Hurricane Basic Wind Speed
Hurricane Basic Wind Speed
(OP)
Customer specified category 5 hurricane level for wind loading. What basic wind speed should be used for wind analysis based on IBC/ASCE 7?
Thanks, Ibro V.
Thanks, Ibro V.
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Hurricane Basic Wind Speed
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RE: Hurricane Basic Wind Speed
http://www.nhc.noaa.gov/aboutsshs.shtml
The 2003 IBC wind loads come from ASCE 7-02. Typical 3-second gust basic wind speed criterial are specified and used for design. ASCE 7-98, figure C6.11, "Durst curve" can be used to convert to the fastest-mile basic wind speed.
Vfm=(V3s-10.5)/1.05 ASCE Figure 6-1
Cheers
Boo1
RE: Hurricane Basic Wind Speed
RE: Hurricane Basic Wind Speed
Ibro, what are you designing? Three second gust near over 173 MPH seems excessive unless you aredesingin a shelter. Let me caution you about using the ASCE-7 importance factor of 1.15 is you are designing a shelter or critical facility. The text below is my explanation:
FEMA Standard 361 requires the use of importance factor of 1.0, for shelter designs, in accordance to section 3.5.2. The following quote is FEMA’s rational for using importance factor of 1.0 “The importance factor (I) is set equal to 1.0. The importance factor for wind loads in ASCE 7-98 is designed to adjust the velocity pressure to different annual probabilities of being exceeded (different mean recurrence intervals [MRIs]). Since the wind speeds in Figure 2-2 are already based on very great MRIs (i.e., low exceedance probabilities), they do not need to be adjusted with the importance factor.”
I got your e-mail on the crane runway. I have been out of town. Do you still need my input?
Regards,
Lutfi
RE: Hurricane Basic Wind Speed
where did you get your equation? A few years back, I attended the ASCE Wind Loads Seminar. They told us that to use the Durst curve, you must take your fastest mile speed, convert it to a 3600-sec "gust" and convert that back down to a 3-sec gust. The reason is, each fastest mile speed corresponds to a different "gust duration" and you need to convert to a common base, they used 3600 secs. This way, there is a different multiplier for each and every value of fastest mile speed.
regards,
chichuck
RE: Hurricane Basic Wind Speed
I looked at the link you provided. It says those winds are based on a 1-min duration. That means there is a unique conversion factor for changing over to 3-sec gust, just as your formula indicates. ASCE 7-98 doesn't refer to fastest-mile winds, it uses the 3-sec gust. I think what you meant was use the Durst Curve to change from 60-sec duration to 3-sec duration.
regards,
chichuck
RE: Hurricane Basic Wind Speed
The problem you have is a Category V hurricane is not a 155mph wind speed- it is that "or greater". IE, the design range you're looking at begins at the 155mph mark, rather than ending there.
RE: Hurricane Basic Wind Speed
RE: Hurricane Basic Wind Speed
These two links explain it well:
<http://flo
see Table G-1. Equivalent Basic Wind Speeds
For the equation reference see:
http://www
Code Development: 2004-2005 Code Development Cycle / structural: Errata S32-04/05, R301.2.1.3 page 97-99
Ibro, consider what importance factor apply, I have seen FEMA referencing the use of 1.0 (improtance factor) vs 1.15 when the Cat5 wind loads were imposed.
Cheers
Boo1
RE: Hurricane Basic Wind Speed