Aniket Gohil | K1127347

Kingston University

AN IN-DEPTH RESEARCH ABOUT PROBLEMS CAUSED AT BRIDGEWATER PLACE Supervisor: Dr. Anna Cheah

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ABSTRACT

Construction of a building links to major changes of microclimate in the vicinity, particularly

high-rise buildings where great wind speeds are experienced at pedestrian level causing

dangerous hazards and accidents. Therefore, the design of the building has to take outdoor

climate into account at the same level as the indoor climate, comfort, and environment. Wind

environment in outdoor climate has been given little attention by designers and engineers

and with growing demand of the topic, before the construction process, designs are studied

for wind speed at pedestrian level, highlighting building aerodynamics. The present

dissertation focus on pedestrian comfort, where a case study of Bridgewater Place, Leeds is

taken as the subject. Prior to completion of the building in 2007, high wind speed between

67mph – 79 mph (BBC, 2011) were captured by pedestrians. At present, the structure is

involved in 25 serious complaints and in process to provide a viable solution to the problem.

Brief illustrations and comparisons will be commenced on related projects and the use of

traditional wind tunnel machine and CFD (computer fluid dynamics) will also be presented.

KEY WORDS: Microclimate, outdoor climate, pedestrian comfort, building aerodynamics,

wind tunnel, CF.

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CONTENTS

ABSTRACT............................................................................................................................................ I

LIST OF FIGURES, TABLES AND APPENDICIES ..................................................................... IV

FIGURES .......................................................................................................................................... IV

TABLES ............................................................................................................................................ V

APPENDICIES ................................................................................................................................. V

ACKNOWLEDGEMENT .................................................................................................................... VI

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

1.1. GENERAL ............................................................................................................................. 1

1.2. OBJECTIVES ....................................................................................................................... 2

1.3. APPROACH .......................................................................................................................... 2

1.4. OUTLINE ............................................................................................................................... 3

2. LITERATURE REVIEW .............................................................................................................. 4

2.1. BUILDING STRUCTURES ................................................................................................. 4

2.1.1. BUILDING’S SHAPE, SIZE, AND ORIENTATION ................................................ 5

2.1.2. BUILDING AERODYNAMICS ................................................................................... 5

2.2. PEDESTRAIN WIND LEVELS ........................................................................................ 10

2.2.1. DIFFERENT TYPES OF WIND EFFECTS ............................................................ 11

2.2.2. PEDESTRIAN COMFORT CRITERIA .................................................................... 14

2.3. WIND COMFORT CRITERIA ........................................................................................... 18

2.4. METHODOLOGY AND CONCLUSION ......................................................................... 19

3. METHODOLOGY AND LIMITATIONS ................................................................................... 21

3.1. CURRENT PROBLEMS ................................................................................................... 21

3.1.1. SHAPE ......................................................................................................................... 21

3.1.2. LOCATION .................................................................................................................. 24

3.1.3. ORIENTATION ........................................................................................................... 25

3.2. USE OF CFD SOFTWARES ............................................................................................ 25

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3.2.1. ADOBE PROJECT VASARI .................................................................................... 25

4. RESULTS .................................................................................................................................... 28

4.1. SOLUTION 1 ....................................................................................................................... 28

4.2. SOLUTION 2 ....................................................................................................................... 30

5. ANALYSIS .................................................................................................................................. 32

5.1. USE OF MATERIALS ....................................................................................................... 32

5.1.1. SOLUTION 1 ............................................................................................................... 32

5.1.2. SOLUTION 2 ............................................................................................................... 33

5.2. AESTHETICS ..................................................................................................................... 33

5.2.1. SOLUTION 1 ............................................................................................................... 33

5.2.2. SOLUTION 2 ............................................................................................................... 34

5.3. COMPARISON TO CURRENT SITUATIONS ............................................................... 34

5.3.1. SOLUTION 1 ............................................................................................................... 34

5.3.2. SOLUTION 2 ............................................................................................................... 34

5.4. PREFOUND SOLUTION .................................................................................................. 34

5.4.1. PROPOSED SOLUTION AND PLANS .................................................................. 35

6. DISCUSSION .............................................................................................................................. 37

6.1. HYPOTHESIS AND CURRENT STUDY ........................................................................ 37

6.2. COMPARISON BETWEEN FOUND SOLUTION AND CPPI SOLUTION ............... 38

7. CONCLUSION ............................................................................................................................ 39

8. REFERENCES ........................................................................................................................... 40

9. APPENDIX 1: SUPERVISOR SIGN OFF SHEET ................................................................ 43

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LIST OF FIGURES, TABLES AND APPENDICIES

FIGURES

Figure 1: Wind flow around a high-rise building (Blocken & Carmeliet, 2004) ........................ 6

Figure 2: Short-circuiting pressure caused by passage through building (Blocken &

Carmeliet, 2004) ................................................................................................................... 8

Figure 3: Effects of short-circuiting pressure on building with a passage. (Vardoulakis, et al.,

2001)..................................................................................................................................... 8

Figure 4: Four case scenarios of passage between buildings. (Vardoulakis, et al., 2001)...... 9

Figure 5: Lawson comfort criteria (Waterman Group, 2012) ................................................ 13

Figure 6: Wind speed in a Middle Eastern city. (a) Annual speed, (b) daily variation of wind

speed. (Ghosh & Mittal , 2012) ............................................................................................ 15

Figure 7: Scour technique wind tunnel diagram (Blocken & Carmeliet, 2004). ..................... 16

Figure 8: Smoke aided wind tunnel technique (Blocken & Carmeliet, 2004) ........................ 17

Figure 9: Section one of Bridgewater Place (Gohil, 2014) ................................................... 21

Figure 10: Downwash wind after being reflected from building surface (Gohil, 2014) .......... 22

Figure 11: Section two of Bridgewater Place (Gohil, 2014) .................................................. 22

Figure 12: Section three of Bridgewater Place (Gohil, 2014) .............................................. 22

Figure 13: 2D and 3D viewpoint of Bridgewater Place (diagram not in scale) (Gohil, 2014) 23

Figure 14: Wind direction viewpoint (UK) (Met Office, 2014) .............................................. 24

Figure 15: Wind direction viewpoint (Leeds) (Met Office, 2014) .......................................... 24

Figure 16: Bridgewater Place orientation against wind direction. (Google Maps, 2014) ....... 25

Figure 17: Original orientation of Bridgewater Place against wind. (Gohil, 2014) ................. 26

Figure 18: 90° orientation of the building (Gohil, 2014) ........................................................ 26

Figure 19: 270° orientation of the building. (Gohil, 2014) ..................................................... 26

Figure 20: Wind reaction when hit building surface (Gohil, 2014) ........................................ 27

Figure 21: Solution 1 (Gohil, 2014) ...................................................................................... 28

Figure 22: Solution one: (a) top view (b) western view (c) zoomed in view of the solution

(Gohil, 2014) ....................................................................................................................... 29

Figure 23: Solution 2 (Gohil, 2014) ...................................................................................... 30

Figure 24: Solution two: (a) top view (b) western view (c) zoomed in view of the solution

(Gohil, 2014) ....................................................................................................................... 31

Figure 25: Wind travel around a structure after installation of canopy (Gohil, 2014) ............ 33

Figure 26: Bridgewater Place wind reduction proposal (Bridgewater Place, 2014) .............. 35

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Figure 27: 3d view of Bridgewater Place wind reduction scheme (Bridgewater Place, 2014)

........................................................................................................................................... 36

Figure 28: Proposed solution: (a) top view (b) western view (c) zoomed in view of the

solution (Gohil, 2014) ......................................................................................................... 36

TABLES

Table 1: Wind effects on people based on beaufort scale (Baniotopoulos, et al., 2011) ...... 12

Table 2: Definition of pedestrian activity categories (PAC) (Koss, 2006) ............................. 19

APPENDICIES

Appendix 1: Supervisor sign off sheet….…………………………………………………………42

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ACKNOWLEDGEMENT

I would never have been able to finish my dissertation without the guidance of my friends,

family and my supervisor.

