wind notes

Reputation Resources Results

Canada | USA | UK | UAE | India | China

www.rwdi.com

• Slide transitions: Fade through Black is our standard. Never use dissolve to stop the spread of this problematic transition. • To copy slides from one file to this file, copy slides from the other file in the slide sorter view, paste into this file in slide sorter view, select all slides in slide view and

Home>reset all slides to update to the new template • Regarding dates, have a look at Insert>date • If something is to appear on every slide, view slide master and modify the top most template in left pane • To turn off the black last slide, click the office button (top left), PowerPoint Options (bottom), Advanced, Slide Show, End with black slide

1

WIND ENGINEERING Ensuring the Safety and Performance of

Tall and Unique Structures in Singapore

The Institution of Engineers Singapore

May 31, 2012

Mark P. Chatten

Project Director, RWDI

[email protected]

mailto:[email protected]




www.rwdi.com



2

Acknowledgements

I appreciate the opportunity to work on challenging projects with

talented and motivated people. Many people at RWDI contribute to

the work and projects presented here.

Additionally, we are honored to work for our many loyal

clients…architects, engineers and developers…who engage us to

participate in their projects

Finally, I appreciate the Institute of Engineers Singapore for their

support in facilitating this seminar!


Local Presence…Global Capability

Guelph (WT 1 & 2)

United Kingdom (WT 3)

United Arab Emirates

India

Saudi Arabia (RO) Miami (WT 4)

Vancouver

Calgary

Windsor

Ottawa

Thunder

Bay

RO: Representative Offices

Santiago (RO)

Sāo Paulo (RO)

• Established in 1972

• 300 employees

• International reputation

• Exclusive methods and equipment

• Proven problem solving track record

Shanghai

www.rwdi.com


International Experience

www.rwdi.com


Wind Load Chain

www.rwdi.com

Aerodynamic Response

Dynamic Response

Design Criteria

Local Wind Climate

Terrain & Surroundings


Dynamic Response

Local Wind Climate


Design Criteria


1st Link - Local Wind Climate

www.rwdi.com


Dynamic Response

Design Criteria

Local Wind Climate


Local Wind Climate


Origins and Characteristics of Wind

Type equation here.

www.rwdi.com


Origins and Characteristics of Wind

Type equation here.

W E

W

W

E

North pole

Polar easterlies

Polar front

30E

10E

60E Westerlies

Horse latitudes

Trade winds

Doldrums

General Circulation

Hadley cell

Ferrel cell E

Equator

www.rwdi.com


Singapore Wind Climate

9

November - April May - October



10


Mostly Calm!



11


Extreme Winds


Monsoon Winds

Low wind speeds!

www.rwdi.com


Singapore Wind Climate - Monsoons

13

• Large scale meteorological systems (synoptic

winds)

• Generate highest winds over periods of several

hours or days

• Strongly directional

• Low wind speeds, not significant for strength

design

• Important for serviceability, evaluation of

thermal comfort and natural ventilation

• Wind Profiles well characterized by wind

profiles in codes (Deaves and Harris model)


Thunderstorms

Type equation here.

Gust front

Direction

of

movement

of storm

Singapore: Highest Measured Gust 145 km/hr (40m/s)

www.rwdi.com


Wind Profiles

www.rwdi.com


Singapore Wind Climate – Extreme Winds

16

Thunderstorms & Squalls (“Sumatra’s”)

• Unpredictable, short duration events

• Impact relatively small area

• Convective weather systems associated with

non-directional “downbursts” (strong winds can

blow from any direction)

• Wind profiles not well characterized by Deaves

and Harris model

• Area of ongoing wind engineering research

(current methodology likely conservative for

design of most rigid buildings)


Characterizing Wind Climate for Design

17

Design Wind Speed Definition

• Height of Wind Speed

• Averaging time of wind speed

• Exposure profile wind speed is measured in

• Return Period

Example - Singapore

50 Year Return Period Design Wind Speed

= 33 m/s 3-Sec Gust in Open Terrain (CP3 Terrain 1)


Probability Distribution of the Wind

18

Hourly records of wind speed and direction over many years allow the joint probability of wind speed and direction to be evaluated. It is found that typically a good fit of this distribution is given by the Weibull distribution

In this expression

Typically 16, 24 or 36 wind directions are used.

