3-second gust wind speed in ASCE 7-05 1

[Monash123]

I have been reading ASCE 7-05 which mentions about 3-second gust wind speed. I have a basic question from this end: I know that basic wind speed is 3-sec gust wind speed at 10m above ground. I also know that 3-sec gust wind speed is average of wind speed over an interval of 3-seconds. If that is right then what exactly is wind gust? Is wind gust average of wind speed over 3-second interval? If it is, then how is wind gust any different from wind speed? Basically, I am struggling with the concepts of wind speed and wind gust.

 

[klaus.]

well I would say....wind gust is the highest wind speed in that time interval of 3 seconds

 

[UcfSE]

In this context, there is no difference between 'wind gust' and 'wind speed'. What is important is the averaging time. Using the descriptor "gust speed" does not add value/understanding or change the meaning.

 

[Monash123]

Thank you kclaus and UcfSE. That is very helpful. So just to sum it up in general according to ASCE 7-05, wind speed is average wind speed measured over 3-second interval and wind gust is the maximum wind speed measured over 3-second interval, is this correct?

 

[UcfSE]

There is no difference between 'gust' and 'speed' at an averaging time of 3 seconds. Anemometers we use do not measure faster than that. For other averaging times, it might be more clear to differentiate between peak speeds measured in a time interval and average speeds in that same interval. I've never used or needed to make this distinction.

 

[Monash123]

That makes it clear. Thank you so much UcfSE. Just one question further down the line, what is the standard averaging time for wind speed then? Also, is wind gust measured to be distinct from wind speed using a different averaging time according to U.S. standards?

 

[UcfSE]

I think you should wash the term "wind gust" as it relates to speed out of your mouth . It seems to be confusing you more than anything.

The term likely gets used because the averaging time in the US is 3 seconds, and because that is as instantaneous as we can measure some call it gust speed. When the averaging time is 3 seconds, then wind gust and wind speed are often used interchangeably though in my opinion that just confuses things. When the averaging time is not 3 seconds, wind gust and wind speed mean different things, though at that point "wind gust" as it relates purely to speed looses its usefulness for basic calculations.

 

[Monash123]

That is very helpful. I now understand the importance of averaging time.

Now how does the definition vary when the averaging time is increased to 2 minutes or 10 minutes? I've read somewhere (don't know about the strength of the source) that WMO standard defines a wind gust as maximum wind speed exceeding mean speed by 5m/s during 10 minute interval. Does this hold any strong base in your experience?

 

[UcfSE]

For calculation of static design pressure, you would need to convert the speed at the averaging time you receive to an averaging time consistent with the code you are using.

How meteorological sources define things may not be the same as how the "general purpose" engineer uses the terms. Wind engineers I expect will be more well-versed; unfortunately I'm not one of those.