SCHOOL: LOVELY SCHOOL OF BUSINESS AND ARTS

COURSE CODE: ARC 431

COURSE TITLE: ARCHITECTURAL DESIGN & THESIS I

Name of student: Divyanshu Krishna

Registration Number: 10810562

Roll Number: RA1801B37

Section Number:

Academic Year: 2008-2013

Name and Signature of faculty advisor / mentor:

Name and Signature of Thesis Coordinator: _______________________________________

Name and Signature of HOD: __________________________________________________

Name and Signature of DOD: __________________________________________________

Name and Signature of HOS: ___________________________________________________

CERTIFICATE

This is to certify that Divyanshu Krishna bearing Registration no. 10810562 has

completed dissertation titled, “WIND FORCES ON HIGH RISE STRUCTURES” under my

guidance and supervision. To the best of my knowledge, the present work is the result of her

original investigation and study. No part of the dissertation has ever been submitted for any other

degree at any University.

The dissertation is fit for submission and the partial fulfillment of the conditions for the

award of .........................

Signature and Name of the Research SupervisorDesignationSchoolLovely Professional UniversityPhagwara, Punjab.

Date :

DECLARATION

I, Divyanshu Krishna , student of B.Arch under Department of Architecture of Lovely

Professional University, Punjab, hereby declare that all the information furnished in this

dissertation / capstone project report is based on my own intensive research and is genuine.

This dissertation / report does not, to the best of my knowledge, contain part of my work

which has been submitted for the award of my degree either of this university or any other

university without proper citation.

Date: Divyanshu Krishna

Registration No. 10810562

Dissertation Topic: Wind Forces on High Rise Structures

Abstract: - In the fields of architecture, construction is a process that consists of the building

or assembling of infrastructure.

Construction technology is a branch in which we study different ways to construct a design on

ground. Construction technology deploys various technological methods to its advantage and

thus helps us to construct a very complex structure in a easy way and also making that structure

very stable to withstand various forces of nature and humans.

Construction technology also helps us to make structure more sustainable and eco friendly so

that we do not harm the surrounding of that structure in a broad way. Modern construction

technologies can even make a building self sustainable and also helps in increasing the

environment.

In construction technology of high rise buildings we study the different ways of making a high

rise structure viable and resistant to forces of nature i.e. gravitational pull, wind force (especially

in buildings above 25 floors), seismic forces(In location of high seismic activity). However the

one thing that is most important around the world that is always taken care of is wind pressure

because not every region is earthquake prone and gravitation pull is same throughout. Wind

pressure on the other hand is omnipresent and is different everywhere.

Wind forces play a very major role in deciding the overall form of building in case of high rise

buildings as the force increases drastically with increase in height. Form and shape of building is

often decided keeping in mind the wind forces of the surrounding, also the structure of building

is designed keeping in mind the wind velocities at the top floors of a high rise.

Methodology: -

Study about winds, their types and various components of winds that can potentially

affect the building

Study will be based on the data research of various high rise structures, their case studies

and what measures they have taken to minimize the effect of wind pressure on building

more then 25 floors high.

Researching books on wind pressure and effect of wind pressure on tall buildings.

Research will be in progress with the help of surveys with architects having experience of

designing high rise structures.

Objectives:-

To study the various wind conditions and its effect on sky scrapers.

To prepare a solution for construction of high rise building so that it is stable and can

bear the forces of nature i.e. gravitation, wind forces, seismic activity.

To derive methods for construction of buildings that can be safer for workers.

To derive methods for cost effective building methods.

To derive forms and methods so that building has to bear the minimum wind pressure on

it.

Chapters:-

1. Introduction

2. Study about winds, their types and different components of wind.

3. Effects of winds on a High rise structure.

4. Case Examples of

a. Petronas Towers

b. Taipei 101

c. Burj Khalifa

d. The Gherkin

5. Architectural based designs for effective high wind pressure sustaining building and use

of advance construction technology to attain maximum efficiency in doing so.

