all the beam-column connections in the building have

to fail before the collapse of the ground floor columns. Architects should know

that strong Column-Weak Beam design is not only advisable but also

obligatory according to new Turkish Earthquake Code.

80

Figure 4.38 Collapse Mechanisms in Various Systems106

106 Gönençen, Kaya. Figure 14 Mimari Proje Tasarımında Depreme Karşı Yapı Davranışının Düzenlenmesi, Ankara: Teknik Yayınevi Pub. 2000, 34.

81

4.3.9 Irregularities in Foundations

The design of the foundations is considered mostly as the job of the engineers

by the architects; however, one shouldn’t forget that the earthquake energy is

transferred to the structure through the foundations of the building. A failure in

the foundations may cause the total collapse of a building having a strong

superstructure. Irregular foundations (Figure 4.39 A.) will cause additional

torsions and excessive displacements in the structure. Footings at different

levels may create short column effect; therefore, the foundations of a building

should be on the same level whenever possible. All the footings should be

connected to each other with beams to prevent individual displacements

(Figure 4.39 B.).

A. B.

Figure 4.39 Irregular vs. Regular Foundation107

107 Tuna, Mehmet Emin, Figure 5.68/5.73 Depreme Dayanıklı Yapı Tasarımı. Ankara: Tuna Eğitim ve Kültür Vakfı Pub. November 2000, 158-160.

82

CHAPTER V

THE EFFECT OF COMMONLY ENCOUNTERED SEISMIC

DESIGN FAULTS ON THE BUILDING STRUCTURE: A

SAMPLE STUDY CONDUCTED WITH COMPUTER

GENERATED STRUCTURAL MODELS

5.1 The Objective of the Study

It has been previously mentioned that one of the aims of this thesis is to create a

basic awareness of seismic behavior in architecture students. It is very

important for learners to see that the theoretical knowledge they receive is

applicable to real life conditions. Since it is very difficult, too costly and

impractical to simulate the seismic behavior of an entire building in a

laboratory, computer generated structural models are used in this chapter to

demonstrate the effect of the most commonly encountered seismic design faults

on the building structure.

83

5.2 The Scope and The Procedure

This study is conducted on six types of building models. The first two of these

models are based on actual buildings that were located in İzmit, Bekirpaşa

District. Both of these buildings have collapsed in Marmara 1999 Earthquake.

Due to the lack of detailed engineering reports on the reasons of collapse, it is

impossible to say that the buildings have collapsed due to the seismic design

faults mentioned in this chapter; however, it is a strong possibility that these

faults have played an important role in the failure of these structures. The

remaining four models are derived from architectural configurations that are

likely to occur in the real life. The buildings, the structural and architectural

elements are dimensioned similar to the R/C residential buildings that exist in

Turkish urban pattern.

The scope of this study is limited with the structural knowledge expected from

an architect. That means: this study doesn’t make a detailed structural analysis

of the buildings. There isn’t any discussion about the properties of the structural

materials, the amount of reinforcement or the load carrying capacity of

individual structural elements. This study simply shows that, if a building

contains one or more of the seismic design faults mentioned before, there will

be a significant increase in the stresses and moments that the building has to

resist during an earthquake.

84

The structural modeling of the buildings is made with SAP90 and SAP2000

software. Each building model is prepared to reveal the effect of one major

design fault on the structure. To be able to isolate and demonstrate a particular

defect, the models are simplified. The buildings are assumed to be made of

R/C. Most of the non-structural elements are omitted except the partition walls

in some models, where their effect on the seismic behavior is critical. The self-

weight of the structural elements are included into the calculations. The

earthquake loads are applied as if the buildings were located in a first-degree

earthquake zone in Turkey.

Figure 5.1 A Soft Storey Formation in İstanbul108

108 Tezcan, Semih. S. Figure 16.1 Depreme Dayanıklı Yapı İçin Bir Mimarın Seyir Defteri İstanbul: Turkish Earthquake Foundation Pub., 1998, 92.

85

5.3 Computer Models of Defective Buildings

5.3.1 A Residential Building with Irregular Plan

This is a building model based on a two-storey R/C residential building

collapsed in Marmara 1999 Earthquake. The building was located on a road

junction, which generated an irregular building site (Figure 5.2). Due to

economic reasons the building was designed to make the maximum use of the

site, which resulted in an irregular structural plan. The actual reasons of the

collapse are unknown; however, this building contains some of the seismic

design faults mentioned in Chapter IV, which may have played a critical role in

the failure of the structure.