k

C

U

eAUP)(

)(),(

hour oneany in direction wind thefrom

exceeded be will velocity y that theprobabilit ),(

UUP

direction. each windfor constants are and kC


Extreme Value Analysis of Design Wind Speed

19

50 Year Return Period Design Wind

Speed in Singapore

= 33 m/s 3-Sec Gust in Open Terrain


Mean, RMS and peak gust velocity

www.rwdi.com


Defining Wind Speed – Durst Curve

1

1.1

1.2

1.3

1.4

1.5

1.6

U(

t)

/U

(3

60

0)

1 10 100 1000 10000 t, seconds

1.52 factor for 3 second gust

Relationship between gusts and mean hourly

speed at 10 m height in open terrain

Necessary for conversion between codes – but derived from regions

where sustained strong winds occur. Misleading in Singapore, where

short duration events cause extreme winds. (BS6399 based on mean hourly; Eurocode based on 10 min mean)


2nd Link – Terrain & Surroundings

www.rwdi.com



Planetary boundary layer

www.rwdi.com


0

5 0 0

1 0 0 0

1 5 0 0

2 0 0 0

2 5 0 0

He

igh

t, m

0.0 0.5 1.0

U/Ug

A

0

5 0 0

1 0 0 0

1 5 0 0

2 0 0 0

2 5 0 0

He

igh

t, m

0.0 0.5 1.0

U/Ug

B

0

500

1000

1500

2000

2500

He

igh

t, m

0.0 0.5 1.0

U/Ug

C

0

500

1000

1500

2000

2500

Heig

ht, m

0.0 0.5 1.0

U/Ug

D


Mud flats, water

outside hurricane

regions

Open terrain

with few

obstructions

Suburban terrain Heavily built up

urban terrain

Planetary boundary layer and effect of

surface roughness - mean velocity

profile

www.rwdi.com


0

5 0 0

1 0 0 0

1 5 0 0

2 0 0 0

2 5 0 0

He

igh

t, m

0.0 0.5 1.0

U/Ug

A

0

5 0 0

1 0 0 0

1 5 0 0

2 0 0 0

2 5 0 0

He

igh

t, m

0.0 0.5 1.0

U/Ug

B

0

500

1000

1500

2000

2500

He

igh

t, m

0.0 0.5 1.0

U/Ug

C

0

500

1000

1500

2000

2500

Heig

ht, m

0.0 0.5 1.0

U/Ug

D


Mud flats, water

outside hurricane

regions

Open terrain

with few

obstructions

Suburban terrain Heavily built up

urban terrain

Planetary boundary layer and effect of

surface roughness - mean velocity

profile

No longer included in

Analytical Method of

ASCE-7 Code!!

www.rwdi.com


Eurocode Terrain Categories

www.rwdi.com


Origins of European Wind Codes

Typical European City Skyline

www.rwdi.com


Eurocode Terrain Categories

www.rwdi.com


Challenge: Urbanization & Tall Buildings

Singapore Skyline

www.rwdi.com


Influence Effects

Channeling & Funneling of Wind Flow

CFD Simulation of

Wind Flow

www.rwdi.com

Limited guidance provided in Eurocode (UK NA 2.27) – considers only

the influence of a single neighboring building!


Influence Effects

Wake Buffeting

Ferrybridge Power Station Collapse

Wind

www.rwdi.com


Influence Effects

Wake Buffeting

www.rwdi.com

Eurocode – Exclusion of Wake Buffeting for Slender, Dynamically

Sensitive Buildings


3rd Link – Aerodynamic Response

www.rwdi.com



Turbulent Wind Impacting Building

w

v

U

z

x

y

Wind velocity

components

Note lack of correlation of wind pressures at

separate points on the building

www.rwdi.com


Bluff Body Aerodynamics

www.rwdi.com


Surface Wind Pressures

www.rwdi.com


Pressure Coefficient

Cp

qp

ref

p

qref

Wind


Pressure Fluctuations

Wind

www.rwdi.com

Reputation Resources Results 40

Cladding Damage

Reputation Resources Results 41

Analytical Code Wind Loads

Pressure coefficients

Cpe for 0°

Wall net Cp = 1.06

rear = -0.5

-0.5

-1.3 -0.9 -1.3

-0.4 / +0.2

-1.1/+0.2 -0.8/+0.2 -1.1/+0.2

-0.8

3.2m

1.6m

plan

1.6m

plan

8m

B=40m b=16m D/H=1.875 B/D=2.67

+0.78 -1.3

Zone G Cpe = -0.5

1.88m plan 1.94m true

Zone E Cpe = -1.3 1.66m true

Wind at 0° (qs = 812Pa for ridge) Internal pressure (assume worst range for enclosed building)