I would like to express my sincere gratitude to my supervisor, Dr. Anna Cheah without whom

I would not have been able to choose this project. With her excellent thorough knowledge

and understanding on my topic along with great guiding, I have been successful to complete

this project without any issues.

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1. INTRODUCTION

1.1. GENERAL

The awareness of high wind speeds caused by buildings has been raised through many

years. The construction of many high-rise structures have created dangerous environments

for pedestrians and other road users. This shows the lack in study of outdoor climate effect

in relation to building by both engineers and architects.

It has been showcased in most cases that the main area of concern is the location,

orientation and the shape of the structure. In Roman times, during these issues Vitruvius (a

Roman architect, engineer and an author) had recommended the orientation of streets

diagonally to prevailing winter winds (Aynsley, 1989).

With modernisation of construction materials and construction methods, taller buildings are

constructed in both cities and towns. Among the effects of high wind speeds created in the

vicinity of the buildings, the most significant ones is the pedestrian comfort and safety. Note

that a death of a man had been reported when a lorry toppled over him due to high wind

speeds (BBC, 2011), a woman was severely injured when a gust of wind blew her away

(BBC, 2013).

With growing awareness of high wind speeds at pedestrian level, measures and tests have

been progressed around the world in the last 30 years. Growing amount of cities and

governments are planning to pass a bylaws and acceptance criteria on the amount of wind

conditions at pedestrian level. A permit on satisfactory wind environment is required in order

to build a new structure in cities such as London, Tokyo, San Francisco, Calgary and

Montreal (American Society of Civil Engineers, 1989).

Wind environment and pedestrian wind speeds are usually influenced by building geometry,

building vicinity and local metrological data. It is essential for designers and engineers to

consider wind environment at preliminary stage where alteration are acceptable.

Unfortunately, there is yet not a general theory to determine wind environment or a theory to

develop a solution to upcoming unacceptable wind conditions. Any errors that arise can only

be checked on wind tunnel or on CFD (Computer Fluid Dynamics) at preliminary stages.

Therefore, it is essential to obtain a systematic approach on designing for being able to

make changes to the designs if necessary.

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1.2. OBJECTIVES

The literature knowledge on wind tunnel effects and its effects at pedestrian levels had

thoroughly been reviewed during the first stage on progression of the current project. A

general feedback received from the literature review was the lack of knowledge on minor

aspects of wind environment and unclear explanation of complex materials in many

circumstances.

The main aim of this project is a complete understanding of wind aerodynamics, wind

environment at pedestrian levels and around building vicinity and to also find a viable

solution to set case study. Elements that react to different wind behaviour are to be

thoroughly checked via CFD method in terms to find the most suitable solution to the known

problem. The general objectives of the project are as follows:

(1) Re-evaluation of literature review to present clear understandings of complex

subjects;

(2) Obtain and express great knowledge of unknown subjects;

(3) Using the CFD tools to understand the aerodynamics to produced solutions; and

(4) A detailed explanation of material usage in final solutions.

1.3. APPROACH

In order to achieve set goals and objectives, a unique approach has been adopted in the

current study.

Although most of previous case studies and research were conducted on a traditional wind

tunnel to record wind interaction with the structure, CFD method is to be conducted to test

and work out the solutions. In this way the time spent on the construction of the model is

obliterated. The offset approach forms a strong foundation for an advanced knowledge.

Wind tunnel testing is widely used in understanding of wind environments, wind flow around

building and pedestrian wind level. Integration of methods within this testing can provide high

quality results; such as surface pressure, flow visualisation and thermal anemometers.

Further insight into the problems can be obtained by more fundamental studies. Construction

of appropriate models has been done to gain a well-established knowledge onto main area

of problems from which isolated sections are constructed as a benchmark model.

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Instead of using the traditional method, the designs can be integrated on CAD software to

understand the wind flow allowing easier and quicker modification. The use of knowledge

achieved from literature review is applied on the CAD model to obtain in-depth accurate

results.

1.4. OUTLINE

The dissertation consists of seven chapters, a list of references and appendices.

The literature review on pedestrian wind levels is presented in Chapter 2 with wind

environment and aerodynamics. Detailed information on methods to test wind environment

at pedestrian level are also presented along with use of diagrams and tables for clear

understanding. Identification of current problem at Bridgewater Place is explained in-detail in

Chapter 3 with the possibility in use of CFD experimental technique.

Chapter 4 presents the final two solutions to Bridgewater Place with aid from imagery and

the CFD software used. In-depth solution with complex data, comparisons of before and

after building solutions will be shown in Chapter 5 along with building affect to the

surrounding area after solutions along with isolated sections viewpoints.

Based on literature information obtained, the found solutions achieved from previous chapter

are referred back to Chapter 2 in Chapter 6. The system is described with its general

architecture, components and application examples in this chapter.

As a conclusion of this project, Chapter 7 summarises the contribution of this project to both

building applications and wind aerodynamics. Future elements are also considered where,

recommendations are provided for any similar upcoming problems to other structures such

as the many ways to experiment wind environment, modelling of the structure, and the

potential areas of concerns with improvements.

References are provided in Chapter 8 and useful documents are presented in Chapter 9 as

“Appendices”.

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2. LITERATURE REVIEW

Before the design and construction phase of a structure, the structure plays a major role

dealing with both indoor and outdoor climates. Indoor climate deals with user comfort;

outdoor climate in other hand is given relatively less attention where pedestrian comfort is an

issue to investigate. The construction of a building inevitably changes the microclimate at the

site, e.g. wind speed, air pollution, light reflection, and wind direction (Blocken & Carmeliet,

2004). It also depends on its shape, size, and orientation, causing unfavourable changes

around the site, such as: high wind speeds causing dangerous conditions for pedestrians

and road users; low wind speeds causing insufficient removal of pollution caused; sunlight

reflection off the building; and visual pollution (blocking the view). Wind speed at pedestrian

level can be calculated and compared to previous records, if exceeding set frequencies,

models are tested on wind tunnel or CFD to produce long term viable solutions.

Climate is another key aspect in variation of microclimate of an area, e.g. moderate climate

conditions during cold days with reduced wind speeds can create discomfort at pedestrian

level. Wind speed could create rain infiltration (Blocken & Carmeliet, 2004b) and snow

accretion (Beyers & Waechter, 2008) causing local floods and levels of snow on road. Both

methods CFD and wind tunnel testing were conducted by Blocken, et al., (2012) and Tsang,

et al., (2012) respectively to assess pedesterian wind level and wind comfort in urban

regions.

With raising demand and interest on the matter from past incidents including deaths and

other serious injuries caused to road users (trajic death of a man after a lorry being toplled

over him due to high wind speeds), authors, architectures, and engineers such as:

Stathopoulos, (2006); Moonen, et al., (2012); Blocken & Carmeliet, (2008), etc. have been

publishing journals and articles in order to raise awarness and provide solutions to present

occuring incidents.

