relationship between outrigger position and...

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RELATIONSHIP BETWEEN OUTRIGGER POSITION AND EXTERNAL

COLUMNS SIZE IN MINIMIZING BUILDING RESPONSE TO WIND

ABDULKAREEM MUYIDEEN OLADIMEJI

A project report submitted in fulfilment of the

requirements for the award of the degree of

Master of Engineering (Civil - Structure)

FACULTY OF CIVIL ENGINEERING

UNIVERSITI TEKNOLOGI MALAYSIA

JUNE 2010

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ACKNOWLEDGEMENT

I would like to acknowledge my supervisor, Dr. Roslida Abd. Samat, for the

guidance and assistance she gave me in understanding the behaviour of tall building

during the course of this thesis.

I also wish to express my sincere appreciation to my dad, Prof. Y.A.

Abdulkareem and my entire family for the support given to me during my course of

study at the University Teknologi Malaysia (UTM).

I am also grateful to Mr. Ibrahim Bamgbopa, Dr. Joseph Dodo and Mr. Zinas

Bako for their efforts during my admission. I would like to thank all my friends, both

at UTM and Nigeria for their moral support and understanding.

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ABSTRACT

This research presents the relationship between the position of outrigger and

the size of the external columns in minimizing the building responses to wind.

Outrigger system has been one of the many structural systems in tall buildings used

to reduce the building responses to wind load. The study on the usage of this system

has been given little or no attention to the effect of the size of the external columns to

the optimum position of outrigger. This research involves the position of the

outrigger being varied and the responses: displacement and acceleration being

computed. The procedure is repeated for each different size of the external columns.

This analysis is carried out with the use of structural analysis computer software to

determine the natural frequency of the building and Excel spreadsheet to determine

the responses. The observations from the analysis will provide the conclusion on the

relationship between the size of the external columns and the outrigger location with

respect to the building response to wind.

Keywords: outrigger, wind, column size, tall building, building response.

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ABSTRAK

Penelitian ini menyajikan hubungan antara kedudukan cadik dan saiz medan luaran

dalam meminimumkan tanggapan bangunan untuk angin. sistem outrigger telah

menjadi salah satu sistem struktur bangunan tinggi banyak digunakan untuk

mengurangkan tanggapan bangunan untuk beban angin. Kajian mengenai

penggunaan sistem ini telah diberikan sedikit atau tidak ada perhatian pada pengaruh

saiz medan luaran ke kedudukan optimum outrigger. Penyelidikan ini melibatkan

kedudukan outrigger yang sedang bervariasi dan respons perpindahan dan percepatan

sedang dikira. Prosedur ini diulang untuk setiap saiz yang berbeza dari medan

luaran. Analisis ini dilakukan dengan menggunakan perisian komputer analisis

struktur untuk menentukan frekuensi alami bangunan dan spreadsheet Excel untuk

menentukan jawapan.Pengamatan dari analisis tersebut akan memberikan

kesimpulan tentang hubungan antara saiz medan luaran dan lokasi outrigger

berhubung

Kata kunci: outrigger, angin, saiz medan, bangunan tinggi, bangunan respon.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