Cpi = +0.2 / -0.3 Volume of building = (6.1 + 8)/2 x 15 x 40 =4230m3 a = 10 x 34230 = 161.7m Ca = 0.738

Highest loaded purlin

B = 40m

b = 16m

D/H = 1.875

Area = 1.94 x 8 = 15.53m2

Proportion of zone E = (1.66 – 0.97)/1.94 = 0.355

Average Cpe = (0.355 x –1.3) + ((1 – 0.355) x –0.5) = -0.784

Diagonal dimension a = (1.942 + 82) = 8.23m Cae = 0.962

Uplift on purlin : P = qs x (Cpe Cae – Cpi Cai) x A

P = 812 x (-0.784x0.962 – 0.2x0.738) x 15.53 = 11.4kN (enclosed, most onerous Cpi) P = 812 x (-0.784x0.962 + 0.3x0.738) x 15.53 = 6.7kN (uniform porosity)


Limitations of Analytical Code Methodology

• Only accounts for isolated buildings

• Does not account for complex “influence effects”

• Dynamics effects > only accounts for low & midrise buildings

where “along-wind” loading dominates

Strengths of Analytical Code Design Loads

• Simplified – easy to apply

• Apply to majority of “box-type” buildings

• Generally conservative


www.rwdi.com



• Only applies to isolated “box-type” buildings


Examples of “Box-Type” Building Shapes in Eurocode

www.rwdi.com


Challenge: Iconic Architectural Design

Singapore

Milwaukee London

www.rwdi.com


Challenge: Iconic Architectural Design

Beijing Beijing

Dubai Kuala Lumpur www.rwdi.com


Kinematic similarity – simulates mean and turbulence

characteristics of wind

Boundary Layer Wind Tunnel Method

Market Street Office Tower - Singapore


Kinematic similarity – simulates mean and turbulence

characteristics of wind

Boundary Layer Wind Tunnel Method


Boundary Layer Wind Tunnel Methodology

CCRC Building - Singapore Gardens on the Bay - Singapore

Geometric Similarity - Captures Unusual or

Complex Architecture



Gehry’s Architectural 3D CAD Model RWDI’s Pressure Study Scale Model

Integrated with 3D Design Process

www.rwdi.com



• Rapid schedule

• Complex 3D Geometry

• Captures small details (eqv 30cm at full scale eg. Canopies)

Rapid Prototyping of Wind Tunnel Model

www.rwdi.com


Simulates “Influence Effects”


W Hotel Development – Kuala Lumpur

www.rwdi.com



Identify “Hotspots” using Cladding Wind Tunnel Model

www.rwdi.com


CCRC Building („The Rock”), Singapore

www.rwdi.com


Example Cladding Pressure Block Diagrams

2.75kPa!!

www.rwdi.com


Misconception

“The analytical method in the code

can always be used safely to

determine design wind loads as

the method is conservative….”


Misconception

“Wind tunnel studies tend to add

costs to the project…”


Comparison: Wind Tunnel vs. Analytical

57


Comparison: Wind Tunnel vs. Analytical

58


4th Link – Dynamic Response

www.rwdi.com


Dynamic Response

Design Criteria

Local Wind Climate


Dynamic Response


Dynamic Response

www.rwdi.com

HFFB / HFPI Aero Image Courtesy: BLWT


Building height

Importance

of wind

loads

Relationship between wind loads and height

“Across-wind” loading important

• Height is over 120m

• Slenderness more than 4:1

• Natural period greater than 4 seconds

www.rwdi.com


Limitation of Code Analytical Loads

www.rwdi.com

Eurocode – Limitation of Analytical Procedure

What about “Across-wind” loading?!!

Guidance provided for Chimneys &

Masts, but not buildings


Relationship between wind loads and height

Wind velocity

Across-wind

Response

Vortex shedding

No vortex shedding

www.rwdi.com

“Across-wind” loading


Importance of Vortex Shedding

John Hancock Building, Boston

• 1970’s. No wind tunnel testing

• Problems after opening…

– Wind & Thermal Displacements >

Glazing popped out!