2.1. BUILDING STRUCTURES

Building’s body and aerodynamics play a critical role in effect to wind response. Tall

buildings can be susceptible to excessive motion during wind events leading to pedestrian

and occupant discomfort, reducing the overall impact and appeal of the structure (Merrick &

Bitsuamlak, 2009).

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With aid of methods such as CFD and wind tunnel, solutions can be found in preliminary

stage of design finalisation on wind response to building structures.

2.1.1. BUILDING’S SHAPE, SIZE, AND ORIENTATION

With modern studies and technology, unique shapes and sizes have been introduced to

building structurs and the possibilites of these designs working with due respect to wind

speed and load are growing day by day. However, some designs may not refer to wind in the

area of construction, causing wind tunnel effect.

A structure submerged in given flow field is subjected to aerodynamics flows and forces.

Typically, there are three different forms of forces involved around tall building structures

(Amin & Ahuja, 2010):

> Drag froces (along – wind): Along wind forces act in the direction of mean flow

(horizontal). This force includes structure’s response to pressure fluctuation on windward

and leeward faces with response to building. Use of wind tunnel or CFD helps a user in

understanding wind flow along a building and note the events occuring.

> Lift forces (across – wind): Across wind forces act perpendicular to direction of

mean flow (vertical). Tall buildings highlights on division of wind flow from the surface of the

building, following structure’s body contours.

Across wind achieved from division in addition to along wind, when meeting ground level

creates vortex around the structure resulting in human discomfort.

> Torsional motion: Torsional motion is established when there is a vast difference

between elastic centre and aerodynamics center of a structure. This results in vibration of

the structure leading to failure (structure collapses).

2.1.2. BUILDING AERODYNAMICS

Wind flow around a building is crucial to understand human comfort. In this sections two

case scenerios will be accounted to assess a full scale wind flow around a single high rise

and wind flow around multiple high rise buildings with aid of CFD and wind tunnel:

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> Wind flow around a single high rise building:

Shown below in figure 1 is a schematic representation of wind flow around a single high rise

building:

Figure 1: Wind flow around a high-rise building (Blocken & Carmeliet, 2004)

As wind approaches the building it diverges: (1) some of the wind flows over the building (2)

high amount of wind is then flown towards stagnation point which is located at approximately

70% of the building height. From this point, wind flow is divided into three sections where it

flows over the building (3), flows sideways (4), and downwards (5). Wind flown downwards

from stagnation point, creates vortex when hit ground level (6). There are three different

types of vortexes that could occur: standing vortex, frontal vortex, and horseshoe vortex. The

main position of standing vortex near ground level is opposite to the flow mean wind

direction. When both of these flow meet, a stagnation point at ground level with low wind

speeds is created (7). The standing vortex created at point 6 is then stretched outwards to

be passed from corners of the building where seperation occurs and corner streams with

high wind speeds are achieved (8). The corner streams then merge with the general wind

flow from point 2 (9). At leeward side of the building, the general flow is turned into backflow

and recirculation flow (10, 13). This is where an underpressure zone is created. At the end of

backflow and recirculation flow, another stagnation point is created at ground level of the

building where low wind speeds exist (11). At the end of stagnation zone, the wind is flown

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with the general mean flow at low speed for a considerable distance (12). The backflow in

the leeward side of the building creates slow vorticies (13). With the mixture of these slow

vorticies at point 13 and corner streams at point 9, a high velocity gradient zone is generated

which comprises of small fast rotating vorticies (16).

From the discussed diagram there are two pressure systems discovered. The first pressure

occurs on the front façade of the building, where high wind speeed pressure are experienced

at the stagnation point and lower wind speed pressure at the rest of the façade. This

pressure system is generated by the approaching of wind force with respect to height

creating standing vortex that slip off through the corners of the building, called “corner

streams”. The second pressure system is created between windward side and leeward side

of the building where overpressure and underpressure meet causing recirculation

downstream of the building and also contributing to the flow at corner strems. Both of these

pressure systems illustrate the complexity in wind flow pattern in response to a structure.

> Wind flow around different building arrangements

In this section, wind flow around two different building arrangements are discussed:

(1) Passage through a building

Passages through building are designed to improve accessibility for cars, pedestrians, and

cyclists. These passages provide easier access to the front and the back façade of the

building. Figure 2 shows a diagram of short-circuiting pressure caused by passage through

building. With an example, building with a dimension of 160m x 10m x 25m and passage

dimension of 10m x 10m is used to test wind interface around the structure. As seen from

the diagram, short-circuiting pressure is created between the leeward and windward façade

of the building creating unfavourable wind condition in the passage.

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Figure 2: Short-circuiting pressure caused by passage through building (Blocken & Carmeliet, 2004)

Figure 3: Effects of short-circuiting pressure on building with a passage. (Vardoulakis, et al., 2001)

Short-circuiting pressure

Wind

Under-pressure zone

Over-pressure zone

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Shown in Figure 3 are the effects of short-circuiting pressure caused due to passage through

a building. Due to these conditions, standing vortex on front façade doesn’t make much

effect. However, through passage and corner streams experience high wind levels of up to

1.8 m/s. The easiest ways to avoid the high wind speeds would be to introduce the use of

screens through the passage to increase flow resistence.

(2) Parallel buildings with passage in between

As opposed to through passages in building, passages between buildings are pervasive.

The effects of these passages between two high rise buildings are reported uncomfortable

for pedestrians. Wind tunnel studies undertaken on the subject have provided remarkable

results. Figure 4 shows four different case scenerios, each with decreasing passage

between two buildings:

Figure 4: Four case scenarios of passage between buildings. (Vardoulakis, et al., 2001)

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Two buildings shown in figure 4a with a width of 80m displays that there is slight interaction

between two building and wind flows as it would with around an isolated building. Both

buildings have their own stagnation points, corner streams, and standing vortecies. As the

width is decreased (figure 4: b, c, and d) the wind interaction between building passages

increases, standing vortecies, opposite corner streams, and stagnation point start merging

creating one large zone. However, the intriguing factor seen is that as the opposite corner

streams are moved closer, the amplifications between the building decreases (especially

behind the buildings). According to pedestrians, higher wind speeds are experienced as the

passage width decreased. In order to work out the solution to the matter, writer Blocker, B.

and Carmeliet, J. inform that pedestrians walking through the passage shown will tend to

avoid corners, experiencing lower wind speeds. As the passage width is decreased, the

corner streams will merge meaning high wind speed region created between these buildings

cannot be avoided leaving unfavourable experience for pedestrians.

2.2. PEDESTRAIN WIND LEVELS

Wind speed at ground levels is one of many important factors in construction of a building. It

is vitial to acknowledge the speed of the wind at ground levels in order to understand its

effect to human comfort. The use of CFD and wind tunnel aid on this. The complexity of wind

generally relies on the aerodynamics of the building to gain knowledge on how it streams

around a structure. In order to design a solution to obtain pedestrian level wind speed, CFD

and wind tunnel tests are directed to achieve practical results according to which building

design can be changed to fit the criteria. These processes raise awarness in areas that need

improvement in comfort and safety for pedestrians.