ACKNOWLEDGMENT iii

ABSTRACT iv

ABSTRAK v

TABLE OF CONTENT vi

LIST OF TABLES ix

LIST OF FIGURES x

LIST OF SYMBOLS xiii

LIST OF APPENDICES xvi

1 INTRODUCTION

1.1 Introduction 1

1.2 Problem statement 2

1.3 Hypotheses 3

1.4 Objective of study 3

1.5 Scope of study 3

1.6 Significance of study 4

2 LITERATURE REVIEW

2.1 Nature of wind 5

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2.1.1 Gradient height 7

2.1.2 Design for wind effects 8

2.2 Design criteria 9

2.3 Tall building response to wind affects 10

2.3.1 Wind interference 12

2.3.2 Along-wind response 13

2.3.2.1 Maximum along-wind response 15

2.3.2.2 Maximum along-wind acceleration 16

2.3.3 Across-wind response 16

2.4 The use of outrigger in tall buildings 20

2.4.1 Benefits of outrigger 28

2.4.2 Problems with outriggers 28

2.5 Dampers 29

2.6 Columns in tall buildings 33

3 METHODOLOGY

3.1 Modelling 34

3.2 Building properties 34

3.3 Outrigger positions and columns sizes 35

3.4 Wind speed 36

3.5 Along-wind Response 36

3.6 Along-wind acceleration 37

3.7 Across-wind response 37

4 RESSULTS AND DISCUSSION OF RESULTS

4.1 Introduction 39

4.2 Frequency 42

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4.3 Responses 47

4.3.1 Along-wind Response 47

4.3.2 Across-wind Response 52

4.4 Validation of Analysis using Staadpro 57

4.4.1 Analysis using manual calculation 57

4.4.2 Analysis using Staadpro 60

4.5 Calculations 62

4.5.1 Modal mass 65

4.5.1.1 Building with Column size: 1.3m x 1.3m 65

4.5.1.2 Building with Column size: 2m x 2m 66



5 CONCLUSION

5.1 Introduction 68

5.2 Variation of outrigger position and column size 68

5.3 Conclusion 69

5.4 Further research 69

REFERENCES 71

APPENDICES 73

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LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Terrain category and roughness length 8

4.1 Frequency table 37-38

4.2 Along-wind response 42-43

4.3 Across-wind response 46-48

4.4 Mass of Buildings 57

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Mean wind profiles for different terrains 7

2.2 Buildings in a row with the wind direction 12

2.2 Computed wind flow pattern around a row of three

square-plan buildings 13

2.4 Vortex formation 17

2.5 A typical wind tunnel 18

2.6 A schematic of a typical open-circuit wind tunnel 18

2.7 Wind on a tall building 20

2.8 braced-core walls with and without outrigger 21

2.9 A typical plan of an outrigger-braced building 22

2.10 An outrigger and belt truss system 23

2.11(a) Building with belt truss as ‘virtual’ as outrigger 24

2.11(b) Force transfer using belt truss 24

2.12 Force transfer using basement as virtual outrigger 25

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2.13 Simplified plan of building 26

2.14 Shear wall with outrigger truss 27

2.15 Damped outrigger concept 29

2.16 Tuned mass damper in test fixture 30

2.17 Conceptual detail at outrigger level 31

2.18 Typical layout at outrigger levels 31

2.19 Tendon control mechanism 32

3.1 Plan of the model to be used 35

3.2 Cross-section of Models 38

3.3 Balsa wood model sample 38

4.1 Buildings with various outrigger positions and

columns sizes 41

4.2(a) Along-wind frequency vs. outrigger position 44

4.2(b) Across-wind frequency vs. outrigger position 44

4.2(c) Torsional frequency vs. outrigger position 45

4.3(a) Along-wind frequency vs. column size 45

4.3(b) Across-wind frequency vs. column size 46

4.3(c) Torsional frequency vs. column size 46

4.4(a) Along-wind displacement for different outrigger

positions and different column sizes 50

4.4(b) Along-wind displacement for the same position

of outrigger and different column sizes 50

4.5(a) Along-wind displacement for different outrigger

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4.5(b) Along-wind displacement for the same position of

