Wind Speed. 1

You are correct. For properly designed buildings the FS is about 1.0 for the ultimate wind and 1.67 for Allowable Stress Design. But mother nature is very good at finding chinks in the armor (glass windows, antennas, architectural features, etc.) so there is likely some damage.
They will not go unscathed. It's usually pre engineered metal buildings or secondary buildings, like garages or fast food.

I understand the safety factors and how they are applied. I was just wondering if there was anything more to it then "well, we had a measured gust of 109 mph sooo.... we are currently at code limits".

It's always possible that the measuring station has some height/exposure/topographical element that needs to be normalized out. And a few weather standards report gusts other than 3s gusts.



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just call me Lo.

The climate changes, wind map may follow soon. Also, local can set their own requirement that is higher than the code.

I think one thing that is relevant and i honestly don't know for sure, so please correct me, but the ASCE number is based on a 3-second gust which i'd consider is long enough for pressures to actually normalize, it isn't sustained but 3-seconds isn't short either. I think the reported wind loads may be a maximum measured movement not essentially for a duration. In other words it may be an odd spurt of 110mph but the longest 3-second gust is less and then the sustained is some 50% of that.

The only reason i've convinced myself of this is i've been in areas that report 70mph and it was just what i'd deem windy and when i've looked at data for some forensic jobs the data was a small little spike in recorded velocity, the max peak was the value the news centers published.

I think one thing that is relevant and i honestly don't know for sure, so please correct me, but the ASCE number is based on a 3-second gust which i'd consider is long enough for pressures to actually normalize, it isn't sustained but 3-seconds isn't short either. I think the reported wind loads may be a maximum measured movement not essentially for a duration. In other words it may be an odd spurt of 110mph but the longest 3-second gust is less and then the sustained is some 50% of that.

The only reason i've convinced myself of this is i've been in areas that report 70mph and it was just what i'd deem windy and when i've looked at data for some forensic jobs the data was a small little spike in recorded velocity, the max peak was the value the news centers published.

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I've never gotten the "3 second" gust either. I will say though (about the part I put in bold): I've seen those kinds of reports as well (i.e. radar on your local weather station). But a lot of times, what is going on at the upper levels (where the radar is) isn't what is happening down low.

I remember one time the local weather guy said there was 80 mph wind right on top of me.....and outside it was maybe 20 mph.

I think the most dangerous and destructive wind pressure/force is the burst effect, duration is not that important.

One of the reasons presented by the ASCE 7 commentary for making the change from the 2005 to 2010 wind speed maps is, "The new maps, by providing the design wind speed directly, more clearly inform owners and their consultants about the storm intensities for which designs are performed."

Per the ASCE 7-10 commentary, "The wind speeds correspond to 3-sec gust speeds at 33 ft (10 m) above ground for exposure category C." This means that it is the maximum average wind speed over a period of 3 seconds. Wind storms will often have sustained speeds that are lower than the gust speed - here in central NE we often have 20 mph sustained winds (speed averaged over 1 minute or more) with 40-50 mph gusts (speed averaged over 3 seconds). The max wind speed being reported by a news station is usually very close to the wind speeds that we would use per ASCE 7, this is because many official weather stations are located at airports where the exposure category is exposure C and the anemometer will be mounted at a height of 33 feet. Furthermore, 3 seconds is the shortest time frame most anemometers use for measuring wind speed.

And just to round out a complete discussion, the 3 second gust wind speeds that we are all used to seeing and hearing shouldn't be confused with the winds speeds that are used to determine the scale (category) of a hurricane. This scale (the Saffir-Simpson Scale) uses the sustained wind speed with a 1-minute average (as opposed to 3 second average) at 33ft over open water. So, when you are told a Category 5 hurricane has wind speeds over 155 mph, this would be approximately 171 mph for a 3-sec gust in exposure C (Per ASCE Table C26.5-2)