Human comfort level varies according to the shape, size, height, and orientation of the

building. As known, wind is normally deflected around or downwards to the ground when hit

building surface. The speed however varies according to the height, called “wind speed

gradient”. In relation to the height of the building, the speed of the wind vaires; the taller the

structure, the higher the wind speed. Although, speed is recognised most, it is also

significant to consider other factors such as, wind direction; height of the building; location of

the building; and turbulance effects.

Influence of wind speed on building’s vicinity and its effects is crucial to predict the overall

effect on the environment. It is vital to know the response of gust speed in an area, e.g.

during gust effects: the speed of the wind that will be experienced, the direction, and the

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variation in direction of wind. As wind speeds are low on ground level with high shear stress,

sudden change in atmosphere with low turbulance frequency can result in hazardous control

and safety. Therefore, a structure has to accomplish these needs with viable, realistic, low

cost, and high accuracy designs which are both safe for the environment and pedestrians.

2.2.1. DIFFERENT TYPES OF WIND EFFECTS

There are a range of wind effects which need to be taken account of when designing and

constructing a building structures. These wind effects convey results on speed at which

safety is changed to hazard. The following are types of wind effects to take count of

pedestrian safety:

> Wind Effects: Wind effects are generally distinguished into two parts: mechanical effects

and thermal effects. Mechanical effects are tests where wind speed can be adjusted from a

breeze to a gust. These tests are taken in order to understand its effects on people. Based

on research led by Penwarden, A.D., (1973) the effect of different wind speeds are shown in

Table 1. This table is divided into different wind speed levels for which its effects are given.

The table is divided into three groups when urban area is taken as the subject:

1. Wind speed less then 5.4 m/s are counted as moderate wind speed with least

effect to human body. The most a pedestrian can feel is gentle breeze. This type of

wind speed is ideal for urban areas.

2. Wind speed between 5.5 m/s – 13.8 m/s are counted as harsh wind speeds with

low damage to pedestrians. The most a pedestrian can feel is strong breeze.

3. Wind speed between 13.9 m/s – 24.4 m/s are counted as hazardous and

dangerous wind speed which causing high damage to pedestrians.

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Wind type Speed

(m/s) Description of wind effects Description of wind

Moderate wind

speeds

1 Less than

1.5 No noticable wind Light airs

2 1.6 – 3.3 Wind felt on face Light breeze

3

3.4 – 5.4

> Wind extends light flag.

Gentle breeze > Hair is disturbed.

> Clothing flaps.

Harsh wind

speeds

4

5.5 – 7.9

> Wind raises dust, dry soil, and loose

paper.

Moderate breeze

> Hair disarranged.

5

8.0 – 10.7

> Force of wind felt on body.

Fresh breeze > Drifting snow becomes airborne.

> Limit of aggreable wind on land.

6

10.8 –

13.8

> Umbrellas used with difficulty.

Strong breeze

> Hair blown striahgt.

> Difficult to walk steadily.

> Wind noises on ears unpleasent.

> Windborne snow above head height

(blizzard)

Dangerous /

hazardous

wind speeds

7 13.9 –

17.1 Inconvenience felt when walking. Moderate gale

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17.2 –

20.7

> Generally impeds progress.

Fresh gale > Great difficulty with balance in

gusts.

9 20.8 –

24.4

> People blown over by gusts.

Strong gale

Table 1: Wind effects on people based on beaufort scale (Baniotopoulos, et al., 2011).

Thermal wind effects are more complex than mechanical. As thermal wind effects deal with

real time wind, more than one parameters involved in this effect, such as: wind speed, wind

direction, temperature, humidity, weather condition, radiation, etc.. These parameters

conclude on a pedestrian’s overall thermal comfort, so in order to keep a pedestrian feel safe

in the environment, number of parameters have to be considered.

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Considered by researchers such as SKF, mechanical effects wind test can be more reliable

and cost effective as changes and predictions can be done in order to modify structure

designs to meet wind speed criteria. However, when compared to thermal effects, a whole

set of environment has to be set up in order to test the situations.

> Wind Comfort: Wind comfort is a comfort criteria where people not only feel comfortable

indoors, but outdoors too. Although, there are a range of comfort criterias for different types

of road users who have diverse perceptions on thermal wind effects, e.g. road users look for

clamer wind speeds when sat in park than what they would expect when walking to work.

However, wind speed is not an important factor in this matter, wind presistence and wind

frequency are considered too. The use of mechanical wind effects can be a good guidance

to work out precise human comfort under certain wind speeds. Figure 5 shows Lawson

comfort criteria for safe wind conditions required for certain types of activities. The given

figure relates to data from Table 1 shown above.

Lawson developed a criteria to assess wind conditions in an urban environment and how

they relate to wind presistence and treshold. It defines comfort level/ tolerable wind speeds

(Beaufort force) for certain types of road users ranging from sitting to leisure walking to

business walking. If given wind speed goes over the set parameters, then it is not suitable

for that certain activity any longer. However, if gone under the set parameters then activity is

considered allowable. For example: wind parameters for sitting are 0 – 3 Beaufort force for

1%, if the wind speed went over 3 Beaufort force then sitting is considered unsafe.

Figure 5: Lawson comfort criteria (Waterman Group, 2012)

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> Wind Climate: Wind affects the climate of an area. Wind unlike other types, wind climate is

not highly based on wind speed. It is however divided into three sections where in order to

achieve wind climate for a certain area, long term statistical metrological data and wind

stastics are collected from metrological stations. This data is then linked to the aerodynamics

of the geometrical site of the building, where wind climate is to be calculated. Once the first

two steps are complete and wind climate for a particular geometrical site is achieved, then a

comfort criteria is produced in order to review local wind climate and take any precausions if

need to.

> Wind Danger: Wind danger is a similar factor to wind speed. It takes account of the speed

of the wind at which an activity gets dangerous. As mentioned in wind comfort about Lawson

comfort criteria and wind speed about ranging wind speeds in relation to description of its

effect.

Falling into group three, number of incidents were caused at Bridgewater Place due to

strong gale. Dangerous and hazardous wind speeds experienced caused a lorry to be

toppled over causing death of a man. Other serious incidents such as torn liver and internal

bleeding were caused due to strong gust experienced.

2.2.2. PEDESTRIAN COMFORT CRITERIA

In order to determine pedestrain wind comfort, this section is divided into three sub-sections:

1. Metrological data of local area, study of wind in different weather conditions.

In order to collect metrological data for a local area, a long term wind data is required. This

data provides the user with information such as range in wind speeds and wind directions.

The data collected are then used to design stastical models.

To obain thermal comfort and other microclimate data, in-detail wind analysis for the

following parameters is required (Wu & Kriksic, 2012):

Concurrences of winds with other weather events (e.g., snow, rain, fog, sand

storms);

Joint probability of wind, temperature, humidity and other weather parameters; and,

Diurnal variations in wind speeds and directions, as they are related to the variations

of air temperature, humidity and solar radiation throughout the day.

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Wu & Kriksic, (2012) describe about the use of achieved metrological data to draw out wind

speed diagram (Figure 6) for a Middle Eastern city. As shown in figure 6, on annual basis (a)

high winds approach from northwest direction with secondary winds from southeast. When

annual data is divided into different times during a day (b), there are high wind speeds

approaching from northwestern direction during midday and afternoon bringing in hot and

humid sea breezes at the speed of 9.0 – 10.0 m/s. These hot conditions are amplified by

solar radiations during midday and afternoon. However, when the sun is not up (morning,

evening, and night), low wind speeds are achieved. As seen, there is more orange and

green bands bringing in wind speeds of up to 6.0 m/s achieved from land breeze. These

types of wind are cold and not as humid ad midday and afternoon breeze.