Figure 5.2 Site Plan and Typical Structural Floor Plan109

109 Graphics are created with SAP90/SAP2000 Software. Input data available in Appendix A

86

Figure 5.3 Perspective Views

Irregularities:

• Torsion Eccentricity

• Non-Parallel Axis of Structural Elements

• Non-Continuous Beams/Frames

• Irregular Spans

• Beams Intersecting without Vertical Support

87

The most critical of these irregularities for this case is the torsion eccentricity,

which creates a significant torsion stress on the single column located near

corner B. Whether this stress is within the load carrying capacity of the column

or not is an engineering issue. It is related with the cross-section, the choice of

material and the amount of reinforcement. What an architect should see here is

that, in this structural configuration, the torsion stress on Column No: 2 is

nearly 8 times greater then the stress on Column No: 1. This irregularity is the

result of the architectural design of the building. It is the architect’s duty to be

aware of such an irregularity in the load distribution and make sure that the

structural engineer takes the necessary precautions.

Figure 5.4 Torsion Diagram

88

5.3.2 A Building with Deficient Column Configuration

This model is based on a four-storey R/C residential building collapsed in

Marmara 1999 Earthquake. The building site has a rectangular shape, which is

typical in Turkish urban pattern (Figure 5.5). The ground floor of the building

is designed as a store; therefore, the number of the vertical support members is

kept in minimum. The position of the building on the site suggests that it once

was wall-to-wall adjacent with another building of similar typology.

Figure 5.5 Site Plan and Typical Structural Floor Plan110

110 Graphics are created with SAP90/SAP2000 Software.

89

Figure 5.6 Perspective Views

Irregularities:

• Torsion Eccentricity

• Non-Continuous Beams

• Irregular Spans

• Beams Intersecting without Vertical Support

• Deficient Column Configuration

• Eccentricity in Shear-Wall Locations

90

All the columns of this structure are positioned with their larger cross-section

parallel to x-direction. Since the lateral rigidity of a column is proportional to

the moment of inertia, this structure has very low lateral rigidity in y-direction.

As a result, the building makes large displacements in this direction. The only

shear-wall of the structure is positioned with eccentricity to the center of

rigidity; therefore, the displacements are not only large but also irregular. It has

been mentioned that the building was possibly wall-to-wall adjacent with

another one. In that case, the lack of lateral rigidity may have caused a

pounding effect with the next building, resulting the collapse of the structure.

Figure 5.7 Large and Irregular Floor Displacements

91

5.3.3 Building Model with Soft Storey Formation

This is the first of the building models based on architectural configurations

likely to occur in the R/C residential buildings in Turkey. The four following

models are generated from the same structural floor plan (Figure 5.8). The

dimensioning is made regarding the size of an average residential building in

Turkey. The floor spans are similar to actual spans encountered in R/C

structures. The aim of these models is to isolate and demonstrate the effect of a

particular design fault; therefore, the other factors, such as the column

configuration and dimensioning of spans are made not to create any critical

effect on the structure. This model demonstrates the stresses created by the soft

storey formation.

Figure 5.8 The Structural Floor Plan for Sections 5.3.3/4/5/6

92

In this model, the height of the ground floor is chosen greater than the average

floor height with reference to the actual buildings of which the ground floors

are used as shops. While the floor height increases, the column cross-sections

remain the same. The façades of the upper floors (residential use) are covered

with partition walls while the façades of the ground floor are open (openings for

shop windows). When the earthquake forces are applied it is observed that the

shear stresses in Column No: 1 are 18 times greater than the ones in Column

No: 2 (Figure 5.10) and the Torsion stresses in Column No: 1 are 8 times

greater than Column No: 2. (Figure 5.11) The architect should be aware of this

stress concentration in the ground floor columns and take the necessary

precautions consulting the structural engineer.

Figure 5.9 Model Building with Soft-Storey

93

Figure 5.10 Shear Force Diagram


94

5.3.4 Building Model with Short-Column Formation

The building is generated from the same structural plan with the previous

example (Figure 5.8). The storey heights are equal. The façades are covered

with partition walls. In the ground floor there is a 1m wide opening. This is to

simulate the effect of strip windows. The earthquake forces create significant

shear and torsion stresses in the short-columns. The shear stress in the

freestanding upper portion of Column No: 1 is 3045 times greater than the

stress in lower part (Figure 5.13). The torsion stress in the upper portion is 340

times greater than the stress in lower part (Figure 5.14). The formation of short

columns should be prevented with the use of earthquake joints (Section 4.3.1).

Figure 5.12 Model Building with Short-Column

95

Figure 5.13 Shear-Force Diagram


96

5.3.5 Building Model with Weak-Storey Formation

The structural floor plan is again the same (Figure 5.8). Floor heights are equal.

The partition walls on the façades are omitted in the second floor. There is a

rigid central core (i.e. shear-walls around the service space.). This time, the

lateral forces create significant stresses in the second floor columns. The shear

stress in Column No: 1 is 32 times greater than the average shear stress on other

floors (Figure 5.16). The torsion stress in Column No: 1 is 4 times greater than

the average torsion stress on other floors (Figure 5.17).

