1. WIND LOADS ON BUILDINGS
ASCE SEMINAR
WIND LOADS ON BUILDINGS
AND OTHER STRUCTURES
Jon D. Raggett, PhD, PE, SE
President
West Wind Laboratory, Inc.
2320 Del Monte Ave., Suite A-4
Monterey, CA 93940
ASCE Wind Loads

2. WIND LOADS ON BUILDINGS AND OTHER STRUCTURES
ASCE SEMINAR
WIND LOADS ON BUILDINGS AND OTHER STRUCTURES
SESSIONS 1 AND 2 - Theory
DESCRIPTION OF WIND
BLUFF BODY AERODYNAMICS
STRUCTURAL DYNAMICS
SESSIONS 3 AND 4 - ASCE 7-10, CHAPTERS 26-31
DESCRIBE HOW ASCE 7-10 CHAPTERS INCLUDES THEORY
SESSIONS 5 AND 6 - EXAMPLES
HIGH-RISE BUILDING
LOW-RISE BUILDING
OPEN STRUCTURES
SIGNS
INDUSTRIAL STRUCTURES
SESSION 7 - EXAMPLES
LOW-RISE BUILDINGS
(COMPARISON OF METHODS)
SESSION 8 –WIND-BORNE DEBRIS AND EXPERIMENTAL METHODS
ASCE Wind Loads

3. Course Objectives At the end of this course you will:
Learn the fundamentals of bluff-body aerodynamics and structural dynamics;
Learn how those fundamentals are included in ASCE 7-10
Learn how to use ASCE 7-10 through a series of examples; and
Have your questions answered.
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4. SESSION 1 Wind Engineering Theory: Wind Characteristics
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5. Snapshot of Wind Courtesy of Wind Science and Engineering, Texas Tech Univ.
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6. Nature of Winds Averaging time Wind speed profile Wind turbulence
Topography
Wind Hazard Risk
Wind directionality
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7. Tornadoes Courtesy of Wind Science and Engineering, Texas Tech Univ.
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8. Wind Speed Time Histories
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9. Wind Speed Time Histories
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10. Wind Characteristics As A Function of Averaging Time
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11. Wind Speed Characteristics As A Function of Time and Elevation
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12. Ratio of Averaging Time to Mean Hourly Courtesy of Wind Science and Engineering, Texas Tech Univ.
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13. Power Law Profiles Courtesy of Wind Science and Engineering, Texas Tech Univ.
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14. Power Law
Vz = Vg
Vz = Vg z > zg
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15. Wind Turbulence: Intensity Courtesy of Wind Science and Engineering, Texas Tech Univ.
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16. Wind Turbulence: Frequency Content (Spectrum) Courtesy of Wind Science and Engineering, Texas Tech Univ.
Wind speed fluctuates randomly at all frequencies.
The Gust Frequency Spectrum is a non-dimensional measurement of energy in the wind versus frequency (Hz). The power spectral density Su(n) is multiplied by frequency n and divided by standard deviation (σu2) to yield the non-dimensional energy expression.
The peak energy in the wind is found at a frequency of approximately Hz.
The energy has reduced significantly at frequencies greater than 1.0 Hz.
If the building or structure has a fundamental frequency greater than 1.0 Hz, the gustiness in the wind induces negligible dynamic resonance (buffeting).
“Rigid” structures have fundamental frequencies greater than 1 Hz.
“Flexible” structures have fundamental frequencies less than or equal to 1 Hz.
ASCE Wind Loads

17. Logarithmic Law
Atmospheric boundary layer (alternate used primarily by laboratories - similar results)
Basic law for one-hour averaged mean wind speed
EXPOSURE
Z0 (m)
Z0 (m) IMPLIED IN ASCE 7-05 B
0.300
5.25
0.150 C
0.030
6.00
0.020 D
0.005
6.50
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18. Logarithmic Law (cont)
Change exposure
t(sec)
c(t) 1
3.00 3
2.85 60
1.28
300
.54
600
.36
3600
.00
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19. Logarithmic Law (cont)
Longitudinal turbulence spectrum
All consistent and derived from fundamental principles
(Simiu, E., and Scanlan, R. H. Wind Effects on Structures,
Third Edition, John Wiley & Sons, New York, 1996).
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20. Escarpment Courtesy of Wind Science and Engineering, Texas Tech Univ.
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21. Topographic Effect
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22. DESIGN WIND SPEED Design wind speed is based on probability
Objective is to obtain a maximum reference wind speed with a specific mean recurrence interval (MRI), or mean return period, or probability that a specific wind speed is exceeded (equal to 1/MRI)
Obtain from historical wind speed data a specific site
Obtain from hurricane simulation models
Smooth data over regions
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23. (FROM HISTORICAL PEAK ANNUAL WIND SPEEDS)
EXPECTED WIND SPEED
(FROM HISTORICAL PEAK ANNUAL WIND SPEEDS)
where
V(N) Peak wind speed with a return period of N years
Mean peak annual wind speed from n years of data
Standard deviation of the peak annual wind speeds from
n years of data
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24. Expected Wind Speed - Example (From Historical Peak Wind Speeds) Courtesy of Wind Science and Engineering, Texas Tech Univ.
Year
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978 60 57 78 99 65 56 58 59 61
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990 66 74 55 70 88 49
1991
1992
1993
1994
1995
1996
1997
1998 44 75 54
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25. Expected Wind Speeds - Example (From Historical Peak Annual Wind Speeds) (Cont) Courtesy of Wind Science and Engineering, Texas Tech Univ.
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26. Expected Hurricane Wind Speeds (From Numerical Simulation Procedures) Courtesy of Wind Science and Engineering, Texas Tech Univ.
TRACKS OF HURRICANES PASSING WITHIN 250 km OF GRAND CAYMAN ISLAND
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27. Expected Hurricane Wind Speeds (From Numerical Simulation Procedures) (Cont) Courtesy of Wind Science and Engineering, Texas Tech Univ.
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28. References for Hurricane Numerical Simulation Procedures
Dr. Peter Vickery Papers (that describe hurricane simulation procedures)
Vickery, P. J., Skerlj, P.F., and Twisdale, L. A., "Simulation of Hurricane Risk in the U. S. Using Empirical Track Model", Journal of Structural Engineering, October 2000.
Vickery, P. J. et al, "Hurricane Wind Field Model for Use in Hurricane Simulations", Journal of Structural Engineering, October 2000
Vickery, P. J., et al, "Hurricane Gust Factors Revisited", Journal of Structural Engineering, May 2005
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29. Wind Directionality
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