An Overview of Wind Engineering Where Climate Meets Design

An Overview of Wind Engineering

Where Climate Meets Design

Presented by

Derek Kelly, M.Eng., P.Eng. Principal/Project Manager

www.rwdi.com

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Allied offices around the world Overview

. Overall building aerodynamics . Building motion and supplementary damping . Snow drifting and loading Instantaneous Pressure Distribution About a Building Experimental Process Planetary boundary layer and effect of surface roughness - mean velocity profile

Local wind climate assessment and distribution of wind speeds

120

100

80 \ bridge alignment 350 0 10 included 340 100100 20 330 30 60 320 Bridge 40 10 310 10-year 50

40 300 1.01 60

Meanhourly wind speed(mph) 290 70 0.10.1 20 280 80

Winds Exceeding 90 mph 270 0.010.01 90 0 0.1 1 10 100 1260103 100-year 1104 100 100 Return Period (years) 250 110 10 240 120 1-year 1 230 130 220 140 0.1 210 150 200 160 Percentage of Time 190 180 170 0.01 10 60 110 160 210 260 310 360 Wind Direction (degrees) Why we need shape optimization?

Across-wind response whereMx mean loads are negligible

4.0E+09

2.0E+09 Peak Maximum Mean 0.0E+00 Peak Minimum

-2.0E+09 Base Overturning M om ent (N-m ) Along-wind response -4.0E+09

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

For a slender tall building with almost uniform cross-section, the wind loads can be governed by across-wind response due to vortex shedding. This normally becomes an issue for both strength design and serviceability. Why we need shape optimization?

Across-wind response whereMx mean loads are negligible

4.0E+09

2.0E+09 Peak Maximum Mean 0.0E+00 Peak Minimum

-2.0E+09 Base Overturning M om ent (N-m ) Along-wind response -4.0E+09

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

Wind response can be significantly reduced by shape optimization. Across Wind Response and Vortex Shedding Strouhal Number

St= Strouhal number tUS D = a characteristic dimension, taken as f  the width D U = the velocity of the approaching wind

Strouhal numbers have been determined for a variety of shapes such as rectangular, circular and triangular bodies. Typically between 0.12 to 0.16 for squared objects, and 0.2 to 0.22 for circular bodies.

B Df Ucrit  St

12 Mitigating Cross-Wind Response – 432 Park Avenue Mitigating Cross-Wind Response – Taipei 101

Corner options tested Original

25% - 30% Modified REDUCTION IN BASE MOMENT Tapered Box 120o Configuration 180o Configuration

100o Configuration

15 110o Configuration Final15 Configuration Benefits of Optimization due to Twist & Building Orientation

Comparison of Base Overturning Moments Assume the same structural properties for all configurations (Vr=52m/s, 100-yr wind, damping=2.0%)

Configuration Test Date My (N-m) Ratio Mx (N-m) Ratio Ref. Ratio Resultant Reference Base (Tapered Box) 08/22/2008 5.45E+10 100% 4.98E+10 100% 6.22E+10 100%

100o (107o) 07/28/2008 4.53E+10 83% 4.19E+10 84% 5.18E+10 83%

110o (118o) 08/22/2008 3.97E+10 73% 4.31E+10 87% 4.92E+10 79%

180o (193o) 07/28/2008 3.39E+10 62% 3.65E+10 73% 4.18E+10 67%

120o (129o) - 0° Rot. Estimated 3.43E+10 63% 4.29E+10 86% 4.75E+10 76%

110o (118o) - 30° Rot. 09/29/2008 3.92E+10 72% 3.60E+10 72% 4.48E+10 72%

120o - 40° Rot. 09/29/2008 3.57E+10 66% 3.53E+10 71% 4.15E+10 67%

Ref.Resultant ()(.)Max2 06  Min 2 0° Rot. – Original 110° Shape Footprint Position 30° Rot. – Optimal Orientation of 110° Shape 40° Rot. – Optimal Orientation of 120° Shape Controlling Motions Taipei 101 Comcast Tower - Philadelphia 432 Park Avenue – in action! Specialty Studies Aeroelastic of a Super Tall Building Aeroelastic model of a construction stage

Image of a Rigid Aeroelastic Model Under Construction Aeroelastic Models of Completed Bridges

Tacoma Narrows Bridges Tacoma, Washington (suspension bridges)

Cooper River Bridge - Charleston, S.C. (cable-stayed bridge) Aeroelastic scaling Time and velocity scaling tU Non-dimensional time = t *  ref b U Non-dimensional velocity = U *  ref 0b Reynolds Number Tests

In fluid mechanics, the Reynolds number is a measure of the ratio of inertial forces to viscous forces, and quantifies the relative importance of these two types of forces for given flow conditions. It is primarily used to identify different flow regimes passing by a given object. Typically, Reynolds number is defined as follows:

