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 831-883-1533 raggett@westwindlaboratory.com ASCE Wind Loads

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 26-31 6 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

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. ASCE Wind Loads

SESSION 1 Wind Engineering Theory: Wind Characteristics ASCE Wind Loads

Snapshot of Wind Courtesy of Wind Science and Engineering, Texas Tech Univ. ASCE Wind Loads

Nature of Winds Averaging time Wind speed profile Wind turbulence Topography Wind Hazard Risk Wind directionality ASCE Wind Loads

Tornadoes Courtesy of Wind Science and Engineering, Texas Tech Univ. ASCE Wind Loads

Wind Speed Time Histories ASCE Wind Loads

Wind Speed Time Histories ASCE Wind Loads

Wind Characteristics As A Function of Averaging Time ASCE Wind Loads

Wind Speed Characteristics As A Function of Time and Elevation ASCE Wind Loads

Ratio of Averaging Time to Mean Hourly Courtesy of Wind Science and Engineering, Texas Tech Univ. ASCE Wind Loads

Power Law Profiles Courtesy of Wind Science and Engineering, Texas Tech Univ. ASCE Wind Loads

Power Law Vz = Vg Vz = Vg z > zg ASCE Wind Loads

Wind Turbulence: Intensity Courtesy of Wind Science and Engineering, Texas Tech Univ. ASCE Wind Loads

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 0.01 - 0.10 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

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 ASCE Wind Loads

Logarithmic Law (cont) Change exposure t(sec) c(t) 1 3.00 3 2.85 60 1.28 300 .54 600 .36 3600 .00 ASCE Wind Loads

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). ASCE Wind Loads

Escarpment Courtesy of Wind Science and Engineering, Texas Tech Univ. ASCE Wind Loads

Topographic Effect ASCE Wind Loads

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 ASCE Wind Loads

(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 ASCE Wind Loads

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 ASCE Wind Loads

Expected Wind Speeds - Example (From Historical Peak Annual Wind Speeds) (Cont) Courtesy of Wind Science and Engineering, Texas Tech Univ. ASCE Wind Loads

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 ASCE Wind Loads

Expected Hurricane Wind Speeds (From Numerical Simulation Procedures) (Cont) Courtesy of Wind Science and Engineering, Texas Tech Univ. ASCE Wind Loads

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 ASCE Wind Loads

Wind Directionality ASCE Wind Loads