6. Conclusion.

Introduction:-

Wind Forces in High Rise Buildings

To understand Wind Forces and how to counteract on them to attain a Stable design for a high

rise building we must first understand what wind is

Wind: It is a flow of air from a high pressure area to a low pressure area. Since Earth is a

rotating planet hence wind is also affected by Coriolis Effect except at equator as it always

remain at a particular rotational plane.

But in architecture this phenomenon is greatly changed due to fact that there are various

structures that govern the movement of wind. It is composed of eddies of different magnitude

and rotational characteristics moving along a general stream. Turbulent character (unsteady

movement of wind) is due to these eddies. Because of the turbulent character of wind there arises

various consequences i.e. dynamic (moving not static) loading on that structure depends upon

size and magnitude of wind eddies. Big eddies which can be as big as structure give rise to well

co-related pressure which cover the building and form a kind of envelope around the structure

whereas small eddies result in different pressures on different parts of structure which is more

problematic and has to be resolved to achieve a strong structure.

Because of surface features like structures, rocks, organic things the gustiness (strong rush of

wind) of wind arises in lower levels of atmosphere.

Wind Speed: Speed of wind is basically due to the amount of pressure difference between two

zones and also the distance between them. It is also governed by the friction between air and

different surface features. Hence speed of wind increases with increase in height because there is

less friction and less barriers which allows it to flow smoothly and gustiness decreases. The

image below gives annual average wind speed measured 50 meters above the ground or sea.

meters per second

0.0 1.3 2.7 3.5 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 >12.0

                             

0.0 2.9 6.0 7.8 10.0 11.2 12.3 13.4 14.5 15.7 16.8 17.9 19.0 20.1 >26.8

miles per hour

©www.climate-charts.com

© IS 875: Wind loads on building and structure

Wind Direction:

Wind Loads: The properties of wind pressure on a structure are a function of properties of the

flowing wind, the shape , size and form of structure under consideration. The wind pressure are

never steady, they are highly fluctuating due to gustiness of wind and form of structure. These

fluctuations in wind pressure cause fatigue damage to structure.

Different Kinds of wind effects:-

Environmental Wind effects: They are the wind effects caused by the structure after it is

completely erected on the surrounding and close proximity of it, on other buildings, the

walkways roads and everything around it.

Wind Loads on Façade: They are the wind effects that act on the exterior surface of any

structure. They are considered very important because a large proportion of money is

spent on creating a façade and choosing the material for it so it doesn’t collapse.

Wind Loads on Structure: Structure is the most important aspect of any building as it has

to take care of all the exterior and interior forces acting on a building and has to

withstand them. Wind load on structure is major issue when it comes to high rise

buildings as wind pressure at high altitude is great and capable enough to cause enough

torsion and force to collapse a building.

Design Implementations:-

Stability of Structure: One of the most important aspect to keep in mind while designing

a building is that the building after completion should be stable and don’t move or shake

due to different forces (primarily wind forces) else in due course of time building will get

disintegrated and finally get collapsed.

Strength of Structure: Building should be strong enough to handle all the forces acting on

it. Especially in case of high rise buildings because of presence of high wind forces that

work all the time to make building unsuccessful.

Serviceability: Structure should be strong enough so daily works can be performed inside

it. There shouldn’t be vibration above permissible amount else it would hinder routine

life in that structure. Noise due to winds has to be reduced because at high altitude the

noise can be a source trouble. Damping is another phenomenon that keeps a building

intact if it is constructed in a windy region.

During the past 200 years, 3 major types of structures have been employed in tall structures:

Evolution of Tall Buildings,

1850 onwards

1st Generation 2nd Generation 3rd Generation

Cast Iron Buildings Framed Structures Structural Core

Gravity Load was carried Skeleton of welded or riveted A core, made of steel

Mostly by external walls, steel columns and beams run or concrete or a mix

Generally made of cast through. Exterior being just a the two containing

Iron. curtain wall. Eg. Empire State many services. Eg.

Building. Taipei 101, etc

Examples:-

Petronas Towers: Located in Malaysia the Twin towers have a height of 452m and the

tallest building on its completed date. Its plan is inspired from Muslim architecture

Methods to reduce wind pressure used are :-

Building is designed in two squares overlapping each other creating a eight

pointed plan which is susceptible to much less wind pressure as compared to a

regular square or rectangular plan.

