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

RWDI Leadership & Consulting Expertise RWDI Consulting Engineers & Scientists offering design guidance and problem solving for structural and environmental issues Established in 1972 440+ employees Multi-disciplinary teams Senior scientists; engineers; specialists; meteorologists; engineering technologists; technicians; support staff

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 Mean hourly wind speed (mph) 80 60 40 20 \ bridge alignment included 290 280 300 320 330 310 10-year 0 10 340 350 100 20 Bridge 10 1.0 1 0.1 30 40 50 60 70 80 P e rc e n ta g e o f Ti m e 0 100 0.1 1 10 100 1 10 260 3 Return Period (years) 100-year 1 10 4 250 10 240 1 0.1 0.01 Winds Exceeding 90 mph 270 0.01 10 60 110 160 210 260 310 360 Wind Direction (degrees) 230 220 210 200 0.01 190 180 1-year 170 160 90 100 110 120 130 140 150

Why we need shape optimization? Across-wind response where mean loads are negligible Mx 4.0E+ 09 Base Overturning Moment B a s e O v e rt u r n in g M o m e n t ( N -m ) 2.0E+ 09 0.0E+ 00-2.0E+ 09-4.0E+ 09 Along-wind response 10 60 110 160 210 260 310 360 Wind Direction (degrees) Wind Direction (degrees) Peak Maximum Mean Peak Minimum 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 where mean loads are negligible Mx 4.0E+ 09 Base Overturning Moment B a s e O v e rt u r n in g M o m e n t ( N -m ) 2.0E+ 09 0.0E+ 00-2.0E+ 09-4.0E+ 09 Along-wind response 10 60 110 160 210 260 310 360 Wind Direction (degrees) Wind Direction (degrees) Peak Maximum Mean Peak Minimum Wind response can be significantly reduced by shape optimization.

Across Wind Response and Vortex Shedding Strouhal Number f S U t D S t = Strouhal number D = a characteristic dimension, taken as the width 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. U crit f B S D t 12

Mitigating Cross-Wind Response 432 Park Avenue

Mitigating Cross-Wind Response Taipei 101 Original Corner options tested Modified 25% - 30% REDUCTION IN BASE MOMENT

Tapered Box 120 o Configuration 180 o Configuration 100 o Configuration 110 o Configuration 15 Final 15 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%) Reference Configuration Test Date My (N-m) Ratio Mx (N-m) Ratio Ref. Ratio Resultant Base (Tapered Box) 08/22/2008 5.45E+10 100% 4.98E+10 100% 6.22E+10 100% 100 o (107 o ) 07/28/2008 4.53E+10 83% 4.19E+10 84% 5.18E+10 83% 110 o (118 o ) 08/22/2008 3.97E+10 73% 4.31E+10 87% 4.92E+10 79% 180 o (193 o ) 07/28/2008 3.39E+10 62% 3.65E+10 73% 4.18E+10 67% 120 o (129 o ) - 0 Rot. Estimated 3.43E+10 63% 4.29E+10 86% 4.75E+10 76% 110 o (118 o ) - 30 Rot. 09/29/2008 3.92E+10 72% 3.60E+10 72% 4.48E+10 72% 120 o - 40 Rot. 09/29/2008 3.57E+10 66% 3.53E+10 71% 4.15E+10 67% Ref.Resultant 0 Rot. Original 110 Shape Footprint Position 30 Rot. Optimal Orientation of 110 Shape 40 Rot. Optimal Orientation of 120 Shape ( Max) ( 0. 6 Min) 2 2

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

Non-dimensional time = Time and velocity scaling Non-dimensional velocity = t * U tu * b ref U ref b 0

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, [m 2 /s] Often overlooked in bluff body aerodynamics for sharp edged objects Typical ranges at model scale Re values are 10 4 Typical ranges at full scale Re values are 10 7

Plot of Drag Coefficient of a Cylinder vs. Reynolds Number 4.0 Drag coefficient 3.5 3.0 2.5 2.0 1.5 1.0 u b Drag Force 1 u A C D 2 2 A b 4 2 0.5 0.0 1E+01 1E+02 1E+03 1E+04 1E+05 1E+06 1E+07 Reynolds number [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

Shear Force (lbf) Fx 1.80E+04 1.60E+04 1.40E+04 1.20E+04 1.00E+04 8.00E+03 6.00E+03 4.00E+03 2.00E+03 0.00E+00-2.00E+03 260 270 280 290 300 310 320 330 340 350 360 Wind Direction (degrees) Full Stage Equipment - Full Roof No Stage Equipment - Full Roof Shear Force (lbf) 5.00E+03 Fy 0.00E+00-5.00E+03-1.00E+04-1.50E+04-2.00E+04-2.50E+04-3.00E+04 260 270 280 290 300 310 320 330 340 350 360 Wind Direction (degrees) Full Stage Equipment - Half Roof No Stage Equipment - Half Roof

Indiana State Fair Collapse Incident Wind Engineering Services Scale Model Tests

SNOW CONTROL FEATURES IN BUILDING DESIGN

Understanding the Local Climate All Winter Winds Winds during Snowfall Percentage of Snow over All Winds: 12.9% Wind Speed km/h Winter Winds Probability (%) During Snowfall Blowing 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 Grade Level Drift Roof Step Accumulation Example Snow Drift Simulation www.rwdi.com

Reduced Accumulations Large Structural Loads Evaluation of Mitigation Measures www.rwdi.com

Snow Drifts Pushed Away from the Building Facade Wind Deflector Device Evaluation of Mitigation Measures www.rwdi.com

Wind Deflectors above Clearstory Windows

Building Massing to Promote Controlled Sliding Image Courtesy www.vikings.com

Large Catchment Gutter for Storing Sliding Snow Sliding Snow and Ice Snow Deflector for Directing Snow into Large Catchment Gutter 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

Reputation Resources Results Canada USA UK India China www.rwdi.com 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 Page 47 Example of Flow Fields Obtained from Wind Tunnel Testing

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 Multi-Purpose Stadium Roof Loading for the Winter of 1981-1982 Example of Typical Roof Snow Accumulation for the Winter of 1981-1982 Page 48

Through knowledge and understanding, we can anticipate and control the impact of the climate in the built environment. Performance and precision.

MERCI BEAUCOUP