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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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 bridge alignment 0 350 10 100 100 340 20 included 330 30 60 Bridge 320 40 10 10 310 50 10-year 40 300 60 1.0 1 290 70 0.1 0.1 20 280 80 0.01 Winds Exceeding 90 mph 270 0.01 90 0 P e rc e n ta g e o f Tim e 1 10 3 260 1 10 4 100 0.1 1 10 100 100-year 100 Return Period (years) 250 110 10 240 120 1-year 230 130 1 220 140 0.1 210 150 200 160 190 170 180 0.01 10 60 110 160 210 260 310 360 Wind Direction (degrees)
Why we need shape optimization? Across-wind response where mean loads are negligible Mx 4.0E+09 B as e Ov ert urning M om ent (N -m ) 2.0E+09 Base Overturning Moment Peak Maximum Mean 0.0E+00 Peak Minimum -2.0E+09 Along-wind response -4.0E+09 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 where mean loads are negligible Mx 4.0E+09 B as e Ov ert urning M om ent (N -m ) 2.0E+09 Base Overturning Moment Peak Maximum Mean 0.0E+00 Peak Minimum -2.0E+09 Along-wind response -4.0E+09 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 S t = Strouhal number S U D = a characteristic dimension, taken as t 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. f D B U crit S t 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
120 o Configuration 180 o Configuration Tapered Box 100 o Configuration 15 110 o Configuration Final Configuration 15
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% 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% 2 2 ( ) ( . 06 ) Ref.Resultant Max Min 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 = * ref t b U Non-dimensional velocity = * ref U 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 3.5 u b Drag coefficient 3.0 2.5 2.0 1.5 1.0 0.5 Drag Force C D 2 1 0.0 u A 2 1E+01 1E+02 1E+03 1E+04 1E+05 1E+06 1E+07 Reynolds number 2 b 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 Shear Force (lbf) 1.20E+04 Shear Force (lbf) 1.00E+04 -1.00E+04 8.00E+03 -1.50E+04 6.00E+03 -2.00E+04 4.00E+03 2.00E+03 -2.50E+04 0.00E+00 -3.00E+04 -2.00E+03 260 270 280 290 300 310 320 330 340 350 360 260 270 280 290 300 310 320 330 340 350 360 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 -5.00E+03 Shear Force (lbf) 1.20E+04 Shear Force (lbf) 1.00E+04 -1.00E+04 8.00E+03 -1.50E+04 6.00E+03 -2.00E+04 4.00E+03 2.00E+03 -2.50E+04 0.00E+00 -3.00E+04 -2.00E+03 260 270 280 290 300 310 320 330 340 350 360 260 270 280 290 300 310 320 330 340 350 360 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
SNOW CONTROL FEATURES IN BUILDING DESIGN
Understanding the Local Climate All Winter Winds during Winds Snowfall Percentage of Snow over All Winds: 12.9% Probability (%) Wind 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 Winter Winds Directionality (Blowing From) Events 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 Simulation www.rwdi.com • • • • •
Reduced Large Structural Accumulations Loads Evaluation of Mitigation Measures www.rwdi.com • • • • •
Wind Deflector Device Snow Drifts Pushed Away from the Building Facade Evaluation of Mitigation Measures www.rwdi.com • • • • •
Wind Deflectors above Clearstory Windows
Building Massing to Promote Controlled Sliding Image Courtesy www.vikings.com
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