Designers have used tapering form so as we go up the building becomes thinner

and thinner. As we go up the building its radii keeps on decreasing which causes

a great decrease in amount of wind pressure structure has to bear at great heights.

© http://www.tripadvisor.com/Attraction_Review-g298570-d317521-Reviews-

Petronas_Twin_Towers-Kuala_Lumpur_Wilayah_Persekutuan.html

Taipei 101: Located in Chinese Taipei, this building has a height of 510m.

Being located in tropical zone Taipei 101 is subjected to typhoons as well as

severe earthquakes.

Methods used to reduce wind pressure are:-

The structure is reinforced by a Moment Frame System linking the

columns on all floors.

Tapering of the twin towers as the height increase reduces area exposed to wind pressure and thus decrease wind pressure on such height.

The sky bridges between floors 41 and 42 are not rigidly connected to either tower so in case of high wings the bridge can move independently of the towers and can stabilize the towers.

36 columns provide vertical support, including eight mega columns

around the perimeter.

Massive Steel Outrigger Trusses span between the columns on every eight

floors.

The Tower is built on 380 concrete piles, sunk 80 meters into the ground.

They used corner softening technique to the initially proposed square of

52.99m which resulted in 25% reduction in wind pressure effects.

©http://www.executivecentre.com/service-office-locations/floor-plans/taipei-101.html

Secondly they installed Tuned Mass damper between floors 87 to 92. It has a

diameter of 5.5m and weighs 660 metric ton. It can reduce buildings movement

due to strong winds by 30-40%. It works on phenomenon of oscillations.

The W-shaped corners minimises the wind load on the structure

Eight mega columns around the perimeter

provide the vertical support to Taipei 101.

8’ x 10’

Burj Khalifa : Located in Dubai. It’s the tallest building ever made with a height of

828m height. They have used tapering method, Setbacks, changing cross-section and

orientation to reduce wind pressure.

Methods used to reduce wind pressure are:-

The tri-axial ‘Y’-shaped plan was used which has following advantages.

o The shape lent itself beautifully to the ‘buttressed’ core structural concept.

Changing Cross Sections

The damper will reduce the tower’s peak vibrations by more than one- third, The damper will not have any role during earthquakes.

o Furthermore, by stepping back one wing at each tier of the tower and

varying the distance in height between steps, helps to reduce the wind

forces on the tower.

o Designers purposely shaped Burj Dubai to reduce wind forces on the

tower, keeping the structure simple and to foster constructability. The

structural system could be described as a structural core. The result being

that the tower is extremely stiff torsionally.

The building has essentially 6 wind directions. 3 of these are when the wind

directly blows into a wing. The other 3 directions are when the wind blows in

between two wings.

These wind directions were kept in mind when orienting the tower to the most

strong wind directions for Dubai: North West, South East.

As wind whirls around a tall building it can build into powerful vortices that in

turn generate powerful winds on the ground. But the wide base of the Burj Dubai

prevents wind from causing these disturbances.

Also, varying the plan and cross-section as the tower rises tends to ‘confuse the

wind’. That is to say, the wind vortexes never become organized because at each

new tier the wind encounters a different building shape, allowing for a very

economical structure.

Therefore, through a combination of re-orienting the tower, adjusting its shape, modifying the

structural properties, the construction of Burj Khalifa became possible.

The Gherkin :- Located in London, England and has a height of 180m. Designed by Sir

Norman Foster. It is one of the tallest building in London.

Methods used to reduce wind pressure are:

Based on the mathematics of turbulence, simulate a building‘s aerodynamic properties.

The model showed that a cylindrical shape responds better to air currents than a square

one and reduces whirlwinds.

The tower bulges out in the middle, reaching its maximal diameter at the 16th floor, also

helps to minimise winds at its slimmer base.