Figure 6: Wind speed in a Middle Eastern city. (a) Annual speed, (b) daily variation of wind speed. (Ghosh & Mittal , 2012)

2. Based on the data, CFD or wind tunnel test is conducted to predict theoretical wind

speed at pedestrian level.

There are a number of techniques used to determine wind at pedestrian level. However, the

two main techniques widely used are: wind tunnel testing; and computational fluid dynamics

(CFD) testing.

> Wind tunnel testing: Wind tunnel testing is said to be the best method to assess wind flow

at pedestrian level around tall buildings. There are two different types of methods available

16

which aid in assessing the environment near building’s vicinity. These are point method, and

area method. Point method provides the user with quantitative data where range of sensors

are placed around building parameters, recording wind speeds and temperature. Area

method on the other hand provides a continous qualitative data. This method makes use of

scour technique, where placed model (in wind tunnel) is coated with a uniformly thin layer of

particulate material. The wind speed is increased and left for some time till it reaches a

steady state. The results of this method demonstrates the wind speed is greater than or

equal to predetermind scour speed of material (Livesey, et al., 1990). Advantage of using

this method is that a complete overview of pedestrian wind level for the entire area is

provided.

The use of area method with scour technique is marked ideal for a complete test of wind

speed of an area. Scour technique is set out in two steps: (1) Prior to the placement of

model, turntable floor in wind tunnel is firstly covered with fine uniform layer of dried sand;

then, (2) after the placement of the model, another layer of fine sand is applied to the

turntable and the wind speed is increased in stages. Sand erosion occuring at each step of

wind speed is allowed to reach a steady state. Once the experiement is conducted, areas

with most sand erosion show that wind speed at pedestrian level is high.

Figure 7: Scour technique wind tunnel diagram (Blocken & Carmeliet, 2004).

Shown in diagram above, for each UWT value, there is a comparable UG and UGB value. UWT

denotes the speed of that is set by the operator/ user which is increased in steps until

reached a certain value. UG denotes ground level wind speed (not affected by building), UGB

denotes ground level wind speed influenced by building causing sand erosion.

Other techniques used within wind tunnel to gain wind speed at pedestrian level are:

17

> Oil streak: In oil streak technique, wind tunnel floor around the model is coated with a

mixture of kaolin and paraffin oil. Once the wind speed is increased, the oil moves in the

direction of the wind, on the turntable. Due to air flowing over the mixture, paraffin oil

evaporates leaving streak patterns showing direction of the wind flow around the building.

The shape and the density of the streak define the turbulance in the flow. This technique is

similar to scour technique which does not provide directional wind flow.

> Smoke visualisation: Smoke visualisation test is a technique that demonstrates the wind

flow around structure. Shown in Figure 8, is a smoke aided wind tunnel test. Two factors can

be visualised from the picture: (1) The flow of the smoke is divided into three parts. At 2/3’rd

of the height of the building, some of the divided smoke flows upwards, some passes

sideways, while the remaining flows downwards to the base; (2) The vortex generated

between the low and the tall building from the divisional downward smoke flow. This

technique is most adventageous as it reveals the direction of wind flow and any possibilities

of vortex.

Figure 8: Smoke aided wind tunnel technique (Blocken & Carmeliet, 2004).

> Computer Fluid Dynamics (CFD) testing: CFD is an alternative study of wind flow at

pedestrian level. With its advantages in being cheaper and less time consuming than wind

tunnel test and having the ability to demonstrate wind flow at any given moment providing in-

detail results, there is a major disadvantage. In order to be able to use CFD the model has to

be validated.

18

With growing demand on the use of CFD, there has been increase in publications by authors

such as Bert Blocken and Shuzo Murakami, and growing demand of this studty by architects

and engineers. Not having any limitations on the use over the method, the softwares have

been used by designers to test wind flow over vehicles, and many other products.

The use of CFD allows engineers to easily alter design criteria and other configurations. The

use of CFD is complex as a huge set of data has to be inputed in order to run the test, such

as: choosing of precise equation in order to test the flow, size of the computational model,

dimensions of the grid, boundry, etc.

As known, in order to test pedestrian wind flow around building, a validation has to be

required and in huge number of cases, it has not been achieved. Due to this restriction there

are few publication based on pedestrian wind flow with the aid of CFD. Recent research led

by (Blocken, et al., 2012) about wind safety and wind comfort for pedestrians in urban area

with the use of CFD, best practice guidelines were discussed. Differences between three

cases were discussed where wind comfort and wind safety studies were required (Blocken,

et al., 2012):

Case 1: new developments within an existing urban configuration, for which on-site

measurements are available or will be conducted;

Case 2: new developments within an existing urban configuration, for which no on-

site measurements are available or will be conducted;

Case 3: development of a new urban configuration, for which – evidently – no on-site

measurements are available during the design stage.

2.3. WIND COMFORT CRITERIA

As previously discussed, wind speeds around tall buildings tend to vary from high to

average, from pedestrians feeling no effect to being blown over by gusts. Therefore, comfort

and discomfort can both be linked to this instance. With range of parameters involved, such

as: wind speeds, wind direction, temperature, humidity, etc. it is hard to calculate comfort

criteria for a particular area. It also depends on psycological factors such as regular change

in wind speeds, mean wind speeds, gustiness, wind speed occurance.

It is appropriate to calculate wind comfort criteria according to particualr pedestrian activity in

particular areas in combination frequencies of wind occurance or exceedance with certain

duration of time (Koss, 2006).

19

For a particular pedestrian activity, accepatable wind speed according to the comfort criteria,

ulim is to be defined. The general criteria assessing pedestrian’s location fulfills the

requirement for the intended utilisation or not shall comprise on the followinf two equations:

(1) Gust wind speed, ug = ū + g · σu ≤ ulim

(2) Probability of exceedence, Tp(ug ≥ ulim) ≤ pcomfort

Shown above in equation 1, ū is mean wind speed, σu is the corresponding standard

deviation (represented by the rms value), p resembles the probability with

which ug exceeds ulim within a given period of time (T), and pcomfort is the maximum allowable

probability of exceedence for which a comfort level is achieved. Almost each parameter

contained in the two equations above differs from criterion to criterion, not only in value but

also in meaning (Koss, 2006).

There are various numbers of wind comfort criteria, designed and calculated by number of

authors. Presented below are few of many criteria discussed [two of the criterias have been

presented in this paper as Table 1 (pg. 10), and Figure 5 (pg. 12)].

PAC Description

A Sitting for a long period of time, laying steady position, pedestrian sitting, terrace,

street café or restaurant, open field theatre, pool

B Pedestrian standing, standing/sitting over a short period of time, short steady

positions, public park, playing field, shopping street, mall

C Pedestrian walking, leisurely walking, normal walking, ramble, stroll, walkway,

building entrance, shopping street, mall

D Objective business walking, brisk or fast walking, car park, avenue, sidewalk,

belvedere

Table 2: Definition of pedestrian activity categories (PAC) (Koss, 2006)

2.4. METHODOLOGY AND CONCLUSION

Bridgewater place being the only skyscraper in Leeds, generates wind tunnel effect causing

unfavourable experience for road users and has been involved in dangerous incedents since

its construction in 2007.

