Tornado Missile Impact

[StoyanAndreev]

The structural team I work for is currently assessing a structure for tornado loading. Since most civil code have little or no information on tornadoes other than hazard maps we are using the US NRC Reg Guide 1.76 Design-Basis Tornado and Tornado Missiles for Nuclear Power Plants. Regarding the tornado missile there are three classes of missiles - Schedule 40 Pipe, Automobile and Solid Steel Sphere. The relevant automobile is 5m/2m/1.3m, weighting 1.8 tons and flying with 41 m/s. I want some recommendations or methodology how to transfer this information to a simple and robust design data - a transient load-time function or a pseudo-static force.

 

[BadgerPE]

FEMA 361 has some information relating to missile impact for tornadoes and hurricanes. I believe their design missile is a 15# 2x4 though, so I don't think there will be any guidance for an automobile.

 

[JAE]

Here is the FEMA 361 link.
Also for buildings you could consider ICC 500 (go to the ICC website for the link).

http://www.fema.gov/media-library/assets/documents/3140?id=1657

Also - for a typical building I'm not sure using nuclear criteria is warranted.



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[IRstuff]

What type of structure are you designing? There are structures where this severe an impact is impossible to design for; it would be unreasonable to expect a typical wood frame house to survive a 90+ mph car impact. There aren't any cars that can survive that kind of impact, for that matter.

On the other hand, if you are actually designing a shelter, then the place to look might be FEMA:

http://www.fema.gov/pdf/plan/prevent/rms/453/fema453.pdf

US Amry Corps of Engineers would be another place to look

TTFN
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[Bagman2524]

I believe there is a Stanford formula for calculating depth of penetration for missiles

Faith is taking the first step even when you can't see the whole staircase. -MLK

 

[JLNJ]

A blast consultant might be able to provide some of the services you are looking for. (ABS Consulting comes to mind.)

I believe most of the FEMA wood 2x4 data on different wall assemblies was derived from actual asembly testing rather than pure theory. I don't know how much testing has been done on other types of projectiles.

 

[IRstuff]

not exactly easy to throw around 1.8 ton objects at 60 mph

TTFN
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[glass99]

I saw a department of homeland security spec recently for a facade for a new command facility in Kansas which included the nuclear tornado criteria. We told them that the glass was going to be 4in thick, along with gigantic steel mullions, and they rethought the performance spec back down to the FEMA 361 mentioned. Dupont has a bunch of testing available now for the 2x4's at tornado speeds. The nuclear spec implies 3ft thick concrete.

 

[concretemasonry]

Not a structural response, but regarding life safety for occupants (the major loss of life from tornadoes, there a hundreds of tests done regarding penetration from projectiles that have been funneled through FEMA regarding personal protection provided by wall and some window sections. This was part of the thrust by FEMA to prevent loss of life by projectiles (which is the major item regarding fatalities). It is an essential part of the FEMA resources. Most were real laboratory tests conducted using the "air cannon" 2x4 projectiles fired at actual wall assemblies and are well documented. The final criteria was no penetration through the assembly.

It is a companion to the over-all structural concept regarding a different scale of conceptual loads/failures.

Dick

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