For structure, reinforced central core is provided which supports the building and prevent

it from collapsing

Wind Tunnel Test:

Wind tunnel testing is a powerful tool that allows architects and engineers to determine the

intensity and nature of wind forces acting on complex structures. Wind tunnel testing is very

useful when the complexity of the structure and the surrounding environment, result in complex

wind flow and does not allow the determination of wind forces using simplified methods (i.e.

code provisions by that county or city). Wind tunnel testing involves blowing air on the model of

a building under consideration and its surroundings at various angles relative to the building

orientation representing the wind directions. This is typically achieved by placing the complete

model on a rotating platform within the wind tunnel. Once testing is completed for a selected

direction, the platform is simply rotated by a chosen increment to represent a new wind direction.

In order to use wind tunnel results to aid in the prediction of wind forces acting on full-scale

structure, the behavior of the natural wind must be satisfactorily modeled by the wind tunnel.

Wind Tunnel Test for a 76 floor high building:

The 76 story benchmark building for this study is 306 meter high and has a base of 42 meter

square plan. Therefore, the height to width ratio of 7 with low natural frequency. As the building

has a high aspect ration the effect of wind on such a structure is going to be more then the same

heighted structure with a larger base. The building also has 2 chamfers of 7m each on opposite

corners in the plan which will lead to uneven wind pressure distribution, thus to determine the

complex wind forces on such a building the only reliable method available is wind tunnel

studies. This wind tunnel test was performed in No.1 boundary layer wind tunnel in Department

of Civil Engineering at University of Sydney. A 1:400 scale model of building is made to test it

for wind pressure in tunnel using natural winds by augmented growth method in tunnel.

In order to use the results of wind tunnel in prediction of wind forces that would act on full scale

structure, the behavior of wind must be modeled in wind tunnel, for this all properties of wind

must be taken into account. Following variables are of great importance if we want to imitate

natural winds: U¯ (z)= mean longitudinal wind velocity at height z (m/s); σU = standard deviation

of velocity fluctuations (m/s); n = frequency related to velocity fluctuations (Hz); SU(n) = power

spectral density of the velocity fluctuations (m2 s-2 Hz-1); L = measurement of length (m); λL =

Length scale associated with the modeled building and natural wind, and λT = time scale.

For determination of Wind Time histories a 1:400 model of building was fabricated using

Perspex as material. Model was divided into 16 equal panels height wise. Each panel was then

pressure tapped on two opposite sides the measured pressure was pneumatically averaged using

a 12:1 manifold, from 12 pressure tapings on each panel. The pressure measurement system was

of the closed form and had a frequency response of approximately 300 Hz, capable of responding

accurately to pressure fluctuations with frequencies up to 2.25 Hz on the prototype. With a time

scale of 1:133, wind data for 27 seconds was recorded which would be about an hour data for the

prototype. The model was then placed on a turn able table to check for cross wind pressure on

the model.

From above table it is clear that mean across wind pressure coeff. Are not zero and that they

change magnitude and direction with change in height. This is because of the asymmetric plan of

building and also because of the turbulence intensity characteristics that alternate the fluid

separation and reattachment processes with height.To verify above words the same test was later

conducted on no chamfered symmetrical plan building and the result was that mean pressure

coefficients were negligible for the whole height of building.

Now we have to convert these combined pressure coefficients into across wind forces that would

act on the full scale building. To do so we use following equation.

F(t) = 0.5.p.U¯ 2.Cp(t).A

Where p = density of air (kg/m3), A= area of each panel and Cp is combined wind pressure

coefficient. In this study, for the generation of wind forces, a serviceability design mean wind

speed at the top of the building of 47.25 m/s was taken from wind speed data records over the

past 50 years. Using above equation and a time scale of 1:133, the pressure coefficient over 27

seconds were converted into an hour long data. However, only first 15 min data of across wind

was used for computation of building response in order to decrease burden of computation

BIBLIOGRAPHY:

Hira A. and Mendis P. (1995) Wind Design of Tall Buildings. Conference on

High-rise Buildings in Vietnam.

Chew M. (2009) Construction Technology for Tall Buildings.

Samali B., Kwok K. C. S., Wood G. S. and Yang J. N. Wind Tunnel Tests for

Wind-Excited Benchmark Building