20

Bridgewater Place is located in the heart of Leeds, next to River Aire. Relating to Figure 1,

the high wind levels faced at the stagnation point of the building, divides into three sections

with high winds flowing downstream. This downastream flow was recorded to be between

67mph – 79 mph at pedestrian level. The effects from standing vortices led a lorry to be

toppled over to the side of the road causing death of a man. Relating to Table 1, the possible

wind speeds experienced at the location could be between breeze – gust with a dangerous/

hazardous wind speed as wind type.

Following the conclusion of this presented report, possible solution will be followed in order

to reduce wind speeds at pedestrian levels. The solutions provided will be shown to Leeds

council and also be referred to the given budget by the council.

21

20.2m

3. METHODOLOGY AND LIMITATIONS

As mentioned in abstract about the issues being caused by Bridgewater Place and a brief

mention of what the actual problem is, this chapter aims on showing how the mentioned

problems are caused.

The Bridgewater Place building located in Leeds has experienced high wind speeds at

pedestrian level since its construction completion in 2007. In windy circumstances, due to

high reflected wind on ground level, there has been junction closures. During these

conditions there has also been fatal incidents, one of with was a death of a man (BBC, 2011)

and the warning emails sent by council representative (BBC, 2013).

Experimental techniques are used to understand the current problem with the use of CFD

software such as Project Vasari.

3.1. CURRENT PROBLEMS

There are three different problems involved with the building: shape, location and orientation.

3.1.1. SHAPE

The building shape is divided into three sections, which are then conjoined to form the actual

structure. It is not only the shape but also the size of the building, which also matters when it

comes to wind interaction.

Section 1: 38.4m

18.2m 112m

Figure 9: Section one of Bridgewater Place (Gohil, 2014)

Shown in Figure 9 is the main section of the building located on the back side of the

structure, used for residential purposes. With the total height of building being 112m, the

building spans with the length of 38.4m and width of 18.2m. Due to this being the tallest

structure in Leeds, the wind reflected from the building surface does not travel well around

22

41.1m 64.7m

the structure, instead is downwash to ground level. An illustration of this is shown in figure

10.

Figure 10: Downwash wind after being reflected from building surface (Gohil, 2014)

Section 2:

84.1m

32.2m 37m

Figure 11: Section two of Bridgewater Place (Gohil, 2014)

Shown in figure 11 is the second section of Bridgewater Place. Located on the front face of

the entire structure, this particular building is used for office purposes. Since it being the front

face of the building, the wind is blocked and diverted past it from the tallest section of the

structure.

Section Three:

8.2m

12.2m

64.7m

74.6m

18.3m

40m

Figure 12: Section three of Bridgewater Place (Gohil, 2014)

Shown in figure 12 is the third section of Bridgewater Place. This section is located on the

east side of the structure as a car park, dealing minimum damage. The wind downwash from

section one flows around on the ground level of the structure.

23

Entire Structure:

Figure 13: 2D and 3D viewpoint of Bridgewater Place (diagram not in scale) (Gohil, 2014)

* Area shaded in purple resembles the joining section to form the entire structure

Section

1

Section

2

Section

3

24

3.1.2. LOCATION

Shown below in figure 14 and figure 15 as an example is wind direction in UK and Leeds.

Figure 14: Wind direction viewpoint (UK) (Met Office, 2014)

Figure 15: Wind direction viewpoint (Leeds) (Met Office, 2014)

As see in first images (fig. 14), the arrows resembling wind direction flow from eastern

direction to western; same goes with the zoomed version (fig. 15). The original location of

the Bridgewater Place is marked in black place marker on both maps.

In next section wind interaction with the building is to be explained in detail.

25

3.1.3. ORIENTATION

Figure 16: Bridgewater Place orientation against wind direction. (Google Maps, 2014)

The back and the right side of the building (section 1 and section 3) are facing the eastern

direction. Shown in figure 16 is the location of the building on a map along with arrows

resembling wind direction. As seen that the wind flows around the building when hit building

surface. This is due to its height, shape and orientation. The wind travelling towards the

building is deflected and forced to travel around when hit building surface. Taking other

building in consideration it can be seen that the wind flow is not interrupted at all.

3.2. USE OF CFD SOFTWARES

CFD softwares are used to achieve a full understanding of how a structure would

look and how it would react under possible loads, winds, solar radiation and energy

use. In order to get the aerodynamics of the building, CFD software Adobe Project Vasari

helps aid in precision of final results that are produced. In this case, Adobe Project Vasari is

the program used to test the building under computer-based wind tunnel.

3.2.1. ADOBE PROJECT VASARI

When testing the Bridgewater Place model onto this program against wind, the following

results are presented:

26

Figure 17: Original orientation of Bridgewater Place against wind. (Gohil, 2014)

Shown above in figure 17 is the original orientation of Bridgewater Place against wind

direction. As noticed from the image, the wind interaction with the building causes errors and

high wind point areas. The range of 0 m/s – 35 m/s was the wind speed considered for this

project, due to the highest wind speed recorded at the site was 79 mph (BBC, 2013). The

red sections seen on the image resemble the highest wind speed of 35 m/s.

Wind interactions with the building acts in different ways according to the building’s

orientation. Both figure 18 and 19 show that if the building was orientated 90° and 270° from

its original orientation, the flow achieved would have been better creating least to no issues.

Figure 18: 90° orientation of the building (Gohil, 2014)

Figure 19: 270° orientation of the building. (Gohil, 2014)

27

The red sections visible on the original figure have now been disappeared. This

demonstrates that the main area of issue in this situation is the orientation of the structure.

However, orienting the entire structure would be almost impossible.

Figure 20: Wind reaction when hit building surface (Gohil, 2014)

In order to understand the problem in a smart manner, figure 20 should how the building

reacts when wind is directed towards the building.

Shown in the above figure:

At point 1: The prevailing wind is directed towards the building surface from western to

eastern direction.

At point 2: The prevailing wind deflected off the building surface is flown to ground level, also

known as ‘downwash’.

At point 3: The prevailing wind from western direction travels around the building surface.

At point 4: The downwash wind from point 2 escapes onto water lane.

At point 5: Wind downwash from point 2 travels in backwards direction and wind travelling

along building surface on ground level causes mini vortices to form.

In order to design solution to the matter, point two and four are major concerns. It has to be

made sure that the downwash wind and wind escaping to Water Lane is minimised.

3 2

2

1

5 5

4

28

4. RESULTS

Two solutions were planned in order to cut down on wind speed at pedestrian level with

recommendation in use of two main elements – canopy and barriers. The designed solutions

were implemented onto the CAD image of Bridgewater Place and tested on Adobe Project

Vasari. The worked solutions are then analysed and compared back to the original state of

the building in the next chapter to see how the differences make changes to the pedestrian

wind environment.

As shown in previous chapter section 3.2.1. (pg. 26-28) on how wind travels around the

building with the main area to focus are at section 2, 4 and 5 (refer to figure 20).

4.1. SOLUTION 1

Figure 21: Solution 1 (Gohil, 2014)

Solution 1 implements the use of wind barriers. Breakers placed on the building face at each

floor breaks and deflects the wind; meaning there will be less wind speed on pedestrian

level. Barriers have also been placed on the building face at each floor for breaking and

deflecting of the wind travelling along the building face. Another barrier is placed on the

ground so the downwash wish escaping to Water Lane is deflected back upwards.