outrigger and different column sizes. 51

4.6(a) Across-wind displacement for different outrigger


4.6(b) Across-wind displacement for the same position of

outrigger and different column sizes 55

4.7(a) Across-wind acceleration for different outrigger


4.7(b) Across-wind acceleration for same position of

outrigger and different column sizes 56

4.8 Free body diagram of the cantilever beam 58

4.9 Cross-section of cantilever beam 58

4.10(a) Core wall 60

4.10(b) Meshed diagram of core wall 61

4.11(a) 3-D Solid core-wall 61

4.11(b) 3-D meshed core-wall 62

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LIST OF SYMBOLS

b - breadth

- mean hourly wind speed factor

- 3-sec gust speed factor

C - turbulence intensity factor

Cfx - mean along-wind force co-efficient

D - diameter of building

E - modulus of elasticity

f - frequency of vortex shedding

Gf - gust factor

gp - peak factor

gQ - peak factor for resonant response

gR - peak factor for resonant response

gV - peak factor for resonant response

h - height

I - moment of inertia

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I - intensity of turbulence

K - wind directionality factor

L - length

L - integral length scale of turbulence

ℓ - integral length scale factor

m1 - modal mass

meff - effective mass

N1 - reduced fequency

n1 - building natural frequency

∅( ) − fundamental modal shape ( ) − rms along − wind acceleration

P - applied load

ρ - air density

Q - background response factor

R - resonant excitation

RB, Rh, RL - values from Eq 6-13

Rℓ - reduction facrtor

r - roughness factor

S - stroudal number

Sg - gust speed

Sm - mean speed

T - length of time – 3600s

t - thickness

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µ(z) - mass per unit height

V - 3 sec gust speed at height Vol - volume

− 3 sec ℎ ℎ ℎ =( 33) X(maz)(z) - maximum along-wind displacement

y - deflection

z - height above ground level

- equivalent height of structure

α - 3-sec gust speed power law exponent

- mean hourly wind speed power law

- reciprocal of α

� - mode exponent

∈ - integral length scale power law exponent

- mode exponent

- natural frequency of vibration

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LIST OF APPENDICES

APPENDIX TITLE PAGE

A Terrain category and roughness length 73

B Natural frequency tables 74

C Along-wind response tables 76

D Across-wind response tables 78

E Mass of Buildings 80

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CHAPTER 1

INTRODUCTION

1.1 Introduction

Wind effects on tall buildings have been a major determinant in the

architecture and design of such buildings. Several structural systems have been

developed and incorporated in many tall buildings to control and reduce the response

of these buildings to the lateral loads caused by wind.

The acceptable drift limit (top deflection in tall building) according to the

Malaysian Code (M.S 1553:2002) is 1/500 of the building height. The ASCE7-02

states that the drift limit is 1/400 of the building height (ASCE Task Committee on

Drift Control, 1988). The acceleration is also an important factor of the drift that

brings about the feel of the building drift (motion) to human notice. A building

response of acceleration up to 0.5m/s2 causes difficulty to walk naturally and also to

lose balance when standing at the top of such buildings (Yamada and Goto, 1975).

The use of core-wall system has been a very effective and efficient structural

system used in reducing these responses due to lateral load. But when the building is

taller than 500ft (152.4m), the core does not have the adequate stiffness to keep the

wind drift down to acceptable limits.

A structural system known as outrigger system is added to this tall building.

This outrigger system consists of a deep horizontal cantilever beam connecting the

main core of the building to the outer (exterior) columns. This outrigger helps in

tying-down the exterior columns to the core wall. Here the column double functions

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as gravity loads support and also as a restraint to the lateral movement of the core.

The movement of the core is reduced as compared to a free-standing core alone

resisting the lateral loads. The restrain introduces a point of inflection in the

deflection curve thus reducing the lateral movement at the top. The stiffness created

by the inclusion of the outrigger is increased up to 25 to 30 percent of the original

structure without the outrigger in place (Taranath, 1988).

Wu and Li in 2003 suggested that the location of outriggers should be as near

as possible to the building foundation in order to reduce the base moment in the core.

Samat, Ali and Marsono in 2008 stated that the optimum location to construct the

outrigger is between the one-quarter to the two-third of the height of the building to

minimize the wind responses of the building.

The exterior columns acting as a tie-down of the core is definitely of great

importance to the entire system to function properly. The size of these exterior

columns will have a great impact in the degree of the stiffness required for the

system to perform. To this, the size of the exterior columns will play a vital role in

affecting the best location of the outrigger to minimize the building’s response to

wind.

1.2 Problem statement

The use of outrigger-braced system is gaining more widely acceptance as a

structural system to reduce drift in tall buildings. This system contains three main

elements, i.e. deep outrigger beam, the core wall and the exterior (external) columns.

