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Converting Wind Averaging Speeds 3
- Thread starter mblewis
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The durst curve, developed by C.S. Durst, is used for non-hurrican winds and thr Krayer-Marshall curve, developed by W.R. Krayer and R.D. Marshall, is used for hurricane winds (may no longer be valid. Both are plotted on a curve, using the peak wind speed, (Vt), and the hourly peak speed, (V3600), can be used to convert wind speeds to various averaging times.
These curves can be conveniently used for converting the hourly mean speed (Vmh) and the fastest mile wind speed (Vfm) to 3-second gust speed (V3s) and vice versa.
Try this link for durst, krayer-marshall graph (A little more than 1/2 way through the paper):
Example of conversion:
Conversion of hourly mean speed of 80 mph to 1-second and 3 second gust speeds.
Hourly mean speed = V3600. From the graph, read the value of Vt/V3600 on the y-axis for t = 1 second on the x-axis. Note that t = 1 second lies at the origin of the durst curve. this value is 1.57 (approx). Therefore,
V1s/V3600 = 1.57, whence V1s = 1.57 mh = 1.57(80) = 125.6 mph.
Similarly, for t = 3 seconds on x-axis we read Vt/V3600 = 1.53 (approx) on the y-axis.
Therefore:
Vt/V3600 = 1.53, whence V3s = 1.53Vmh = 1.53(80) = 122.4 mph.
These curves can be conveniently used for converting the hourly mean speed (Vmh) and the fastest mile wind speed (Vfm) to 3-second gust speed (V3s) and vice versa.
Try this link for durst, krayer-marshall graph (A little more than 1/2 way through the paper):
Example of conversion:
Conversion of hourly mean speed of 80 mph to 1-second and 3 second gust speeds.
Hourly mean speed = V3600. From the graph, read the value of Vt/V3600 on the y-axis for t = 1 second on the x-axis. Note that t = 1 second lies at the origin of the durst curve. this value is 1.57 (approx). Therefore,
V1s/V3600 = 1.57, whence V1s = 1.57 mh = 1.57(80) = 125.6 mph.
Similarly, for t = 3 seconds on x-axis we read Vt/V3600 = 1.53 (approx) on the y-axis.
Therefore:
Vt/V3600 = 1.53, whence V3s = 1.53Vmh = 1.53(80) = 122.4 mph.
I have been told that the 3-second gust is approximately 1.2 times the fastest mile wind velocity!
(for example, if you have a fastest mile velocity of 120 MPH, then the 3-second gust would be 1.2*100= 120 MPH).
Please note that the factors used to compute the pressures are not the same as those for the fastest wind)
I think this would be a good approximation.
I hope this helps.
(for example, if you have a fastest mile velocity of 120 MPH, then the 3-second gust would be 1.2*100= 120 MPH).
Please note that the factors used to compute the pressures are not the same as those for the fastest wind)
I think this would be a good approximation.
I hope this helps.
Table 1609.3.1 in the 2003 International Building Code is titled "Equivalent Basic Wind Speeds" and is for converting between fastest mile wind speed and 3-second gust wind speed. The 1.2 factor mentioned by Lutfi seems to work pretty well for a ball park estimate.
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