Tornado Design Criteria

[DWHA]

I was reading some design criteria for a structure and it stated that the structure for tornado design parameters:

It stated the following parameters:
Maximum Tangential Velocity of 200mph & Translational velocity of 50 mph.

Does anyone know how this relates to the standard wind design for structures such as you would see in IBC/ASCE7?

It also stated a pressure drop of 2 psi in 3 seconds.

I have never came across anything like this before, so I just thought I would see what any of you know about the subject.

Thanks

 

[JAE]

Not seen it before either. I'd see if that criteria, which sounds like someone's attempt to provide statistically sourced load criteria, matches that of FEMA 361 or ICC 500.

 

[ishvaaag]

Respect to the wording, it sounds as if the tangential velocity would be that of the air in the vortex around its axis, and the translational, the velocity expected for the advance of the vortex. These obviously need be vectorially compounded to obtain the velocity respect a point fixed to the soil.

Then the other magnitude would be the rate to which depression can be created by the tornado, generating then suction force.

From the first compounded velocity something can be made for everything, pressures and suctions, looking for the wind pressures effects beyond laminar flow. From the rate of generation of pressure drop, this can be passed to study additional suction loading in some kind of dynamic analysis. But it would be better to find the correlations you ask to avoid some pains.

 

[dik]

I know little about tornado design, but, I would think the tangential velocty and the huge suctions created would greatly overshadow any effect of the trnaslational velocity. Just a thought...

Dik

 

[DWHA]

ishvaag
To clarify what you are saying. A tornado with 200 mph wind speed (internal to the tornado) and to tornado itself is moving along the ground at 50mph?

I follow that reasoning.

 

[ishvaaag]

Yes, the tornado would be showing 200 mph at the outer face of the spirally rotating wind whilst advances in any direction at 50 mph, seem likely numbers.

 

[BAretired]

Since tornadoes carry large amounts of flying debris, a tornado-proof building cannot have windows, so why not simply build underground with a few feet of earth over the roof? That way you avoid having to worry about wind pressure.

BA

 

[DWHA]

Who needs windows, lol.

 

[BAretired]

Doors are a problem too.

BA

 

[ishvaaag]

http://bbaa6.mecc.polimi.it/uploads/selezione/Eb11.pdf

http://cedb.asce.org/cgi/

http://WWWdisplay.cgi?251300

http://books.google.es/books?id=o9A...jgU#v=onepage&q=Tornado loading study&f=false

http://www.iawe.org/Proceedings/11ACWE/11ACWE-Sarkar.pdf

http://www.eng-tips.com/viewthread.cfm?qid=56164&page=560

http://etd.lib.ttu.edu/theses/available/etd-08072009-31295000983006/unrestricted/31295000983006.pdf

http://adamswebsearch2.nrc.gov/idmw...7f70fbf06964916343869f9ecdd6a75b&id=052730176

http://bbaa6.mecc.polimi.it/uploads/abstract_files/EB11_STAMPA2.pdf

http://text.lsuagcenter.com/en/fami...nd+Water/Hurricane+and+Tornado+Resistance.htm

There is something to start with these, hope this helps.

 

[azcats]

If you do make a structure with door(s) that survive a tornado, be sure the doors open to the inside...

 

[JAE]

Per BARetired's suggestion - if you do go underground - make sure you aren't in a flood area.

 

[concretemasonry]

Much of the FEMA suggestions are based on projectile damage and the loss of life, which the one of the major problems because tornados are quick unpredictable concentrated sources of energy without a noticeable core and are not intended for the structural design of an above grade structure.

To draw a parallel, it is akin to a storm surge for building destrction that is costly and impractical to design for.

It is a building, design for the appropriate requirement for the structure and recommend interior "safe cells"(reinforced concrete or CMU with a concrete roof and inward swinging doors) that are close of quick human protection. - They are commonly built in homes and used as storage area or closest in many geographic areas.

Dick



Dick

Engineer and international traveler interested in construction techniques, problems and proper design.