Figure 5.15 Model Building with Weak-Storey

97

o



98

5.3.6 Building Model with Shear-Wall Eccentricity

In this model the partition walls are omitted in all floors. There is a rigid core

near the corner C. of the building (i.e. shear-walls around the service space.).

The structural behavior of this model is similar to the buildings with curtain-

walls. Under earthquake forces we observe that the shear and torsion stresses

significantly increase in the structural elements far from the rigid core (near

corner A.). The shear stress in Column No: 1 is 6 times greater than the shear

stress in Column No: 2 (Figure 5.19). The torsion stress in Column No: 2 is

two times greater than the torsion stress in Column No: 2 (Figure 5.20).

Figure 5.18 Model Building with Shear-Wall Eccentricity

99



100

5.4 The Results of the Study

This study with the computer generated structural models, demonstrates that the

seismic design faults mentioned in Chapter IV have an important effect on the

earthquake behavior of R/C structures. The most critical of these effects is the

extreme irregularities in the stress distributions. In some cases, structural

elements with similar cross-sections are subjected to considerably different

stresses (Shear stresses in Section 5.3.4). It is very difficult for structural

engineers to calculate such unpredictable loading conditions. Even if we

assume that the calculations and engineering designs are properly made, it is

quite possible that one may end up with uneconomic cross-sections and

structural system details that are difficult and risky to produce.

Designers should always be able to use their creative freedom and the means of

technology in a balanced manner. Architects may choose to design an irregular

building structure if they believe that such a solution will contribute to the

quality of the architectural space but the choice must be made consciously. The

architect should be aware of the structural implications of this choice and take

the necessary precautions consulting the structural engineer.

101

CHAPTER VI

CONCLUSION

This thesis has two objectives. The primary objective is to demonstrate that the

architectural design of a building has a significant effect on its seismic behavior

and that, many defects that cause the collapse of a building are due to its

architectural design. The secondary objective is to create a source, especially

for students of architecture, about the nature of the earthquake phenomenon, the

earthquake behavior of reinforced concrete and the commonly encountered

seismic design faults in Turkey. As a student and an architect, the author

believes that such a study, prepared by one of them would help the young

architects grasp the essence of earthquake behavior of reinforced concrete

buildings.

Turkey is a developing country with limited economic resources. Like in many

other disciplines, the role of the architects in building production and the

professional quality are far from the standards of the developed world. The

102

majority of the R/C buildings built in this country are mass-produced by

ignorant contractors without the real involvement of an architect. The market is

full of architects who sell their signatures without any sense of professional

ethics. Even when a building is truly designed by an architect there is always

the powerful influence of the project owner whose primary concern is to make

the maximum profit even at the expense of compromising the security of

human life. However, none of the factors stated above can be an excuse of

ignorance for a self-respecting member of the community of architects. As the

members of a society, which is a candidate for the European Union

membership, it is a personal duty to make one’s best to achieve the finest

standard in one’s discipline.

The message of this thesis shouldn’t be confused. This thesis doesn’t claim that

an architect should have the structural knowledge of an engineer, nor does it

say that earthquake resistant building design is solely an architectural issue.

This thesis states that the design of an earthquake resistant building starts in the

drawing table of the architects, who should have the necessary amount of

structural knowledge to evaluate the structural implications of their

architectural decisions. The grasp of the architect about the seismic behavior of

a building is and should be mostly intuitive but to acquire this intuition an

architect must have at least a basic knowledge of the earthquake phenomenon

and the how it effects the structures. The most efficient way of designing an

earthquake resistant building is the full co-operation between the structural

103

engineers and the architects. This co-operation can only be provided if the

engineers and the architects are able to speak each other’s language.

Earthquake should be considered as the judgment day for everyone involved in

the building construction sector from architects to engineers; from contractors

to construction workers. An earthquake doesn’t care about the awards that an

architect has won; it doesn’t care about the beauty or the elegance of the design.

The philosophy of the building becomes meaningless when the earthquake

strikes. Only one thing is important and that is the strength of the structure.

Architects can only design an earthquake resistant building if they are familiar

with the dynamics of seismic behavior. Earthquake resistant building design is

one of the rare moments in architecture where only knowledge matters. It is the

moral obligation and the duty of an architect to acquire this knowledge.

In conclusion, there is a lot to be done to establish the tradition of making

earthquake resistant buildings in Turkey. If one considers the various factors

and the amount of politics involved in the construction industry, it would be

unrealistic to think that the building quality will dramatically increase in a short

period of time. Reaching this target requires a lot of effort and it is easy to be

discouraged on the way; however, one shouldn’t forget that the price for

ignorance is the loss of human lives. This thesis hopes to take one more step in

creating a higher standard in Turkish architecture.

104

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