Design Wind Speed Comparisons

[dannoMD11]

Can anyone recommend references or literature to compare different design wind speeds such as the 3 second gust and the fastest mile?

I frequently design tower crane foundations in the Southeast of the US so out of service wind speeds play a larger role in the foundation design. I am looking to better understand the different wind speeds.

 

[rday]

2009 IBC Section 16 Table 1609.3.1 is equivalent basic wind speeds fastest mile vs. 3-sec gust.

It's a place to start.

 

[rowingengineer]

thread507-78530


How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban

 

[rowingengineer]

http://www.rci-online.org/interface/2005-10-dregger.pdf

How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban

 

[keenaseng]

I too have come across this question whilst looking at wind loads on tower cranes.
I found the tower crane manufacture supplies the out of service base foundation load due to an average wind speed (over a minute or 10mins etc) rather than a gust for stability calculations. I realise that some building codes specify winds as an average generally, but it got me thinking - Do the crane manufactures do this because there is not sufficient 'work energy' in a 3 second wind gust to overturn a tower crane, and therefore the 3 second gust wind speed is not applicable? I guess this lodgic would not apply when designing the steel elements of the crane structure that could become overstressed in a 3 second event.

 

[dannoMD11]

keenaseng, this is exactly my issue. Most, if not all tower cranes, have been designed for out of service wind speeds of 94 mph from the rear in accordance with the old FEM 1.001 rules. The 94 mph is a 10-min average, which if I am doing the conversion correctly with the Durst curve is a 133 mph 3-sec gust speed. According to the design code, this speed is applied to the crane from a height range of 66 to 328 feet. From 0 to 65 feet a wind speed of 115 mph is used. When you convert the speeds to 3-sec gust speeds they look better but the code does not include gust factors to account for dynamic amplification since the tower crane is obviously a flexible structure.

I will note there is a new Euro code for tower crane design for newly developed models that is similar to the ASCE. However, here in the US we will be very unlikely to see any of these new models for a very long time. We are stuck with what we have.

 

[keenaseng]

From my understanding the new FEM 1.005 code basically accounts for out of service wind load case also coming from the front (i.e not relying on the crane weathervaning). I think the wind speeds are still 10 min average. This will significantly increase base overturning moments for new cranes designed to this standard.
Do you know why they have introduced this? I'm pretty sure it is mandatory practice to leave slewing ring free to rotate out of service, and therefore impossible for crane not to weathervane at the out of service wind speeds.
I'd like to see a worked examle of the wind load calculation on a tower crane structure, including drag along the jib - Its a pretty complex calculation (I have tried to do it before)