29

Figure 22: Solution one: (a) top view (b) western view (c) zoomed in view of the solution (Gohil, 2014)

a b

c

30

4.2. SOLUTION 2

Figure 23: Solution 2 (Gohil, 2014)

Solution 2 brings use of canopy and wind barriers. The canopy are placed from the back

face to the western face of the building. The downwash wind is deflected by the canopy and

preventing any sort of wind to reach ground level. Implementing the use of wind barriers on

top of canopy has a function of stopping and deflecting any wind that travels along the

canopy surface. This means that any wind travelling on canopy surface and escaping onto

Water Lane is prevented and deflected in various directions.

31

Figure 24: Solution two: (a) top view (b) western view (c) zoomed in view of the solution (Gohil, 2014)

c

b a

32

5. ANALYSIS

5.1. USE OF MATERIALS

The use of materials is important in designing the solution to the matter as different materials

react in a different manner to wind. With use of canopy and barriers, it is vital to make sure

that materials used for solution blend well with the building aesthetics and not diverse.

5.1.1. SOLUTION 1

The main element of this solution is the use of wind barriers. The wind barriers placed on

building surface at each level acts as wind breakers meaning the downwash wind is broken

and deflected. Similarly, the barrier placed on ground floor has same function along with

preventing remaining downwash wind to escape onto Water Lane.

The choice of material to be used for barriers placed throughout the structure is concrete.

Concrete is known to withstand high amount of pressers and deals well with wind. In an

article by Sauter, (2011) it was said by Joseph E. Salbia (provost at the University of Dayton

and former Dean of the School of Engineering) that while all natural disasters provide a

challenge, designing for wind “is the ultimate test for an engineer…”. To design for hurricane

and tornado proof buildings across the world, concrete is widely acknowledged, withstanding

wind speeds of more than 70 mph. At current stage, the highest wind speed recorded at

Bridgewater Place was of 35 m/s equivalent to 78 mph (BBC, 2011).

Initial plan involves in placing concrete beams and concrete elements on the building face,

leading up to the building’s stagnation point. A stagnation point of the building is located at

building’s approximately 70% of the height where wind is deflected into multiple directions

(refer to figure 1); for Bridgewater Place, the stagnation point is approximately located at the

height of 78.4m which is up to 23rd floor.

33

5.1.2. SOLUTION 2

This solution implements the use of canopy and barriers. Canopy spread from the back face

to the western face of the building along with wind barriers installed on top of these canopy

at the back face. The downwash wind from stagnations point is deflected after reaching

canopy surface and wind travelling along the canopy surface is deflected by barriers,

preventing it to escape to Water Lane. Below, figure 25 shows an example of how wind

travels around a structure after installing a canopy; similar idea is applied to solution 2.

Figure 25: Wind travel around a structure after installation of canopy (Gohil, 2014)

The choice of material to be used for canopy and barriers is glass and metal. With different

range of materials, it is believed that glass and metal improves the overall look of a structure.

With not only aesthetical features as an advantage, glass is an easy material to clean and

maintain. Implementing of glass canopy involves high standard regulation manufacture,

minimising the chances of failing of material. The material is also affordable and perceptible

than concrete.

5.2. AESTHETICS

5.2.1. SOLUTION 1

As previously mentioned, solution one implements the use of wind barriers along the building

face and on ground level. The building has a high use of glass and concrete and the use of

concrete for the solution is an ideal option. With the dimension of the barriers on building

face for breaking down downwash wind is: 5m x 0.3m x 0.5m and the dimension of the

barriers on the building face to break and deflect wind travelling along building face is 0.3m x

1.5m x 0.5m along with , the wind barriers will blend in well with Bridgewater Place.

34

The barrier placed on the ground floor of the building between the building back face and

water lane has dimensions of. 7m x 5m x 1m. The barrier can also be used to provide a

pleasant welcome to users and advertise Bridgewater Place logo on the wall facing Water

Lane.

5.2.2. SOLUTION 2

The use of glass canopy and barrier for solution two gives a vibrant feel. With its function of

protecting pedestrians from high wind speeds, the canopy add a modern look to the building.

Glass canopy can also be installed with LED lights improving its overall quality during night

hours.

5.3. COMPARISON TO CURRENT SITUATIONS

5.3.1. SOLUTION 1

Shown in figure 22 is the solution two tested on CFD program. The highest wind speed

recorded was 13.8 m/s. Compared to the original of 35 m/s the difference of 21.2 m/s is

good and the hazardous red flow lines on water lane have now turned orange/ dark green.

However, the wind speed recorded is still harsh on water lane and can be cut down further

for pedestrian safety.

5.3.2. SOLUTION 2

Figure 24 demonstrates solution two under CFD test. The highest wind speed recorded was

6.2 m/s. Compared to the original of 35 m/s the difference of 28.2 m/s and 7.2 m/s against

solution one shows improvement. The hazardous red lines appearing on water lane (figure

17) and orange/ dark green (figure 22 a) have turned into bright green/ dark blue.

5.4. PREFOUND SOLUTION

Prior to designing and planning solutions for the current problem at Bridgewater Place, CPPI

unveiled the wind reduction scheme. The solution consists the use of canopy, barriers and

wind baffles.

35

5.4.1. PROPOSED SOLUTION AND PLANS

The proposed scheme implements the use of four perforated wind baffles with the

dimensions of 20m x 4m and will be supported 6m above road level in order for all vehicle

access. Prevailing wind flowing from western direction is broken and deflected through each

baffle allowing minimum wind to pass through by Wind Baffle A. The design also implements

the use of three perforated wind barriers. Three barriers will be placed along the building

with the height ranging from 12m – 18m for another small barrier placed on the eastern face

of the building with the height of 4m. Along with baffles and barriers, the design also

comprises with glass canopy from the back face to the western face of the building

protecting the entry and exit points to Bridgewater Place (Bridgewater Place, 2014). Figure

26 and 27 shows the proposed design in detail. The highest wind speed achieved at the site

was 5.3 m/s.

As per plans, CPPI are currently in process of finalising the design while taking feedbacks

and reviews for the published scheme. Once finalised, the scheme will be forwarded to

Leeds County Council in order for approval to construct.

Figure 26: Bridgewater Place wind reduction proposal (Bridgewater Place, 2014)

36

Figure 27: 3d view of Bridgewater Place wind reduction scheme (Bridgewater Place, 2014)

Figure 28: Proposed solution: (a) top view (b) western view (c) zoomed in view of the solution (Gohil, 2014)

c

a b

37

6. DISCUSSION

Understanding the difference in microclimate by Bridgewater Place, possibility of relation

between building’s shape, location and orientation and the wind speed at pedestrian level is

investigated. In order to test the wind aerodynamics, highest wind speed recorded at the

location is used for testing. The results to the investigation are shown above in chapter 4 and

5 with a clear understanding on wind distribution and wind flow before and after the solution.

However, In this chapter, the presented results are discussed for and against the research

found in chapter 2, 3 and 5.

6.1. HYPOTHESIS AND CURRENT STUDY

Bridgewater Place is an office and a residential structure built in 2007. Since its construction

the building has been involved in various incidents about high wind speeds recorded at

ground level such as; death of man due to lorry toppling over (BBC, 2011), woman severely

injured when walking past the building (BBC, 2013), woman left with torn liver and internal

bleeding due to high wind speeds (BBC, 2013). The aim of this dissertation was to

understand and design a viable solution to pedestrian wind problems.