VD Re   where:

V - mean fluid velocity, [m/s] D - diameter of pipe, [m] ν - kinematic fluid viscosity, [m2/s]

. Often overlooked in bluff body aerodynamics for sharp edged objects . Typical ranges at model scale Re values are 104 . Typical ranges at full scale Re values are 107 Plot of Drag Coefficient of a Cylinder vs. Reynolds Number

4.0

3.5 u 3.0 b

2.5

2.0

1.5

Dragcoefficient 1.0

F orce Drag Force 0.5 CD  1 2 0.0 2  Au 1E+01 1E+02 1E+03 1E+04 1E+05 1E+06 1E+07 b2 Reynolds number A  4

[After Clift, Grace and Weber Bubbles, Drops and Particles, Academic Press, 1978] Addressing Reynolds Number

• Because the Reynolds number is a function of Speed, Width of the object, and viscosity, one can do the following to achieve a high Reynolds number:

• Test a large model • Test at a high speed • Change the air density in the experiment* *difficult to do, need a pressurized wind tunnel

• For projects that RWDI has worked, a large model has been built and tested at a high speed.

• These experiments are then compared to a similar experiment conducted at a smaller scale in RWDI’s facilities.

• The results from each are then compared to original wind tunnel tests.

• The outcome is typically the overall responses, i.e. overall loads on a tower and building accelerations reduce, whereas the local Cladding loads may increase slightly and the distribution will change.

High Reynolds Number Tests (option)

Example High Reynolds Number Tests High Reynolds Number Tests – Shanghai Center Fx 5.00E+03 1.80E+04 Fy 1.60E+04 0.00E+00 1.40E+04

-5.00E+03 1.20E+04 1.00E+04 -1.00E+04 8.00E+03 -1.50E+04 6.00E+03 Shear Force (lbf) ForceShear Shear Force (lbf) ForceShear 4.00E+03 -2.00E+04 2.00E+03 -2.50E+04 0.00E+00 -2.00E+03 -3.00E+04 260 270 280 290 300 310 320 330 340 350 360 260 270 280 290 300 310 320 330 340 350 360 Wind Direction (degrees) Wind Direction (degrees)

Full Stage Equipment - Full Roof Full Stage Equipment - Half Roof No Stage Equipment - Full Roof No Stage Equipment - Half Roof Indiana State Fair Collapse Incident

Wind Engineering Services – Scale Model Tests Fx 5.00E+03 1.80E+04 Fy 1.60E+04 0.00E+00 1.40E+04

Full Stage Equipment - Full Roof Full Stage Equipment - Half Roof No Stage Equipment - Full Roof No Stage Equipment - Half Roof SNOW CONTROL FEATURES IN BUILDING DESIGN

Understanding the Local Climate

All Winter Winds during Winds Snowfall

Percentage of Snow over All Winds: 12.9%

Wind Probability (%) Speed Winter During Blowing km/h Winds Snowfall Snow 1-20 50.1 41.0 2.1

21-25 18.3 19.1 4.9

26-30 14.7 18.7 15.7

31-35 7.3 10.2 24.6

>35 5.5 8.2 52.8

Blowing Snow Events Winter Winds Directionality (Blowing From) Toronto International Airport (1953-2015) Site surroundings and topography… …also something we also have little control over

Drifting Snow in Urban Areas Unbalanced Structural Snow Load

Approaching Wind Flow

Large Problematic Roof Step Grade Level Drift Accumulation Example Snow Drift www.rwdi.comSimulation

Evaluation of Mitigation www.rwdi.comMeasures

Building Massing to Promote Controlled Sliding Image Courtesy www.vikings.com Scale Model of Minnesota Multi-Purpose Stadium in RWDI’s Boundary Layer Wind Tunnel Velocity Vectors from Wind Tunnel Tests

• RWDI’s FAE (Finite Area Element) study was used to derive detailed snow loading patterns on the roof for 58 years of historical winter weather data

• The study accounted for: • snow and rainfall on the roof • the velocity field (drifting) across the roof • thermal effects or heat loss • sliding

Example of Flow Fields Obtained from Wind Tunnel Testing Page 47

Reputation Resources Results Canada | USA | UK | India | China www.rwdi.com Example of Roof Loading Pattern

Example Time History of Ground Accumulation for the Winter of 1981-1982

Example Time History of Minnesota Example of Typical Roof Snow Accumulation Multi-Purpose Stadium Roof Loading for for the Winter of the Winter of 1981-1982 1981-1982

Page 48

Reputation Resources Results Canada | USA | UK | India | China www.rwdi.com Through knowledge and understanding, we can anticipate and control the impact of the climate in the built environment.

Performance and precision. MERCI BEAUCOUP