– Police shutdown streets when wind

exceeded 20m/s

– Excessive Motion > Occupants

experience motion sickness

– Retrofitted with TMD

• Reputation“…the world’s tallest

plywood building”!

• Cause ? Vortex-Induced

Oscillations (VIO)

• Only accounts for isolated buildings

• Does not account for “influence

effects” of neighboring buildings

www.rwdi.com


Vortex shedding

b

USN

S = Strouhal number

U = wind speed

b = building width

Shedding frequency N is

given by

wind

Magnitude of

excitation damping density

1

Directions of

fluctuating

force

www.rwdi.com


Vortex Induced Oscillations (VIO) – Taipei 101

Wind

www.rwdi.com


Control of VIO - Shaping Strategies

• Softened corners

• Tapering and setbacks

• Varying cross-section shape

• Spoilers

• Porosity or openings

www.rwdi.com


Taper Effect

Petronas Towers – Kuala Lumpur

www.rwdi.com


Soften Corners

International Commerce Centre – Hong Kong

www.rwdi.com


Soften Corners & Taper

Signature Tower – Jakarta

www.rwdi.com


Changing Cross Section & Orientation

Shanghai Center – China

www.rwdi.com


Changing Cross Section, Orientation & Taper

Burj Khalifa – Dubai

Lower impact

wind direction

Higher impact

wind direction

NORTH

www.rwdi.com


Wind Induced Torsional Loads

Wind

Unsymmetrical pressure

distribution due to skewed wind

direction, shape and

surrounding influences

Modal coupling, excitation of

sway modes induces torsion.

Not covered by analytical

method

www.rwdi.com


• Torsion loading ignored by some codes e.g. Indonesian

• Best Int‟l codes account for torsion wind loading for “box-type”

low and midrise buildings, e.g. ASCE 7-10, Eurocode


Eurocode

• Guidance for low & midrise “box-type” buildings (Section 7.1.2)

• Excludes torsional vibrations, e.g. tall buildings with a central

core

Wind Induced Torsional Loads

www.rwdi.com


N (0 deg.)

View from North

C

-8E+07

-6E+07

-4E+07

-2E+07

0E+00

2E+07

4E+07

6E+07

Ba

se

To

rsio

na

l M

om

en

t o

n T

ow

er

C (

N-m

)

10 60 110 160 210 260 310 360 Wind Direction (degrees)

Without Upstream T ower B With Upstream T ower B

-3E+08

-2E+08

-2E+08

-1E+08

-5E+07

0E+00

5E+07

1E+08

2E+08

Ba

se

Sw

ay

Mo

me

nt,

Mx

on

To

we

r C

(N

-m)

10 60 110 160 210 260 310 360 Wind Direction (degrees)

Without Upstream T ower B With Upstream Tower B

max

min mean

Mx

X

Y

Influence Effects – Wake Buffeting

Typical Example of Wake Buffeting

Wind from 230º

D

www.rwdi.com


F t p t AGx ij xi ij ijji

( ) ( ) cos

High Frequency Pressure Integration (HFPI)

Level i

Level (i-1)

Level (i+1)

Location

j-1

j

j+1

Location

Location

Tributary Area Aij

x = direction

of modal

deflection

Normal to

tributary area

Aij

ij

xi

Aij

pij = pressure on

tributary area Aij

Obtain Generalized Force by Pressure Integration

www.rwdi.com


High Frequency Force Balance (HFFB)

The Met, Bangkok

Torsion

Flexure

Sway

Flexure

Rigid,

lightweight

model

F t f z t z dz

f z tz

Hdz

M t

H

G

H

H

( ) ( , ) ( )

( , )

( )

0

0

z

f(z,t) = force per

unit height

www.rwdi.com


Aeroelastic Wind Tunnel Modelling

What is Aeroelastic Effects?