The performance of this system has been proven to be influenced by the size of the

core wall and location of the outrigger beam (Samat, Ali and Marsono. 2008).

Presently, the relationship between the size of the external columns and the optimum

position of the outrigger is not known. Therefore to find this relationship, a 64

stories building, each story with a height of 4.5m, will be considered with several

positions of outrigger for each different column size.

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1.3 Hypotheses

It can be guessed that the drift of the tall building will be decreased with an

increment of the column size to a specific size having the position of the outrigger

beam being changed. The decrement in wind response will reach a minimum at a

certain position of the outrigger, for each size of external column used.

1.4 Objective of study

The objectives of this study are as follows:

i. To investigate the effect of the external column size to the optimum position

of the outrigger in tall building to minimize the wind response (acceleration

and displacement).

ii. To suggest the optimum column size for any position of the outrigger in tall

building to get the minimum wind drift response.

1.5 Scope of study

The scope of this work will focus on the wind response of tall building with

regards to the external column sizes and outrigger positions. A building with a square

plan of 48m x 48m with a height of 288m is used for the model. Here, the column

size and outrigger position are being varied and the response of the building being

computed.

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1.6 Significance of study

The response to wind by tall buildings which are outrigger-braced is

influenced by the position of the outrigger. In this study, computer model analysis

together with computation of responses by a program written is used to investigate

how the size of the exterior columns influences the optimum position of the

outrigger. This study will help dictate the appropriate positioning of the outrigger

beam for a particular column size and vice versa in order to get an optimum

response. The application of a particular outrigger position for a particular external

column size and vice versa can be comprehensive and recommended for the

engineers in the construction industry for the construction of tall buildings. This will

also help in saving time, materials and labor costs.

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REFERENCES

1) Taranath, B. S. (1988) Structural Analysis and Design of Tall Buildings.

McGraw-Hill Book Company, New York.

2) Smith, B. S., Coull, A. Tall Building Structures: Analysis and Design. John

Wiley and Sons, Inc, New York.

3) Mendis, P., Ngo, T., Haritos, N., Hira, A., Somali, B., Cheung, J., (2007).

Wind loading on Tall Buildings. Journal of Structural Engineers, Special

Issue.

4) Lam, K., Leung, M. Y. H., Zhao, J. G., (2008). Interference effect on Wind

Loading of a Row of Closely Spaced Tall Buildings. Journal of Wind

Engineering and Industrial Aerodynamics, pages 562-583

5) Pan, L. B., Liu, P.C., Bakoss, S.L. (1993). Long-Term Shortening of

Concrete Columns in Tall Buildings. Journal of Structural Engineers.

6) Nair, R. S., (1998). Belt Trusses and Basements as “Virtual” Outriggers for

Tall Buildings. Engineering Journals.

7) Samat, A. R., Ali, N.M., Marsono, A. K., (2008). The Optimum Location of

Outrigger in Reducing the Along-wind and Across-Wind Responses of Tall

Buildings. Malaysian Journal of Civil Engineers.

8) Kian, P. S., Siahaan, F. T., (2001). Use of Outriggers and Belt Truss System

for High-Rise Concrete Buildings. Dimensi Teknik Sipil.

9) Wu, J. R., Li Q.S., (2003). Structural Performance of Multi-Outrigger-Braced

Tall Buildings, Journal of Structural Design of Tall and Special Buildings.

10) Ziedabadi N. A., Mirtalae K., Mobasher B., (2004). Optimised Use of the

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Journal of Tall and Special Buildings.

11) Hoenderkamp, J. C. D., (2008). Second Outrigger at Optimum Location on

High-Rise Shear Wall. Journal of Tall and Special Buildings.

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13) Smith, R. J., Willford M. R., (2007). Damped Outrigger Concept for Tall

Buildings. Journal of the Structural Design of Tall and Special Buildings,

pages 501-517.

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Journal of Structural Engineers, Vol. 109, No 3.

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