Multiple-vortex/Wedge Tornadoes, Bernoulli, and urban areas

[Joshua T. Clark]

To All,

Something that has always bothered me to no end is the potential damage that an upper-EF scale tornado would do to an urban area such as downtown OKC. The May, 31st 2013 monster could have impacted the downtown OKC area if it had stayed on the ground. My biggest question would be, taking into consideration the funneling effect of channeling winds through a venturi, what kind of wind speeds would be possible with a tornado such as this one? Also, could a tornado of significant magnitude cause a large building such as a skyscraper to collapse.

Joshua

 

[Shane Adams]

I've always suspected a large area of steel-constructed high rises would do more to deter tornadic winds than enhance them, but there's no scientific (or even provable logic) behind that opinion other than I assume friction would have something to do with it.

 

[Greg Higgins]

Go back and read the engineering report from the Lubbock TX tornado of 1970. The Great Plains bank building took a near direct hit and the damage was fairly significant to the superstructure to the point that there was serious consideration given to dropping the building. Now imagine a downtown area with numerous highrises taking a hit. As Shane said "there's no scientific data" on how the winds would or would not effect the damage pattern. Tim Marshall???

 

[mikedeason]

This is definitely a subject that would require playing out a lot of scenarios involving a lot of variables: size and magnitude of the wind field, speed and direction of movement, density and height of buildings, etc. Besides just the more simple aspects, issues such as vortex shedding and induced vibration are also going to have a big impact. I have seen some studies on modeling of these scenarios before, but can't remember where they were offhand.

Even though this publication is dated a bit, it should provide some insight into the wind related considerations that architects much put into building design:

http://www.aia.org/aiaucmp/groups/aia/documents/pdf/aiap016809.pdf

 

[Skip Talbot]

You'll definitely want to check out this presentation by David Lewellen at the Severe Local Storms conference when they upload the slides and audio. There is a paper you can download and read in the mean time though:
https://ams.confex.com/ams/27SLS/webprogram/Paper254357.html

There was quite a bit of discussion on the May 31, 2013 tornado as well. I forgot who commented on it, but it was suggested that the 300 mph winds in that tornado might not have been over a spot long enough to inflict EF5 damage. The subvortices were relatively small and moving so fast that most locations would experience these winds for only a fraction of a second.

 

[Skip Talbot]

The recorded presentation for the SLS talk I mentioned above is now online, and it shows several amazing animation sequences. Check it out:

https://ams.confex.com/ams/27SLS/recordingredirect.cgi/id/28354

 

[Stuart Wilson]

Very interesting presentation. Thanks for posting the link Skip