An aeroelastic effect is one in which wind loading, which causes

motion of the structure, is itself affected by the motion of the

structure. Examples are Flutter and Galloping

This results in a strong coupling between the aerodynamics and the

motion

Advantages of Aeroelastic Modeling

Identifies Aeroelastic Instabilities

Includes effect of aerodynamic damping

Includes detailed nature of response (peak factor)

Allows load combinations and accelerations to be measured

directly

Allows higher modes of vibration to be simulated

Disadvantages

More costly and time consuming


Aeroelastic Model

Aeroelastic Model of Rooftop Spire of Freedom Tower, NYC


5th Link – Design Criteria

www.rwdi.com


Dynamic Response

Design Criteria

Local Wind Climate


Design Criteria


Wind Design Criteria

81

Serviceability Limit States

• Deflections (Drift)

• Occupant Comfort (Accelerations & Torsional

Velocities)

• Pedestrian Wind Comfort & Safety

• Fatigue

Ultimate Limit States

• Strength

• Aeroelastic Stability


Motion Criteria

www.rwdi.com


Motion Simulator

www.rwdi.com


Motion Simulator

Moving Room Simulations

www.rwdi.com


Wall Centre, Vancouver

Cross Section

prone to vortex

shedding

30 Story Residential Building in downtown Vancouver

www.rwdi.com


Wall Centre, Vancouver

Tuned Liquid Column Damper

www.rwdi.com


Use of tuned mass damper – Taipei 101

www.rwdi.com


Wind Load Chain

www.rwdi.com


Dynamic Response

Local Wind Climate


Design Criteria


Selection of a Wind Tunnel Consultant

89

• Local & International Experience

• Reputation (References from Past Clients)

• Consultant or just a Lab?

• Range of capabilities

• Quality assurance

• State of the Art

• Responsiveness

• Knowledge of local requirements, codes

• Equipment: Boundary Layer Wind Tunnels,

Instrumentation, Model Building, CFD


Concluding Remarks

90

• A commonly held misconception is that wind

engineering is not of importance in Singapore because

of its location in a relatively benign wind region that is

sheltered from typhoons, tornadoes and strong

synoptic wind-storms that dominate elsewhere.

• However over the lifetime of a building in Singapore,

individual extreme thunderstorms and squall lines

(“Sumatras”) will impose significant wind effects -

especially those structures that are tall or have unique

architectural forms which are not covered by the

analytical methods in the Eurocode, CP3 or BS 6399.


Concluding Remarks

91

• The concept of the “Wind Loading Chain”

demonstrates, in any region the overall design

reliability and efficiency of a wind-sensitive structure is

only as good as the least reliable of the links.

• Presently, wind tunnel model studies offer the best

estimate of the wind loading acting on a building for

cladding as well as structural frame design.

• Most of the time, the small amount of money spent for

wind tunnel study will be paid off by saving significant

overall savings in either cladding or structural frames.


Unique Structures - When to use Wind Tunnel

The analytical code methodology applies to the majority of site locations and buildings and structures, but for some projects these provisions may be inadequate. Examples that may require other special studies using applicable recognized literature pertaining to wind effects or using the wind tunnel procedure include: 1. Site locations that have channeling effects or wakes from upwind obstructions.

Channeling (Funneling) effects can be caused by topographical features (e.g. valley) or buildings (e.g. neighboring tall buildings). Wake can be caused by hills or buildings or other structures.

www.rwdi.com


Unique Structures - When to use Wind Tunnel

2. Buildings with unusual or irregular geometric shapes, whose shape in

plan or vertical cross-section differs significantly from the shapes illustrated in the codes. Unusual or irregular geometric shapes include buildings with multiple setbacks, curved facades, or irregular plans resulting from significant indentations or projections, openings through a building, or multi-tower buildings connected by bridges.

www.rwdi.com


Tall Structures - When to use Wind Tunnel

3. Buildings with response characteristics that results in substantial vortex-induced

and/or torsional dynamic effects, or dynamic effects resulting from aeroelastic instabilities such as flutter or galloping. Such dynamic effects are difficult to anticipate being dependent on many factors, but should be considered to apply when any one or more of the following apply:

• The height of the building is over 200m (Eurocode Limit). • The height of the building is greater than 4 times its minimum effective width

Bmin • The lowest natural frequency of the building is less than n1 = 0.25 Hz (i.e. 4

second natural period) • The reduced velocity is less than 5 (see ASCE 7 code for definition)

www.rwdi.com



www.rwdi.com



95

Thank you!!

Questions?

Mark P. Chatten

Project Director / Consultant

[email protected]


wind notes

Documents

slide view

black slide

slide sorter view

slide transitions

view slide master

link local wind climate

wind engineering

wind load chain