When designing the solution it was vital to understand the current problem for which a 3D

model was designed on CAD software and then uploaded onto CFD program. The areas

and the problems were then highlighted to which solutions were designed (pg. 28-31).

In order to design solutions, aerodynamics flow were considered. Based on journal produced

by Blocken & Carmeliet, (2004) wind and pressure distribution were understood and tested

onto Bridgewater Place aiding in clear understanding of building’s stagnation point and wind

and pressure distribution. Based on research produced by Amin & Ahuja, (2010) the use of

drag forces and lift forces were considred. Drag froces were considered at the building’s

stagnation point in order to witness on how the structure reacts the pressure distribution.

Tested on CFD program, Bridgewater Place produced positive results on dealing with

oncoming wind, part of wind flown around the structure. Lift forces were considered after the

pressure distribution form stagnation point. During pressure distribution high wind speeds

were recorded to be downwashing causing high damage at pedestrian level. Minimal amount

of wind was flown in the upwards direction to join mean wind direction.

Highest wind speed recorded at site was 35 m/s to which two solutions were designed to

control the wind speed at pedestrian level. Solution 1 resulted with 13.8m/s as the highest

38

wind speed with implementation of wind barriers installed on building face. On the other

hand, solution 2 resulted with 7.2m/s as the highest wind speed with implementation of

canopies and wind barriers.

Refereeing the data to table 1 presented by Baniotpoulos, et al., (2011), original wind speed

of 35m/s is considered dangerous and hazardous with strong gale. Solution 1 presents

harsh wind type with strong breeze experienced by pedestrians. Solution 2 on the other

hand presents a moderate breeze resulting in minimum damage caused to pedestrians.

6.2. COMPARISON BETWEEN FOUND SOLUTION AND CPPI SOLUTION

Following the completion of literature review, CPPI (owner of Bridgewater Place) unveiled

the proposed plans on ongoing high wind speed at pedestrian level caused by building

aerodynamics on 8/02/2014 (BBC, 2014). With aid of wind baffles along water lane, barriers

and canopy the wind speed at Leeds’ skyscraper were set to minimise.

In order to understand how successful the solution is, a 3D model was designed and tested

on a CFD software and the results achieved (pg. 35 - 36) were similar to user found

solutions. The highest wind speed achieved at the site was 5.3 m/s with a difference of 1.9

m/s compared to solution 2. CPPI successfully produced a better result however; concerns

were raised by public on the time frame of construction of the solution. The proposed

solution plans to take almost two years to construct protecting pedestrian and other road

users from high wind speeds. On the other hand, it is believed that the installation of wind

baffles along water lane not only increase the construction time frame but also increases the

overall cost of the project. When compared to solution 2, the installation of canopy and wind

barrier takes less time with lower overall cost.

39

7. CONCLUSION

Based on knowledge gained on the literature of structure aerodynamics and the effect of

wind, this dissertation successfully presents the working of Bridgewater Place and an

attempt of minimising wind speed at pedestrian level. This dissertation implements the use

of CFD program “Adobe Project Vasari” to test on wind speed and wind distribution around

the designed structure and the understandings gained can be applied to the vicinity in order

to gain the overall effect of the wind in the area. The specific aims and objectives of this

project were to gain a clear understanding of building aerodynamics in order to design a

viable solution to the matter.

A complex correlation between wind and aerodynamics is discovered. Multiple factors need

to be taken in count when designing for wind speed problems. First, mean wind speed, wind

direction and building shape, location and orientation are considered following which

stagnation points are discovered defining wind distribution and pressure fluctuations. These

points help understand the areas of concerns to which solutions are designed. For

Bridgewater Place, it was understood that the main area of concern was caused by the

downwash wind and the flowing of wind in Water Lane to which solutions are presented.

However further work can be put into the project to test the model in a traditional wind tunnel

to compare and contrast between both methods resulting in more accurate solutions.

Finally, this type of method can be used by professionals to understand wind flow around

multiple structures and objects but due to risks involved in trying the method first time has

resulted in following the tests and results produced in a traditional wind tunnel. Through this

case study, they are now able to understand the advantages and disadvantages in using

CFD program and wind interaction with a structure.

40

8. REFERENCES

American Society of Civil Engineers, 1989. Outdoor Human Comfort and Its Assessment:

The State of the Art. Montreal: American Society of Civil Engineers.

Amin, J. A. & Ahuja, A. K., 2010. AERODYNAMIC MODIFICATION TO THE SHAPE OF

THE BUILDINGS: A REVIEW OF THE STATE-OF-THE-ART. Asian Journal of Civil

Engineering (Building and Housing), 11(4), pp. 433-450.

Aynsley, R. M., 1989. Politics of pedestrian level urban wind control. Building and

Environment, 24(4), pp. 291-295.

Baniotopoulos, C. C., Borri, C. & Stathopoulos, T. eds., 2011. Extended Land Beaufort Scale

shwoing wind effects on people (Lawson and Pendwarden 1975; Isyumov and Davenport

1975). In: Environmental Wind Engineering and Design of Wind Energy Structures. Wein:

Springer, p. 10.

BBC, 2011. Wind death in Leeds prompts tower safety fears. [Online]

Available at: http://www.bbc.co.uk/news/uk-england-leeds-12717762

[Accessed 29 11 2013].

BBC, 2013. Birstall woman injured by wind at Leeds skyscraper. [Online]

Available at: http://www.bbc.co.uk/news/uk-england-leeds-25271999

[Accessed 23 01 2014].

BBC, 2013. Bridgewater Place 'wind tunnel caused Leeds injuries'. [Online]

Available at: http://www.bbc.co.uk/news/uk-england-leeds-21633206

[Accessed 12 12 2013].

BBC, 2013. Bridgewater Place: Council official warned of wind fears. [Online]

Available at: http://www.bbc.co.uk/news/uk-england-leeds-24364159

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9. APPENDIX 1: SUPERVISOR SIGN OFF SHEET

Date Subjects discussed Progress since last

meeting Signature

02/10/13 Possible dissertation topics.

General field of study. Case study discussions. Lab based experiment

discussion.

10/10/13 Dissertation topic finalised. Researching dissertation topic.

18/10/13 Draft outline check. Improvements to make. Update on Bridgewater

Place.

Project outline written.

05/11/13 Outlining interim report. n/a 08/11/13 Finalising on topics to

cover in interim report. Topics and subtopics

laid out for interim report.

13/11/13 Interim report progress check.

Interim report writing.

19/11/13 Interim report progress check.

Interim report writing.

28/11/13 Interim report progress check.

Interim report writing.

02/12/13 Draft interim report check. Interim report writing. 12/12/13 Finalising interim report. Improvements added to

draft interim report.

09/01/14 Discussion about topics to cover in presentation.

n/a

23/01/14 Outlining final report. n/a 04/02/14 Presentation progress

check. Final report progress

check.

Starting of final report writing.

20/02/14 Discussion about the unveiling of CPPI solution.

Final report writing.

06/03/14 Draft presentation check. Final report writing. Presentation writing.

19/03/14 Finalising presentation. Presentation writing. 10/04/14 Draft final report check. Final report writing 29/04/14 Finalising final report. Improvements added to

final report.

Completion Date Component % of total module marks

25th Oct 2013 Outline Pass/Fail

13th Dec 2013 Interim Report 20

Feb 2014 Oral Presentation 10

01th May 2014 Final Report 70